Nigel Parkes Joints for Slabs-on-Ground
C2009. PNA Construction Technologies, Inc. All rights reserved.
KEY REFERENCE DOCUMENTS • • •
• • • • •
•
Plate Dowels for Slabs on Ground, July 1997 Cost Effective Slabs on Ground, May 2004 ACI 302.1R-04 – Concrete Floor and Slab Construction – Also: ACI 302.2R-06 Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials Performance Based Dowel Design, January 2007 ACI 360R-10 – Design of Slabs on Grade ACI 223-10 – Shrinkage Compensating Concrete ACI 330.2R-17 – Concrete Paving for Industrial & Trucking Facilities Consideration of Spacing in the Design of Dowel Systems, R. Rodden, March 2018
Other related publications: – Post-Tensioning Manual (PT Only; reducing market) 11/27/2019 – British Concrete Association’s TR34 (Europe and World-Wide)
CONCRETE FLATWORK FUNDAMENTALS Slabs & Pavements Designed to Carry Load Concrete Shrinks, Curls & Cracks: • Concrete Shrinks + Restraint = cracks or joints
CONCRETE IS A GREAT MATERIAL FOR FLOORS, BUT IT… Curl + Load = Top-Down Cracking
&/or Joint Spalling
Main failures of Slabs-on-Ground: • Joint Spalling • Cracking • Surface defects: 11/27/2019
•
Dusting, crazing, delamination, etc. 4
CURLING (WARPING) CONSIDERATIONS
5
“ALL SLABS [AND PAVEMENTS] CURL” JERRY HOLLAND, STRUCTURAL SERVICES INC.
HOW CURLING AFFECTS TOLERANCES
7
CURLING PROFILE & JOINT SPACING
(3.5m)
(4.5m)
8
CURLING & JOINT SPACING: ACI 360R-10
Not a lineal relationship!
WHY DO LOTS OF CRACKS APPEAR MID-PANEL?
Computer model of the slab flat on the ground before curling stresses occurs Slab has curled-up and lifted off the base below
Curling stresses on the slab’s deflected shape for 25 ft. joint spacing
Cracks develop at high curling stress locations and crack the panel into four quadrants
(Slide courtesy of Jerry Holland, P.E. Structural Services, Inc.)
WHY IS SIGNIFICANT CURLING A PROBLEM? MID PANEL “CURLING CRACKS” ARE TOP-DOWN AND CAN BE QUITE WIDE!
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WHY IS SIGNIFICANT CURLING A PROBLEM? CORNER CRACKING Typical corner cracking in curled joints with poor joint stability
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CURLING REDUCES JOINT FILLER PERFORMANCE; NO DOWELS & UNMAINTAINED JOINT FILLER = JOINT SPALLING
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WHY IS SIGNIFICANT CURLING A PROBLEM? JOINT SPALLING
WHY IS SIGNIFICANT CURLING A PROBLEM?
JOINT SPALLING Longer slab = greater joint openings
Curl = loss of support at slab edges
HIGH DIFFERENTIAL DEFLECTION + HARD WHEELS
Curl + Load = Top-Down Cracki
RESULTS IN EDGE SPALLING
• Pneumatic tire = 85-120 psi (0.6-0.8 MPa) • Solid or cushion solid rubber tire = 180-250 psi (1.2-1.7 MPa) • Polyurethane or steel wheel = 1,000+ psi (6.9+ MPa) • Wearing of wheel increases contact pressures!
WHY ARE WE EXPERIENCING MORE JOINT SPALLING THAN EVER BEFORE?
FORKLIFTS Pallet Riders
Smallest, Hardest Wheel Loads
Note: Due to Heavier Loads, Frequent Traffic and Smaller Wheels on New MHV’s, Industry is moving towards Shore Hardness of A 85 or 90+)
WE KNOW WHAT JOINT STABILITY WE NEED; BUT… “Joint stability measurements below 0.010” (0.25 mm) for joints subjected to small hard wheels will have good service life”. For lift truck traffic with large, cushioned rubber wheels, a joint stability measurement of 0.020” (0.51 mm) should have good service life.” ACI 360R-10
0.51mm (20 mils)
0.25mm (10 mils)
Note: While ACI 360R-10 doesn’t provide equations for dowel design, presenting failure criterion allows us to design for service!
SMALL AMOUNTS OF CURLING, SMALL HARD WHEELED LIFT TRUCK TRAFFIC AND NO DOWELS = JOINT SPALLING
Spalled joints in 1 year old facility 21
RECAP: WHY IS CURLING A PROBLEM?
