Influencing mechanism of nano-Al2O3 on concrete performance based on multi-scale experiments

Multi-scale experiments were conducted to comprehensively explore the influencing mechanism of nano-Al2O3 (NA) on concrete performance. The experimental results indicated that the addition of 1% NA in concrete significantly improved its physical and mechanical properties and durability. Compared with the concrete without NA, this addition of 1% NA also made the internal structure denser, increased the early and late compressive strengths by 13.8% and 19.1%, respectively, and enhanced the ability to resist chloride ion pene-tration. However, with increasing NA content, the NA stabilized concrete gradually performed poorly in the workability and resistance to chloride ion penetration (RCP). Furthermore, it exhibited a decreased dry density and compressive strength, and an increased open porosity and water absorption. Through the mercury intrusion porosimetry (MIP) test, we found that the addition of NA effectively reduced the porosity and the most probable aperture of mortar in the concrete so that the proportion of gel micro-pores in the concrete increased and the proportion of capillary pores decreased. Moreover, NA had a pozzolanic effect and could react with calcium hydroxide (CH) to generate more nanofibers, which could fill pores and bond cracks to improve concrete per-formance under microscopic experiments.