Effect of unconventional supplementary cementitious materials on the hardened cement pastes exposed to high temperature

Abstract

An investigation was conducted to determine how Ordinary Portland Cement and several unconventional cementitious additives, such as magnetite, chamotte, perlite, boron carbide, and more common powdered quartz, affected the behaviour of hardened cement paste when subjected to high temperatures. The test was conducted using a constant water–fines ratio of 0.3. The water–cement ratios were nevertheless 0.25 and 0.222 as a result of the two fine replacement ratios (20% and 35%, respectively). Seven heat steps were used to heat the specimens of hardened cement paste to 900 °C. On the cooled specimens, comparisons between relative residual compressive strength and residual compressive strength were made. Additionally, a new approach known as "temperature endurance" is used to express the total area under each strength curve. Furthermore, the specimens were analysed using a scanning electron microscope. Our research has shown that perlite, when employed as additional cementitious material, performs remarkably well and has favourable effects, even at high temperatures. Up to 600 °C, it has the longest-lasting, practically constant residual strength values. In this area, the relative strength reductions are less than 15%. Furthermore, it is shown that boron carbide increases compressive strength at 900 °C in comparison to values at 600 °C. Due to the material's low melting point and the formation of secondary bindings at the highest heat step, this effect results. The other materials under investigation, such as powdered quartz, magnetite, and powdered chamotte, perform only slightly better than the reference homogeneous Ordinary Portland Cement, particularly in the mid and high heat ranges. In low heat ranges and by lower addition of fines, particularly in the well-known local strength maximum of 200–300 °C, homogeneous matrixes perform better.