Concrete Contractor August/September 2015

Polished Concrete Floor Contributes to Facility’s Sustainable Message

50

August/September 2015

Now available online and on your iPad!

The Evolution of a Poured Wall CONTRACTOR 18 Does COLD CURING WATER Cause Concrete Surfaces to Crack? 32

A New Bridge for the

ST. CROIX RIVER

22

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ROAD AND MINERAL TECHNOLOGIES

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August/September 2015 | Issue 5, Volume 15

WHAT’S INSIDE Cover Photo Credit: MNDot

Departments 4 Editor’s Letter 6 Challenging the System 10 New Products 12 Legal Matters

Cover Story

46 Foundations Q&A 58 The Last Placement

22 A New Bridge for the St. Croix River Engineers and contractors collaborate to build a high-tech bridge.

Features 14 Slabs-On-Ground: Slab Thickness and Base Tolerances Using special care to establish and maintain the fine grade elevation will ensure a successful and profitable project.

18 The Evolution of a Poured Wall Contractor For one concrete contractor, adding precast concrete walls to the firm’s product offerings yields success and profitability.

26 Hardscape Design Creates A Canvas for Historic Post Office The relationship between the concrete contractor and the design team was crucial to the success of the decorative concrete work on a restoration project.

30 CFA Unveils Member “Risk Management” Insurance Program The Concrete Foundations Association Board of Directors

approved Arthur J. Gallagher as insurance broker for the new program.

32 Does Cold Curing Water Cause Concrete Surfaces to Crack?

while also making a near zero carbon concrete with enhanced durability.

40 Why You Should Care About Resilience

Tests were conducted to determine if curing water wasn’t heated, would the concrete crack?

36 CERATECH Cement – Setting New Measures for Concrete Durability and Sustainability A non-portland cement concrete offers contractors the ability to use less water in a concrete mix,

What’s Online

50 Polished Concrete Floor Contributes to Facility’s Sustainable Message 54 Edge Grinder Product Showcase

Read these online exclusive articles at www.ForConstructionPros.com/concrete.

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Concrete Services Beats The Heat and High Winds with Somero Enterprises Beating the high California winds and heat on a new 80-acre Business Park located in Livermore, California are proving to be calm and cool. Search: 12097703

www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 3

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EDITOR’S LETTER

New Trend: Cement Companies Merge Together Ryan Olson, Editor

L

ast month, the world’s two largest cement makers, Larfarge and Holcim finalized a merger of both companies, thereby creating LafargeHolcim the largest firm in the “building materials industry.”

According to a statement from the company, LafargeHolcim has a unique business portfolio, is the industry benchmark in R&D and offers its customers the widest range of innovative and value-adding products, services and solutions.

In essence, the merger allows both companies to come out as one and aims to turn the cement business into a service. Combining the companies blends technological know-how into developing new, innovative products that will lead to greater profitability.

Coming on the heels of the LafargeHolcim merger, HeidelbergCement announced their plans to acquire Italcementi.

According to the company, this acquisition is an opportunity to accelerate the growth of HeidelbergCement. Italcementi operates across 22 countries with strong market positions in France, Italy, the United States and Canada.

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ROlson@ ACBusinessMedia.com (800) 538-5544

Once again, this acquisition will combine the R&D capabilities of both companies. While Italcementi brings strong capabilities in process and product innovation, the company has also developed several highperformance and technologically advanced materials for new building models and innovative biodynamic cement.

The combination with Italcementi will create the global market leader in aggregates, the second largest producer of cement and the global number three in ready-mix concrete.

What does this mean for the concrete contractor? On initial glance, I wouldn’t expect much—yet. Further down the road however, contractors may begin to see new and different concrete formulations developed out of the synergies of these companies. Additionally, the merging of these leading companies creates a globalization effect that in theory would create greater competition on a global scale and potentially higher quality products.

Follow us @ Concreteinsider

Kim Basham KB Engineering Cheyenne, Wyo.

Jim Cuviello Cuviello Concrete Polished|Stained|Crafted Stevensville, Md.

Jim Baty Concrete Foundations Association Mt. Vernon, Iowa

Chris Klemaske T.B. Penick & Sons, Inc. San Diego, Calif.

Search: Concrete Polishing

Dennis Purinton Purinton Builders, Inc. East Granby, Conn.

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CHALLENGING THE SYSTEM

Acceptance of Concrete

Test Results

Ward R. Malisch, PE, PhD, FACI is concrete construction specialist for the American Society of Concrete Contractors. Reach him at wmalisch@ascconline.org.

Bruce A. Suprenant, PE, PhD, FACI, is technical director for the American Society of Concrete Contractors.

Reach him at bsuprenant@ bsuprenant.com.

Why is it still a struggle?

C

onsider the following scenarios for a project on which the specified compressive strength (fc’) is 3,500 psi at 28 days.

• A single seven-day-old cylinder breaks at 2,250 psi. The Architect says this is less than 70 percent of fc’. and the concrete strength is suspect.

• A 28-day test result is 3,150 psi and the testing laboratory states in its report that this result does not meet project specifications.

• The average of three consecutive 28-day strength tests is 3,400 psi and the Owner wants the concrete removed and replaced.

These are all examples of incorrect interpretations of the acceptance criteria for concrete strength test results in accordance with ACI 318 “Building Code Requirements for Structural Concrete” and ACI 301 “Specifications for Structural Concrete.”

Both of these documents define a strength test as the average strength of two 6x12-in. or three 4x8-in. cylinders tested at 28 days or at a test age designated for fc’. ACI Acceptance Criteria The acceptance criteria for concrete strength tests has been the same since the early 1970’s but for more than 40 years they have often been interpreted incorrectly.

Fortunately, ACI committee E702 published “Designing Concrete Structures: Acceptance of Concrete Test Results” in March, 2007 to

provide a step-by-step example of concrete test-result evaluation and an explanation of the acceptance criteria. The document is a free download on the ACI web site. The data used in this article is based on that ACI document.

ACI has two requirements for the acceptance of concrete test results as shown below: Strength level of a concrete mixture shall be acceptable if (1) and (2) are satisfied: 1. Every arithmetic average of any three consecutive strength tests equals or exceeds fc’.

2. No strength test falls below fc’ by more than 500 psi if fc’ is 5,000 psi or less; or by more than 0.10 fc’ if fc’ exceeds 5,000 psi Note that ACI does not require: • A minimum strength at seven days.

• A minimum strength for an individual cylinder that is part of the test.

• All strength test results to exceed fc’.

ACI 318 accounts for concrete strengths less than fc’ by multiplying the calculated strength of a member by a strength reduction factor, which is always less than one. ACI 318 Commentary states that one of the purposes of the strength reduction factor is “to allow for the probability of understrength members due to variations in material strengths.”

Thus ACI has already considered that the concrete may be less than fc’ and that is why an individual strength test result may be below fc’ by up to 500 psi or by not more than 0.10 fc’ when fc’ exceeds 5,000 psi.

It’s unfortunate that after 40 years of use, the provisions for acceptance of strength test results are still incorrectly interpreted.

BEFORE CHECKING THE ACCEPTANCE CRITERIA Don’t reject concrete represented by strength test results until you confirm that the test results are valid. Use the checklist below to ensure the strength test results meet ACI testing requirements.

Sampling frequency is adequate (once a day, once every 150 cubic yards, once for each 5,000 square feet of surface area for slabs or walls) [ACI 318:26.12.2.1] ✔Samples taken on a random basis (concrete not sampled due to appearance, convenience or other possibly biased criterion) [ACI 318:R26.12.2.1(a)] ✔ Each set of cylinders comes from a different batch of concrete [ACI 318:R26.12.2.1(a)] ✔ For each strength test, is the average of at least two 6x12 in. cylinders or three 4x8 in. cylinders [ACI 318:26.12.1.1(a)]

6 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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water was added to the concrete [ACI 318:R26.12.2.1(a)] ✔ Testing agency performing acceptance testing complied with ASTM C1077. [ACI 318: 26.12.1.1(b)] ✔ Q ualified field testing technicians performed the test on the fresh concrete [ACI 318: 26.12.1.1(c)] ✔ Q ualified laboratory technicians performed the laboratory strength tests [ACI 318: 26.12.1.1(d)] ✔ Sampling, making and curing, and testing of the cylinders were in accordance with ASTM C172, C31, and C39. [ACI 318:26.12.3.1]

Acceptance of Concrete Strength for fc’ = 3,500 psi Based on ACI Criteria

✔ No

CALCULATIONS NEEDED FOR ACCEPTANCE OF STRENGTH TEST RESULTS It’s best to develop a tabular format where the individual cylinder strengths are averaged to calculate the strength test result. After calculating test results, the average of any three consecutive strength tests can be calculated. The table, top right, shows one format for accomplishing this.

WHAT IF THE ACCEPTANCE CRITERIA ARE NOT MET? If the average of three consecutive strength tests falls below fc’, but no strength test result is more than 500 psi below fc’, steps must be taken to increase the average of subsequent strength results. Note that nothing needs to be done with regard to the previous test results. Steps must be taken to increase future strength test results.

In addition, if an individual strength test result falls below fc’ by more than 500 psi if fc’ is 5,000 psi or less; or by more than 0.10 fc’ if fc’ exceeds 5,000 psi, a low strengthtest investigation is required as described.

THE STRUGGLE CONTINUES It’s unfortunate that after 40 years of use, the provisions for

Test #

Cylinder #1 (psi)

Cylinder #2 (psi)

Strength Test Result (psi)

Average of Three Consecutive Strength Test Results (psi)

1

4,100

4,320

4,210

-----

2

4,320

4,190

4,255

-----

3

4,310

4,310

4,310

4,258

4

4,420

4,380

4,400

4,322

5

4,200

4,160

4,180

4,297

6

4,250

3,810

4,030

4,203

7

3,880

4,040

3,960

4,057

8

3,570

3,680

3,625

3,872

9

3,570

3,210

3,390

3,658

10

3,780

3,780

3,780

3,598

11

3,680

2,980

3,330

3,500

12

3,300

3,740

3,520

3,543

13

3,470

3,210

3,340

3,397*

14

2,770

2,750

2,760*

3,207*

15

3,200

3,480

3,340

3,147*

The individual cylinder results cannot be used for acceptance or rejection.

ACI 318 Acceptance Criteria

■ Investigation needed

The strength test results and average of three consecutive strength test results are used for acceptance or rejection.

No strength test less than fc’ – 500 (3,000 psi)

Average of three consecutive strength tests equal to or greater than fc’.

■ Need to increase averages of subsequent strength test results

ACI REQUIREMENTS FOR INVESTIGATING A LOW STRENGTH-TEST RESULT a. If any strength test of standard-cured cylinders falls below fc’ by more than the limit allowed for acceptance, or if tests of field-cured cylinders indicate deficiencies in protection and curing, steps shall be taken to ensure that structural adequacy of the structure is not jeopardized. b. If the likelihood of low-strength concrete is confirmed and calculations indicate that structural adequacy is significantly reduced, tests of cores drilled from the area in question in accordance with ASTM C42 shall be permitted. In such cases, three cores shall be taken for each strength test that falls below fc’ by more than the limit allowed for acceptance. c. Cores shall be obtained, moisture-conditioned by storage in watertight bags or containers, transported to the testing agency, and tested in accordance with ASTM C42. Cores shall be tested between 48 hours and 7 days after coring unless otherwise approved by the licensed design professional. The specifier of tests referenced in ASTM C42 shall be the licensed design professional or the building official. d. Concrete in an area represented by core tests shall be considered structurally adequate if (1) and (2) are satisfied: 1. The average of three cores is equal to at least 85 percent of fc’.

2. No single core is less than 75 percent of fc’. e. Additional testing of cores extracted from locations represented by erratic core strength results shall be permitted. f. If criteria for evaluating structural adequacy based on core strength results are not met, and if the structural adequacy remains in doubt, the responsible authority shall be permitted to order a strength evaluation in accordance with Chapter 27 for the questionable portion of the structure or take other appropriate action.

www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 7

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CHALLENGING THE SYSTEM

acceptance of strength test results are still incorrectly interpreted.

Contractors have had to repair or remove and replace concrete that was acceptable because the parties involved did not understand the ACI acceptance criteria.

Perhaps this struggle will end if concrete contractors use the ACI E702.3 document and this article to explain the Code and specification requirements for accepting strength test results.

Ed. Note: The current “Building Code Requirements for Structural Concrete (ACI 318)” and “Specifications for Structural Concrete (ACI 301)” can be purchased at www.concrete.org.

