Study On Properties Of Kevlar Fiber-Cement Based Material Modified By Silane Coupling Agent

Cement-based materials have the advantages of high quality and low price,easy access to raw materials and convenient construction,and are widely used in engineering construction.However,traditional cement-based materials have their own objective problems such as low tensile strength and poor toughness,which greatly limit their application in specific engineering fields.Kevlar fiber compared with other organic fibers has higher tensile strength and toughness,can effectively improve the toughness of cement-based materials,and kevlar fiber is difficult to effectively bond with inorganic cement substrate,greatly reducing its enhancement effect in cement substrate.Silane coupling agent as a link between organic interface and inorganic interface "bridge",in the theoretical level can improve the interface between kevlar fiber and cement substrate bond state,get higher strength,better toughness kevlar fiber reinforced cementitious composites,the specific effect remains to be further explored.In this paper,the effect of three silane coupling agent(KH550,KH792 and KH570)on the macroproperties and microstructure of kevlar fiber,kevlar fiber reinforced cementitious composites and cement substrate was studied by using silane coupling agent to improve the reinforcing effect of kevlar fiber in cement substrate composites.The mechanism is analyzed based on relevant test results.In this paper,SEM,grafting rate and TG test,it is proved that the selected self-mixing detergent water bath + anhydrous ethanol ultrasonic cleaning method can be applied to kevlar fiber surface pretreatment.Kevlar fibers modified by silane coupling agent were characterized by SEM,FTIR,XRD,XRF,TG,grafting rate,monofilaments breaking strength and cement mortar composite strength tests.The results showed that the three silane coupling agent selected in this study changed the surface properties of kevlar fiber,and did not damage the fiber structure.Kevlar fiber surface roughness and modified graft rate with the increase of modified concentration significantly improved,fiber modified graft rate is the highest 9.37%,single wire fracture strength is first increased and then decreased,compared with the unmodified fiber,the maximum increase of 0.66%,the maximum decrease of 0.71%.Although the surface properties of modified kevlar fiber and the untreated reference group have obvious changes,but the mechanical properties of cement mortar composite material is not significantly improved compared with the reference group,the maximum increase of flexural strength is 2.99%,the compressive strength is generally flat,and even decreased by5.11% due to the appearance of fiber aggregation.In this paper,the macroscopic mechanical properties,toughness and durability of kevlar fiber reinforced cementitious composites and their substrate blended with silane coupling agent are tested.The results show that the incorporation of silane coupling agent can effectively improve the reinforcing effect of kevlar fiber in cement substrate composites,so that the mechanical properties of kevlar fiber reinforced cement substrate composites are up to44.95% higher than the substrate,far higher than the reference group without silane coupling agent.And generally improve the durability of the material(carbonization resistance,frost resistance,chloride penetration resistance).Because the mechanical properties and toughness of the substrate in kevlar fiber reinforced cementitious composites are reduced compared with the benchmark group,only part of the mechanical properties and toughness of kevlar fiber reinforced cementitious composites are significantly improved compared with the benchmark group with the same ratio and equal fiber dosage.Taking the test group mixed with KH550 as an example,at the age of 28 days,the compressive strength of cement mortar increased from49.3MPa to 53.2 MPa,and the bending strength increased from 10.1MPa to 11.5 MPa,with the largest increases of 7.91% and 13.86%.The compressive strength of concrete increased from 33.18 MPa to 37.44 MPa,with an increase of 12.84%.The splitting tensile strength increased from 3.16 MPa to 3.40 MPa,increasing by 7.60%.The impact resistance ratio increased from 1 to 1.36,with an increase of 36%.The effects of silane coupling agent on cement hydration process,hydration products and microstructure of kevlar fiber reinforced cementitious composites were studied by means of hydration heat,TG,XRD,SEM,nitrogen adsorption and mercury injection.The macroscopic phenomena were explained and the action mechanism of silane coupling agent was revealed.The results show that the silane coupling agent can inhibit the hydration process of cement,and no new hydration products are formed.The inhibition effect decreases with the growth of age.In kevlar fiber reinforced cementitious composites,add KH550 and KH792 can increase gel pore volume and reduce the volume of large pores,so that the hardened body pore structure is refined,add KH570 will improve the volume of medium pores and large pores,so that the hardened body pore structure appears coarser;Silane coupling agent "bridging" mechanism is parents by silane coupling agent molecules such as hydration,condensation reaction and cement particles are connected by chemical bonds,and rachel around the kevlar fiber,induction of hydration products in the process of hydration growth in fiber surface,so as to effectively improve the interface bonding between the kevlar fiber and cement substrate performance.