Slab cracking (Mid-panel & corner) Crack spalling
Joint spalling Joint filler or sealant failure Lowered load-carrying capacity Slab rocking Worsened vehicle rideability Floor covering materials distress Reduced tolerances 11/27/2019
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JOINTS FOR WHAT SLAB DESIGN TYPE?
DIFFERENT JOINTS REQUIRED FOR DIFFERENT SLAB DESIGNS…WHICH DESIGN TO CHOOSE? • Information required to recommend a design type • Loads • Static loads; racks, stacks or materials, mezzanines, etc. • Dynamic; lift truck type, wheel type and spacing • ACI Slab-on-Grade Design Types • Examples: • Food Distribution Center • High Bay Racked Warehouse • Recreation Center • Spec Warehouse
INFORMATION NEEDED FOR DETERMINING THE BEST DESIGN FOR A SPECIFIC FACILITY Questions to get answered: • Facility use • Loads – Static; rack loads (leg loads, back to back, height, earthquake, roof supporting) – Dynamic (vehicle and wheel types) – Frequency (fatigue in pavement) • Tolerances required for logistics equipment • Surface requirements (general appearance, abrasion resistance, slip or skid resistance, light reflectivity, hygiene requirements) • Budgetary constraints • Subbase, concrete strength, location, etc.
[SLAB &] PAVEMENT DESIGN • “It is imperative that the designer consider all factors that influence the performance of a concrete [slab &] pavement. Such factors include truck traffic or other vehicular loads, patterns and frequencies, subgrade/subbase support, concrete strength, pavement panel thickness, joint spacing, joint stability (load transfer), the use of curbs and widened lanes, humidity and ambient effects (humidity and temperature).” • Other considerations for slabs: – Tolerances required; and – Construction method
Thickness is directly related to joint spacing, curling / warping and load transfer…and CAN NOT be designed independently!
SLAB DESIGN STARTS WITH THE LOADS
Bottom-Up Cracking
Top-Down Cracking
Punching Shear
Bearing (Double Shear) … where are joints w.r.t. these loads? … can also have lifting moment in earthquake areas! … vehicular loads and their interaction with racks!
HOW MANY JOINTS: ACI 360 SLAB TYPES
•
Conventionally jointed with designed load transfer – –
•
Moderately extended joint spacing –
•
Strategically reinforced – global Enhanced aggregate interlock (0.1% steel) – US only, TX mostly Nominal joint - 7.5 lb/yd³ (4.5 kg/m3) macrosynthetic fiber – semi-global
Extended joint spacing – – – –
Post-tensioning tendons (PT) – semi-global Shrinkage-compensating concrete (SCC) – US & Chile mostly High volume steel fiber - 65 lb/yd³ (38 kg/m3) – global High volume of steel reinforcement (>0.5% by cross sectional area) – semi-global
FLOOR DESIGN AND JOINT PATTERN
330 ft (100 m)
330 ft (100 m)
• Standard 109,000 sf (10,000 m2) facility • 3 joint types • Construction (Formed or Armored) • Contraction (Saw Cuts) • Isolation (doweled or undoweled) • Joint type and location depends on: • Facility use • Location of columns and racks • Traffic crossing the joint • Tolerances required • Placement techniques available • Amount of reinforcement used
ACI JOINT SPACING RECOMMENDATIONS; MODIFIED FOR CHILE
ACI 360R-10, Fig 6.6
Chilean Joint Spacing Line
DESIGN TYPE & ABILITY TO SPACE JOINTS Design Type
Reinforcement Levels
Joint Spacing Recommendations
Strategically Reinforced
No mid-panel reinforcement
2.5 to 3.5M (8 to 12 ft.)
Nominally Jointed
5lb to 7.5lb Macro Synthetic Fiber / Yd3
12 to 18M (40 to 60 ft.)
Shrinkage Compensated Concrete
Rebar
30 to 40M (100 to 130 ft.)
High Dosage Steel Fiber
65lb. Type 2 / Yd3
40 to 45M (130 to 150 ft.)