ACI E702.3 is available as a free

ACI RECOMMENDATIONS TO INCREASE THE AVERAGE OF SUBSEQUENT STRENGTH RESULTS The steps taken to increase the average level of subsequent strength test results will depend on the particular circumstances but could include one or more of (a) through (g): a. Increase in cementitious materials content; b. Reduction in or better control of water content; c. Use of a water-reducing admixture to improve the dispersion of cementitious materials; d. Other changes in mixture proportions; e. Reduction in delivery time; f. Closer control of air content; g. Improvement in the quality of the testing, including strict compliance with ASTM C172, ASTM C31, and ASTM C39.

Such changes in operating procedures or small changes in cementitious materials content or water content should not require a formal resubmission of mixture proportions; however, changes in sources of cement, aggregates, or admixtures need to be accompanied by evidence that the average strength level will be improved.

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8 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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10 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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LEGAL MATTERS

By David Whitlock

Recruiting Keepers Contractors need to explore new or different means of recruitment, as well as maximize the value of recruiting methods already in use.

N

ow that the concrete industry is recovering from economic woes, most contractors report that they have more work than they can comfortably do.

This makes the hiring process more important than ever.

The traditional recruiting strategies include online recruiting, job fairs, high school/college presentations, employee referral or word-ofmouth, staffing companies, search firms, “old school” methods, and stealing your competitor’s workers.

Some of these strategies work in the concrete industry, but some of them are not very good for finding labor.

Let’s take a closer look.

Online recruitment works for employers seeking younger workers, i.e. those who have and regularly use smart phones and social media.

Unfortunately, it is rare that these workers will last more than a couple of weeks in the field before they move onto something new and different.

Job fairs hosted by schools and alumni offices generally share the same fate as online recruiting. When job fairs are hosted by a local chamber of commerce, they may bring a richer mix of recruits to you but generally the recruits will be looking for professional or staff positions instead of field labor jobs.

High schools and colleges are increasingly being used to find field laborers. Some contractors report success working with the school’s coaching staff or vocational crafts faculty. Coaches want to keep their athletes in shape during the off-season. Since most contractors are

placing concrete during the summer months, this means you want to look for athletes in winter sports because they generally cannot start practice until around October 1 and their season will end in early spring.

Remember that OSHA restricts what younger workers can lawfully do, so you will want to make sure that your student recruits are old enough to perform the work in question.

Word-of-mouth recruitment can be the best source for finding keepers. Basically, you start by asking your good workers to bring their friends to work. Unlike traditional systems where you might pay your worker a bonus for bringing a new worker, given the nature of this work, it probably makes better sense to pay your worker multiple bonuses tied to the new hire’s longevity.

Perhaps a bonus at 30, 60, and 90 days makes the most sense.

Staffing companies can be an expensive way to find labor, but they can be useful. To be truly effective recruiters for you, the staffing company really needs to understand the work and the job you are trying to fill. Consider inviting the staffing company representative to a job site so that you can demonstrate the work in person. Ideally, the staffing company is not paid just for bringing a worker on board, but instead is paid a little at first and more as the worker keeps working.

Search firms are generally not much good for finding laborers.

They are focused more on the professional positions in your organization.

“Old school” recruitment includes methods we used before

David C. Whitlock has over 25 year’s experience in business immigration, compliance, employment counseling and training. He is the founding attorney of Whitlock Law LLC and can be reached at (404) 626-7011 or via e-mail at davidcwhitlock@gmail.com.

the advent of social media and modern telecommunications. These include posting notices at grocery stores, laundromats, bowling alleys – anywhere there is a bulletin board.

You can also try newspaper advertising but that is a little more expensive. The “art” of this recruitment is how you describe the job and your company. Be certain to give a range of compensation and benefits that will be attractive to the average reader. Consider advertising a bonus system for keepers.

Stealing your competitor’s workers is always tempting but problematic. The worker lured by an extra dollar an hour can easily be lured away from you. Plus, you won’t retain many friends in your area if you are known to take good workers away from others in your industry.

Before starting a recruitment program think about where your best workers came from. Go back there. At the same time, think about where your worst workers came from and vow to ignore those sources of recruitment completely.

For any small to medium sized contractors, these additional recruitment tasks can become quite burdensome, especially when you see good workers leave after a few weeks. That suggests that maybe it is time to “retool” the HR function within your business.

In the past we have looked at the traditional process for hiring.

Perhaps, at least for field labor, we can abbreviate some of that hiring process to make it easier for most contractors to recruit keepers. We’ll look at that in the December issue.

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FLATWORK / SLABS

By Kim Basham, PhD PE FACI

Slabs-On-Ground: Slab Thickness and Base Tolerances Using special care to establish and maintain the fine grade elevation will ensure a successful and profitable project.

Bases for slabs-on-ground must be smooth, hard and compacted.

Photo Credit: Kim Basham

S

lab thickness is the greatest single factor controlling the loadcarry capacity of a slab-on-ground. While other factors including concrete compressive strength, the thickness and quality of the base material and sub-grade stiffness are important, they are minor players as compared to the slab thickness. For this reason, slab thickness and base tolerances are critical and typically specified in the contract documents.

SUPPORT SYSTEM The support system consists of the base, sub-base and sub-grade. The base course, directly beneath the slab, typically consists of crushed rocks and gravels and directly supports the slab.

Sometimes the designer may specify a subbase consisting of crushed rock, gravels, select or stabilized soils to help stiffen the support system, especially if the sub-grade or existing soils are of poor quality.

top of slab elevation tolerance.

The ±3/4 in. fine grade elevation tolerance for the base or the soil immediately below the slab-onground corresponds directly with the -3/4 in. slab thickness tolerance for individual samples. For a more stringent fine grade tolerance, ACI 117-10 recommends a ±1/2 in. tolerance due to the sophisticated equipment available for establishing the fine grade elevation.

Since the base material is in direct contact with the slab, it must be smooth, hard and well compacted.

Additionally, the contractor must grade the base material to the proper elevation. Otherwise, the slab thickness may be thicker or thinner than the specified thickness.

Assuming the top of slab elevation is correct, the slab will be thicker if the base elevation is low and thinner if the base elevation is high.

TOLERANCES ACI 117-10 states1: - 4.4.5 Fine grade of soil immediately below slabs-on-ground........±3/4 in.

- 4.5.4 Thickness of slabs-on-ground Average of all samples.……-3/8 in.

Individual sample….-3/4 in.

The slab-on-ground thickness tolerance sets both an average thickness for all samples measured and a minimum thickness for individual samples. ACI 117-10 does not specify a plus slab thickness tolerance but does specify a ±3/4 in.

ACTUAL SLAB THICKNESS Measured slab thicknesses indicate most slabs are much thinner than specified. Based on 30,000 measured data points reported by Suprenant and Malisch, the average slab thickness was about 3/8 in. less than the specified thickness and the average standard deviation for the slab thickness was about 1/2 in.2 The average standard deviation reported was centered on the -3/8 in. value and not on the specified thickness.

Suprenant and Malisch concluded the -3/8 in. average measured value appeared to agree with ACI’s -3/8 in. tolerance for the average of all samples. However, they took exception with ACI’s -3/4 in. tolerance for an individual sample due to the 1/2-in. average standard deviation for the measured slab thicknesses.

Using a tolerance value of three standard deviations indicates a thickness variation of ±1½ in. Therefore, Suprenant and Malisch reported an actual plus tolerance of +1-1/8 in.

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FLATWORK / SLABS (-3/8 + 1½ = +1-1/8in.) and a minus tolerance of -1-7/8 in. (3/8 – 1½ = -1-7/8 in.) for the slabs tested. Three standard deviations on a Bell Curve (standard normal distribution) show 99.7 percent of slab thicknesses would fall within the ±1½ in. tolerance. For 2.0 standard deviations, 95 percent of the thicknesses would fall within ±1 in. For 1.5 standard deviations, 87 percent would fall within a tolerance of ±3/4 in. and 68 percent thickness would fall within a ±1/2 in. tolerance for a 1.0 standard deviation.

The computed minus tolerance of -1-7/8 in. is significantly larger than ACI’s -3/4 in. thickness tolerance.

Based on the ½ in. average standard deviation for the measured slab thicknesses, Suprenant and Malisch state a ±1½ in. tolerance would be more realistic for slabs-on-ground.

Wheel Load Slab Base

-3/4 in. thickness tolerance, you’ll need better quality control than the contractors that installed the slabs where 30,000 date points were measured.

COSTS OF THICK OR THIN SLABS

Slabs thicker than the specified thickness will cost more money.

Thicker slabs increase concrete costs. For every 1/8-inch the grade Subgrade is low, the volume of concrete increases about 0.39 cubic yards per 1,000 square feet. This may What does all this mean? In reality, not seem like a lot of extra concrete ACI’s -3/4 in. thickness tolerance may but for a 30,000 square foot placenot be achievable for 100 percent of ment and 1/8-inch low grade, you’ll the slab. Using the test data reported need about 11.6 cubic yards of extra

by Suprenant and Malisch, only 87 concrete. If the grade is 1/4 or 3/8percent of the slab will fall within ACI’s inch low, then you’ll need about 23 thickness tolerance. On your next or 35 cubic yards of extra concrete job, use special care establishing and for a 30,000 square foot placement. maintaining the fine grade elevation.

This can really add up for a large slab.

Also, to ensure compliance with ACI’s Purchasing extra concrete will please Subbase (optional)

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the concrete supplier but will reduce your profits.

Slabs thinner than the specified minimum thickness may also increase costs, especially if thickness samples or measurements are part of the acceptance criteria for the slab. Slabs that fail to satisfy the specified thickness requirements may be subject to monetary penalties or rejection even though there are few reported cases of slab failures caused by out-of-tolerance or thin slabs.2 Building owners are sensitive

about paying for slabs that are thinner than the specified thicknesses for several reasons including contract requirements and potential reductions in the load-carrying capacity of the slabs. A change in the actual thickness of the floor does affect the load-carrying capacity of the slab.

For example, reducing a 6 inch thick floor slab to 5-1/4 inches reduces the load-carrying capacity of the slab by roughly 23 percent assuming all other factors are constant.3 However, this reduction should not be a serious concern because the concrete strength of the as-built slab and stiffness of the support system beneath the slab Fine grading with laser-guided grader boxes provides a fast, efficient way to fine grade base materials for slabs-on ground to tolerances approaching ±1/4 in. and as tight as ±1/16 in.

Photo Credit: Level Best

typically exceed the design values used to establish the slab thickness.

On your next job, be sure to give the fine grading the attention it requires to ensure a successful and profitable project.

REFERENCES 1. ACI117-10 Specification for Tolerances for Concrete Construction and Materials (ACI 117-10) and Commentary, An ACI Standard, Reported by ACI Committee 117, American Concrete Institute, www. concrete.org 2. Suprenant, B.A. and Malisch, W.R., Tolerance for Cast-in-Place Concrete Buildings - A Guide for Specifiers, Contractors, and Inspectors, American Society of Concrete Contractors, 2009, pgs. 61 & 62, www.ascconline.org 3. Ringo, B.C. and Anderson, R. A., Designing Floor Slabs on Grade, 2nd Edition, The Aberdeen Group, 1996, pg. 184

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FOUNDATION & WALLS

By Ryan Olson

The Evolution of a

Poured Wall Contractor

For one concrete contractor, adding precast concrete walls to the firm’s product offerings yields success and profitability.

R

ich Kubica, owner of K-Wall Poured Walls, LLC has spent his entire life in the concrete foundation and wall business.

In fact, one could say Kubica is a visionary for what a foundation and wall contractor should be doing.

Like most futurists who have the

foresight to take on radical ideas, Kubica decided it was time to consider adding precast walls to his business.

In the 1950s, his father formed Jerry Kubica Foundations (which later became K-Wall) located in Chesaning, Michigan. Jerry retired and shut down the business in the late 1970s. By 1992, Rich revived K-Wall in Traverse City, Michigan and operated the business until 2011.

In the 1990s, he invented a concrete wall system called E-Max—an insulated wall system which fits inside aluminum wall forms. E-Max is now sold by Western Forms.

“I grew up in the poured wall business,” Kubica proclaims. “All throughout my adolescent years, I never had a job except for pouring concrete walls.”

The MonoKast Precast Wall System is manufactured at K-Wall’s factory in Fletcher, North Carolina. When placement is completed, the walls are fully insulated and studded. They are ready for finishing and require no additional framing.

Photo Credit: Rich Kubica

Along with his wife Patty, the Kubica’s relocated their family and the business to Asheville, North Carolina in 2006. K-Walls began its North Carolina operations in 2007.

