Research On Impact Compression Mechanical Properties Of Basalt Fiber Reinforced Concrete After Freeze-thaw Cycles

A large number of infrastructure projects have been carried out in perennial freezing areas and seasonal freezing areas in China.Concrete materials are commonly used in them,and are often in a freeze-thaw cycle.Therefore,studying its mechanical properties after freeze-thaw damage is of great significance to the construction and protection of concrete projects in freezing areas..To make an analysis of the influence of freeze-thaw cycles,impact speed and basalt fiber(BF)volumetric content on the compressive performance of concrete,the quasi-static compression test and Split Hopkinson Pressure Bar(SHPB)impact compression test were carried out on Basalt Fiber Reinforced Concrete(BFRC)after freeze-thaw damage.The modified Ottosen constitutive model and Z-W-T constitutive model were improved with the introduction of the freeze-thaw-load damage factor.Besides,the method of neural network modeling was applied to construct the constitutive model,and the three models are compared.To analyze the unobservable phenomenon in the experiment,the SHPB impact compression test of BFRC after freeze-thaw cycles was numerically simulated by a software named ANSYS.The conclusions are as following:(1)The number of surface cracks,cracking degree,mass loss rate and porosity of concrete specimens increased as the number of freeze-thaw cycles increasing.If the proper amount of BF is added,the frost resistance of concrete can be improved,and the effect is best when the volume of BF is 0.2%.(2)The mechanical tests are carried out on the BFRC specimens damaged by freezing and thawing,it is indicated that adding proper amount of BF can improve the compressive resistance of concrete.When the volume of BF is 0.2%,its anti-pressure performance is the best.Freeze-thaw cycles exhibit damage and degradation effect of concrete.The strain rate has a strengthening effect on the impact compressive mechanical properties of concrete.(3)The fitting results of the three models are good,and the constitutive model based on neural network has the best fitting effect.(4)In the numerical simulation of the impact compression test,the crushing law of the BFRC specimen is basically in line with the actual test results.By analyzing the crushing process of the specimen,it can be seen that when the specimen are impacted,compression deformation is generated along the axial direction and transverse deformation is generated along the radial direction.The stress distribution of the specimen gradually decreases from the center of the circle to the outer surface,and the crushing develops inwards from the weak parts at the edge in a ring.