Tanks For Everything: Waterproofing Our Concrete Infrastructure

Thousands of municipalities are facing the fact that their concrete infrastructure is deteriorating. Waste, potable, and other water systems are approaching the later phases of their lifecycles. They typically show signs of cracking, positive or negative side leaks, spalling, reinforcement deterioration, freeze-thaw cycling, and all other manifestations of weathering and aging.

For towns with aging concrete water tanks, the dilemma is usually the same: repair or build new. In repair, re-waterproofing can buy another decade or two so they can budget for the new expense.

A solid example of this is the Vergennes-Panton Water District in Vergennes, Vermont. At 750,000 gallons, the 38-year old tank serves as the drinking water for the towns of Panton and Vergennes (serving 4,198 people); sourcing its water from Lake Champlain. According to a March 2021 presentation by the district, the water distribution system includes 54 miles of district- and privately-owned waterlines plus 3 miles of waterline owned by the Ferrisburgh Fire District. The tank’s interior dimensions are 70 by 70 ft.

The standards that govern tanks vary but usually want to limit any leaking to at or below 0.1% of the total volume of water for a 24-hour period. In large tanks, this can be negligible and typically within the evaporative levels. For a 750,000-gallon tank, 0.1% would be 750 gallons of allowable leakage.

In Vergennes’ case, the square tank was experiencing leaks from cracking, spalling from freeze-thaw cycling, and joints that had separated. New England Dry Concrete worked with the Vermont-based engineering firm DuBois & King Inc. on what has become the state’s approved method for dealing with such problems. Based on the repairs done for similar sized and aged tanks, repairs were estimated to take approximately two to three weeks.

New England Dry Concrete LLC removed all deteriorated and weakened spalled concrete along with any loose and foreign material. The surface was chipped by mechanical means to expose a minimum of 1/16-in. of new aggregate concrete with a minimum depth of repair up to 1/2-in. with neat saw-cut dovetails at the perimeter.

Industrial-grade corrosion inhibitors were applied to any exposed reinforcement that showed signs of corrosion or loss of circumference, thickness or other

The Allnex water tank

Gregory Maugeri / Bill Della Sorte

measurable and meaning metric greater than 25%. Contractors can use different methods depending on what is discovered and how much degradation. Reinforcement should be cleaned via brushing, grinding and blasting and then treated with the inhibition agent. The areas were finished with a crystalline mortar out to flush with Kryton International’s Baricote or Krystol Repair Grout crystalline cementitious mortar or high strength mortar with NEDC Type E mortar admix. The interior was pressure washed prior to applying the surface waterproofing slurry. The pressure washing contained Gregory Maugeri / Bill Della Sorte sporocidin (a phenolbased bactericidal, virucidal, moldicidal, fungicidal and tuberculocidal) as a broadspectrum disinfecting agent. This allowed workers to continue to work in the tank environment safely. The Kryton Krystol line of crystalline repair materials were used exclusively– requiring a cure of 72 hours depending on conditions. The tank could then be refilled with water after 48 (curing will continue). At that time, leakage testing was conducted using the AWWA standard for concrete tanks and disinfected using AWWA 652 Method 3. This situation extends beyond municipal tanks as there are many private and public industries that maintain

Repair Spalling for a Concrete Water Tank

New England Dry Concrete’s spall repair preparation involves the following: • Remove deteriorated and weak concrete and remove all loose and foreign material.

