Influence of recycled fine aggregate content on dynamic mechanical properties of mine supporting mortar

The high porosity of recycled concrete aggregate have a positive effect on the resistance of mortar to impact load. In order to study the feasibility of recycled fine aggregate mortar used in underground support,4 types of cement mortars with different recycled fine aggregate mass replacement rates(0,10%,30% and 50%,resdetiuely) were made. 50 mm Split Hopkinson Pressure Bar (SHPB) test device was used to test these cement mortars under different pressure loading(0.25,0.35,0.45 MPa). And the compressive strength of these mortars was also tested. Comparing the dynamic characteristics of cement mortar under different impact pressure loading,the impact resistance performance of recycled fine aggregate mortar was studied. The results show that the compressive strength of recycled fine aggregate cement mortar increases first and then decreases with the increase of the substitution rate,and reaches the maximum when the substitution rate is 10%,while the substitution rate is 30% and 50%,the compressive strength is not lower than that of the control group. Under the same impact pressure,with the increase of the replacement rate of recycled fine aggregate,the impact load that the mortars can bear also increases. Under the same substitution rate,the dynamic compressive strength and ultimate toughness of the mortars increases with the increase of impact pressure. Within the strain rate range from 60.29 to 143.379 s-1,the dynamic increase factor (DIF) of the recycled fine aggregate mortar with 50% substitution rate was higher than that of other groups. The recycled fine aggregate cement mortar with 50% substitution rate has the highest dynamic compressive strength and ultimate toughness under three different pressures,and its compressive strength is no less than that of the control group.