Post Tensioned
60M + (200 ft. +)
Example | General Use, Randomly Trafficked Warehouse
• Loads = Racks & 4 kip (1,800 kg) lifts • Typical flatness and levelness • Surface requirements • General appearance = Must be consistent • Abrasion resistance = Must not dust • Slip or skid resistance = Moderate • Light reflectivity = Moderate • Owner wants the best value and there are no construction constraints
Example | General Use, Randomly Trafficked Warehouse
•50M (165 ft.) construction joint grid with a 2.5 to 3.5M contraction joint grid • Construction and contraction joints are interchangeable • Design alternatives • Strategically reinforced • Enhanced aggregate interlock • Flood pours with laser screed finishing
100M (330 ft.)
100M (330 ft.)
Joint Type: Isolation | Formed | Armored | Saw Cuts
“Nominally Jointed”…moderately spaced joints ( Macro synthetic fibers – column line joint spacing
330ft. (100M) Diamond-shaped plate dowels – construction joints
330ft. (100M)
Tapered plate dowel basket assemblies - sawcut contraction joints
Example | Freezer Distribution Center (FDC) • Loads • Racks = High bay / wide aisle • Lift trucks = 4,000 lb (1,800 kg) standards and pallet jacks • Typical flatness and levelness • Surface requirements • Abrasion resistance = Very high • Slip or skid resistance = Moderate • Light reflectivity = Moderate • Hygiene requirements = No open joints or cracks allowed • Will spend to prevent any need for repair
Example | Freezer Distribution Center (FDC) • 165 ft (50 m) square armored joint grid with no intermediate joints • Design alternates • Shrinkage compensating concrete • 2-directional post tensioned • High volume steel fiber • Rebar (0.5%+ by cross-section)
330 ft (100 m)
330 ft (100 m) Long panels = Greater joint opening = Need armored edge to protect joint! Joint Type: Isolation | Formed | Armored | Saw Cuts
Conventional Concrete Vs. Shrinkage Compensated
SHRINKAGE COMPENSATED CONCRETE
48,600 Linear Feet of Joints
vs.
4,400 Linear Feet of Joints
Example | High Bay Racked Warehouse • Loads • Racks = High bay / narrow aisle • Lift trucks = reach / cherry picker with small / hard wheels • Typical flatness and levelness in free movement areas, very flat and level in the very narrow aisles (VNAs) • Surface requirements • Abrasion resistance = Very high • Slip or skid resistance = Moderate • Light reflectivity = High • Joints must be sealed • Will spend to prevent lost productivity
“SUPERFLAT” FLOOR DESIGN
Owner DC, Fmin 100 #5's, 8" OC Longitudinal, 120-FT Run 0.500 0.400
D e v i a t i o n
* I n c h e s *
0.300 0.200 0.100 0.000 -0.100
0
10
20
30
40
50
60
70
80
90
100
110
120
-0.200 -0.300 -0.400 -0.500
Distance (Feet) 38
Example | High Bay Racked Warehouse
330 ft (100 m)
330 ft (100 m)
• Aisles • PT or rebar (0.5%+) • 16.5 ft (5 m) max. construction joint spacing • No transverse joints • Armored joints at ends • Remainder of area • Strategically reinforced or shrinkage compensating • 16.5 ft (5 m) max. crackcontrol joint spacing • Construction and contraction joints can be interchanged
Joint Type: Isolation | Formed | Armored | Saw Cuts
Example | Recreation Center w/Roller Rink • Loads • Foot traffic and roller skates • Relatively flat and level in the roller rinks and typical flatness and levelness other parts of facility • Surface requirements • General appearance = Polished • Abrasion resistance = Moderate • Slip or skid resistance = N/A • Joint free in roller rinks • Owner wants the best value
Example | Recreation Center w/Roller Rink
330 ft (100 m)
330 ft (100 m)
• Roller rinks • 100 ft (30 m) x 66 ft (20 m) joint spacing • Nominal joint design • Remainder of area • Strategically reinforced • 16.5 ft (5 m) max. crackcontrol joint spacing • Construction and contraction joints can be interchanged • All can be laser screed but requires a qualified contractor to achieve the required tolerances
Joint Type: Isolation | Formed | Armored | Saw Cuts
TODAY’S DISCUSSION – OUR VALUE PROPOSITION
• Fundamentals of Concrete Flatwork – Why Concrete for flatwork? – Shrinkage, Curling (Warping) & Cracking – Design & Construction Considerations; what causes cracking?
• Design methods: – Designed to crack; Reinforced with rebar or fibers; or
– Designed not to crack; SR or TX 3s [Jointed], PT, SCC.)
