Influence of freeze–thaw cycles on fracture behaviors of Nano-SiO2 modified high-strength high- ductility alkali-activated material

Nano-SiO₂ (NS) can effectively improve the mechanical properties of cement-based materials and alkali-activated materials, but its effect on the durability and fracture properties of high-ductility concrete has not been revealed. The influences of freeze–thaw cycles on the bending fracture behaviors of NS modified high-strength high-ductility alkali-activated material (HSHDAM) were studied herein. There were 4 wt content of NS (0 %, 4 %, 8 % and 12 %) and 4 numbers of freeze–thaw cycles (25, 50, 75 and 100) assessed. The results indicated that with the increase of freeze–thaw cycles number, the compressive strength, dynamic modulus of elasticity, fracture toughness of initiation and instability and fracture energy of HSHDAM were all decreased continually and significantly, but the ductility index was increased. With the increase of the NS weight content, the compressive strength, dynamic modulus of elasticity, fracture toughness of initiation and instability, and fracture energy and ductility index of HSHDAM were all increased continually, while the bending strength seems to be optimal at 4 % NS content. 75 freeze–thaw cycle was the threshold value for the strengthening effect of NS on bending strength and ductility index. With the addition of NS, the better bonding properties of polyethylene fiber, more fully cracking behaviors, and compact alkali-activated matrix contributed to these good fracture and anti-freeze–thaw behaviors. The addition of NS can alleviate the deterioration of HSHDAM mechanics and fracture properties caused by freeze–thaw cycle.