Impact of coupled low temperature and saturation degree on the mechanical properties of nanosilica-modified ECCs

The change mechanisms of the compressive and tensile properties of engineered cementitious composites (ECCs) under coupled low temperatures and moisture contents were investigated. The bonding properties between polyvinyl alcohol fibres and different ECC matrices were explored through single-fibre pull-out tests, and the relationships with compressive and tensile properties were analysed. The results showed that the chemical bond energy and the initial interfacial friction bonding strength were positively correlated with compressive and tensile strengths and negatively correlated with ultimate tensile strain. The effects of temperature (T = 20, 0, −30, −60°C) and water contents (dry, semi-saturated, saturated) on the mechanical properties of ECCs modified with nanosilica (NS) were studied using uniaxial compression and tensile tests. With decreasing temperature and increasing saturation, the compressive strength, initial cracking strength and tensile strength increased significantly. However, the ultimate tensile strain and strain energy in the saturated group decreased with a decrease in temperature, while no significant changes were observed in the dry and semi-saturated groups. The addition of NS increased compressive strength by up to 2.6 times at −60°C under semi-saturated and saturated states compared with the dry state, but no tensile strain hardening was observed.