Testing and Analysis of CAP Concrete Stress and Strain due to Shrinkage, Creep, and Expansion. Final Report

摘要

In-situ decommissioning of SRS P and R Reactors will entail filling the reactor vessels with a special concrete and entombing the reactors with protective cover layers of Ordinary Portland Cement (OPC) concrete, called Cap Concrete. It is known that concrete experiences shrinkage strains during drying with the potential for tensile stresses to develop. A risk thus exists for cracking, allowing ingress of water into the reactor vessels with implications for possible transport of radioactive contamination to the environment. The extent of shrinkage for the Cap Concrete and the potential for surface cracking needed to be assessed, and means for mitigating the resulting stresses needed to be evaluated An experimental program and accompanying analytical study was thus initiated to investigate the phenomena of drying, shrinkage, creep and use of admixtures that affect the performance of the Cap Concrete during the early periods of curing and drying. The experimental program utilized four slab specimens measuring 229 mm x 229 mm x 305 mm each. The concrete mixture had a water-to-cement ratio of 0.64, 46.4 wt% coarse aggregate, 29.2 wt% fine aggregate, 3 wt% fly ash, Conex, an expansive admixture, and other admixtures. Slab specimens were installed into two environmental chambers (ECs) at controlled temperatures of 23 degrees C, and 40% and 80% relative humidity (RH), respectively for 50 days and at ambient field conditions for another 34 days.