Microstructure of calcium carbonate whisker reinforced cement paste after elevated temperature exposure

Calcium carbonate whisker (CW) could improve mechanical properties of cementitious composites at room temperature. Aiming at using CW as high-performance and low-cost microfiber at high temperature, the microstructural changes of cementitious composites with CW exposed to high temperature are clarified in this research. From room temperature to 500 °C, additional hydration of unhydrated binder grains in steam environment occur (“internal autoclaving”). Moreover, CW transferred from aragonite to calcite in cement paste at about 375 °C (“phase transformation”). Under these coupling effects, calcite CW forms stronger bond with these rehydration products than that at room temperature, also improving the pore distribution and compressive strength. At 800 to 1000 °C, CW increases the pore size and decreases the compressive strength of cement paste due to CW decomposition. From 1000 to 1100 °C, the residual compressive strengths of CW reinforced cement pastes increase slightly because of the forming of calcium silicate and Ca(OH)2.