“We all know what happened in 2008. At that time, I had one year in the new business. I was a brand new wall contractor in Western North Carolina and then, the whole world seemed to die. Just about every concrete wall contractor in this area went out of business; but we survived.”

While so many contracting firms

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faded away during the downturn of the economy Kubica says he survived because of diversification.

“We did our own footings and walls. We took on flatwork projects and became licensed applicators of gypsum concrete underlayment. We poured Gypcrete apartment buildings and multi-family units,” he says.

“We started doing our own decorative concrete work and performed a tremendous amount of epoxy floor coating jobs. These are the things that kept us alive.

When we weren’t pouring walls because nobody was building houses, we were skimming along doing those kinds of jobs.”

As the economy improved and competing contractors started coming back to the market, Kubica became seriously interested in adding precast walls to his portfolio of services.

The basic profile of a MonoKast wall includes a 10-inch wide header beam at the top and a 10-inch wide footing beam at the bottom; both of which are 3-1/2 inches thick with solid concrete and reinforced steel. The concrete shell is two inches thick, fiber reinforced, and is a 5,000 psi code compliant.

Photo Credit: Rich Kubica

THERE’S A MARKET FOR PRECAST WALLS Considering the mountainous location of Asheville, the market for precast walls was in high demand.

Several factors contributed to his decision to become a precast wall contractor in addition to being a poured concrete wall contractor.

• Materials: The supply source is very limited for ready-mix concrete. Eight years ago, contractors in the area purchased concrete from Southern Concrete or they made it themselves.

• Heavily engineered walls: In Western North Carolina, when a builder gets a blueprint for a job, a structural engineer becomes heavily involved in the construction process. The walls are thick and require huge footings. There is plenty of rebar incorporated into the walls. These factors all drove the price of a standard, poured wall foundation up. In fact, Kubica says poured walls aren’t even considered normal for home owners in the area as they are too expensive.

• 2012 IRC Code Book: For the first time in history, the 2012 IRC Code Book addresses precast walls.

The recognition of precast walls eliminated the precast walls as a proprietary product.

• Labor saving: Given the shortage of qualified laborers, it became increasingly difficult to find someone who wants to work extremely hard. Pouring concrete walls is extremely labor intense because of the engineering issues. And as Kubica notes, “The generation of workers we have today do not have the same work ethic I had growing up.”

When it comes to precast walls, they are made in a factory. Workers are standing on level ground, lifting nothing heavy and not putting wear and tear on their bodies. The installation of precast walls involves a crane and a bolt which is installed at the top of the wall to secure each wall section. With minimal heavy manual work, it becomes an attractive option to both the older crew members as well as the younger, less seasoned laborers.

“As a poured concrete wall contractor, it’s in

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FOUNDATION & WALLS my blood, but there is also an evolution too,” he explains. “The foundation industry is changing.

Poured concrete walls are the king of foundations. When all other foundations fail, poured walls excel.

However, as I examined my business and crews, I continually asked myself, ‘How do we do it easier?’ And my answer was precast walls.”

MONOKAST PRECAST WALLS Kubica knew he needed to partner with someone who was forward thinking enough to develop the MonoKast Precast Wall system.

He contacted Ron Ward, CEO of Structura Technologies for assistance.

“Ron had enough foresight to come to North Carolina and examine everything that was going on in

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the market,” He says. “We’ve been watching precast walls for 20 years.

The timing wasn’t right at that time. They weren’t addressed in the building code. They were still a proprietary product and most importantly, no one believed in them.

At that time, it was more expensive to build concrete walls with a precast product.”

What has changed over the course of 20 years?

“We use a lot more concrete when pouring foundations, but when we build a precast wall, I use 70 percent less concrete. The time has come for precast walls. It’s a great wall and it’s a good thing for the poured concrete wall contractor to finally have another product in their hands.”

While poured concrete walls have dominated the foundation market since the 1950s, the precast concrete wall market is new and it’s growing.

According to Kubica, for the last 10 to 15 years, other wall systems have been eating into the poured wall market share. “You have ICF’s making a comeback into the market.

Precast is starting to make its dent.

Every new foundation system that comes out on the market has to pull from another market.”

The MonoKast Precast Wall System is manufactured at K-Wall’s factory in Fletcher, North Carolina.

The walls are delivered to the jobsite via truck and trailer. The walls are set in place using a crane and rest on a crushed stone footing as specified by the 2012 IRC building codes.

When placement is completed, the walls are fully insulated and studded. They are ready for finishing and require no additional framing. The stud cavities can have commonly used insulation added to them to further increase the R-Value of the wall. In addition, MonoKast Precast Walls can be combined with traditional cast-in-place walls creating a “hybrid” foundation.

The basic profile of a MonoKast wall includes a 10-inch wide header beam at the top and a 10-inch wide

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footing beam at the bottom; both of which are 3-1/2 inches thick with solid concrete and reinforced steel.

The concrete shell is two inches thick, fiber reinforced, and is 5,000 psi code compliant.

MonoKast precast walls were designed by poured concrete wall contractors FOR poured concrete wall contractors.

wood, only the material we’re using is concrete.”

If you think precast walls is just a fad, think again. It’s a growing market and contractors have a choice to offer another product that goes hand-in-hand with the work they are already performing. Precast walls meet the newest building codes and energy codes, reduces the volume

of materials required for a job and opens up new revenue streams.

“I didn’t say I only poured walls, no, I build walls,” he says. “I came to the realization that I better figure out how to build the next generation of walls before my competitor does.

Poured walls will always be around and will always be the leader.”

PRECAST IS NOT THE ENEMY Precast concrete has its benefits for the builder too—faster construction times, reduced cost of construction, and the versatility of precast makes it an option contractors should consider adding to their service offerings.

“We recently set a MonoKast wall, 180 lineal feet, and the job was completed in three and a half hours, on a Saturday,” he says. “We caulked all the joints, cleaned up and never went back to the job. No one was tired. Everybody was happy and the builders in this area love it.”

Part of Kubica’s drive to promote precast concrete walls as an option for contractors is because they can be set up anywhere. According to Kubica, just about everything is a combination of poured and precast concrete in Western North Carolina.

“While this notion isn’t true for most other markets, it’s an opportunity for the contractor to have a one-stop shop to do everything for the builder–prep the slab, pour the retaining walls and set the MonoKast walls.”

Kubica says it’s difficult for some contractors to see the value of adding precast to their offerings, but the concept of precast walls is simple.

“I’ll always be a poured concrete wall contractor. It’s in my blood, but the difference between that and offering precast walls is it’s like framing. If you’re going to get into the construction of precast walls, you become a framer. We install cripple studs, jack studs and headers.

We’re doing the same thing as the contractor who frames homes with

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COVER STORY

By Joe Nasvik

A New Bridge for the

St. Croix River Engineers and contractors collaborate to build a high-tech bridge.

T

he St. Croix River marks the boundary between Minnesota and Wisconsin. It’s also designated as a National Scenic Riverway by the federal government and is managed by the National Park service. As such, the federal government manages the character of the river, including the bridges crossing over it. The existing steel lift-bridge was built in 1934, crossing the river at Stillwater, Minn. and is only a few feet above water. It has only one lane for traffic in each direction and is worn out. Traffic lines are very long during rush hour and even worse when the bridge is

lifted to allow boats to pass by. Also, the bridge deck is regularly flooded in high rain and watershed events— clearly time for a new bridge.

Michael Beer is the Project Director for the new bridge project for the Minnesota Department of Transportation (MnDOT). He says studies for a new bridge began over 30 years ago to find the least obtrusive and most cost productive location. The following criteria became their decision points: • The new structure should extend from river bluff to river bluff to avoid conflicts with boat traffic.

• The bridge should have a minimum profile to protect the wild nature of the waterway.

• It should be affordable.

A sticking point was portions of the National Scenic River Act of 1969 protecting further development of the river—a bridge must be removed to build a new one and the old bridge had historic status, so it can’t

The new St. Croix River crossing between Minnesota and Wisconsin near Stillwater is an “extra-dosed precast segmental” structural concrete bridge. Shown here are the first three 180 ton segments on either side of the pier, held in place by posttensioned tendons. The blue device is called a “segment lifter” and it also supports a working platform on the edge of the segment that iron-workers use to do the cable tensioning.

Photo Credit: Joe Nasvik

be demolished. So a bill passed

by Congress in 2012 and signed

by President Obama overrode the restriction, permitting the addition of a bridge. The old bridge will get some rehab funding and become part of a walking/biking trail.

DECIDING ON THE DESIGN There was discussion early in the process about what type of bridge to design. Kevin Western, the bridge

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Design Manager for MnDOT, said the 40 or so stakeholders (cities along the river, Dept. of Natural Resources, National Park Service, and others) had to agree on a structure that wasn’t too imposing, would have low impact on the landscape, and design appeal. They settled on an extra-dosed, precast segmental bridge. The extra-dosed part of the design refers to the inclusion of towers about one-quarter the height (approximately 67 feet), of those for a cable-stay bridge. The low-angle support cables together with the post-tension (PT) cables in the precast segments provide the support for the bridge. The new bridge will be an architecturally graceful structure approximately 150 feet above the water on the Wisconsin side and 110 feet on the Minnesota side. The two states share responsibility equally for the project.

NUMBERS AT A GLANCE Total project cost: $640 million (including engineering, right-ofway, approach roadways, rehab of old bridge and five mile bike path) Cost for the bridge construction: $332 million Overall length: 5,075 feet Length over the river: 3,360 feet without expansion joints Width: 100 feet Pier height above water: 175-215 feet Extra-dose tower height: 67 feet Distance between the five piers in the river: 650 feet Number of precast segments over the river: 650 Number of segments over land on the approaches: 330 Concrete: 139,219 cubic yards total. 50,000 cubic yards for segments from Grey Cloud Island.

Post-Tension cable: 2,000 miles Post-Tension for cable stays: 400 miles Steel reinforcement: 42.3 million pounds

Each river pier is split in half. The 1,100 cubic yard concrete cross beams extend through the split and carry most of the weight of the segments and bridge traffic.

Photo Credit: Joe Nasvik

Concrete performs best under compression and the amount imposed by the massive amount of three-dimensional PT reinforcement is awe inspiring.

FOUNDATIONS Beer says the first phase of construction started in the spring of 2013. Ed Kraemer and Sons Company, Plain, Wis., won the bid to construct the foundations for the five piers including pilings, nine-foot diameter drilled shafts, and piers up 15 feet above the level of the river.

Working off a precast concrete platform they de-watered the area and cast mass concrete mixes for the drilled shafts. Each pier foundation has four drilled shafts followed by a pile-cap and then a foundation pier extending 15 feet above water. The contractor went through 25-feet of water and 85-feet of muck to drill sockets 25 feet into the sandstone rock.

PIERS In 2014 the joint venture of Lunda Construction Company, Black River Falls, Wis., and Ames Construction Inc, Burnsville, Minn., started pier construction. The five sets of piers in the river separate into two very graceful, architectural concrete columns with changing geometry as they rise, joined together near the top with massive 1,100 cubic yard cross-beams to carry the precast segmental deck. EFCO supplied steel forms for this work. On top of the piers the extra-dosed columns rise another 67 feet, bending outward to counter the forces of the stay-cables.

Delivering concrete for the piers wasn’t easy. Concrete from ready-mix trucks is delivered to a pump located on a dock constructed for the purpose and pumped into a ready-mix truck mounted on a barge. Tugboats deliver it to a concrete pump mounted on a barge at the placement site.

PRECAST SEGMENTS The method for casting segments for bridgework can either be cast-in-place or precast. Only one section of curving approach is cast in place explains Paul Kivisto, MnDOT Bridge Engineer for this project.

“The changing geometry and height change of the segments made this less expensive.” Dale Even, Lunda/ Ames project manager, says the decision to precast the segments allowed for a more aggressive construction schedule because segments could be cast all year long, with several placed in position each day.

The bridge approach segments are all cast on site and vary in depth from 10 to 14 feet, weighing approximately 80 to 120 tons each.

The segments over the river have a constant 18 foot depth, making them much easier to cast in a precast facility. Even says they searched along the shores of the St. Croix and Mississippi Rivers for a good precast site before settling on Grey Cloud Island on the Mississippi, 33 miles from the bridge site. They leased the space from Aggregate Industries who is quarrying aggregate and sand there and is also supplying concrete for the extra-dosed segments. Mobilization work included building a slip for 200 foot long barges with compacted subgrade to support the 250 ton straddle crane used to load segments on the barge. Even says they had to remove up to 14 feet of poor soil and replace it with compactable fill

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COVER STORY before the 1.5 acre climate controlled building could be constructed. In addition, outdoor storage areas had to be conditioned to support the weight of several hundred segments.