• Jointing; (Load Transfer & Joint Stability, Joint Protection [Filling or Armoring], Joint Details, Joint Layout)
LOAD TRANSFER & JOINTS
DOWELS; TYPE, SIZE & SPACING Construction Joints: • Keyways (not recommended!) • Round Dowels (through forms) Contraction Joints: • Aggregate Interlock • Round Dowels (in baskets) • Enhanced Aggregate Interlock (TX 3s) • Plate dowel baskets (rectangular & “diamond”)
Construction Joints: Round Dowels (Adopted as the Industry Standard from the Highway, Street & Road Market)
Note: Industry Standard for Size & Spacing – 1/8” for 1” of Concrete Thickness at 12” o.c. (Example ¾” dowel for 6” slab)
Round Dowels – Construction Joints
Dowel Removal Void area created from spinning and removal of dowels prior to stripping forms
Dowel Removal
Round Dowel Restraint – Misaligned Dowels
Round Dowel Restraint – Adjacent Placements Potential Cracks
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Round Dowels at Joint Intersections
Round Dowel Restraint – Adjacent Placements & Corners
As early as 1956, ACI 325 stated a caution on using aggregate interlock “Aggregate Interlock • -Use of aggregate interlock to transfer loads across joints and to maintain mutual alignment of abutting slabs is generally associated with nonreinforced pavement. Experience indicates that aggregate interlock may be satisfactory as a means of load transfer only under unusually favorable conditions of joint opening and foundation support. It is not satisfactory under a large volume of heavy commercial traffic”.
ACI Committee 325, 1956, “Structural design Considerations for Pavement Joints,” ACI JOURNAL, V. 53, July, pp 1-29 Impact Point
Aggregate looses contact and slab faults when joint opens
Round Dowels – Contraction Joints (Saw Cut)
LASER SCREED ALLOWS FOR BLOCK PLACEMENT
•
•
Use driven by: – Efficiency – Flatness – Levelness Slipformers are now using lasers too
A floor is made up of many individual panels
TWO DIRECTIONAL DOWELING
What causes cracks in concrete?
THIS CHALLENGE LEAD TO TAPERED PLATES Potential Cracks
PNA‘S TAPERED PLATE DOWELS FOR LOAD TRANSFER Diamond Dowels @ construction (cold) joints
Dowel Baskets @ contraction (sawcut) joints PD3 Tapered Plate Dowels
Plate vs. Round Dowels Same slab deflection* at dowel locations
Same maximum shear stress* Same maximum flexural stress* Top of slab on ground
Plate thickness or dowel diameter
Same maximum bearing stress* on the concrete Total dowel or plate length
* = Criteria used to compare dowel & plate performance
…WHAT SIZE, SPACING & GEOMETRY OF DOWELS ARE NEEDED TO PROVIDE THESE LEVELS OF JOINT STABILITY?
Reference: ACI 360R-10
‘Performance Based Dowel Design’ Example - 4,000 lb standard, 6” slab
26” oc January 2007
PNA HAS ADVANCED THE STATE OF JOINT DESIGN
PROJECT-SPECIFIC DOWEL OPTIMIZATION INCLUDED IN EVERY DESIGN
Critical Responses Calculated
… and Plotted
CONCRETE SLAB DESIGN
Thickness
Sub Grade Support BottomUp Cracking
Each input affects the others and cannot be ignored in the design…
& Curling / Warping
Load Transfer
Joint Spacing
Top-Down Cracking
…& BOTH Top-Down & Bottom-Up Cracking Should be considered
FEA MODELING + DOWEL OPTIMIZATION
+
SLAB CRACKING PREVENTION Via Modern Designs & FEA
JOINT STABILITY Via Modern Models
JOINT PROTECTION
Joint Filling: Armored Joints: • Armor-Edge® with Joint Fill Stop (Partial Depth & Full Depth) • “Wavy joints”; carry load across joint without joint filler
JOINT PROTECTION
“Joints should be protected to ensure long-term performance. Regardless of materials chosen for protection, the joint needs to have adequate load transfer” For wheel traffic, there are two ways to protect a joint; fill the joint with a material to restore surface continuity or armor the edges of the joint with steel plates”. Reference: ACI 360R-10
WITHOUT JOINT STABILITY FILLERS DON’T WORK…JOINT STABILITY MEASUREMENT – ACI 360R-10 “Joint stability can be easily measured…by using a device with an inclinometer having 12 in. contact point spacing located 6 in. on each side of the joint that gives you a visual readout of the vertical movement as it occurs (Type II Apparatus).” Reference: ACI 360R-10
IF YOU DID NOT USE DOWELS IN A PROJECT THERE IS A SOLUTION…PNA JOINT STABILIZERS ACI 360R-10 Guide to Design of Slabs-on-Ground Section 6.2 “Joints or crack stability measurements below 0.010 inch (0.25mm) for joints or cracks subjected to lift truck wheel traffic with small hard wheels will have good service life. For lift truck traffic with large, cushioned rubber wheels, a joint or crack stability measurement of 0.020 inch (0.51mm) should have good service life.”
