Development of Improved Guidelines and Designs for Thin Whitetopping: Environmental Response of Full-Scale BCOA Sections
Fifteen bonded concrete overlay of asphalt (BCOA) sections were built at the UCPRC facility in Davis, California, from February 23 to 25, 2016. The concrete mixes included Type II/V and Type III portland cements and calcium sulfoaluminate cement, and they were designed to provide 2.8 MPa (400 psi) flexural strength after either 4 or 10 hours. Six of the 15 sections were instrumented with a total of 245 sensors to measure the responses to environmental actions and cement hydration. Based on the analysis of the data collected by these sensors up until May 31, 2017, preliminary conclusions were drawn regarding how the different section configurations and concrete types responded to moisture and temperature-related actions. A clear link between drying shrinkage, concrete relative humidity, and environmental conditions was verified. Very high levels of drying shrinkage were measured in all portland cement mixes. For these mixes, the topical use of a shrinkage-reducing admixture proved to be an effective and efficient way to reduce drying shrinkage. Due to the low water/cement ratio of the portland cement mixes, very high levels of autogenous shrinkage occurred except in the mix that had been internally cured with pre-wetted lightweight aggregates. Autogenous shrinkage barely occurred in the internally cured mix. The mix with calcium sulfoaluminate cement did not present any autogenous shrinkage and presented much lower drying shrinkage than the mixes with portland cement. Despite the high levels of drying shrinkage in the mixes with portland cement, the concrete and asphalt remained fully bonded. For all the mixes, the apparent coefficient of thermal expansion was clearly influenced by the environmental conditions. Overall, thermal deformations of the mixes were much higher than predicted using the coefficient of thermal expansion determined in the laboratory under saturated conditions.