Setting time in Roller-Compacted Concrete (RCC)

Abstract

The principal differences of RCC from conventional concrete pavements are workability, rheology, paste content, and compactive effort. RCC pavements obtain significant strength during compaction and, therefore, can be opened to traffic in less time than conventional concrete pavements. For both types of concrete, there are methods to evaluate workability in the fresh state, e.g., slump and Vebe test. However, no standard method is available for either concrete pavement type for evaluating setting time in-situ. Construction activities such as tining/texturing, curing membrane, and sawing of contraction joints are related to the concrete setting time. A recently developed technique for setting time of conventional mortar and concrete with fully contactless ultrasound has shown promising results with higher paste content mixtures. This recently proposed method monitors the initiation time of leaky Rayleigh waves (LR-wave) signals in time and space over the conventional concrete surface. The objective of this study is to determine the setting time in RCC pavements which has significantly lower paste volume and higher aggregate content. Preliminary results have shown that the setting time of an RCC mixture with overfilled paste can be successfully determined. Additional tests on a wider range of RCC mixture constituents and proportions, e.g., lower aggregate void and paste contents, are being conducted to evaluate the limitations of this contactless sensing method and necessary adjustments. Reliable set time determination in RCC pavements can improve QC/QA practices and indicate repeatable triggers for other construction activities like sawing contraction joints.