Effects of water saturation and impact load on the mechanical properties of geopolymer concrete

In terms of quality test, ultrasonic wave velocity test, static mechanical test and dynamic compression test, the physical and static mechanical properties of geopolymer concrete after water immersion for 180 d were studied, and the effects of water saturation and impact load on the mechanical properties of geopolymer concrete were analyzed. The results show that the geopolymer concrete reaches the water saturated state after water immersion for 180 d, and the ultrasonic wave velocity of geopolymer increases after water saturation, while the compressive strength, splitting tensile strength and flexural strength decrease. Water saturation increases the strength and stiffness of geopolymer concrete under impact load, while reducing its deformation capacity, with no significant effect on its energy consumption characteristics. The dynamic compressive strength and dynamic elastic modulus of geopolymer concrete increase after water saturation, the dynamic peak strain and pre-peak toughness decrease, and the impact toughness exhibits no significant alteration. The dynamic compressive strength of geopolymer concrete after water saturation increases by 8.61%~19.01%, the dynamic elastic modulus shows an average increase of 52.20%, the dynamic peak strain shows a maximum reduction of 28.88%, and the pre-peak toughness decreases by 14.07%~43.26%. The dynamic increase factor (DIF) of geopolymer concrete increases significantly after water saturation, and the fractal dimension of fragments decreases. The Comité Euro-International du Béton (CEB) model can well predict the DIF of geopolymer concrete in dry state, but significantly underestimate the DIF value of geopolymer concrete in water saturated state. Based on the test results, a DIF fitting formula for geopolymer concrete in water saturated state is proposed.