Effect of red mud addition on oil well cement at high temperatures

Abstract

Red mud is a byproduct of the aluminium industry and is typically considered hazardous waste owing to its high alkali content and resulting environmental pollution. In this work, Bayer process red mud was used to partially replace oil well cement and its influence on the compressive strength of hardened cement pastes was explored under hydrothermal conditions. X-ray diffraction, scanning electron microscopy, nitrogen adsorption and thermal analysis were used to determine the phase composition, microscopic morphology, pore size distribution and bound water content, respectively, of hardened cement pastes to investigate the reasons underlying the observed strength change. The results obtained revealed that red mud can exert pozzolanic activity at addition levels of up to 5%, promote the cement hydration reaction and the production of calcium silicate hydrate (C–S–H), and ultimately increase the strength of hardened cement pastes. Higher red mud contents decreased the degree of cement hydration, which resulted in an increased volume of macropores (d > 50 nm), a decreased volume of mesopores (d = 4·5–50 nm) and a remarkably decreased strength.