Surface Modification Of PP Fiber And Its Effect On The Sulfate Corrosion Resistance Of Cement Mortar

Sulfate erosion is one of the most complex and harmful chemical corrosion action.After sulfate erosion,concrete will expand,crack,dissolve,peel off and decrease in strength,which affects the durability of structures.Polypropylene fiber(PP)is widely used in various concrete structures because of its good mechanical properties and chemical corrosion resistance.However,PP fiber has some shortcomings such as smooth surface,poor hydrophilicity,lack of active groups on the molecular chain,and agglomeration and poor dispersion in cement-based materials,which limits its application in cement-based materials.Using silane coupling agent to modify the surface of PP fiber is an effective method,but the influence of modified PP fiber on the sulfate resistance of cement-based materials is still not deep.In this paper,the effects of different modification conditions(type of silane coupling agent,concentration of silane coupling agent,modification temperature,modification time)on the dispersion of modified PP fiber in cement mortar were studied by single factor method.Two parameters,fiber effective utilization rate and fiber dispersion coefficient,were introduced to evaluate the dispersion of modified PP fiber in cement mortar.The fluidity,flexural strength and compressive strength of cement mortar mixed with unmodified PP fiber and modified PP fiber were studied under different cement-sand ratio and fiber content.The influence of modified PP fiber on sulfate resistance of cement mortar was analyzed by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM)and other microscopic testing methods.The results show that:(1)The optimal modification conditions for the composite modification of PP fiber with nano-carbonated carbon and silane coupling agent are as follows: KH-550 silane coupling agent,the concentration of silane coupling agent is 40%,the modification time is 7 hours and the modification temperature is 60℃.The surface of the modified PP fiber is rough,the contact Angle of the modified PP fiber is reduced by 10.6%,and the surface of the modified PP fiber is introduced with carbon-oxygen double bond(C=O)and carbon-carbon bond(C=C)and other functional groups.(2)The dispersion of the modified PP fiber in cement mortar can be evaluated by the effective utilization rate and dispersion coefficient of the fiber;The mortar ratio is 1:1,the volume content of the modified PP fiber is 0.6%,and the modified PP fiber is more evenly dispersed in the mortar when the post mixing method is adopted and the stirring time is 6min.(3)Compared with the unmodified PP fiber,with the increase of the content of the modified PP fiber,the mobility and flexural strength of cement mortar are improved,but it has little effect on the compressive strength of cement mortar.(4)When the cement-sand ratio is 1:1 and the fiber content is 0.6%,the mass loss rate,compressive strength and flexural strength loss of the specimen are the minimum.The surface roughness of the modified PP fiber increases and the diameter of the fiber becomes larger,which improves the adhesion between the modified PP fiber and the cement matrix,which is the main reason for improving the sulfate corrosion resistance of cement mortar.