Nanosilica synergy: unveiling the strength and fracture mechanisms in advanced concrete composites

Abstract

This study explores how nanosilica impacts the mechanical properties and fracture behavior of ultra-high-performance concrete (UHPC). We delved into the role of nanosilica in enhancing pozzolanic reactions and its effects on UHPC’s pore structure. This was investigated using advanced techniques such as scanning electron microscopy and mercury intrusion porosimetry. We prepared UHPC samples with varying nanosilica concentrations, replacing cement by 0 to 7.5%wt, to understand its influence comprehensively. Our findings reveal that higher nanosilica content, while beneficial in some aspects, compromises the self-compacting nature of UHPC. This necessitated conducting slump tests to evaluate workability. Remarkably, the addition of nanosilica led to a reduction in both capillary and macropores, enhancing the density and strength of the concrete. Specifically, a maximum of 5%wt nanosilica addition resulted in a 13% increase in compressive strength. However, this improvement in strength comes with a trade-off. The fracture energy of UHPC decreased by 23.2%, indicating an increase in brittleness due to nanosilica. Interestingly, tensile strength saw a 10.5% increase, primarily attributed to the enhanced formation of the C-S-H gel, a key component for concrete strength. This study illuminates the dual-edged effects of nanosilica in UHPC, presenting a nuanced view of its role in concrete technology and fracture mechanics.