Preparation And Performance Study Of Early-Strength And High Toughness Desert Sand Cement-Based Composite Materials

Engineered cementitious composite(ECC)has excellent ductility and durability,which can effectively overcome the problems of low tensile strength and poor durability in the expansion joint anchorage zone,but its matrix is mainly composed of ordinary Portland cement and fly ash,resulting in low strength in the early stage.In this paper,sulphoaluminate cement(SAC)was selected as the matrix and polyvinyl alcohol(PVA)fiber as the toughening material,and an early strength and high toughness cement-based composite(SAC-DSECC)was proposed to improve the early strength of the material.The water-binder ratio and sand-binder ratio were used as quantitative measures.The effects of fly ash,desulphurized gypsum,silica fume and PVA fiber on the working performance,drying shrinkage and mechanical properties of SAC-DSECC were systematically studied.The main research conclusions are as follows:(1)When the desert sand replacement rate is 60%,80%and 100%,the compressive strength of SAC-DSECC for 1 day and 3 days is reduced by 16.9%,24.4%,6.2%and 10.6%,5.9%,4.7%compared with that of the samples prepared by quartz sand.When the replacement rate of desert sand is 100%,the ultimate tensile strength of the specimens at day 3 is reduced by 21.3%,and the ultimate tensile strength at day 1 is increased by 9.2%,the ultimate tensile strength at day 1 is increased by 8.2%and the ultimate tensile strength at day 3 is increased by 5.9%.When the content of rubber powder is 1%,the 3d ultimate tensile strength and ultimate tensile ratio of the specimen are increased by 14.8%and 75%compared with that of the specimen without rubber powder.Therefore,SAC-DSECC can be prepared with 100%desert sand replacement rate and 1%rubber powder content.(2)Fly ash can improve the fluidity and fiber dispersion of SAC-DSECC.When the fly ash content reaches 40%,the material fluidity is increased by 21.3%compared with the experimental group without fly ash,and the initial setting time and final setting time are extended by 9min and 11min respectively.When the content of desulphurized gypsum is 5%,the fiber dispersibility of the material is improved,but when the content of desulphurized gypsum is increased to 10%,the material fluidity is reduced by 17.3%,and the initial and final coagulation time are shortened by 6min and 5min,respectively,compared with the experimental group without desulphurized gypsum.Wollastonite can significantly improve the fiber dispersibility of the material.When the content of wollastonite is 5%,the fluidity is the highest and the initial and final coagulation time are extended.With the increase of PVA fiber volume content,the fluidity of the material decreased significantly.When the PVA fiber volume content reached 2%,the fluidity of the experimental group decreased by 43.5%compared with that of the experimental group without adding fiber.(3)Fly ash can reduce the occurrence of dry shrinkage of the specimen.With the increase of fly ash incorporation,the dry shrinkage of the specimen decreases gradually.When the addition of desulphurized gypsum increased from 0%to 10%,the drying shrinkage rate of the sample showed a trend of decreasing first and then increasing,and reached the lowest value at 5%,while at 10%,the drying shrinkage rate increased but was still lower than that of the test group without desulphurized gypsum.Therefore,the introduction of desulphurized gypsum was conducive to maintaining the volume stability of the material within 28 days.The addition of silica fume can inhibit the shrinkage of the material.When the addition of silica fume increases,the drying shrinkage of the specimen gradually decreases,and the drying shrinkage of the specimen decreases the most at 7 days.When the volume content of PVA fiber increased,the drying shrinkage rate of the specimen gradually decreased.(4)By changing the fly ash content,desulfurized gypsum content,silica fume content and PVA fiber volume content,the early compressive strength of SAC-DSECC can be between 20MPa and 30MPa.The increase of fly ash and silica fume content will reduce the compressive and flexural properties of the material but improve its uniaxial tensile properties.The addition of 5%desulfurized gypsum can improve the compressive and flexural properties of material 1d,and at the same time improve the ultimate tensile strength of material 1d.The addition of PVA fiber can significantly enhance the flexural and uniaxial tensile properties of SAC-DSECC.