Macroscale and Microscale Studies on Time-Dependent Mechanical Properties of Concrete with Alkali Silica Reactions

Abstract

The time-dependent mechanical properties of concrete that expands because of alkali–silica reactions (ASRs) were studied. Compression tests were conducted with concrete specimens, which have several levels of expansion and material ages (14, 26, and 52 weeks). The specimens with larger expansions showed smaller stiffnesses at 14 weeks, while all specimens with different expansion levels had similar stiffnesses at 52 weeks. To investigate the cause of stiffness recovery of ASR-expanded concrete, the time-dependent chemical compositions and mechanical properties of ASR products inside cracks were investigated. With the scanning electron microscopy energy dispersive X-ray spectroscopy analyses of ASR products inside the specimens at 14 and 52 weeks, it was shown that matured concrete had considerable calcium in the ASR products. E-moduli of ASR products inside cracks located in cement paste were determined by nanoindentation, the stiffness increased as the distance from the aggregate increased, and the stiffness of ASR products outside aggregates was higher than the values for ASR products inside aggregates in previous studies. The stiffness of the ASR products increased as the calcium contents in the ASR products increased. Thus, the relationships between the stiffness and calcium–silica ratios of the ASR produces were understood. However, there seem to be some other dominant factors than the stiffness of ASR products that govern the time-dependent mechanical properties of concrete that suffer from ASR.