The precast facility houses five molds plus an area for preassembling rebar reinforcement.

Workers place stainless steel rebar in the top region of segments (deck area) to eliminate the possibility of corrosion. Even says they can produce two castings per mold per week year-round at the facility and they plan to cast until next June.

All precast segments on site or at the precast plant are “matchcast,” meaning that the edge of the previous casting becomes the mold-face for the next casting.

After concrete placement and initial curing, the castings are separated, the original is moved to the storage yard and the new one is removed from the mold to become the formface for the next one. In this way, geometry for the project is controlled and there is only one location for each segment. Even says important segment dimensions must be controlled to within 0.001 of a foot tolerance.

PROJECT PARTICIPANTS Owner: MnDOT and WisDOT General Contractor: Lunda (Black

River Falls, Wis.) and Ames Construction (Burnsville, Minn.) joint venture General Contractor, Foundations: Ed Kraemer and Sons Com-

Segments are “match cast.” The segment shown here serves as the mold face for the segment about to be cast inside the green steel mold.

They will be positioned beside each other on the bridge. Two castings per week are produced in each of the five molds at the precast plant.

Photo Credit: Joe Nasvik

pany, Plain, Wis. Engineer of Record:

PLACING SEGMENTS OVER WATER

HDR Omaha, Neb.

Each barge makes the 33 mile trip down the Mississippi and up the St. Croix River with up to 12 segments. On location, “Segment Lifters” secured to the top of the last segment erected, lift a segment off the barge and move it into position.

Workers quickly spread epoxy on the interface of the castings so that when joined, there will be no voids for moisture to penetrate.

There is no support for segments after they are secured to the structure, so a pier is like a balance beam, when you place a segment on one side of the pier you must place one on the other side to balance the load. Kivisto says the ninth segment from a pier is the first one to receive an extra-dose PT cable and thereafter every other segment. In this way segments span

land Taylor, Vancouver, Canada Consultant to Lunda/Ames: McNary Bergerson, Longmont, Colo.

Consultant to Lunda/Ames: Figg Engineering

Consultant to Engineer: Buck-

Reinforcement and PT:

Lunda/Ames Ready-mix Concrete: Cemstone,

Mendota Heights, Minn.

Ready-mix Concrete: Aggregate Industries, Egan, Minn.

Concrete Pumping: RS (Rick and Shirley), Baldwin, Wis. Concrete mix designs: Beton Consulting Engineers, Mendota Heights, Minn.

Construction Engineer and Inspection Consultant: Parsons,

Pasadena, Calif.

As many as 12 segments are loaded on a barge and brought to the bridge site. The segment lifter attaches to four bolts on the casting and lifts it into place. The lifter can move vertically and horizontally and advances as the deck lengthens.

Photo Credit: MnDOT

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approximately 320 feet without support before they are joined to those coming from the opposing pier.

POST-TENSIONING The miracle of segmental bridge construction is post-tension reinforcement. When a segment is lifted into position workers quickly install 12 temporary PT bars in ducts located at the top of the 50 foot wide segments—two segments side by side make up the full lane width of approximately 100 feet.

Kivisto says they tension each bar to 175,000 pounds. Then 25 PT cables are installed per duct at the top of segments to its mate on the other side of the pier. Each is tensioned to 42,000 pounds for a total force of over 1 million pounds.

Tendons placed at the top of a segment are referred to as “cantilever tendons” and are used to secure segments during construction.

Tendons installed at the bottom of castings occur when all segments are in place between piers. They extend from pier to pier and are called “continuity tendons.” They are draped to create a lifting force on the segments and their purpose is to carry the load once the bridge is opened to traffic.

Each of the 76 extra-dosed cables is stressed to approximately 33,000 pounds for a total of more than 2 million pounds for each stay.

PILES, PILE CAPS, FOUNDATIONS: They are classified as mass concrete and non-air entrained. Without the aid of cooling tubes the mixes were designed not to exceed 160 degrees Fahrenheit during the curing process nor exceed a differential temperature of more than 35 degrees Fahrenheit anywhere within the placement for the first two days.

For the next seven days, 50 degrees Fahrenheit is allowed and then 60 degrees Fahrenheit thereafter.

PIERS: Air-entrained, 8,000 psi mass concrete with enough strength development to strip forms one or two days after placement. MacDonald says

The pier foundations in the river extend approximately 140 feet below the surface of the water, more than half that depth being river mud.

Photo Credit: MnDOT

this was his greatest challenge for the project. He adds that predictive software now makes it possible to determine what the required stiffness (modulus of elasticity) will be.

The extra-dose towers have different mixes than the piers.

SEGMENTS CAST ON SITE: Air-entrained, 6,000 and 8,000 psi concrete with enough strength to strip forms a couple days after placement.

Segments over the river: 3,500, 6,000, 8,000, and 9,000 psi requirements depending on where the segments are located. Even says early strength is required to remove castings from molds within 12 to 18 hours.

CONCRETE AT ITS BEST The bridge is entirely structural concrete and represents state-of-theart technology. It’s the second extradosed bridge in the U.S. The spec documents require a minimum 100 year service life with minimal maintenance—something not possible with structural steel. Placing segments will stop this winter when there is too much ice on the river for barge traffic and will continue through the 2016 summer. It will open for traffic that fall.

Ed. Note: See more pictures from this project at www.ForConstructionPros. com. Search “St. Croix River Bridge”.

CONCRETE MIXES Kevin MacDonald, president of Beton Consulting Engineers, Mendota Heights, Minn., says he developed 19 concrete mixes for the project and Cemstone supplied all the ready-mix concrete on site.

Aggregate Industries developed two mixes for the segments created at the Grey Cloud Island precast plant.

MnDOT required granite aggregate for some mixes and allowed for up to a 70 percent replacement of cement—fly ash and slag used as replacements. Here’s a run-down on the requirements:

“Cantilever tendons” are inserted into the white duct holes just under the driving surface, 25 tendons per hole. They secure segments to the structure. “Continuity tendons” are installed at the bottom of the segments and run from pier to pier after all the segments are placed.

Photo Credit: Joe Nasvik

www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 25

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DECORATIVE CONCRETE

By Ryan Olson

Hardscape Design Creates A Canvas For Historic Post Office

The close working relationship between the concrete contractor and the design team was crucial to the success of the decorative concrete work on a restoration project.

F

or the Wallis Annenberg Center for the Performing Arts, located in Beverly Hills, California, architects were challenged to restore the historic 1933 Beverly Hills Post Office and a new 500 seat theater. The Post Office also includes an additional 150 seat theater. The new, modern building was designed to reflect the activity of what happened on the site so many years ago. The sides of the building display what appears to be open and partially opened letter envelopes, a nod to the historical nature of the site.

“The building was so extravagant.

There was this beautiful post office building and the striking new building.

We worked primarily with the landscape architects, Lutsko Associates to achieve something subtle which would create a nice canvas for the building,” says Lance Boyer, president of Trademark Concrete Systems, Inc. and Chairman of ACI 601D (Decorative Concrete Certification).

Trademark Concrete Systems Inc., Anaheim, California, was tasked with constructing the cast-in-place planter walls and decorative concrete pedestrian and vehicular paving. In business since 1997, Trademark Concrete Systems Inc. focuses on providing

higher-end decorative concrete work.

Considering the job was a project spotlighted in Beverly Hills, Boyer says the expectations were quite high.

“This Los Angeles market is a sophisticated decorative concrete market. The architects and landscape architects understand decorative concrete and they have a good understanding of concrete in general.”

The project called for 940 lineal feet of cast-in-place concrete walls ranging in height from four feet to 14 feet; 34,000 square feet of EcoCast finish pedestrian and vehicular paving and 1,100 lineal feet of cast-inplace steps. The pedestrian and vehicular paving as well as the steps featured Beverly Hills Beige integral color seeded with Feldspar, a reflective aggregate.

While the vast majority of the walls were straight, some curved walls reached heights of 14 feet.

The walls were built using site-built plywood forms and finished with a smooth texture. Walls which were less than five feet were stripped and finished on the same day.

“A lot of contractors don’t do that, however, in doing so, we get a more consistent finish on the concrete when we strip and finish decorative concrete walls the same day,” Boyer says.

The project called for 940 lineal feet of cast-in-place concrete walls ranging in height from four feet to 14 feet; 34,000 square feet of EcoCast finish pedestrian and vehicular paving and 1,100 lineal feet of cast-in-place steps.

Photo Credit: Trademark Concrete Systems Inc.

According to Boyer, the biggest challenge of the project were the multitude of parallel saw cuts, over 16,700 lineal feet which would provide the linear hardscape design.

During the design stages of the project, Boyer and his team communicated with the landscape architect to discuss the technical issues of the project.

“We focus a lot on controlling cracking. We work with the design team and submit shop drawings, something most decorative concrete contractors don’t do, but they should,” he says. “We take the design and recommend ways to minimize shrinkage cracking and improve the concrete paving as a whole.”

Since the design itself was very lineal and many of the joints were

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THE PLAYERS Concrete Contractor: Trademark Concrete Systems, Inc. Architect: SPF:a, Studio Pali Fekete architecture Landscape Architect: Lutsko Associates General Contractor: Matt Construction Products Used on the Job: EcoCast surface retarder Feldspar Trademark Beverly Hills Beige integral color

placed in a longitudinal direction, Boyer said he recommended adding transverse joints to break it up in smaller areas. “Architects don’t want to interrupt the design with cuts, but we try to minimize the disruption to their design and always explain that a joint is far better than a crack.”

consistency throughout the project.

Boyer’s team hand cut all joints by hand using a circular saw on rollers outfitted with diamond blades. “We don’t use a large walk-behind saw. We have a team of dedicated craftsmen who saw cut the joints and they are great at it.”

SAW CUTS

SAMPLES AND SHOP DRAWINGS

“A big challenge, especially in concrete, is to have a long straight line,” Boyer says. “You’re cutting a 600 foot straight line and you’re making multiple [concrete] placements between the starting point and the ending point.”

The whole job was based on a grid, which should have made the project easier. However, as Boyer notes, “another significant challenge in decorative concrete is to maintain a square— parallel and perpendicular lines—that extend for several hundred feet.”

To make the saw cuts accurate, Trademark’s crews utilized a total station unit. He says, contractors should embrace technology to assist with

Making samples of the potential work, providing site mockups and utilizing shop drawings of the project have been key factors to the success Trademark Concrete Systems Inc. has achieved. As an architectural concrete contractor, color and texture play critical roles in the projects the firm chooses to build.

In the case of this project, the architect was looking for a higher value concrete but not necessarily at a higher cost. Trademark submitted a series of samples for consideration which included the Feldspar reflective aggregate.

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nor are there any questions as to what is being called for in the design plans.

“A contractor can learn a lot working with design professionals,” Boyer says.

“They look at concrete differently than we do. And I think they (architects) push contractors to be more creative. But the relationship also gets the contractor involved on the front end of the project. It separates you from your competition and gives you more credibility.

Contractors often complain about the specifications on a project but I have to stop and ask – ‘What are we doing about it?’ If the contractor can be an advisor to the architect, it makes the whole industry better. This is exactly why more contractors should be involved in the American Concrete Institute. When you get involved, you’re growing the industry. Contractors are good mechanics, but not necessarily designers. The partnership between the contractor and the architect creates a position to educate the design professional.

We can talk to them about the things they can do with concrete, and of course, tell them how to achieve it.

As a contractor, that’s our responsibility, to make the industry better.”

VAPOR BARRIER

Making samples is a regular practice for Trademark.

The samples are used to offer assistance with the visualization of the project. In fact, he says the firm makes and distributes well over 500 samples a year in the Southern California marketplace.

“We visit with the architects at the front end of the project, helping with the design. We want to be an information hub for architects and landscape architects, it’s very important,” Boyer says.

“I think contractors tend to be more reactive, and ask ‘Why should I make a sample if I don’t have the job?’ Well, you make the sample to show people what you can do. It helps you get jobs like this one and it helps you separate yourself from the competition.”

The other key to Trademark’s success is the use of shop drawings during the preparation stage of the project. Boyer says his team typically coordinates the civil engineering plans, the architectural plans and landscape plans and incorporates the information into a shop drawing. He says the shop drawing is a great communication tool when performing the work. There are no surprises for the work that is expected to take place,

SLAB-on-GRADE

Photo Credit: Trademark Concrete Systems Inc.

