The reinforced concrete clarifiers and adjacent channels of the Los Angeles County wastewater treatment plant in Carson, California, had been in service for approximately 15 years when surface deterioration was observed. The aggressive nature of the wastewater had carbonated and softened the surfaces of the structures in the Stage I and Stage II areas.
CTLGroup conducted a condition assessment of the concrete in these areas to evaluate the extent and significance of concrete deterioration. Testing included both in-place destructive and nondestructive testing as well as laboratory examinations of samples obtained in the field. After determining the cause and extent of the concrete corrosion, a repair approach was developed. The repair involved removing the deteriorated concrete and applying a high quality shotcrete overlay.
CTLGroup developed the repair approach, prepared the shotcrete and surface preparation specifications, and monitored the repairs along with the owner during a full-scale pilot project. The pilot project developed by CTLGroup allowed the owner to screen a variety of proposed repair materials. This included evaluation of the associated costs and performance of up to six different materials. Construction methods were also examined and helped refine the specifications and minimize local complaints concerning dust and noise. The overall repair project included more than 50 tanks and adjacent channels staged through a four-year period. The repairs are expected to increase the service life of the tanks by 20 years.