Deterioration behavior and microevolution of limestone-calcined Hwangtoh clay cement (LC3) with wollastonite after high-temperature exposure

Abstract

This study utilized the high-temperature stability of wollastonite to effectively optimize the high-temperature durability of limestone-calcined Hwangtoh clay cement (LC³). Wollastonite was used to replace limestone in LC³ at ratios of 1/3, 2/3, and 3/3. Various tests were performed on the wollastonite-based LC³ and OPC at the macro–micro scale. The thermal stability and pore structure of the pastes were tested. The residual strength, ultrasonic pulse velocity, and surface cracks after exposure to 105, 300, 500, and 900 °C were studied. The microstructure was observed by scanning electron microscopy. The evolution of the composition at high temperatures was analyzed via X-ray diffraction and Fourier transform infrared spectroscopy. The results indicated that wollastonite is much more stable than the hydration products and limestone. Wollastonite still maintained its intact structure even at 900 °C. Reducing the amount of limestone increased the thermal stability of LC³ and considerably reduced decomposition between 520 and 800 °C. In addition, wollastonite increases pore connectivity by lowering the synergistic effect, which is beneficial for the release of vapor pressure. Compared with those of conventional LC³, the residual strength and surface cracking of wollastonite-based LC³ after exposure to high temperatures were improved. Above 900 °C, the high-temperature decomposition products of LC³ were calcium silicate (C_nS), a part of gehlenite, and a small amount of wollastonite, whereas the decomposition products of OPC were mainly C_nS and CaO.