Test Methods and Bond Performance Characterization of Shotcrete-Concrete Interface
Pizhong Qiao, Ph.D., PE, Professor
Department of Civil & Environmental Engineering
Washington State University
Shotcrete has become attractive for fascia and retaining walls in many states. Shotcrete is particularly well adapted to vertical and overhead work where conventional formworks and repairs are difficult to make, costly, and often short-lived. However, this practice could also possibly reduce the life expectancy of structures if the interface bond properties between shotcrete and concrete are not well developed when the substrate concrete surface is lack of cleanliness and soundness; multi-layered shotcreting makes it difficult to achieve effective integrity without proper preparation. In addition, long-term freeze-thaw weathering in northern states also degrades the bond strength of interface and results in debonding from the existing concrete structures and corrosion of rebars. Thus, properly placing of shotcrete and its bond properties to underneath concrete substrates are of paramount importance to service performance and durability in shotcrete application. In this proposed project, both bond strength and fracture-based concepts combined with finite element modeling, damage mechanics and computational peridynamics are used to develop effective test methods to characterize bond properties, obtain bond strength and fracture energy properties, evaluate long-term performance in cold regions, and predict damage accumulation and life of the interface between shotcrete overlay and concrete substrate in shotcrete application. Laboratory test methods and specimens will be first developed for static bond strength and fracture energy tests, and they will be subsequently used evaluate long-term interface performance and decay under accelerated freeze-thaw action. The results of this study will provide general guidelines for bond performance evaluations of overlays to substrate in shotcrete application, qualifications of existing and new shotcrete structures, and eventually for standardization of test procedures.
Dr. Pizhong Qiao