Working in the Bayou:
T.V. Diversified completes a difficult junction box rehabilitation in a short time frame
Repairing and relining large sewer lines is always a serious undertaking, especially when the lines in question run underneath a Texas bayou. Repipe Texas, a national CIPP contractor, was working on such a project when they ran into a serious snag; after designing and installing a temporary bypass system involving six high-volume diesel pumps and four temporary lines, system engineers were surprised to discover that a critical concrete junction box was badly decomposed by microbiologically induced corrosion (MIC) and in danger of failing structurally. To keep this major infrastructure project on track, the box needed to be cleaned and rehabilitated in a very short time frame, while CIPP work continued. Repipe called on T.V. Diversified, a South Florida-based trenchless rehabilitation contractor, to complete the difficult project under extreme time pressure.
Working Under Pressure
MIC is a familiar evil to public works departments. The warm temperatures, turbulence, organic waste, and low oxygen levels commonly found in wastewater systems form hydrogen sulfide gas, and can make the system a near-perfect incubator for thiobacillus bacteria. Thiobacillus feeds on the sulfur in the gas, and converts it into sulfuric acid—some thiobacillus colonies can thrive in seven-percent acid solutions. The sulfuric acid attacks concrete and turns it into rotten, spongy calcium sulfate. Depending on condition, significant deterioration can take place in just a few months. In Houston, the very large—20-feet wide by 32-feet long by 20-feet deep—junction box was surprisingly close to total destruction… even though it had been protected by a PVC liner!
“It was pretty bad,” says Tom Vitale, Jr., owner of T.V. Diversified, “About eight-inches to a foot of the inner surface was completely corroded and eaten away… and the walls were only 18 inches to begin with. So structural integrity was compromised. And the PVC liner was falling off in sheets, because the corroded concrete just wouldn’t hold it up anymore.”
PVC lining is installed in many wastewater systems as a MIC-prevention measure—in theory, the lining keeps sulfuric acids away from concrete. PVC lining can work well in some situations, but it depends on meticulous application and absolute structural integrity. Even a tiny hole can allow thiobacillus to set up colonies between the PVC and concrete walls. When that happens, the lining actually hides the corrosion, and operators may not notice MIC until serious damage has been done.
Vitale is an expert at rehabilitating MIC-damaged structures, but even he was taken aback by the size, severity, and urgency of this project—“We got the call in Florida, and four days later we were onsite in Texas,” he says.
Rebuilding and Protecting In One Pass
Given the size of the chamber, he needed scaffolding. Rather than rent, he got on eBay and found a seller in Texas. With the scaffolding in place, he and his crew got to work with 5,000 psi pressure washers, thoroughly cleaning the concrete walls and removing all PVC lining and corroded concrete. The cleaned walls were then rinsed with a 10% solution of ConmicShield®, an antimicrobial product made by ConShield technologies. ConmicShield® is not toxic to humans or animals, but creates an environment that permanently inhibits thiobacillus growth. It can be used as a rinse, or mixed with concrete and applied structurally—the additive bonds with the concrete matrix and creates a permanent barrier.
After the anti-microbial rinse, Vitale used Permacast® MS-10,000, made by AP/M Permaform, to fill the voids caused by corrosion and to rebuild the junction box walls. Voids deeper than five inches were filled first with MS-10,000UL, a fast setting underlayment. Both products are silica-modified Portland cement, are corrosion resistant and ultra high strength, and work very well to strengthen and repair concrete structures. Vitale applied the new concrete with low-pressure rotor-stator pumps to minimize backsplash and improve adhesion. The City of Houston performed visual inspections as work progressed.
For the last inch of concrete resurfacing, Vitale continued to use MS-10,000, but for this layer he added ConmicShield® to the mix. “You don’t need the anti-microbial protection in the deeper layers,” he explains, “so to save money we just use it on the surface, which creates a barrier that protects the entire structure.” Vitale used a thickness gauge at this phase to ensure even coverage. By using MS-10,000 and ConmicShield® together, Vitale was able to repair and permanently protect the junction box efficiently and cost-effectively, without the expense or complication of additional linings of PVC or epoxy.
T.V. Diversified spent two weeks onsite, a much accelerated schedule. But things would have gone even faster without the intervention of a massive rainstorm over the bayou. “Some pump stations couldn’t handle the extra flow and backed up, so we were kept out of the box for a couple of days,” Vitale says, then laughs, “It was just Mother Nature acting up—not much you can do about it, except clean up the mess and get started again!”
As municipalities all over the country are forced to deal with long-neglected infrastructure, urgent rehabilitation projects like the Houston junction box are becoming more common. It’s good to know that new technologies are emerging to deal with the significant challenges, and that skilled contractors like T.V. Diversified are able to apply them effectively.