Some things are better off left buried, and the longer the better. Septic tanks top this list.
That's one of the reasons why ABC Precast & Ready Mix of Nanaimo, British Columbia, has turned to advanced sewage treatment systems to make sure concrete tanks remain the product of choice for local residents.
“The biggest problem with septic tanks is leaching, causing degradation to concrete,” says A.J. Hustins, general manager of ABC Precast & Ready Mix, which has been in the tank business for 40 years. “To minimize these problems, we take special care to form our septic tanks with newer molds and high-quality concrete that exceed industry standards for thickness and strength. We also look to new industry advancements to further improve our final product.”
ABC had been testing an additive for waterproofing, protecting, and improving concrete strength in some of its other product lines. The product was performing well, so ABC tested it in its septic tanks.
The producer tested the product, Xypex Admix C500, in a variety of conditions, including compressive strength and sulfate resistance. Added to concrete during batching, the product reacts with calcium hydroxide and other byproducts of cement hydration in the concrete. This causes a catalytic reaction that generates a nonsoluble crystalline formation throughout the pores and capillary tracts of the concrete.
Mixed with Xypex Admix, the concrete becomes permanently sealed against the penetration of water or liquids from any direction and deterioration due to harsh environmental conditions. It resists chemicals and can seal a hairline crack up to 0.4 mm. Unlike a coating system applied to the concrete after it's formed, it never has to be reapplied.
Typically, ABC looks to achieve a minimum 32 MPa in the tank mix design at a 28-day break. With Xypex, the producer averages 45 MPa.
“The crystalline reaction helped the concrete hold more moisture over a longer period of time so we get a longer, slower moister cure, which ultimately yields a higher strength,” says Hustins.
Some of the benefits were visible to the naked eye. “We knew our tanks were working in terms of waterproofing,” says Hustins. “We'd look at a tank that was full of water and see if the color of the concrete was getting darker and showing signs of dampness. Had we seen a color change, it would have been a clear sign that water was leaching through the concrete.”
Not so easily detected is the protection the product provides against sulfate attack. Acid resistance tests show that by blocking the penetration of acids into the concrete, Xypex prevents the formation of sulfoaluminate hydrate, an expansive compound that causes the concrete to self-destruct.
Today, the precast producer uses Xypex in all of its septic tanks, which are available in volumes of 300, 480, 900, 1200, 1440, 2400, and 4800 U.S. gallons. It is added at a dosage rate of 3% by weight of the portland cement for precast tanks.
Many septic tank installers and contractors in British Columbia now recognize the difference. Recently, ABC Precast & Ready Mix was awarded a contract to supply a local registered installation company with a multiple tank system for one of the Gulf Islands, located off the east coast of Vancouver.
For more information on the product in this story, visit www.xypex.com.