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The biggest challenge of the project were the multitude of parallel saw cuts, over 16,700 lineal feet which would provide the linear hardscape design.

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 29

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BUSINESS MANAGEMENT

By Elizabeth K. Schneckenburger

CFA Helps Members Manage Total Cost of Risk (TCOR) Arthur J. Gallagher has been endorsed as the insurance broker to implement the CFA member insurance program.

W

hat is a good insurance renewal?

When we challenged our clients and prospects to explain what a good renewal is they consistently said something relating to a premium decrease. Great renewals should not necessarily be based on the premium. Do you agree that the deceiving part of purchasing insurance is the only visible cost is the premium? Would you purchase the lowest premium if you knew in advance that the Workers’ Compensation claims handling would be in disarray? Of course not! Even though this is the case, the vast majority of insurance deals are based on premium price only with very little consideration given to the insurances carrier’s history of claims procedures, industry expertise, innovation, and the agent/carrier relationship.

Have you ever purchased insurance based on the insurance carrier’s statistical data supporting their expertise in the construction industry or asked for statistical data that supports the carriers’ ability to efficiently settle claims? Managing risk and insurance is always in the top three expenses for a contractor

and deserves a solid process.

When you stop and think about all of the internal costs associated in managing a contractor’s risk it is easy to see it is far more than purchasing insurance. A contractor’s biggest risk and financial exposure lies within the hidden expenses tucked away from the visible cost, your premium. Insurance as a whole is made up of underwriting, insurance companies, agents, adjusters, lawyers, claimants, governing agencies like the NCCI and OSHA, and auditors. If the system is not operating like a well oiled machine it causes friction and disruption which in turn increases the costs to the contractor. We’ve listened to all of the common difficulties contractors experience. Without a doubt the frustrations are consistent: payment of fraudulent claims, mishandling and over payment of claims, fluctuating premium costs, coverage exclusions, contracts, uncovered claims, experience mod, certificates and audits, just to name a few. To pile onto the frustrations the only

Hard Costs

Soft Costs

item that you feel you have control over is the premium.

For this reason 23 Concrete Foundation Association (CFA) members set out on a mission to create a CFA member “risk management” insurance program. The determined group was adamant their program had to be different than the insurance a contractor could buy elsewhere and pursued a partnership with Arthur J. Gallagher (Gallagher).

Being the fourth largest broker in the world with a construction niche placing in excess of a billion dollars in construction premiums, and local offices in the CFA footprint, made them a natural fit for the CFA. The CFA will rely on Gallagher’s market leverage and outstanding insurance relationships to partner with suitable insurance companies to kick the program off in October 2015.

TOTAL COST OF RISK Rolling out the CFA insurance program was part of a strategy that will help CFA member companies manage all of their costs associated with risk. “Total Cost of Risk” or TCOR is made up of premiums and soft costs. Soft costs are typically not being tracked but have a huge overall impact on your total cost of risk. The soft costs we refer to include: production loss/ worker distractions, replacing and training new workers, loss of skill, paperwork (certificates, insurance management, etc.), loss of morale, legal issues, medical expenses, wages, equipment, and workers compensation (experience modifier, claim reporting and lag time, etc.). By focusing on these items and not just the premium the CFA program will be different.

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Understanding that on a typical $100,000 contracted job, your expense breakdown would be roughly $90,000 leaving your profits to be about $10,000. All soft costs associated with risk management are not included within your expense breakdown and immediately eat away at profits. We understand these types of soft cost losses could detrimentally impact a whole year’s worth of hard work.

HOW IS THE CFA PROGRAM DIFFERENT? Insurance agents attempt to provide customers with an advantage but how many actually track the results and show them to you? This is one specific difference that will be the most impactful for the CFA Insurance Program. The CFA and Gallagher partnership will allow for the distribution of powerful data pertaining to the concrete foundation industry. Program members will have

access to benchmarking and CFA trend analysis, coverage comparisons, minimum mod analyses, CFA specific claims management, and risk control designed for CFA members to aid them in managing their TCOR and in making business decisions.

Purchasing power. Yes, purchasing insurance as a group rather than an individual should save companies 10 percent. In addition by using Key Performance Indicators we aim to measure the success of the program on many levels beyond just claims totals.

Creating best practices. Let’s team up and create safety, claims handling, return to work and contract review processes that are proven in the field of foundations for CFA members.

Coverage specifically designed for concrete foundation contractors.

The CFA will have its own coverage forms with state departments of insurance. Gallagher will also be performing policy analyses for each line

of coverage. We’ve seen, on average, about 97 percent of policies we have reviewed have insufficient limits or gaps in coverage.

WHO IS ELIGIBLE TO PARTICIPATE? The companies eligible to join this program are those who have a current CFA membership status.

The CFA insurance program will provide a platform to share best practices, discuss employment and recruiting practices, discuss current industry trends, and much more.

Being able to share ideas, thoughts on bidding jobs, site safety protocols, etc. through a real time blog is an unparalleled resource to have as a decision maker.

Ed. Note: For more information about this program, contact Executive Director of the CFA, Jim Baty, Jbaty@cfawalls.org or Kristen Long at kristen_long@ajg.com.

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 31

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CONCRETE RESEARCH

By Heather Brown and Jason Crabtree

Does Cold Curing Water Cause Concrete Surfaces to Crack?

Tests were conducted to determine if curing water wasn’t heated, would the concrete crack?

F

or many years it’s been assumed that applying cold curing water to hot concrete surfaces can cause thermal shock and cracking. As early as 1971, Section 2.2.1 of ACI’s Recommended Practice for Curing Concrete (ACI 308-71) advised that curing water used for ponding should not be more than about 20 degrees Fahrenheit (11 degrees Celsius) cooler than the concrete, because of temperature-change stresses which would be introduced with resultant cracking. More recently, ACI 308R-01 (re-approved 2008) “Guide to Curing Concrete” broadened the recommendation to not just water used for ponding, but to water used for continuous sprinkling and initial water application before covering with sheet materials.

“Curing water should not be more than 11 degrees Celsius (20 degrees Fahrenheit) cooler than the internal concrete temperature to minimize stresses due to temperature gradients that could cause cracking (Kosmatka and Panarese 1988). A sudden drop in concrete temperature of about 11 degrees Celsius (20 degrees Fahrenheit) can produce a strain of about 100 millionths, which

The form above was was filled to the top. An immersion thermometer was inserted in the slab and the concrete temperature was recorded for two hours and 40 minutes until right after curing water was applied. approximates the typical strain capacity of concrete.”

Some people believe the cold water will result in shallow craze cracking and others believe it will result in deeper thermal cracking.

Section 11.3.7 on Industrial Floors in ACI 301-10, Specifications for Structural Concrete, changed control of curing water temperature for all applications from a recommendation to a mandatory requirement with the statement that: “Temperature of applied [curing] water shall not be

During the test, one form was filled with concrete to an elevation about two inches below the top of the form to allow ponding.

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Table 1: The concrete batch quantities for a cubic yard are shown. more than 20 degrees Fahrenheit colder than the concrete surface temperature.”

That means, in many cases, curing water would have to be heated to meet specification requirements. If a contractor is placing an industrial floor during hot weather and is using well water for curing, the water temperature is likely to be between 55 degrees Fahrenheit and 60 degrees Fahrenheit.

That would limit the concrete surface temperature to between 75 degrees Fahrenheit and 80 degrees Fahrenheit unless the contractor first heated the curing water. Ponding water to a depth of one inch on a 20,000 square foot slab would require about 12,400 gallons of heated water. The largest water trucks will hold between 4,000 and 5,000 gallons of water, so three of these would be needed for ponding.

For an initial water application before covering with sheet materials, the required amount of water to be heated would be significantly less, perhaps 1,600 gallons. Do contractors ever heat curing water? We don’t know, but we’ve not heard of it. Does the surface temperature of flatwork often exceed 75 degrees Fahrenheit to 85 degrees Fahrenheit? Yes. But if the curing water wasn’t heated, would the concrete crack? Data was needed to answer the second question.

THE TEST Forms were built with 2x8-inch lumber, with crushed stone put in the bottom to simulate a base course. Two 2x2-foot square slabs were cast in a parking lot—one to be cured by ponding and the other by wetting the surface then immediately covering it with plastic sheeting to prevent evaporation. Mixing water was heated to achieve a concrete temperature of about 90 degrees Fahrenheit and curing water cooled to 35 degrees Fahrenheit to achieve a temperature difference much greater than 20 degrees Fahrenheit.

The concrete batch quantities for a cubic yard are shown in the table.

Previous testing of concrete with these

Mix Ingredients and Proportions for Concrete Ingredient

Quantity (lbs./cubic yard)

Portland cement, Type I/II

564

Coarse aggregate, #67

1892

Fine Aggregate, natural

1214

Water

253

Midrange water-reducer

4 oz./100 lbs. cement

Water-cement ratio

0.45

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CONCRETE RESEARCH proportions produced an fc’ (specified strength) of 4,000 psi. Cement, sand, and crushed stone were stored at an ambient temperature of 89 degrees Fahrenheit prior to batching and tap water at 108 degrees Fahrenheit was used for mixing.

To avoid possible head pack in the tilting mixer, about 80 percent of the mixing water and all of the crushed stone was first added and mixed for less than a minute before adding the sand, cement, and the rest of the water. The standard laboratory cycle—mix three minutes, rest three minutes, and mix two minutes—resulted in a low slump so more water was added to produce the final slump of 3-½ in. Total mixing time was 10 minutes. The concrete temperature was 85 degrees Fahrenheit and density was 149 pcf.

Because the tilting mixer was loaded to capacity, there wasn’t enough concrete to make test cylinders.

Instead, the slabs will be cored at 28 days to determine in-place strength.

One form was filled with concrete to an elevation about two inches below the top of the form to allow ponding. The other was filled to the top of the form. An immersion thermometer was inserted in the slab filled to the top of the form and the concrete temperature was recorded during the following two hours and 40

TEMPERATURE VS. TIME FOR CONCRETE AND CURING WATER

minutes until right after curing water was applied. After consolidation by tamping, strike-off, and a float pass, the concrete was monitored during the waiting period to determine when to start final floating and troweling.

After the initial floating there was no bleedwater, so final finishing was started when a footprint indentation was about one-quarter inch. After floating the surfaces of both slabs, they were hand troweled, then checked periodically to make sure the troweled surface was hard enough not to be marred by adding curing water.

As soon as water was added to a depth of one inch on the ponded specimen, an immersion thermometer was used to measure ponded water

Pictured above, is the dried surface of the ponded slab after seven days with the rim still on and caulk visible at the edges.

temperature. Results are shown in the graph above. Note that in one minute the curing water temperature rose from 35 degrees Fahrenheit to 50 degrees Fahrenheit, and 15 minutes after ponding, the water temperature had risen to within 21 degrees Fahrenheit of the concrete temperature.

Several gallons of curing water were slowly poured on the other slab at one edge, flooding the entire concrete surface for several minutes.

Plastic sheeting was then placed on the slab and smoothed to eliminate most of the air bubbles. Boards were placed on the slab to hold down the plastic and shield the surface from direct sunlight to minimize mottling so any cracks would be more observable.

Pictured above, the surface of the slab cured with plastic sheeting was wet and also checked for cracks after seven days. No craze or thermal cracks were noted in the slab.

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AND THE RESULTS ARE‌ The surfaces of both slabs were examined for cracking just before curing water was added, and observed for cracking each time the ponded water temperature was measured. No crazing or thermal cracking was noted, including the area where all the curing water was added. The following day the surface was examined through the ponded water and no cracking was noted. A slight discoloration (zebra striping) was noted on the other slab, but no crazing or thermal cracking was noted. After one week, water was drained from the ponded slab and the surface was examined as it dried to check for cracks. The surface of the slab cured with plastic sheeting was wet and also checked for cracks. No craze or thermal cracks were noted in either slab.

CONCLUSION A temperature difference of about 60 degrees Fahrenheit between the concrete and curing water produced

no crazing or thermal cracking. Thus a specified maximum temperature difference of 20F is extremely conservative.

Based on these results it would be interesting to know the origins of the 20 degrees Fahrenheit limit. Other than the statement that a 20 degrees Fahrenheit difference in temperature can produce a strain of about 100 millionths, which approximates the typical elastic strain capacity of concrete, there is no further explanation in the ACI documents cited. The 20 degrees Fahrenheit difference may have been the result of an elastic analysis based on the thermal coefficient of expansion of concrete, and assumptions that thermal contraction was fully restrained and there was an immediate drop of the surface concrete temperature to the curing water temperature. Based on the results of this experiment, assumptions made to calculate the 20 degrees Fahrenheit limit must be incorrect. It would be interesting to determine which assumption or assumptions are incorrect by

performing a similar experiment in which sensors would measure concrete temperature and curing water temperature simultaneously during the curing period.

