Microfracture Characterization of Cement Paste at Early Age by Indentation Test

Abstract

Fracture properties of cement paste at an early age are difficult to determine using conventional methods because of its low strength. By using an indentation technique, this paper reported a fracture test method for early-age cement paste in microscale. Power equations were employed to capture the load-displacement curves, where the power indexes were acquired to be associated with energy constants. The elastic energy constant may be a featured parameter to characterize solid phases. An explicit expression for estimating plastic energy with the effect of holding load at peak force was established based on an energy method. The fracture energy, energy release rate, and fracture toughness of a cement paste cured for 3 days were calculated directly from indentation curves via this model. The microstructure of the cement paste was studied using scanning electron microscopy and backscattering analysis. The results show that the fracture data of the cement paste at an early age from the indentation tests are stable and comparable with those by conventional macrofracture tests. The indentation-based fracture testing method may provide an efficient method to assess the fracture properties of cement-based materials.