Crystalline Concrete Waterproofing for Wastewater Applications
The premise that America's wastewater infrastructure is largely antiquated and overworked seems to be widely accepted by both the AEC community and elected officials.
By Les Faure
The premise that America’s wastewater infrastructure is largely antiquated and overworked seems to be widely accepted by both the AEC community and elected officials. But the scope of the problem can feel overwhelming: in a 2004 report, the U.S. Environmental Protection Agency (EPA) estimated that 34.4 billion gallons of wastewater were transported and treated each day in the United States by more than 21,600 publicly owned treatment works (serving 78 percent of the U.S. population). EPA estimates the network of sewer lines underground in the United States measures 1.2 million miles.
But a wastewater treatment system, including its piping, is more than volume or mileage: it’s also about a multiplicity of toxins, aggressive chemicals and their reactions to each other. In order to collect, contain and decontaminate the wastewater, reliance on a waterproof, corrosion-resistant building material is critical.
Concrete, the world’s most-used building material, offers numerous advantages, but it is permeable to liquids and gases. Its porous nature can create problems within piping and other structures due to moisture penetration and the harmful chemicals dissolved in the water.
One solution to water-proofing new or existing concrete is crystalline technology. It has been used to waterproof, protect and repair concrete structures over the past 40 years in thousands of successful projects in more than 70 countries.
|By means of diffusion, the reactive chemicals in the crystalline technology use water as a migrating medium to enter and travel down the capillaries of the concrete. These photos show pore structure of (1) untreated concrete, (2) initiation of crystallization and (3) mature crystals.|
Crystalline waterproofing technology uses concrete’s own permeability as a delivery system for waterproofing chemicals to travel the concrete’s pore network, plugging the capillary tracts with a non-soluble crystalline formation. The method also bridges micro-cracks that occur as the concrete dries and shrinks. The technology can even self-seal new micro-cracks after they occur, years after the original application.
The crystalline waterproofing chemistry can be introduced into new concrete as an admixture, a dry-shake product, or a surface-applied coating. For existing (i.e., cured) concrete, surface-applied coatings are used. The substrate must be wet for the chemicals to move through the concrete and for the chemical reaction to occur. With a surface coating application, the high concentration of chemicals at the surface naturally seeks to spread out or diffuse into the water saturated substrate. Keeping the concrete moist maintains a conduit for the chemicals to travel. A properly cured crystalline waterproofing application can spread 12 inches into the interior of the concrete structure.
The chemical formulations of crystalline waterproofing products are a manufacturer’s trade secret, but in all cases these materials react with the by-products of cement hydration such as calcium hydroxide – commonly called “lime” – and other minerals within the cement matrix.
Crystalline waterproofing chemistry reacts with these materials to form small mineral-based “needles” that are insoluble in water. The formation of the crystals is a gradual process, requiring two to three weeks for the crystals to reach maturity. The result is the formation of a microscopic, mesh-like barrier that plugs concrete’s pores against the flow of liquids, even against extreme hydrostatic pressure.
Independent laboratory testing, in accordance with U.S. Army Corps of Engineers (ACE) CRD C-48-73, Permeability of Concrete, demonstrated that crystalline-treated concrete could withstand up to 405 feet of head pressure, or 175 psi, which was the limit of the testing apparatus.
|The crystalline waterproofing chemistry can be surface-applied on new or cured concrete.|
In the form of vapor, water molecules can gradually work their way through the crystal formation and escape out on the downstream side, thus permitting the concrete to dry.
Although crystal formation largely matures in two to three weeks, the process can continue virtually as long as there is water in the concrete. Cessation usually occurs due to natural drying of the concrete. The reaction effectively never runs out of lime, meaning that if water re-enters the concrete years later, it automatically reactivates the waterproofing chemicals. New crystallization begins.
At the micro-level, shrinkage-cracking from drying potentially creates passageways for moisture infiltration. If they occur while crystals are still forming, micro-cracks up to 0.4 mm can be bridged. If they occur later and allow water infiltration, the water reactivates the waterproofing chemicals, making the concrete self-healing on the micro scale.
The crystalline waterproofing technology is non-toxic, contains no VOC’s (volatile organic compounds), and is NSF-61 approved for potable water.
A landmark wastewater treatment plant project is taking place in Miami-Dade County, FL. The plant will serve about a third of Miami-Dade’s 2.5 million residents. Adjacent to Biscayne Bay, the South District WWTP is being upgraded to a high-level disinfection facility with a peak flow capacity of 285 mgd, an increase of 27 percent. It is the largest domestic wastewater injection site, and one of the largest deep bed sand filter plants in the country.
In phase one, over 52,000 square feet of surface area was treated with a two-coat crystalline chemical system manufactured by Xypex Chemical Corp. This was done to waterproof and protect the transfer pump station, flocculation tanks and filters.
Phase 2 also uses the crystalline technology, as an admixture, for waterproofing and protection of an oxygenation train, four new clarifiers, associated splitter boxes and a pump station. An estimated 400,000 lbs. of the Xypex product is required for a substantial portion of 70,000 cubic yards of concrete being poured in place.
“We think it brings value to this project by increasing the concrete’s density,” said John Hoffman, PE, Construction Manager for Phase 2.
|The crystalline waterproofing chemistry can be used as an admixture in new concrete, increasing the concrete density.|
Crystalline waterproofing technology can also help protect structures from corrosion. If a concrete sewer is only partially full, the damp surface above the water line is an open invitation to aerobic bacteria that oxidize H2S and produce sulfuric acid (H2SO4). The acid attacks the calcium carbonate constituents of concrete. The key is integral density keeping out the bacteria that causes the problem.
Matt Raysin, a civil and environmental Division Engineer for Genesee County (Michigan) Water and Waste Services, said crystallization technology was used for critical areas of a 21-mile sewer extension project (54 inch and 72 inch pipe) completed in 2006.
“The crystallization product was the mechanism we chose to protect the concrete from developing hydrogen sulfide-induced corrosion,” Raysin said. “There was a noticeable increase in density in the concrete.”
About the Author: Les Faure is Advertising and Promotion Director for Xypex Chemical Corp. (www.xypex.com). He has been working with concrete waterproofing by crystalline technology for 25 years.