Influence of silica fume on the physical properties and microstructure of lightweight cements

This study investigates the impact of silica fume (SF) on the rheological behaviour, compressive strength and microstructure of oil-well lightweight cement pastes (OLCP) that incorporate hollow glass beads. In total, eight OLCP formulations were evaluated, varying SF dosages while maintaining a controlled initial paste density. Various analytical techniques including X-ray diffraction, thermogravimetry, micro-computed tomography and scanning electron microscopy were used to elucidate the mechanisms of SF in relation to OLCP. Results show that incorporating SF enhances the homogeneity of OLCP significantly, refines pore structure and increases compressive strength. These improvements are primarily attributed to the pozzolanic, filling and nucleation effects of SF, which depend on maintaining essential flow properties and adequate dispersion within the OLCP. Notably, a stronger correlation was found between compressive strength and pore structure parameters, particularly the ratio of small to large pores. The results provide valuable references for the development of high-performance lightweight cement with high pressure bearing capacity.