| As China’s " Belt and Road Initiative" construction progresses,the scale of infrastructure is expanding and the contradiction between the sharp increase in demand for sand,an indispensable material for building concrete,and the increasing scarcity of natural sand is becoming increasingly acute.At the same time,the overexploitation of natural resources and the large amount of carbon dioxide emissions from concrete production have led to a series of ecological problems.In the northwest of China,there are abundant desert sand resources,which can be used locally as fine aggregate instead of river sand to prepare desert sand concrete(DSC).However,due to the small particle size of desert sand,DSC is prone to cracking,poor toughness and poor durability,which limits its application in engineering.Therefore,the performance of desert sand concrete needs to be further improved,and the addition of fibers is an effective measure to improve the performance of concrete.In this paper,the DSC was prepared by replacing river sand with Mu Us Desert sand at a certain substitution rate,and further improved with high modulus glass fibers(GF)and high tenacity polypropylene fibers(PF)to form fiber-reinforced DSC.The microscopic reinforcement mechanism of the fibers was revealed through the experimental study.The main findings and conclusions are as follows:(1)Tests on the basic mechanical properties of fiber-reinforced DSC were carried out to investigate the effect of fiber admixture amount and type on the mechanical properties of DSC,and further analysis of the DSC flexural and tensile ratios was carried out.The results show that desert sand partially replaces river sand at a 30% replacement rate and its indexes are similar to those of ordinary concrete.Within the appropriate dosing range,fibers can significantly improve the compressive strength,splitting tensile strength and flexural strength of DSC.In this study,the optimum admixture of GF was 0.2%,the optimum admixture of PF was 0.1% and the optimum admixture of mixed fibers was 0.1% PF + 0.05% GF.Overall,PF was better than GF and mixed fibers were better than single admixture fibers.(2)The fiber-reinforced DSC axial compression strength test was carried out to study the influence of fiber doping and type on the full curve of DSC axial compression.The results show that the slope of the rising section of the axial compression full curve of fiber-reinforced DSC is greater and the falling section is more gentle,showing a certain degree of ductile damage characteristics.(3)A fiber-reinforced DSC frost durability test under freeze-thaw cycles was carried out to investigate the effect of fiber admixture and type on the frost durability of DSC.The results showed that the difference in mass loss and relative dynamic elastic modulus between ordinary DSC and fiber-reinforced DSC gradually appeared and increased with the increase of freeze-thaw cycles.The incorporation of fibers significantly improved the frost durability of DSC,delayed the apparent damage of the specimens and reduced the mass loss and relative kinematic modulus loss caused by freeze-thaw cycles.Two freeze-thaw damage models(quadratic freeze-thaw damage model and Weibull distributed freeze-thaw damage model)were developed to predict the service life of DSC using the relative dynamic elastic modulus as the damage indicator.(4)Fiber-reinforced DSC microscopic tests were carried out to describe the microscopic morphology of the specimens after force damage and freeze-thaw damage,revealing the fiber reinforcement mechanism.The results show that,on the one hand,the fibers play a bridging role across the cracks and form a dense and homogeneous structure with the aggregates and slurry.On the other hand,the fibers play a crack-blocking and toughening role,reducing the number of interfacial weak zones within the concrete and improving the mechanical properties and frost durability of the DSC. |
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