Proceed with Caution: Concrete Cloth GCCM Provides Erosion Protection at Nuclear Power Plant
A nuclear power-plant site in the southeastern United States faced an erosion problem on a steep, 2:1 slope near dry-cast storage containers of spent nuclear fuel. The shotcrete finish covering the slope was intended to serve as a protective layer that would prevent the backfill material from eroding. However, the design of the erosion protection left it susceptible to shrinkage and temperature cracking, as no control joints were constructed. As a result, escape paths for the backfill material through the erosion protection were created.
Cajun Constructors, a nationally recognized specialty contractor in heavy civil, mechanical, deep-foundation and marine-construction projects, along with Industrial Fabrics, visited the site to assess the damage and recommend solutions. Together, they knew the ideal solution would need to have low permeability, enabling the slope to shed runoff water rather than allowing absorption. Equally important, the solution would need to be extremely durable and comply with industry regulations.
One option for repair—pumping more shotcrete on top of the existing concrete—was evaluated as a temporary solution, as it wouldn’t address the existing slope erosion. Alternatively, the shotcrete could be removed and re-applied across the entire slope face—an extremely labor- and time-intensive process, especially considering any adverse weather conditions would delay production further. Even with the addition of a certified nozzleman to the standard crew, unevenly hand-spraying shotcrete may create the potential for future cracking.
The third option to protect the slope was the use of geosynthetic concrete composite mats (GCCMs), flexible, concrete-impregnated fabrics that harden on hydration to form a durable, waterproof and fire-resistant concrete layer. Milliken Infrastructure Solutions’ (MIS) Concrete Cloth GCCM had already been proven effective for an onsite test area and was selected as a consistent, engineered solution that could be installed quickly and evenly over the rest of the slope.
Cajun Constructors partnered with Industrial Fabrics and Milliken Infrastructure Solutions to provide design and engineering support during the installation phase, which began in late October. The repair began by removing the damaged shotcrete and drain pipes in the affected areas. After the eroded portions of the slope were backfilled with limestone and new drains placed, Concrete Cloth GCCM was installed over the repaired slope.
The team strategically planned when to deploy the 900-square-foot rolls based on day-to-day weather conditions, often rolling the GCCM onto the slope in the morning and hydrating the material in the afternoon. In contrast to the requirements of concrete-pouring equipment, Concrete Cloth GCCM provided the flexibility to easily start and stop construction, allowing production to move forward despite heavy seasonal rainfall. On sunny days, the team deployed as many as eight to 10 rolls of the material, expediting the job to meet its early January completion date.
“Working with Industrial Fabrics onsite to determine the most-effective ways to do the laps and cover the corner areas helped us save even more time and expense,” said Matt Swindler, superintendent at Cajun Constructors. “Concrete Cloth GCCM worked particularly well for this project, because we didn’t have to do any of the forming, paving or finishing that is necessary with traditional concrete repairs. It is easy to see the value of a product that installs easily and effectively with minimal equipment.”