After 15 years of service, the top 23 feet of the secondary digester walls were lined with a shotcrete overlay. Delaminations in the overlay were detected shortly after the shotcrete was applied. Reapplication of shotcrete in the debonded areas also resulted in delaminations.
CTLGroup performed an evaluation to assess the cause of the shotcrete delamination. The firm’s work included reviewing project documents, performing field visual inspections and delamination surveys. Laboratory tests on samples removed in the field included tensile bond pull-off tests, petrographic examinations, X-ray diffraction testing, and thermal analyses.
Results of the investigation revealed that the shotcrete overlay failed due to inadequate surface preparation of the concrete substrate. Another contributing factor to the debonding was a lack of overlay thickness control in the field. CTLGroup provided repair recommendations that included guidelines for proper substrate preparation and development of a replacement shotcrete overlay mix.
Water and WasteWater
Comprehensive Building Assessment
Leakage Investigation & Repair
Coatings, Adhesives, and Sealants
Structural Engineering + Evaluation
Repair, Restoration, Retrofit
Structural Condition Assessment
Concrete + Cement-Based Materials
Microscopy / Petrography