Ed. Note: Heather J. Brown, PhD, FACI is Chair and Professor for the Concrete Industry Management Program at Middle Tennessee State University. She can be reached at heather.brown@mtsu.edu.

Jason Crabtree is Laboratory Manager for the Concrete Industry Management Program at Middle Tennessee State University. He can be reached at jason.crabtree@mtsu.edu Acknowledgements: The authors appreciate the assistance of two participants in the National Science Foundation Research Experience for Undergraduates program, Caroline Pounal and Kyle Schuetrum. Thanks to the American Society of Concrete Contractors for assisting with the study.

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PRODUCT FOCUS

By Ryan Olson

CERATECH Cement – Setting New Measures for Concrete Durability and Sustainability A non-portland cement concrete offers contractors the ability to use less water in a concrete mix, while also making a near zero carbon concrete with enhanced durability.

C

oncrete, as the number one building material worldwide, has experienced many advances over the last century. Improvements in transportation, plant/batch equipment, and a multitude of admixtures enhancing the characteristics of portland cement concrete are integrated into everyday activities. In addition, supplementary materials including fly ash (Class C and F), slag cement, and microsilica are part of the cementitious equation with portland cement, enhancing a concrete’s properties. Percentages of these materials used with portland cement are based upon cost, availability, performance attributes, and/ or capacity to meet industry standards—until now.

CeraTech, an American company headquartered in Alexandria, Virginia, with research and development activities based in Baltimore, Maryland, markets a non-portland cement concrete. CERATECH Cement meets

Workers pump CeraTech’s KemROK concrete into a trench for handling molten sulphur during reconstruction.

The trench, previously constructed with Type V portland cement and 7% micro silica, would typically need replacing every 18 to 24 months from deterioration. The KemROK trench has been in place over four and a half years with no deterioration from the 350 degrees Fahrenheit molten sulphur exposed to the concrete on a daily basis.

Photo Credit: Ceratech

ASTM C1157 and C1600 as a hydraulic cement system comprised of 95 percent recycled fly ash and five percent readily renewable liquid additives – making a near zero carbon concrete with enhanced durability. CeraTech’s concrete is accepted in American Concrete Institute (ACI) standards, International Code Council (ICC) building codes, and the many “green” rating systems across the county.

CERATECH Cement forms a denser and less permeable crystalline matrix through the hydraulic reaction between fly ash and their proprietary additives. This is in comparison to the traditional gel structure in portland cement concrete. According to Mike Weber, Corporate Director at CeraTech, “While there is a major distinction between the chemistry of the two cements, the mixing and placing behavior of both systems are very similar. Producers will batch materials in a similar fashion, and with comparable batch weights as portland cement concretes. It is a

‘plug-and-play’ system with an additional added benefit; CeraTech concretes use approximately 50 percent less water than portland mixes.”

Enhanced physical properties and attributes include: • A water cement (W/C) of 0.18 to 0.25 for a typical six to nine inch slump mix offering greater durability from a discontinuous capillary network.

• Approximately 30 percent lower heat of hydration.

• Reduced shrinkage up to 50 percent.

• Early design strengths for in-service applications in as little as seven days.

• Reduced creep value of approximately 50 percent.

• Chemical resistance – in many cases eliminating the need for epoxy coatings.

• Heat resistance of 570 degrees Fahrenheit continual (24/7), and 1,850 degrees Fahrenheit intermittent (15 to 30 minutes).

Comprised of “Class C” fly ash and proprietary liquid additives, when combined the liquids dissolve both the reactive glasses and the

36 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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NEWhp 1.5-nd a hp 2.5- ors t Mo

Optimum concrete consolidation Wacker Neuson’s flex-shaft vibrator system offers a variety of motor, head and shaft combinations to choose from for cost effective concrete consolidation. The new 1.5-hp and 2.5-hp motors are lightweight, extremely durable and the quick disconnect makes flex shaft exchange easy. With a solid reputation for reliable products and service, Wacker Neuson is the brand to you can trust and your partner for the long run.

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PRODUCT FOCUS crystallized hydraulic solids in the fly ash, producing a reactive hydro gel forming a calcium aluminate silicate (CAS) hydrate called stratlingnite. The formation of this CAS hydrate causes set and strength development. It is the physical and chemical properties of this very dense crystal structure that provides for performance advantages over traditional materials in a broad range of applications.

CeraTech’s three most popular brands include: ekkomaxx, KemROK, and FireROK.

EKKOMAXX ekkomaxx uses a non-portland activated fly ash system offering a variety of performance advantages over traditional cement such as improved durability, corrosion resistance in wastewater applications, improved volume stability, low heat of hydration and low retained moisture (fast drying).

Weber says ekkomaxx concrete produces less heat, minimizing the potential for micro cracking due to thermal stresses. “In many cases, secondary methods used for mitigating heat during curing may be eliminated making it ideal for placements of mass concrete.”

If you’re a contractor who performs concrete pavement work, ekkomaxx provides low permeability, freeze thaw durability, scaling and sulfate resistance and immunity to an alkali silica reaction. Additionally, low shrinkage and less micro cracking make it a durable choice for highway and airport concrete pavements.

For projects that require the installation of a flooring or topping, ekkomaxx cement concrete’s rapid drying allows for most systems to be placed in less than 14 days from time of installation without the need for additional chemicals.

Finally, ekkomaxx concrete is

resistant to microbial induced corrosion (MIC) inhibiting sulphuric acid corrosion in wastewater applications.

KEMROK CeraTech’s KemROK cement is designed to restrict access of corrosive liquids through the concrete reducing the potential of reinforcing steel corrosion and concrete deterioration. Typical placements of KemROK include industrial and chemical environments where deteriorated concrete can create plant shutdowns and frequent maintenance issues.

Comprised of acid resistant crystalline hydrates, the calcium content of KemROK is very low and does not contain calcium hydroxide or calcium silicate hydrates.

Because of the very low water to cement ratio (0.18 – 0.25), KemROK creates an extremely dense crystalline concrete matrix with a discontinuous capillary network preventing

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caustic and corrosive chemicals from passing through the concrete and thereby protecting the integrity of the concrete and reinforcing steel.

FIREROK Engineered to produce a structural concrete demonstrating superior durability in environments with high thermal cycles and temperatures, FireROK can withstand intermittent temperatures as high as 1,000 degrees Celsius (1,850 degrees Fahrenheit) and sustained temperatures up to 300 degrees Celsius (570 degrees Fahrenheit) without significant loss of strength.

FireROK cement concrete is made up of a dense interlocking network of crystalline calcium aluminosilicate hydrates that allow for twice the heat capacity and five times the thermal conductivity of typical portland cement concrete. Spherical cement particle shapes reduce yield

stress and viscosity during mixing and allow for low water to cement (w/c) ratio mix designs (0.18 – 0.25).

These characteristics contribute to the FireROK’s ability to handle high temperature environments.

When portland cement concrete is exposed to high temperature, free moisture within the concrete will convert to steam and can cause surface spalling. In addition, at temperatures at approximately 220 degrees Fahrenheit portland cement concrete will start loosing structural integrity.

Conversely, FireROK cement concrete requires less than half as much mix water as portland cement concrete. Additionally, this mix water is consumed in the hydration process leaving little available free water to facilitate the steam spalling process.

According to Weber, FireROK cement concrete conducts heat five times faster than ordinary

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portland cement concrete making it less susceptible to cracking and spalling due to thermal stresses.

Therefore, heat is absorbed more slowly. Because of this characteristic, heat dissipates rapidly, reducing thermal stresses that contribute to loss in strengths and ultimately the structural integrity of concrete.

Stadium Model research currently underway is showing CeraTech’s concrete exceeding 2.6 to 3 times the life cycle of a typical portland cement concrete. In addition, when comparing the in-place concrete system cost, CeraTech concrete is often less expensive than standard alternatives with limited life cycles.

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 39

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CONCRETE SUSTAINABILITY

By Larry Rowland and Jeff Sieg

Why You Should Care About

Resilience

C

oncrete is the most widely used manmade construction material in the world. It is versatile, economical, durable, recyclable, environmentally responsible and most importantly, it is resilient. Resilience is where the promise of sustainability and the real world meet. And while

“resilience” may seem to be just the latest buzzword among green building enthusiasts and building designers, the concept of resilience is something we all need to care about.

It’s not green if it’s not resilient.

As society has embraced sustainable design, more and more owners and end users are questioning tradeoffs made in the name of being

green. This theme was clearly displayed when the cover story of the December 2014 issue of Building Operating Management posed the question: Are Green Buildings Fire Safe? The article pointed out that as the design industry embraced new materials that delivered benefits such as rapidly renewable content, important safety and durability considerations were sometimes

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CONCRETE SUSTAINABILITY ignored. As Louis Gritzo, Vice President of Research for FM Global states: “...a building that burns down is not green, regardless of how it was originally constructed… A green building must be resilient and sustainable in the long-term.” It is this common sense approach that is driving the resilience discussion.

Long term use and serviceability is the key to a building’s sustainability.

During the design phase of a contract, if not before, it is important to understand the risk of using inferior materials and how they can compromise safety and the service life of the built environment. Lessons learned on making long-lasting structures may not be in vogue with designers seeking to embrace cutting edge technologies in building materials. However, materials susceptible to fire, attack by insects, and wind or water damage or that are simply not strong enough to endure their surroundings are not

sustainable and needlessly put lives and property at risk. A tragic example of this is the balcony collapse in Berkeley, California, on June 16, 2015.

The cause of the collapse was directly related to decayed wooden, laminated veneer lumber (LVL) beams.

The collapse resulted in 13 college students plunging four floors to the street below. Six of the 13 perished, including five international students.

According to the report prepared by the City’s Planning and Development Department’s Building and Safety Division, the balcony failed due to severely dry rotted deck joists that were in service for less than nine years!

The reality is that most of us don’t consider long-term safety when we buy a home or when we go to work, to school, shopping or otherwise go about our daily lives.

We assume these structures are safe and resilient. Essentially, we

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trust that regulatory agencies and government officials charged with protecting our interests have the tools and training needed to limit our exposure to risk. For our trust to be justified, it is critical that building code officials and decision makers really understand the hazards our communities face and what building assemblies and types of construction will protect us from those hazards.

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42 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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local and state code adoption groups about the advantages and true cost of building with concrete. The more these groups know about concrete, the more they will recognize that concrete is the ideal material to meet sustainable design considerations, for resilience, durability and safety.

In addition, we must proactively train designers how to design and build with concrete and concrete products to ensure cost effective, enduring assemblies. The result of these efforts will be safer, more resilient communities that make sustainable use of resources and provide a solid foundation for economic growth and prosperity.

While much of the building industry presumes that concrete is resilient, others may insist we back up this claim. The good news is that time and again, concrete has been recognized by organizations such as the Federal Emergency Management

Agency (FEMA), The Federal Alliance for Safe Homes, (FLASH), the National Institute of Building Science (NIBS) and others as the preferred product to withstand the effects of all types of hazards.

Examples of applications where concrete is specified for its non-combustible properties and for its exceptional strength and durability include wildfire safety and tornado protection via safe room construction.1 Likewise, concrete’s robust structural characteristics make it ideal in foundation and wall systems in flood and hurricane prone communities.2 The risk of damage in a hurricane greatly increases as the wind speed and storm intensity; measured by the Saffir-Simpson Hurricane Scale, or storm Category builds. The Florida Homeowners Handbook to Prepare for Natural Hazards,3 states that Category 2 storms

are expected to cause structural damage to poorly constructed or termite infested buildings and even well built, small residences may see damage in a Category 3 storm.

The Handbook goes onto warn that “extensive damage to non-concrete structures” should be expected for Category 4 storms and “extensive or total destruction of non-concrete structures” will likely occur in a Category 5 storm. Only concrete is resilient enough to withstand Category 4 and 5 hurricanes without significant damage.

As impressive as these applications are, there is perhaps no greater universally applicable reason to build with concrete than fire safety. Regardless of your location, fire safety is an important consideration for residential and commercial construction. According to the latest data from the National Fire Protection Association,

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 43

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CONCRETE SUSTAINABILITY firefighters responded to 487,500 structural fires in 2013. Occurring at a rate of about one every minute, these fires resulted in 14,075 civilian fire injuries and 2,855 civilian deaths.

