Study On Activation Modification Of Waste Rubber Powder And Its Effect On The Performance Of Cement Mortar

Due to the high elasticity of waste rubber powder,its application in cement-based materials can improve toughness and reduce the generation of micro-cracks,but rubber powder and cement-based materials are organic/inorganic materials,simple mixing will lead to poor interface adhesion between the two,which in turn reduces the mechanical properties of the material.In this paper,physical cleaning method and chemical modification method were used to activate the rubber powder to improve the polarity and hydrophilicity of it.The influence of the four factors of modified rubber powder mixing order,particle size,amount and types on the comprehensive performance of cement mortar was studied and the optimal combination was selected.The influence mechanism of modified rubber powder on the performance of cement mortar was explore from a microscopic perspective,to provide theoretical support for further promoting the application of rubber powder in cement-based materials.Firstly,the physical cleaning method and chemical modification method were used to activate the rubber powder.The activation index and contact angle were used to characterize the modification effect.It was found that the order of the modification effect in the physical cleaning method was 5wt%NaOH solution modification>CCl₄ solution modification>deionized water modification,the order of the modification effect in the chemical modification method was KH-550 modification>KH-570 modification>KH-560modification>NaClO solution modification.Relatively speaking,the modification effect of KH-550 was better than 5wt%NaOH solution.Secondly,the mechanism of rubber powder activation modification was explored by means of infrared spectroscopy,particle size distribution,and electron microscope scanning.5wt%NaOH solution had the best modification effect in physical cleaning method,because the 5wt%NaOH solution could thoroughly clean hydrophobic impurities such as zinc stearate and pine tar on the surface of the rubber powder,and increased the number of holes on the surface,improved the polarity and hydrophilicity of the rubber powder.The modification effect of KH-550 was the best in the chemical modification method,because after the modification of KH-550,more active substances were generated on the surface of the rubber powder and agglomeration occurred,which significantly improved the polarity and hydrophilicity of the rubber powder.Thirdly,for the two types of activated modified rubber powder,the influence of the four factors of the rubber powder mixing order,particle size,amount and types on the performance of the cement mortar was comprehensively considered,the optimal combination was selected through range analysis and gray correlation analysis.It was found that the comprehensive performance of the optimal level group obtained by using 60 mesh rubber powder modified with KH-550,with 1%of the mixing amount and the later mixing order（the rubber powder and the cement mortar are stirred at high speed for 30 seconds）mixed with cement mortar was the best.Compared with the control sample without rubber powder,under the optimal combination,the toughness and dry shrinkage performance of cement mortar were improved by about 15%and 20%,the fluidity,flexural strength and compressive strength were decreased by about 5%,3%and 15%respectively,and the flexural strength and fluidity had reached the specification requirements.Compared with the unmodified rubber powder sample,under the optimal combination,the toughness and dry shrinkage performance of cement mortar were improved by about 5%and 15%,and the fluidity,flexural strength and compressive strength were improved by about 15%,15%and 10%respectively.Finally,the influence mechanism of the modified rubber powder on the properties of the cement mortar was explored from the microcosmic point of view of the cement hydration products,the micromorphology of the interfacial transition zone and the internal pore structure of the mortar.It was found that the addition of the rubber powder into the cement mortar reduced the degree of the cement hydration around the rubber powder.Adding modified rubber powder could obviously improve the adhesion and internal pore structure of interfacial transition zone between the rubber powder and cement stone.There was almost no crack between KH-550 modified rubber powder and cement stone.Part of the surface of the rubber powder was covered by hydration products,and the adhesion with the cement matrix was better than NaOH modified rubber powder,the pore volume of the macropores and gel pores were also the smallest.The good interfacial adhesion and pore structure were the important reasons for their excellent macroscopic properties.