| Concrete is composite material made up of cementitious material,aggregate,water and some annexing agent.Production process of concrete consist of mixing,vibration,curing and hardening.Concrete has advantages as high strength,compression resistance,excellent durability,wide source of raw materials,low cost and strong plasticity.Therefore,concrete is man-made civil engineering and building materials with the largest consumption worldwide.However,concrete has disadvantages as poor tensile property and toughness,hard brittleness and cracking during application.In recent years,with the development of synthetic fiber industry,yield and properties of synthetic fibers have developed rapidly.It is possible to inhibit the development of cracks in concrete by synthetic fiber grid as secondary reinforcement.Polypropylene(PP)fiber has the advantages as light weight,high strength,excellent toughness,corrosion resistance and low cost which is widely used in the field of fiber reinforced concrete.Nevertheless,PP grid have disadvantages as poor ageing resistance,surface activity and weak interfacial properties with concrete.These disadvantages caused difficulty of concrete promotion in civil engineering.In this paper,PP grid reinforced concrete were studied.Antiaging treatment and surface modification of PP grid were applied to improve the properties of PP grid reinforced concrete.The structure crack evolution behavior of PP grid reinforced concrete was studied by means of test and theoretical model.The main contents are as follows:(1)An anti-aging capsule that was applied to improve the ageing resistance performance of polypropylene fiber was prepared by in situ polymerization and phase separation.The effect of anti-aging capsule on the ageing resistance of PP fiber was tested by the accelerated ageing conditions of the coupling with wet-dry and freeze-thaw cycles.Results indicate that 0.4wt% content anti-aging capsule effectively improved the ageing resistance performance of PP fiber and reduced the effect of ageing on the degradation of PP fiber properties.(2)Based on the acoustic emission technique(AET),the interface damage behavior between PP fibers and concrete was studied by fiber pull-out test.According to AET signals and pull-out test results,interface damage model was established,which consists of five stages,elastic deformation,elastic-softening,elastic-softening-debonding,softening-debonding and debonding.The stress and deformation distribution on the interface during the interface damage process are discussed.The rationality and applicability of the interface damage model were verified by epoxy resin and fine aggregate bonding interface.(3)The PP fibers were woven into PP grid by leno tissue.The graft reaction of acrylic acid and graphene oxide(GO)were used to improve the surface activity of PP grid.The influence of acrylic acid and GO grafting on the surface activity of PP grid was analyzed by the chemical composition,hydrophilicity and morphology.The influence of PP grid surface modification on freeze-thaw resistance of concrete was analyzed,by freeze-thaw resistance of PP grid reinforced concrete.Results indicate that property degradation of concrete under the action of freeze-thaw cycle was inhibited effectively by surface activity improvement of PP grid.(4)The mechanical properties and energy-absorbing properties of PP grid reinforced concrete were studied by compressive and bending properties testing of PP grid reinforced concrete.Based on the study of structure crack morphology and trend on concrete surface after testing,the role of PP grid in structure crack evolution was analyzed.Results indicate that the PP grid improved toughness of concrete and increases the energy absorption capacity.PP grid reduced size of structure cracks in concrete and maintains concrete integrity under load.The results of this paper provide a theoretical basis for further scientific research and engineering application of polypropylene grid reinforced concrete. |
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