On average, fires claim nine lives each day and cause $9.5 billion in property damage. The tragedy of these statistics is that new trends in building codes that allow light frame construction with flammable materials are likely to increase fire related risks.

Since the beginning, building codes in America stressed passive fire safety through non-combustible materials. Since the mid to late 1990s this trend has changed significantly.

Stephen Skalko, who is a principal at P.E. & Associates, LLC, explains it this way: “As the building codes transitioned from the three ‘legacy codes’ to the single International Building Code (IBC) in the late 1990s and early 2000s, the emphasis

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moved from fire safety in buildings for occupant, property protection and fire fighter safety to mostly occupant safety.” Recent changes to the building code have stressed active fire safety (sprinklers) to provide added time for able bodied persons to evacuate without much regard to the costs due to fire and water damage to the structure. As a result, structures made of lightweight combustible materials are being constructed to greater and greater heights. To put it another way, wood has made a big push in the three to six story commercial structures market where it is displacing concrete as the material of choice.

Each community is exposed to the risks and hazards that are most prevalent in its region. Similarly, all structures, be they homes, office buildings, hospitals or schools, are exposed to some level of hazard risk. By understanding the risk our

communities face and offering concrete solutions to mitigate those risks, we help build resilient communities. When we teach designers and agency professionals about the construction practices and materials we deliver, we increase the awareness of our product’s strengths.

The economic case is absolutely clear, as the National Institute of Building Sciences’ Multihazard Mitigation Council has demonstrated: investing in resilience pays huge dividends.

In disaster prone areas “every dollar spent on mitigation saves four dollars in avoided future losses.”4 In its report, Building Codes: The Foundation for Resilience, FLASH President Leslie ChapmanHenderson and Senior Policy Analyst Audrey Rierson declare that “it’s time to embrace the most essential aspect to resiliency—an uncompromising system of building codes and standards that guarantee

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44 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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a minimum level of home safety, durability and sustainability.”5 It is literally a matter of life and death that we influence how elected officials, policy makers and decision makers view the need for building codes and standards. We must insist that building codes ensure a resilient built environment. As concrete producers and contractors who rely on concrete construction materials, we have a responsibility to inform and educate decision makers that the focus of the current building code system has shifted towards cutting construction costs to the bare minimum and building safety has been neglected.

A key approach to achieving this is to work with industry associations such as the Portland Cement Association (PCA), the National Ready Mixed Concrete Association (NRMCA) and the Concrete Joint Sustainability Initiative (CJSI) as well as organizations such as the Federal

Alliance for Safe Homes (FLASH) and the Insurance Institute for Business & Home Safety (IBHS) that help drive building code adoption to provide safer, more secure buildings and infrastructure. As construction/ building industry representatives, we should develop relationships with elected officials, state and local agencies to explain why passive fire safety is critical and how our products can save lives when disasters strike. When you network with engineers and the design community to push for sustainable and resilient roads, bridges and buildings made with concrete, you are helping your community make a solid investment.

REFERENCES: 1. Taking Shelter from the Storm Building a Safe Room for Your Home or Small Business FEMA P-320, Fourth Edition / December 2014

2. Coastal Construction Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth Edition) FEMA P-55 / Volume II / August 2011 3.Gulf of Mexico Alliance – Florida, http://www.gulfofmexicoalliance. org/state-by-state/florida.php, ISBN: 978-0-9850952-2-2 4.Security & Disaster Preparedness, Online Reference, June 30, 2015, Available at https://c.ymcdn.com/ sites/www.nibs.org/resource/resmgr/ Docs/-NIBS_Factsheet_SDP_MMC. pdf 5.Leslie Chapman-Henderson, Audrey Rierson, “Building Codes: The Foundation for Resilience”, May 2014, FLASH, Tallahassee, FL

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 45

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FOUNDATION Q&A

By James R. Baty II

Out of Plumb May Not Mean Damaged and

UNSAFE

The Concrete Foundations Association explains the process of reviewing tolerances and considering the integrity of a properly built foundation wall. This column deals with the concern for the presence of cracks and an out of plumb wall following a backfill operation.

Q

The foundation for my new home has one wall showing two vertical cracks and the top of the wall is not even with the base of the wall. I’m concerned the backfilling has pushed the wall in and the building inspector wants an engineer to certify the wall before the builder can proceed. What should I do?

– Home Owner (Wisconsin)

A

NSWER The process of building a foundation for a home inevitably leads to the two most common issues that have been raised by this inquiry. First of all, any homeowner who begins inspecting the concrete work performed will have concerns when cracks present.

While the two truths of concrete are quite well known in the construction industry: 1) Concrete gets hard.

2) Concrete cracks.

The owner is not prepared to consider this an acceptable explanation.

Cracking, by itself, should never be an immediate cause for concern. There are distinct characteristics of cracking that determine rather quickly whether the crack is problematic or simply a result of the drying and shrinkage

Pictured here is a foundation fully backfilled without a top connection in place. Short walls, corners, offsets and a yard wall provide stability for the backfill before the top connection is in place.

Photo Credit: Concrete Foundations Association

process. More information on cracking can be obtained from our website in a free public download (http://bit.ly/ aboutcracks).

However, in the case of this inquiry, another common concern that presents during the final stages of the foundation work, and unfortunately all to often before the beginning stages of the above-grade structure work, has been identified. That is, the wall is out of plumb and backfilling has been completed. It must first be noted that the primary code references for residential foundation walls both state limitations for the backfilling operation.

For a practical interpretation of the backfill process, the CFA provides a tech note on backfilling, TN-0021. The International Residential Code (2015) states: R404.1.7 Backfill placement. Backfill shall not be placed against the wall until the wall has sufficient strength and has been anchored to the floor above, or has been sufficiently braced to prevent damage by the backfill.2 Furthermore, ACI 332, which provides a broad set of minimum prescriptive code requirements and the performance based design for a majority of the residential foundations, echoes the position of the IRC by stating: 8.2.4 Lateral restraint—The equivalent fluid pressure of the backfill shall be determined, but in no case shall be

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taken as less than 30 psf/ft. The foundation walls shall be restrained top and bottom against lateral movement. The top and bottom restraint for the foundation wall shall be in place before the introduction of backfill against the foundation wall.

Temporary lateral restraint shall be permitted.3 Both code references call attention to the same design assumption for foundation walls, a positive top and bottom connection exist so that the concrete wall performs like a beam and not a cantilever. The difference in performance or applied force can be quite substantial. While it is true there are likely hundreds of thousands of successful constructions where a top connection (the first floor framing) or bracing was not installed prior to backfill, there are enough cases where problems have been created from backfilling with no top connection to validate this code position.

When a concern for movement in a foundation wall exists, however, caution should still be taken to not assume backfilling has cracked or pushed the wall inward. Some basic questions must still be asked.

The first is whether horizontal reinforcement was placed continuous in the wall and does it meet the minimum code requirements? The purpose of the required horizontal reinforcement is to reduce the number and width of cracks resulting from shrinkage.

The second question is whether the wall is bowed out of plane or leaning out of plane. This is an important condition to note. In order to determine the answer to this condition, a string line is the best method to test the position of the wall. A string should be drawn taught from bottom corner to bottom corner and from top corner to top corner. The string should be pulled taught as it approaches the wall so it can be determined if it touches a point near the center of the wall before getting to the corners. There are three potential outcomes from this test.

• String line is true at base of wall; string line at top of wall shows a bow. This is the case most likely to be of concern to an engineer and is the one to be sure to engage the parties on the project. With no bow at the base of the wall, the forms were set up true and it may be assumed that the top of the wall corresponded to the base, since forms are rigid. It should be noted that insulated concrete form walls may vary from this concern if they are plank or block style. The bow evidenced by the string is more likely to be a result of the backfill operation and stability of the wall is the next condition to investigate. An engineer should be involved at this stage.

• String line is bowed at base of wall; string line at top of wall shows a bow. This condition is a bit trickier and may still require an engineer’s assessment. Variation in the bow may still indicate influence in the wall structure by the backfilling operation. However, the bow in both the bottom and top of wall may also indicate a forming tolerance issue and forms that may not have be set completely straight. This is particular so given that the footing connection provides restraint against bowing or movement, further indicating that the wall was likely formed to that shape.

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www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 47

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FOUNDATION Q&A • String line is true at base of wall; string line is true at top of wall. A true string line should be the first indication that a forming tolerance is at hand. Walls that are loaded dynamically and moved from their cast position will evidence stress.

Stress is not applied uniformly and movement does not result uniformly. The wall is confined at the corners where it has a much higher capacity and therefore movement results in a bowing along a longer section or cracking at or near the corners.

In the case of the project at hand, the contractor engaged the owner and demonstrated that a string line was true at both the top and bottom of the wall. The two cracks were spaced relatively evenly across the wall and were located on form joints, which further indicates a pattern of shrinkage cracking. Yet, the top of the wall was out of plumb inward by 1.5 inches,

indicating an issue for tolerances.

It is proper to enter into any project with expectations of perfection and yet construction is a series of processes that require the allowance for tolerance of conditions that are less than perfect.

The CFA Standard4 offers the following when considering tolerances: 8.3 Foundation Tolerances - The wall should be considered within tolerance if the following conditions are met: • The deviations did not cause the building to become structurally unstable.

• The deviations did not encroach on areas reserved for other work.

• The deviations did not severely impede other trades from doing their work.

• The deviations did not put the building out of compliance from the governing building code.

• The deviation or blemish did not contradict the specified class of

A severe foundation wall failure from backfilling prior to top connection or temporary bracing demonstrating crack failures beyond bowing. Notice failure at the corners as well as the mid-span.

Photo Credit: Concrete Foundations Association

architectural finish (unspecified class assumes “unfinished.”)

The project presents the case that the foundation wall was completed with a deviation along

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this particular wall. It was the only wall with such a remarked deviation.

A dialog of acceptable tolerance is the next consideration. There are three references that influence this discussion as the jurisdictional codes do not address tolerances. Those references are 2010 CFA Standard, ACI 1175 and Residential Construction Performance Guidelines of the National Association of Homebuilders (NAHB). The particular tolerance in question for out of plumb of a vertical plane varies greatly across these three industry references.

The NAHB reference is the most directly applicable reference specific to both residential construction and the nature of something being acceptable or not. This reference states: 2-13 – Concrete walls shall not be out of plumb by more than 1.5” in 8 feet when measured from the base to the top of the wall.6 Applying this reference and consideration of the full conditions for this project. The homeowner, builder and contractor should be having a conversation about how to complete the space for effective finishing of the basement. Concern for structural stability does not seem warranted, despite the builder proceeding with backfill ahead of top connection or temporary bracing.

International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL 60478-5795 | Phone: 888-4227233 | www.iccsafe.org 3. Residential Code Requirements for Structural Concrete (ACI 332-14) and Commentary published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 | Phone: 248-848-3700 | www.concrete.org 4. 2010 CFA Standard published by the Concrete Foundations Association, 113 1st Street NW, Mount Vernon, IA 52314 | Phone: 319895-6940 | www.cfawalls.org 5. Specification for Tolerances for Concrete Construction and Materials (ACI 117-10) and Commentary published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 | Phone:

248-848-3700 | www.concrete.org 6. Residential Construction Performance Guidelines for Professional Builders & Remodelers published by the National Association of Home Builders, National Housing Center, 1201 15th Street NW, Washington, DC 20005 | 800-368-5242 | www.nahb.org Jim Baty is the Executive Director for the Concrete Foundations Association after having served as Technical Director since 2001. He is currently chair of ACI 332 and a voting member for ACI 306 with priorities of establishing better guidance and structure for residential concrete construction. For more information on this topic, contact Jim Baty at jbaty@cfawalls.org.

Want to know more? Contact CFA Executive Director, Jim Baty at 866-232-9255 or by email at jbaty@ cfawalls.org. The CFA is a national association with the mission to support the cast-in-place contractor as the voice and recognized authority for the residential concrete industry.

REFERENCES: 1. Backfilling Foundation Walls (TN-002) published by the Concrete Foundations Association, 113 1st Street NW, Mount Vernon, IA 52314 | Phone: 319-895-6940 | www.cfawalls.org 2. 2015 International Residential Code® For One- and Two-Family Dwellings published by the

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By Ryan Olson

Polished Concrete Floor Contributes to Facility’s Sustainable Message Installing an environmentallyfriendly polish and dye system offers the Urban Ecology Center a durable, long lasting, low maintenance floor using sustainable construction methods.

