Mechanical Properties and Microstructure of CaSO₄ Whisker Reinforced Cement Mortar

Abstract

Calcium sulfate whisker (CaSO₄ whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO₄ whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO₄ whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO₄ whiskers were identified by X-ray diffraction (XRD) and scanning electron microscope (SEM). Conclusion can be drawn that CaSO₄ whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO₄ whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry (MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

Keywords

calcium sulfate whisker / reinforcement / mechanical properties / microstructure / toughening mechanism / cement paste