Study On Tensile Property Of Earthen Matrix Reinforced By Glass-fiber Mesh

Earthen ruins are a special type of cultural relics composed of earthen materials,which record the historical information of the era with the surrounding environment.They preserve the imprint of the characteristics of the era,and are an important reference for tracing and restoring the original appearance of history.Based on widely used fiber reinforced cementitious matrix in reinforcement of concrete and masonry structures,it is a developing trend to use a combination of fiber mesh and local earthen materials to reinforce earthen buildings.The tensile properties of the fiber reinforced earthen matrix have a key influence on the reinforced earthen buildings of this composite material,which needs further experimental investigation.the main contents of which are as follows:(1)By soil tests,we analyzed the composition of Dalian soil particle gradation,limiting moisture content,optimal moisture content,dry density and other corresponding parameters,and selected 5% concentration of water and select polyurethane as reinforcement,and the internal particle distribution of the earthen consolidated was more uniform and the degree of compactness was better.The compressive strength and tensile strength reached 4.4MPa and0.8MPa respectively,which verified its reliability.The basic mechanical properties of the glass-fiber material were analyzed by the pull-out test of single glass fiber net.The results show that the glass-fiber material,on the basis of its homogeneous elastic material variation characteristics,also has extremely strong tensile properties and good ductility,which can fully meet the requirements for the use of earthen matrix.(2)The uniaxial tensile tests of glass fiber reinforced earthen matrix composites with different mesh sizes were compared by taking two types of clamps,adhesive clevis grip and frictional clamping grip respectively,to investigate the uniaxial tensile stress-strain curves and the complex interaction between the fiber mesh and the earthen matrix.The tests showed that the uniaxial tensile process of the composites can be divided into two distinct phases,namely the linear elastic phase and the multi-crack development phase.The distinction between the two stages by clevis grip is more obvious,and the specimen failure is mostly manifested as fiber slippage in the multi-crack matrix;there are two types of specimen failure modes by clamping grip,which are the more fiber slippage within the matrix and the adjective of the fiber for the matrix.Elastic modulus of the specimens by clevis grip in the first-stage was significantly enhanced to the clamping grip,and elastic modulus of the specimens in the second-stage was increased in the range of 35%～40%.The cracking strength of the specimens by clevis grip was increased by more than two times compared to the specimens by clamping grip,and the ultimate tensile strength increase by 7%～14% under 6% strain.(3)Based on uniaxial tensile tests,the effects of matrix thickness,layers of fiber nets,reinforcement ratio and bond length on the tensile properties of glass-fiber reinforced earthen matrix were analyzed.The damage of 10 mm matrix thickness single-layer mesh specimen in multi-crack condition,while 16 mm matrix thickness single-layer mesh specimen shows the damage form in single crack condition.Ultimate tensile strength σ and E in crack development stage stiffness of 10 mm matrix thickness specimens were improved by 25%～30%and 6%～23% compared to the specimens with 16 mm substrate thickness.The ultimate tensile strength σ and E of the specimen with double-layered fiber mesh in 16 mm matrix thickness which multi-crack condition increased by 10% and 25.5%,respectively,compared with the specimen with single-layered mesh in 10 mm matrix thickness.The ultimate tensile strength σ and stiffness E increased by 48% and 17.6%.As the reinforcement ratio increases,the tensile strength of the composite increases,which has a certain effect on the ultimate tensile strength;As the bond length increases,the number of cracks in the specimen increases,the ultimate stress increases by 11%～20%,and the ultimate strain decreases by15%.(4)Based on ACK model and Larrinaga model,the tensile behaviors of fiber reinforced earthen matrix were analyzed with the results of experimental data.The results show that the first stage of the test curve has the same trend as the model,and both models can describe the tensile process more completely,and the plateau stage in the ACK model and Larrinaga model does not appear because the tensile strength and elastic modulus of the earthen matrix are significantly lower than those of the fiber material.The differences between the two models and the experimental curve in the last stage are mainly due to the low bond strength between the fibers and the earthen matrix,resulting in stress loss due to the slippage of the fibers within the matrix.