Research On The Properties Of Fiber Reinforced Engineered Geopolymer Spray Composite

The problem of large deformation in deep underground engineering is becoming more and more serious.It is difficult for existing shotcrete or arch structure to meet the requirements of support.It is urgent to develop new type of large deformation supporting structure and material.In this paper,a new type of Fiber Reinforced Engineered Geopolymer environmental protection material with strain hardening and multi-fine crack characteristics based on the proportion principle of fiber cement-based composite(ECC),and it is put forward that it can be used to replace ordinary concrete in underground engineering spray construction.Fiber Reinforced Engineered Geopolymer Composite materials with large deformation characteristics were designed and prepared by micro-mechanism design with fly ash,slag and domestic PVA fibers,and their mechanical properties and extensibility were tested and evaluated.The spray performance,mechanical properties and extensibility of the spray layer were studied and evaluated by spray test.The main research contents and achievements are as follows:(1)The material proportion was designed from the view of microcosmic action mechanism through the testing of fracture property of non-fiber matrix and single fiber pull-out test after selecting fly ash,slag,solid particle alkali activator and domestic PVA fiber raw material.The strain hardening properties under different ratios were evaluated.The results showed that thebJ? /Jtipindex of the composite material can exceed 3 when BHL fiber is selected and the mass ratio of fly ash to slag is 1:1,which satisfies the general mechanical characteristics of strain hardening and multi-crack cracking.(2)According to the preliminary proportioning design,the aggregate-free fiber geopolymer was prepared.The high strength,high elongation and strain-hardening properties of the material were verified by tensile test,and the influence of the fiber on the properties of the material was analyzed.When the volume ratio of 6mm-BHL fiber is 1.4%,the0? /fc? is1.26,and the compressive strength of the material can exceed 70 MPa,the tensile strength can reach 3.3 MPa,and the elongation can exceed 2.3%.(3)The relationship between the development of micro-cracks and the variation of stress-strain curves in Fiber Reinforced Engineered Geopolymer Composite materials under tensile loading were studied by means of spacer photography.The results show that many micro cracks with width less than 100?m were produced in the tensile process,among them,the cracks with width in the range of 30~80?m account for 84% of the total cracks.The surface cracks of the materials doped with 6mm-BHL fiber have a high saturation degree,andthe average crack spacing is about 3.3 mm.(4)The physical and mechanical properties of fiber reinforced engineered geopolymer spray composite with fine sand were studied by laboratory test.The results show that the optimized material has strain hardening characteristics.The spray performance of fiber reinforced engineered geopolymer composite can be significantly optimized by the method of secondary mixing with pseudo-plastic state.The rebound rate is about 5% and the density of spray layer is generally higher than 90%.The elongation is basically the same as that of the cast-in-situ materials,and the crack width on the surface of the four-point bending specimen is generally distributed in the range of 30~60?m.