| Because of the shortage of construction sand and the demand for high-toughness concrete,the polyvinyl alcohol fiber reinforced desert sand cementitious composite(PVA-DSECC)with low-cost PVA fibers and desert sand was studied.The effects of hot water curing,dry air curing,hot water+dry air combined curing,low temperature curing and precuring+low temperature combined curing on the shear failure mode,shear strength and shear toughness of PVA-DSECC were studied by means of X-ray diffraction analysis,scanning electron microscope and stereological principles.The mechanism of PVA-DSECC under different curing systems was revealed.The main conclusions are as follows:(1)The shear strength of the specimens after 90℃ hot water curing was 13.92%higher than that of the standard curing.When the dry air curing temperature is 200℃,the PVA-DSECC specimens had obvious peeling marks on the surface of the shear part,and its shear strength was only 53.49%of the shear strength under standard curing.Under the action of hot water+dry air combined curing,the shear strength of the specimens after 90℃ hot water+100℃ dry air curing was respectively 19.18%,10.51%and 9.94%higher than the standard curing.Increasing the temperature or prolonging the duration of dry air curing reduced the shear strength of PVA-DSECC.(2)Low temperature curing and precuring+low temperature combined curing can improve the shear strength of PVA-DSECC.In low temperature curing,the highest increase was at-10℃,which was 21.31%higher than standard curing.In the precuring+low temperature combined curing,the factors affecting the shear strength of PVA-DSECC specimens include precuring time,low temperature curing temperature and duration.Precuring for 24h+(-10℃)low temperature curing for 2 days can improve the shear strength of PVA-DSECC specimens,which is 46.59%higher than that of standard curing.(3)Using initial energy density Tp as the pre-peak toughness evaluation index and residual shear toughness ratio Rp.k k as the post-peak toughness evaluation index can effectively evaluate the shear toughness of PVA-DSECC specimens under different curing regimes.Taking into account the toughness indicators before and after the peak,the toughness of PVA-DSECC specimen was the best when PVA-DSECC undergoes precuring for 24h+(-10℃)low temperature curing for 2 days,and value of Tp was 131.71%higher than that of standard curing.The shear toughness of PVA-DSECC specimens under 90℃ hot water+100℃ dry air curing was better,and value of Tp was 62.28%higher than that of standard curing.(4)Hot water curing at 90℃ can promote the further hydration of cement particles and the pozzolanic reaction of mineral admixtures,and the generated hydration products made the matrix denser and reduced the porosity of the matrix.When precuring for 24h+(-10℃)low temperature curing for 2 days,abundant hydration products were produced in the matrix of PVA-DSECC,and the surface of PVA fiber was covered with sufficient hydration products,and the fiber-matrix interface was tightly bonded.The desert sand has a small particle size,which can fill the matrix pores and play a role in refining the matrix and optimizing the microstructure.(5)90℃ hot water curing is the best way to significantly improve the shear properties of PVA-DSECC.The shear properties of PVA-DSECC can also be improved by 90℃ hot water+100℃ dry air combination curing for 1 day,-10℃ low temperature curing and precuring for 24h+(-10℃)low temperature curing for 2 days.The above curing system can be selected according to the actual situation to improve the shear properties of PVA-DSECC. |
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