Meso-scale Simulation On Drying Shrinkage And Crack Resistance Of Aligned Steel Fiber Reinforced Cementitious Composites

Drying shrinkage is one of the main reasons which cause the dehiscence of cementitious composites.Aggressive media in the environment enter the interior of the material through cracks,causing material leakage and corrosion.Therefore,lower drying shrinkage is the key to improve the crack resistance of cement-based composites,and it is of great significance for crack control in actual engineering.Mixing steel fibers in to it is conducive to restraining the shrinkage of cementitious composites effectively and enhancing the crack resistance.Obviously,in the aligned steel fiber reinforced cementitious composite(ASFRC),the restriction effect varies from the steel fibers distribute directly and regularly to those distribute in random way.Aiming at the problem of shrinkage cracking of cementitious composites in dry environment,this paper studies the drying shrinkage and anti-cracking performance of ASFRC by numerical simulation and experiment,and deeply studies the mechanism of restrained shrinkage cracking of aligned steel fiber,so as to provide an effective control method for the problem of shrinkage cracking in actual work.The specific research contents and results are as follows:(1)Based on the theory of moisture diffusion and drying shrinkage of cementitious composites,considering the influence of steel fiber directionality,a numerical model for analyzing moisture diffusion,drying shrinkage and cracking of ASFRC and SFRC was established,which laid a theoretical foundation for subsequent numerical analysis.(2)The influence of the aligned distribution of steel fiber on the water diffusivity of cementitious composites was analyzed.The moisture diffusion process of steel fiber reinforced cementitious composites was simulated by establishing the moisture diffusion numerical model,and the relative humidity age curves of ASFRC and SFRC were obtained.The results show that the aligned distribution of steel fiber keeps high relative humidity in the specimen.When the volume content of steel fiber is 0.8%,1.0%,1.2% and 2.0%respectively,the relative humidity of ASFRC is 4.6%,5.7%,7.0% and 12.5% higher than that of SFRC after 360 days drying.(3)The influence of the aligned distribution of steel fiber on the drying shrinkage of cementitious composites was analyzed.Based on the results of numerical analysis of moisture diffusion and the relationship between drying shrinkage and relative humidity,the drying shrinkage process of steel fiber reinforced cementitious composites specimens was simulated,and the drying shrinkage strain age curves of ASFRC and SFRC specimens were obtained.The results show that the restraint effect of steel fiber on the matrix shrinkage is greatly improved in the orientation direction.When the volume content of steel fiber is 0.8%,1.0%,1.2% and 2.0% respectively,after 360 days drying,the drying shrinkage strain of ASFRC prism decreases 19.5%,21.8%,29.6% and 35.0% compared with SFRC.(4)The influence of the aligned distribution of steel fiber on the shrinkage cracking resistance of cementitious composites was analyzed.By establishing the numerical model of shrinkage cracking,the process of initiation,propagation and final penetration of shrinkage cracking of ASFRC and SFRC plate specimens under the action of drying is simulated.The results show that ASFRC is superior to SFRC in anti-shrinkage cracking performance.When the volume fraction of steel fiber is 0.8%,1.2% and 2.0%,the shrinkage cracking length of ASFRC plate after 24 hours drying is 19.2%,42.6% and 24.7% less than SFRC.