| With the implementation of policies such as the Great Western Development and the Southward Development of the Corps,the construction industry in southern Xinjiang has developed rapidly,but the shortage of construction sand resources has become increasingly prominent.Southern Xinjiang is rich in desert sand resources,and replacing ordinary sand with desert sand can alleviate the shortage of construction sand.After consulting the literature,it is found that the physical and chemical properties of desert sand cannot be directly applied to concrete.In this study,the laboratory test method was used to prepare desert sand shotcrete material by replacing ordinary sand in shotcrete in a certain proportion.The influence of desert sand replacement rate on the physical and mechanical properties of concrete and the bonding performance with the base layer and steel reinforcement,the BP model of the mechanical strength of desert sand shotcrete is established to predict the influence of desert sand replacement rate on the physical and mechanical properties of concrete,and the appropriate desert sand replacement is selected.In order to further improve the utilization rate of desert sand in shotcrete,basalt fiber was added when the desert sand replacement rate was 50%.Appropriate basalt fiber content.The research results provide a certain theoretical basis for the application of desert sand shotcrete in engineering.The main results of this research are as follows:(1)By replacing natural sand with desert sand of 0(control group),10%,20%,30%,40%,and 50%,the effect of desert sand replacement rate on the slump and mechanical properties of shotcrete was studied.The results show that: with the increase of desert sand replacement rate,the slump of desert sand shotcrete mixture shows a trend of first increase and then decrease,the highest when the replacement rate is 10%,reaching 113 mm,and when the replacement rate exceeds 30%,the slump of the mixture has not met the specification requirements of 80～120 mm.When the replacement rate was 50%,the slump was the lowest,only 12 mm;the overall compressive strength showed a trend of first increasing and then decreasing.When the replacement rate was 50%,the 28-day compressive strength was 38.22 MPa compared with the control group,After the replacement rate exceeds 50%,it begins to drop significantly,and when the replacement rate of desert sand is 70%,it is only 27.85 MPa,which does not meet the C30 strength design requirements;the splitting tensile strength and flexural strength show a downward trend,and the replacement rate is At50%,compared with the control group,the 28-day splitting tensile strength and flexural strength decreased by 50.68% and 15.97%,respectively.Through comprehensive analysis,it is considered that the optimal replacement rate of desert sand in shotcrete is 10%;the mechanical strength is predicted by establishing a BP model for predicting the mechanical strength of desert sand shotcrete material.The results show that the optimal replacement rate of desert sand in shotcrete is: 15%.(2)To study the bond strength of desert sand shotcrete material with old concrete surface and ribbed steel bar under different desert sand replacement rates.The research shows that the bond strength between concrete and base concrete decreases with the increase of desert sand replacement,and the development trend is similar to the development trend of concrete splitting tensile strength,both of which decrease significantly when the replacement rate is 20%;When ～50%,the bond strength of desert sand shotcrete and steel bars is lower than that of the control group.Through the significant analysis,it is found that the desert sand replacement rate has little effect on the bond strength of shotcrete materials and steel bars.(3)When the desert sand replacement rate is 50%,the influence of different dosages of basalt fiber on the mechanical properties of desert sand shotcrete is studied.Through mechanical properties test and shotcrete strength prediction model,it is found that when the basalt fiber content is 1 kg/m3,the 28-day compressive strength of desert sand shotcrete is 40.61 MPa,which is 5.59% higher than that of the benchmark group,and the 28-day splitting The maximum tensile strength is 2.86 MPa,which is 13.49%higher than that of the benchmark group,and the 28-day flexural strength is 3.69 MPa,which is 18.65%higher than that of the benchmark group.The comprehensive performance of strength is the best,and it can be better used in temporary support. |
