Study On Impact Resistance Of PVA-Nano SiO₂ Concrete After Freeze-Thaw Damage

As a widely used building material,concrete has many advantages,such as low cost,high strength,etc.However,it itself has many cracks.At low temperatures,these cracks will expand further.Studies have shown that the appropriate amount of nanomaterials or fiber materials added to concrete can play an effective effect on the development of cracks.And the concrete in the service will inevitably be affected by the impact load,which has higher requirements for the durability and stability of the concrete.However,the durability of nanomaterials and fiber material reinforced concrete only has a single factor or the performance research under the action of normal temperature and static force.In this paper,four different types of concrete,including ordinary concrete,PVA fiber concrete,nano SiO₂concrete and PVA-nano SiO₂concrete,were tested for their compressive strength,mass loss rate and relative moving mode under freeze-thaw cycle conditions.By combining the test results with the ABAQUS simulation of the effects of PVA fiber and nano SiO₂on the mechanical properties of concrete.Then the impact resistance of the four groups of concrete under the freezing-thaw cycle was analyzed.Finally,a quadratic equation for the number of damage and freeze-thaw cycles was established based on the compressive strength loss,and a freeze-thaw damage evolution model was established using the Weibull distribution.The main results are as follows:（1）After analyzing the strength loss rate,mass loss rate and relative moving form of concrete after freeze-thaw cycle,it is found that nano SiO₂can significantly improve the freezing resistance of concrete.With the increase of freeze-thaw cycle times,the effect on freezing resistance is more obvious;PVA fiber can improve the compressive strength of concrete by about 13.1%,but the frost resistance is not obvious;the concrete strength and frost resistance of PVA fiber with nano SiO₂,and its strength is increased by about 20.7%.（2）After the impact resistance test of concrete after freeze and thaw cycle,it is found that with the increase of freeze and thaw cycle times,the impact resistance of concrete is gradually weakened.Compared to the ordinary concrete,Nano SiO₂concrete is only 11times higher than ordinary concrete,But after 100 freeze-thaw cycles,88 times more impact resistance than ordinary concrete,Was 700%higher than that without freeze/thaw,This is due to the improvement of the freezing resistance of nano-SiO₂on concrete;And PVA fiber directly improves the impact resistance of concrete,The increase in impact resistance times before and after freeze-thaw did not change much,The average increase was about 31.5%;Mix of PVA fibers and nano SiO₂into the concrete,Its impact resistance ability has been significantly improved,Its average impact resistance times reached 47.1%,This result is more remarkable than the effect of adding only one of the materials,It shows its excellent freezing resistance and impact resistance.（3）In order to explore the mechanism of freezing and thawing cycle to reduce the mechanical properties of concrete,An tended study of concrete with the ABAQUS software,Through the simulations of the temperature field,The influence of freeze-thaw cycle on the surface thermal stress of each group of concrete,The results show a positive correlation between concrete surface thermal stress and freeze-thaw cycle,This shows that the concrete is due to the surface thermal stress in the freeze-thaw cycle of the continuous accumulation and caused by the loss of its strength;After the incorporation of the nanometer SiO₂,The cumulative thermal stress caused by freezing and thawing of concrete is greatly reduced,As can be seen from the comprehensive analysis of the test results,Nano SiO₂due to the frost resistance of concrete,Thus increasing the strength of the concrete after freezing and thawing,PVA fiber does not improve the frost resistance of concrete,Mainly is to directly improve the strength of the concrete.（4）The damage of PVA-nano SiO₂concrete after freeze-thaw cycle was studied,and the number of freeze-thaw cycle and the strength damage value were fitted to obtain the quadratic equation of freeze-thaw damage of PVA-nano SiO₂concrete.Subsequently,the evolution equation of PVA-nano SiO₂concrete was established based on the Weibull distribution.