Chip substrate by bush hammering or other mechanical means acceptable to the repair concrete/mortar manufacturer to obtain a minimum surface profile of 1/16-in. with a new aggregate fractured surface. Minimum depth of repair shall be 1/2-in. with a neat saw-cut perimeter. Feather edging will not be permitted. • If steel reinforcing is exposed, chip out behind the reinforcing steel. Chip a minimum of 3/4-in. behind the bar and 3-in. past the point where the bar is exposed. Concrete behind bars shall be removed enough to allow for entire bar to be cleaned. Remove concrete to the point past where sound material begins. • For areas where rebar is to be cleaned, exposed steel reinforcement shall be free of all rust, scale, oil, paint, grease, loose mill scale, and all other foreign matter which will prevent bonding with the repair concrete. Use power chipping or power-driven brushes and clean to an SSPC-SP2 or SP3 surface preparation. Apply a corrosion inhibitor to all exposed cand cleaned bar prior to patching. • For areas where rebar is to be replaced, rebar shall be cut to the limits of severe deterioration as directed by the designer. Rebar ends with minor deterioration shall be cleaned. Proposed rebar shall be welded to existed sound rebar in all locations where rebar has been removed. All new and existing exposed rebar shall be coated with a corrosion inhibitor prior to patching. • Where additional reinforcement in shown to be anchored in and for patches greater than 1 and 1/2-in. in depth and overhead patches, install stainless steel threaded rod J hooks set in epoxy paste adhesive. Anchor is to be 3/4-in. clear minimum from finished face of repair. Hooks are to be embedded a minimum of 3-in. into concrete and shall be installed diagonally to plane of concrete surface. Holes are to be drilled 1/8-in. larger than rod diameter and shall be cleaned thoroughly. Space hooks at 16-in. of center.

concrete tanks for various purposes as well. Allnex, a chemical company located in Wallingford Connecticut, specializes in coating resins. They maintain a 750,000-gallon tank to serve as surplus water for their fire-fighting operations. The large circular dome-lid circular tank was showing signs of its age.

Billy Della Sorte, a partner of New England Dry Concrete, explains “Tanks that are 40+ years old begin to show significant signs of deterioration, in freezing climates or wastewater tanks it can show much sooner.” However, repairs are easier and far less expensive if you get out in front of them. Once you reach a certain tipping point, the repairs are extensive and much more costly. Where early repairs could be X, two years later they can be five times that. It is not a linear progression.

The Allnex tank was experiencing the same type of deterioration as observed among tanks of its age. The circular tank was older and wire-wound. This is a process that wraps a continuous cable around the outer walls of the concrete tank, and then the wrapping is typically covered in a cementitious material, perhaps shotcreted or stuccoed over. Eventually, either weathering or internal leaks begin to corrode the wire and spalling occurs. This process accelerates over time.

REPAIR

Remediation involves removal of all loose and deteriorating material for a more thorough evaluation of the condition and professional engineering consult if required. The next step is to stabilize any reinforcement including the wire cabling. Depending on the extent of the corrosion, this might simply be applying a rust-inhibiting agent to any steel or might be replacing actual

members or strapping. In any case, if there is an engineering recommendation; that is followed. The balance of the repairs is done in crystalline products. The use of surfaceapplied materials, admixes, or other specifically formulated products to deal with cracks, leaks, and spalling are employed. Done correctly, these repairs are solid and should endure. While the Vergenned tank was about 25-ft. high with 5-ft. below grade, the same methods of applying crystalline waterproofing to the negative (the inside of the tank) can be employed when below grade. The concrete water tank is a class of infrastructure that can be vulnerable if ignored. Replacement costs are tremendous and getting in front of repairs is essential. Contractors do have an arsenal of specialized products engineered to address the conditions that plaque this class of infrastructure. In addition to these, there are reliable methods for stabilizing water-challenged assets. Tanks, tunnels, dams, even deep foundations all can benefit from this approach. As remarkable as crystalline products and systems are, firms specializing in these kinds of repairs, designers and asset owners would be well-served to temper expectations. Products and methods are solid, but there are limitations. Remember to get in front of it. If you are after the tipping point or miss the window completely, it The Vergenes- can be very expensive or Panton concrete irreparable; “an ounce of water tank. prevention is worth a pound Gregory Maugeri / of cure” is especially true in

Bill Della Sorte concrete. Greg Maugeri is the co-founder and managing partner of New England Dry Concrete LLC. For more on information on waterproofing, visit

CONC.me/ waterproofing.