Cracking Under Direct Tension Test And Impermeability Behavior Of PVA-SHCC

Low strength and high brittleness are the dominant reasons for the cracking of common cementitious composites. The durability of concrete structure will be deteriorated with the forming and spread of cracks.Strain Hardening Cementitious Composites(SHCC)is a new material recently developed. Applying PVA fiber with high strength and modulus into cementitious composites can significantly improve the toughness,which behavior in a unique performance of pseudo-strain-hardening and multiple cracking. Since the added PVA fiber can reduce crack formation in cement-based materials, SHCC materials have high crack resistance.Polyvinyl alcohol fiber is at low prices and its reinforced effect isn't worse than PP fibers, so polyvinyl alcohol fibers(PVA fibers)are one of excellent reinforced fibers. PVA fibers reinforced will be a great development for cement-based composite materials. This thesis is based on polyvinyl alcohol fibers(vinylon)reinforced cement-based composite materials. In this paper anti-permeability and multiple cracking under direct tension test of PVA-SHCC has been investigated by Rapid Chloride Migration(RCM)test, direct tension test, water-proof treatment test, capillary suction test, chloride ion erosion test and carbonation test.Results of experiments indicate that PVA fiber can enhance toughness of cement-based material. Multiple cracks behavior can limit the overextension of cracks. It takes full advantage of PVA fibers to enhance the performance of toughness and crack resistance. The behavior of strain-hardening make SHCC can bear load continually after cracking. The bearing capacity can even be improved if the strain is limited in certain extent. 4% ultimate tensile strain can be obtained under direct tension test in the thesis. So , it makes best use of the PVA fibers to enhance the strength of SHCC.After adding water repellent agent into SHCC, though the ultimate tensile strain is reduced, it does not affect its engineering application performance. The impermeability behavior of SHCC become better following by the longer curing age and the smaller the maximum size of sand. Adding water repellent emulsion can significantly improve the impermeability of SHCC and the capillary absorption coefficient can be reduced to one third of untreated cement-based material. It can be concluded that an effective chloride barrier can be established by water repellent treatment, which can efficiently prevent concrete from chloride ingress. The carbonation rate of SHCC is accelerated with increasing water-cement ratio. The carbonation rate of SHCC in the laboratory is faster than that on the roof of the laboratory. The natural carbonation not from the rain is faster than in the rain.