PNA JOINT STABILIZERS, ONTARIO EXAMPLE
JOINT FILLING – ACI 302R-04
SELECTING THE PROPER JOINT-FILLER •
The Industry Standard is “Semi-Rigid” Joint-Filler for Contraction/Construction Joints with a Shore ‘A’ Hardness of 80+
•
Note: Due to Heavier Loads, Frequent Traffic and Smaller Wheels on New MHV’s, Industry is moving towards Shore Hardness of A 85+)
JOINT FILLER DEPTH IS CRITICAL Note: Semi-Rigid Fillers Should Be Installed to the Full Depth of the Contraction Joint or 2”, Whichever Occurs First.
Saw Cut Contraction Joint: • Fill full depth of cut
Contraction Joint (Sawn): • Fill full depth of cut
Contraction Joint (Butt) : • Fill min 2” deep
JOINT FILLER PROFILE IS ALSO CRITICAL
= =
HOW DO YOU GET THE JOINT FILLER FLUSH?
Notes: • Flush Profile Requires Overfill-and-Shave Procedure Using Razor Scraper with Disposable Blades • Shaving Polyurea at the wrong time or Epoxy without heat can lead to low filler profile
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JOINT FILLER SEPARATION, REFILLING AND REPAIR Notes: • If joint filler separates more than a credit card width then re-fill with same or less viscous version of same material. • If the joint filler is installed low, saw out top ½” and refill flush with concrete surface.
Separates Adhesively (from Joint Wall) or Cohesively (Internally)
JOINT FILLING – ACI 302R-04
Keys to proper joint filler performance: 1. Choose an appropriate filler material (Shore ‘A80+) 2. Installation timing (wait as long as possible but min 90 days after construction) 3. Clean the joint properly (Saw or Grinder; Preferably Dustless, with Diamond/Abrasive Blade) 4. Fill full depth of cut (provide shoulder support) 5. Ensure filled flush with concrete surface 6. Re-fill if joint opens more than a credit card width
ARMOR-EDGE® INSTALLATION
FINISHING OF JOINTS
ARMOR EDGE RE-ENGINEERED
FEA optimization to meet ACI deflection criterion lead to new rail size and anchor spacing
New offset installation… Standard Design
Joint Fill Stop Design
…supports joint filler by design! Full support to 3/8”
Full support to 3/4”
ARMOR EDGE® WITH JOINT-FILL STOP
ARMOR EDGEÂŽ WITH JOINT-FILL STOP Keys to armored joint performance: 1. Choose the best joint for the application (moving joint or not) 2. Installation vertical / plumb 3. Install at correct height & clean the concrete paste off the joint surface 4. Grind the joint if necessary
ISOLATION & OTHER JOINTS
• Column Isolations • Dock Pits
COLUMN ISOLATIONS
BUILDING ERECTED FIRST - GRID LINE CUT Wrap column with 1/2“ compressible isolation material (fill top with elastomeric sealant) Construction or saw cut contraction joint
Concrete column wash installed prior to placement of floor slab
SLAB CONSTRUCTED FIRST: COLUMN ISOLATION BOX-OUT WITH LEAVE-IN-PLACE FORMS
LOADING DOCKS – ACI DETAILS
JOINT LAYOUT TO DOCK LEVELOR PITS
Column Isolation Joints
Joints
PREFERRED DETAIL AT BACK OF PIT WALL
Floor
Pit sidewall beyond Dock pit floor Bond break on t roweled surface
DOCK AREA LAYOUT
Note: Do not weld these two angles!
Isolat ion joint at each column
Const ruct ion or cont ract ion joint
Provide 1/4" gap where angles int ersect const ruct ion joint (DO NOT WELD ANGLES)
1/4"
Const ruct ion joint Armored edge angle
Const ruct ion joint bet ween pit s A
Col. Line
Col. Line
Col. Line
91
Thank you! Nigel Parkes | +1 (404) 386 8168 / nigel@pna-inc.com
TCPavementsÂŽ projects in the US!