Pore structure optimization and hardened performance enhancement of nanopore-rich lightweight cement paste by nanosilica in swelled bentonite

Nanosilica-modified swelled bentonite used as a pore-forming agent was introduced into cement pastes for the preparation of nanopore-rich lightweight cement pastes (NLCPs). The effect of nanosilica on the pore structure and hardened properties of NLCPs and their influence mechanisms were investigated. The results indicated that the introduction of nanosilica reduced pore size and improved nanopore content, due to increased platelets in voids, voids filled by hydration products and unreacted nanosilica. The percentage of nanopore content improved from 67.2 to 94.7% and 55.5–71.3% after, respectively, introducing a 60% and 80% bentonite slurry with increasing nanosilica replacement from 0 to 20%, and the median pore size decreased from 48.6 to 30.9 nm and 80.4–47.5 nm, respectively. The thermal insulation performance and compressive strength of NLCP were gradually enhanced by adding nanosilica from 0 to 20%. When nanosilica content was 20%, an increasing rate of 55.2% and 220.0% in 7-day compressive strength and 65.3% and 211.1% in 28-day compressive strength, with a 20.7% and 10.5% reduction in thermal conductivity at porosity of 61.3% and 72.3% can be achieved, respectively.