Experimental Study On Toughness Of PVA Reinforced Tailings Sand Cement-based Composites

PVA reinforced tailing sand cement-based composite material,a kind of high toughness environmental protection material,with tailing sand in place of 50% natural sand,fly ash instead of part of cement and PVA fiber to strengthen cement-based composite material,not only has industrial waste recycled and utilized,but also makes the toughness of the original brittle cement-based composite material improved,the benefits of environmental protection and toughening subsequently doubled.Based on the preliminary research of the research group,the toughness of PVA reinforced tailing sand cement-based composite was systematically studied in this paper.First,the mix proportion design scheme was determined in accordance with the basic principle and preparation test of cement-based composite material.Second,through static loading tests,the specimens were studied under different deformation states such as compression,tension,bending and shear.Finally,the impact toughness and fracture toughness of the specimen were researched,in accordance with the drop impact test and fracture characteristic test.In addition,The toughness of the specimen was characterized by toughness ratio and toughness index to discuss the effect of different water-binder ratio and fiber content on the toughness of the test piece.The main research contents and research results are as follows:(1)In terms of the existing research results and a large number of trial-matching experiments,the mix ratio scheme of this study was settled,and the basic mechanical property tests of the samples with different water binder ratio(0.25,0.3,0.35)and fiber content(0%,1%,2%)were carried out.The test results show that the mixture ratio of each group meets the requirements of working performance all and that the mechanical properties and working properties of the specimens are relatively superior,on condition that the water binder ratio is 0.35 and the fiber content is 2%.(2)The load-deformation curve under the corresponding force state and the magnitude of the absorbed deformation energy of the specimen under different deformation states was obtained by means of the axial compression,axial tensile,four-point bending and double-sided shear tests.With the toughness of specimens of different water-to-binder ratios and fiber content characterized by the dual characteristic indexes of toughness ratio and toughness index,the static toughness of the specimens was further evaluated,combined with microscopic scanning electron microscope test and bending self-healing test.The test results suggest that comparing with the typical brittle failure of the specimen without fiber addition,proper addition of fiber can significantly enhance the compression toughness,tensile toughness,shear toughness and bending toughness of the specimen,makingDuctile failure of the specimen,under different loading modes.Within the scope of this test,as the the water-to-binder ratio is continuously increased,the quality and extent of the toughness of the test piece were significantly improved.It is concluded that the proper addition of fiber can enhance the internal adhesion of the cement-based composite,reduce the internal porosity,promote the internal hydration reaction of the matrix,and the hydration product and fiber bond well,by scanning electron microscope test of the tensile specimen under various magnification.According to the bending self-healing test,the higher the curing age of the bending injury specimen is,the greater the bending toughness recovery rate is.(3)Fracture characteristic test and drop weight impact test were carried out on the test piece respectively.After the load displacement curve and P-CMOD curve were obtained from the three-point bending test,the fracture toughness,instability fracture toughness and fracture energy were calculated by the double K fracture criterion.Then,the effects of diverse fiber content and water binder ratio on the fracture energy were discussed,in terms of the double K fracture parameters.After that,the impact energy of initial crack and failure was obtained by drop impact test and the impact toughness index was used to analyze the influence of different fiber content and water binder ratio on the impact toughness.Finally,the toughening mechanism of the material was analyzed from a microscopic perspective by the scanning electron microscope test.The test results indicate that the energy dissipation during initial cracking and the number of impacts during initial cracking are almost constant,and do not change with the fiber content and water-to-binder ratio,while the energy dissipation during impact and the number of impacts during failure are related to the above two influencing factors.The overall trend of initiation fracture toughness declines with the increase of the water-binder ratio,and slightly multiplies with the increase of the fiber content,whereas the unstable fracture toughness of the sample without fiber is almost independent of the change of the water-binder ratio.The water-to-binder ratio of the fiber-incorporated specimen is positively correlated with the fracture energy,all of which exceeds 4800N/m.