T

he Urban Ecology Center (UEC) in Milwaukee, Wisconsin is an urban environmental, non-profit, organization that is open to the public. With the three locations in Milwaukee, the UEC’s mission is to foster an ecological understanding as inspiration for change, neighborhood by neighborhood. These community centers work to educate the public and foster an environmental ethic with urban youth; as well as protection and preservation of urban natural areas. In honor of the 10-year anniversary of the Center’s first green facility, Chris Binder, facilities manager at the UEC was looking to create a scale representation of the shore line of Lake Michigan in Milwaukee County on their existing concrete floor.

“We wanted to create a place where visitors to the center could discover that nature is accessible

In honor of the 10-year anniversary of the Urban Ecology Center’s first green facility, owners of the facility were looking to create a scale representation of the Lake Michigan shore line in Milwaukee County on their existing concrete floor.

Photo Credit: Ryan Olson

to residents in their own neighborhood,” Binder says.

The Waukesha, Wisconsin-based, Floorcare USA, Inc. (FCUSA) was approached by the UEC to create a scale representation of the shore line of Lake Michigan in Milwaukee County on their existing concrete floor.

During the design phase of the building, which opened in 2004, concrete was chosen to act as a heat sink during the winter months. At that time, the UEC had painted the shore line of Lake Michigan on the concrete. Areas of the paint were not holding up to Binder’s satisfaction.

50 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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Fortunately, the UEC already had areas of the building featuring polished concrete, and Binder was happy with how the existing polished concrete was performing. Based on that, he was interested in incorporating an environmentally-friendly polish and dye system to create Lake Michigan’s Shoreline and the tributaries flowing into lake on the floor.

Having a durable, long lasting, low maintenance floor using sustainable methods was the goal of the project.

“I pushed to use the concrete dye,” Binder says. “A big part of our mission at the UEC is to follow sustainable practices and we liked the idea of dye being a more sustainable flooring product.

Everything done in this building models environmentally-conscious decision making.”

In addition to a sustainable flooring product, the UEC features reclaimed wood panels, hand-made furniture made from Poplar trees, solar panels on the roof and many other environmentally friendly products to deliver the sustainable message to the community.

REMOVING THE EXISTING PAINT FCUSA began the process by mechanically scraping the existing paint off of the concrete. Once the paint was removed, FCUSA ground the concrete with 40 grit diamonds and exposed Class B salt and pepper aggregate with a 32-inch Innovatech Predator grinder. The floor was then ground a second time with a 60/80 grit diamonds. Before beginning the polishing process, Quick Cut hybrid

diamonds were used to remove any scratches and further refine the floor. FCUSA began polishing the concrete with 100 grit resin bonds and sequentially polished to 400 grit.

To achieve the artistic vision, FCUSA accurately taped off Lake Michigan’s Shoreline and tributaries flowing into the lake. This would ultimately form the areas to be dyed. “This procedure was probably the most challenging aspects of the project,” Binder says.

“We needed to layout the floor to scale because we wanted to be able to show our visitors how accessible nature is to the local residents in this urban area.” Not only will visitors notice the polished concrete floor featuring the shoreline of Lake Michigan, but the UEC offers visitors scale, aerial images to lay down over the floor to view their schools, homes or other local landmarks in their neighborhood. “It’s our way of educating residents in urban areas that access to nature is right in their own backyard.”

Once these areas were taped off, FCUSA masked off these areas to begin the dying process. To create the water of Lake Michigan, a combination of different color solvent based dyes were used. The dye colors used were Ameripolish Patriot Blue, Slate Blue, and Green. Weeks before the project began, samples were done on an area of the floor that would be hidden.

As a part of the project, contractors were asked to incorporate an environmentallyfriendly polish and dye system to create Lake Michigan’s Shoreline and the tributaries flowing into lake on the floor.

Photo Credit: Floorcare USA

To achieve the artistic vision, Floor Care USA taped off Lake Michigan’s Shoreline and tributaries flowing into the lake.

Photo Credit: Floorcare USA

Many different blues and greens were used in combination to help determine the color that would best represent the water color in Lake Michigan.

Once the dying was complete, tape and plastic were removed.

FCUSA and staff members from the UEC spent time touching up bleeders and adding color highlights to the dyed areas with artist brushes. The floor was then buffed and densified with Prosoco Consolideck LS. After the densifier had cured, the concrete was polished up to 800 grit. The floor was cleaned and a Prosoco stain guard was applied over the top. The floor was then buffed with a highspeed burnisher.

The Urban Ecology Center is open year round and timing was critical. The work was completed over 2015 New Year holiday, so UEC could temporarily shut down while the work was completed. The project required great cooperation between FCUSA and the UEC to complete it with accuracy over this short shut down window. This required long days and late nights by both entities.

Binder is pleased with the end result. “We went from a floor which required constant maintenance to this new, low maintenance floor. That aspect has made it worth it in the end.”

52 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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EDGE GRINDER PRODUCT SHOWCASE

PG 280 SF Floor Grinder

Hum-B Edge Grinder Grind edges on concrete polishing, terrazzo and natural stone projects standing up with the ergonomically designed Hum-B Grinder.

• Dust Grabber shroud with 2-in. dust port • 150-watt halogen light • 6,000 rpm or variable speed grinder • Also use to remove adhesives, paint or epoxy floor coatings ForConstructionPros.com/10080880

The PG 280 SF Floor Grinder from Husqvarna is ideal for concrete surface prep and grinding of adhesive residue, paint and spackle.

• Ergonomic features include a new handlebar design and low noise levels.

• A single grinding plate has multiple diamond tool attachment positions for optimal distribution.

• The shroud may be removed for easy edge grinding. (Pictured) • The unit features high RPM’s and a 3-hp, 1-phase motor.

• The grinder can be coupled with the DC 1400 dust collection unit, equipped with Husqvarna’s non-clogging filtration system.

• A wide range of grinding disks is available.

• Also use to remove adhesives, paint or epoxy floor coatings ForConstructionPros.com/10183992

54 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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CS Unitec’s EBS 125.5 D Grinder CS Unitec’s EBS 125.5 D Grinder, with its 14.5 amp motor, is one of the most powerful 5-in. grinders on the market today. The front of the guard on the EBS 125.5 D is removable to allow the cup wheel to grind against the wall while keeping a tight seal for complete dust extraction, making it the perfect tool for edge grinding.

• Built-in vacuum port for dust-free operation when connected to an industrial vacuum.

• Load speed of 10,000 RPM, the grinder handles the toughest jobs, like removing epoxy, paint and other coatings, as well as smoothing rough concrete surfaces before applying new paints or coatings.

• Designed with handles on both sides of the motor to ensure the operator applies equal pressure on the tool, preventing the cup wheel from digging in and providing a smoother surface. This “H” design differs from traditional right angle grinders and allows the worker to finish larger areas with less fatigue.

• Assorted diamond grinding wheels for concrete, epoxy and masonry material are available.

• An optional walk-behind cart converts the EBS 125.5 D from a hand-held grinder to a walk-behind grinder to eliminate kneeling or bending while grinding and to provide more comfort to the user.

ForConstructionPros.com/12096513

General Equipment Company’s SG7 Surface Grinder The SG7 surface grinder from General Equipment Company is designed to accommodate a wide variety of surface preparation applications with unmatched productivity and versatility.

The SG7 is ideal for removing paint, thin set, adhesives, mastics and other floor coatings. Furthermore, matched with General’s Pro Polish system, the SG7 becomes a low-cost, yet highly productive solution for smaller concrete polishing applications.

• The machine is ergonomically designed to allow the operator to work in a fully upright position, greatly reducing the potential for lower back pain and other occupational-related health issues.

• The operator’s handle provides for vertical height adjustment and can be utilized from either side of the machine, further enhancing ease of use and operator comfort.

• Small footprint and low, 55-pound (25 kg) machine weight make the SG7 easy to lift and transport, fitting in almost any type or size of vehicle.

• Power is provided by a high-speed polisher capable of operating under higher amperage loads while utilizing a wide variety of available 7-in. (178 mm) diameter diamond segment discs.

ForConstructionPros.com/12096527

www.forconstructionpros.com/concrete | August/September 2015 | Concrete Contractor 55

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LevMix Mobile Mixer L13-X Edgers from Superabrasive

CONTRx Systems The Edge Polisher The Edge polisher from Contrx Systems polishes or grinds concrete tightly against vertical surfaces and around columns or other tight areas.

• 7-in. working width • Can polish/grind 500 to 700 lineal feet per hour • Four-position handle • Electric and gas models available ForConstructionPros.com/10092842

Blend edge work with ease - no more lines. The 13-X Edgers from Superabrasive feature: • A level on the head allows the operator to check the flatness of the floor during work.

• Rollers prevent the head from damaging walls, while allowing for the closest possible access to edges.

• A new gauge allows the operator to control the angle of the head against the floor, up to four degrees in each direction, and to blend edge passes.

• Additional controls are now available, including a forward/reverse option.

• Optional water tank • Weight: 137 lbs.

• Grinding pressure: 50 lbs.

ForConstructionPros.com/12096559

HTC 270 EG The new LevMix unites three steps in one operation: • • •

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HTC’s 270 EG edge grinder has a grinding head with a maximum height of 4 1/2 in.

• Equipped with an adjustable, flexible grinding head and flex plate.

• The shroud is fully rotating and floating with adjustable wheels allowing users to polish right up to the wall.

• The unit has a multi-axis adjustable grinding head and uses the same EZchange diamond tooling as other HTC grinding machines.

ForConstructionPros.com/10247544

KRazor EDGE Concrete Grinding and Polishing Edger The KRazor EDGE gives operators the ability to put a hand-held finish on any floor edge from a standing position.

• 3-hp, 220-volt, variable speed unit • Accepts 7-in. standard tooling • Six-position handle • T handle allows for ergonomic use from either side • Two non-marking casters offer 90° locking from four positions • Users can add extra weight to the 155-lb. machine • Attached EDGEKutter Shroud moves flush to the wall • Connects with Kut-Rite’s KleanRite vacuums ForConstructionPros.com/10898729

56 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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THE LAST PLACEMENT: BACK TO BASICS

What are

and

numbers?

Understanding FF (floor flatness) and FL (floor levelness) numbers is critical to a successful floor installation. ince it was introduced in the 1970s, F-numbers have proven to be useful in measuring and improving concrete floor flatness and levelness. With modern finishing equipment, achieving overall floor flatness and levelness has made it easy for flatwork finishers.

F-number measurements are standardized under ASTM E 1155 “Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers” and the ACI 302.1R-04 “Guide for Concrete Floor and Slab Construction” provides F-number recommendations for hard-troweled slabs-on-ground and suspended slab surfaces.

FF/FL NUMBERS

Floor flatness (FF) controls the bumpiness of the floor surface and is primarily affected by the finishing operations after screeding, including re-straightening and power floating.

Essentially, FF numbers evaluate the elevation differences along a sample line at one-foot intervals. F numbers extend from zero to infinity so the higher the F number, the flatter the floor.

Floor levelness (FL) controls the departure of the floor surface from the specified slope or plane of the surface. FL numbers evaluate the elevation differences along a sample line at 10-foot intervals. The higher the FL number, the more level the floor. Levelness of the edge forms and the accuracy of the concrete screeding operation control the overall levelness of the floor. A selfpropelled, laser-guided screed can routinely create FL numbers of about 35 and higher.

FF / FL numbers have the following floor flatness classifications:

later than 72 hours. If you are unable to make a measurement within the specified time frame, FF and FL numbers may not represent the true performance of your work.

Routinely placing very flat and super flat floors requires an understanding of floor flatness and how to properly use the equipment.

More importantly, it requires practice and continuous self-evaluation.

Always review your FF/FL numbers and critique your placing and finishing techniques. Then make adjustments and improve on your next placement.

• FF 25/ FL 20 – moderately flat • FF 35/ FL 25 – flat • FF 45/ FL 35 – very flat • FF 60/ FL 40 – super flat

Ed. Note: To read previous articles on this topic, visit www.

ForConstructionPros.com.

• “How to Finish Flatter Concrete Floors”, search using 10704608.

• “The Limitations of F-Number Specifications”, search using 10843488.

WHEN SHOULD YOU MEASURE FF AND FL?

A word of caution, FF / FL numbers diminish with time due to concrete shrinkage and slab curling. With the passage of time, joints and cracks curl making the floor less flat.

Therefore, flatness and levelness should be measured as soon as possible, preferably within 24-hours after concrete placement but no

REFERENCES ACI 117-10 Specifications for Tolerances for Concrete Construction and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction, American Concrete Institute, www.concrete.org.

58 Concrete Contractor | August/September 2015 | www.forconstructionpros.com/concrete

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