• Protects concrete against alkali aggregate reactions (AAR) by denying water to those processes affecting reactive aggregates.
• Extensive chloride-ion diffusion testing shows that concrete structures protected with a crystalline waterproofing treatment prevent the diffusion of chlorides. This protects reinforcing steel and prevents deterioration that could occur from oxidation and expansion of steel reinforcement.
Michael Brown, P.E., principal with Golder Associates in Seattle, has used crystalline waterproofing in numerous applications, but notably on the Blackbird mine remediation project near Salmon, Idaho, which has very low pH acidic mine water flowing through concrete structures. "We use crystalline waterproofing technology as an additive to concrete to reduce permeability and provide protection for the epoxy coated reinforcing bar," said Brown.
The more traditional methods of protecting concrete, such as membranes and other coatings, may still leave it susceptible to water and chemical damage. Only with the addition of crystalline technology can the pores and microcracks that normally result from the process of setting and curing, allow concrete to be sealed.
Type of Construction and Appropriate Crystalline Technology Application
Crystalline waterproofing and protection technology is available in powder form and is mixed with water. Three different application methods include:
• Applied to the surface of an existing concrete structure, for example, a foundation wall or a floor slab.
• Mixed directly with the concrete batch at the plant as an admixture.
• Shaken as a dry powder, applied to green, or uncured, concrete and toweled into the surface.
Methods and Procedures of Crystalline Waterproofing Coating Applications
When applied to clean, bare and previously saturated substrate as a slurry mixture, the reactive chemical ingredients in crystalline waterproofing can penetrate up to 12 inches deep inside the concrete by using the water as the migrating solution in a process of chemical diffusion. As these chemicals penetrate through the capillaries and pores, the reaction with the mineral by-products of cement hydration creates the crystalline formation that fills the cracks or the pore.
Crystalline waterproofing can be applied by a brush or with spray-on equipment. To ensure the success of the application, care must go into the conditions under which the material is applied related to surface preparation, surface wetting, coat thickness, and curing time.
Because the crystalline waterproofing coating system has a unique chemical diffusing characteristic, proper surface preparation of the concrete is critical to the performance of the material. The concrete surface that will receive the crystalline waterproofing coating needs to have an open pore texture to allow the transfer of the reactive crystalline chemicals from the coating into the concrete substrate. The surface also needs to be clean and free of form oil, laitance and other foreign matter as this can potentially cause de-lamination of the coating.
The three common methods of concrete surface preparation are water blasting, sand blasting and acid etching. When water blasting, the pressure should be 3,000 pounds per square inch (psi) to 4,000 psi. Sand blasting is normally required when steel forms have been used and the concrete has a tight, mirror like finish. Acid etching can be accomplished using either muriatic acid or citrus-based products when the use of an acid is not environmentally acceptable.
The coating systems require that the concrete be in a saturated, surface damp condition for the waterproofing to be effective. The active chemicals in the coating use water as a migrating or diffusing medium that allows the chemicals to transfer from the coating into the capillary tracts of the concrete. To make sure that concrete on vertical surfaces is saturated, wet the walls with clean water and allow the moisture to be drawn into the substrate for approximately ten minutes. Re-wet the walls a second time and allow to stand for 20 minutes.
In hot weather, when evaporation rates are high, it may be necessary to soak the concrete overnight. This can be accomplished using either soaker hoses on the top of the wall, that allows water to flow down the vertical surfaces, or a series of sprinklers can be used if the wall is less than 12 to 15 feet.
If water is not readily available on the job site, the saturation of the concrete should be done early in the morning, when evaporation rates are low and before the concrete begins to heat up. In difficult conditions of hot sun and wind, it is better to attempt small areas that can be controlled, rather than large areas at one time. In hot weather, the use of an evaporation retarder to help keep moisture in the concrete can be considered.
In cold weather, saturation of the concrete should only take place when the ambient temperature is going to be above 33 degrees Fahrenheit for 24 hours.
The crystalline waterproofing coating materials are mixed with water at a ratio of five parts powder to two parts water by volume for brush application, and five parts powder to three parts water by volume for spray application. The coverage rate is 1.25 to 1.5 pounds per square yard per coat. At this rate, a 60-pound pail of material will cover 360 to430 square feet, and a 50-pound bag will cover 300 to360 square feet of surface area. Coatings can be applied by brush, hopper gun or specialized spray equipment. When using a standard six-inch masonry brush, one person can mix and apply approximately 80 to100 square feet per hour per coat. A hopper gun or texture gun uses a two-person crew with one person mixing material and the second person spraying. The gun uses a three-eighths inch nozzle and operates at roughly 25 psi. A two-person crew can apply the coating at a rate of 400 to500 square feet per hour per coat.
Specialized spray equipment is operated with a three-person crew. At application rates of 1 200 to1500 square feet per hour per coat, it is necessary to have all materials pre-measured in order to keep up with the spray equipment capacity. When using this type of equipment, the best procedure is to pre-measure the powder into at least five or six large buckets (five gallon pails) and pre-measure the water. This is done on the basis of five parts powder to three parts water by volume.
On vertical surfaces, the standard application procedure is to start at the top of the wall and work down. When using spray equipment, the first coat of material can be back-brushed using a 20-inch wide janitors broom with a soft bristle or a finisher's broom. This helps ensure an even coverage rate and minimizes any run down of the coating.
When a second coat is specified, it needs to be applied no later than 48 hours after the first coat. Under normal conditions, the crystalline waterproofing coating will begin to set up in two to three hours and application of the second coat can be done at this time. If the first coat has dried out, it should be lightly moistened with water prior to the second coat being applied. Failure to do so may result in lack of bond between the two coats.
When applying the coating materials to a concrete structure, it is better to break the job up into manageable segments rather than try to complete large areas at one time. This becomes even more critical when the weather is hot or windy. ■
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