Effects of raw and different calcined bentonite on durability and mechanical properties of cement composite material

Abstract

Bentonite is a natural pozzolanic material mostly composed of SiO2 and employed in cementing materials for the reduction of cement consumption and CO2 emission besides improving performance of cement composite material by consuming portlandite to form extra C-S-H gel. So, many researchers studied on partial replacement of bentonite to improve concrete performance. However, bentonite mostly exists as a consolidated form that needs treatment for activation of pozzolanic reactivity to improve performance of cement composite materials. However, it is not well known how different replacement of raw and calcined bentonite affects performance of cementing materials in different hazardous environment. Hence, the present study identified the most influential replacement of bentonite, evaluating different calcined and raw bentonite in environments of acids, salt, and elevated temperature in addition to assessing the mechanical and physical properties of cement composite material. So, the results indicate that the employment of raw and calcined bentonite reduces the fresh bulk density, improves compressive strength, and Vicker hardness at 28 days, reduces the mass loss due to 56 days immersion in 5% HCl, 10% NaCl, and 5% HNO3 compared to the control mixture. Moreover, the employment of calcined bentonite at 800 °C significantly improved the durability and mechanical properties of cement composite materials compared to the control mixture. Specifically, replacing bentonite calcined at 800 °C for 3hs by 20% has the highest compressive strength than all samples after 28 and 56 days. Besides these, the study reveals that the corrosion potential of steel bars embedded in the mortar is reduced as the proportion of raw and different calcined bentonite increases. Generally, the employment of calcined bentonite is very beneficial to get improved performance on mechanical and durability properties of cement composite materials.