Test research on flexural strength of soil-cement reinforced with carbon fibers

In order to verify the feasibility of using chopped carbon fibers to reinforce soil-cement, the orthogonal test and verification test of flexural strength had been carried out and the correctness and effectiveness of the test results had been clarified. The test results indicated that the addition of carbon fibers could make the flexural strength of soil-cement improved effectively and change the brittle failure of soil-cement into plastic failure. The flexural strength of carbon fiber soilcement (CFSC) could reach 0.509 MPa, that was 31.5 % higher than that (0.387 MPa) of the plain soil-cement in the standard condition. All the first extreme flexural strength (e.g. the flexural strength), yield strength, second extreme flexural strength and residual strength increased first and then decreased with the increase of either fiber content or fiber length. Thus, excessive fiber content and fiber length were not better and the optimum values were existent with 0.6 % and 15 mm respectively under the test conditions agreed in this study. The change magnitude of the yield strength, second extreme flexural strength and residual strength was much greater than that of the first extreme flexural strength. So the strengthening effect of the carbon fibers on soilcement was better for its toughness and ductility than for its flexural strength. The order of soil type corresponding with the flexural strength of CFSC from high to low was clay, silty clay, mucky silty clay, silt and fine sand. The flexural strength of CFSC increased linearly with the increase of cement content and the economical cement content was obtained as 15 %. The flexural strength of CFSC increased quickly between the 3 d and 14 d, slowly between the 14 d and 28 d and very slowly after 28 d, but still was increasing. The interaction mechanism between carbon fibers and soil-cement had been analyzed from a macro and a micro perspective respectively. The modified multivariate nonlinear regression model was proposed. The results and conclusions above could provide reference and basis for the application and popularization of CFSC in actual engineering.