Study On The Mechanism Of Rubber Particles Distribution In Cementitious Composites And Its Improving Method

Nowadays,the amount of scrappage of automobile tires increases progressively year by year,affecting the ecological environment and causing waste of resources.However,rubber cement-based materials provide a new way to solve the problem of waste tire pollution.Waste rubber products after machining can be produced into particles,which can be added to the cement-based materials to can improve the performance of many aspects of cement-based materials.Nevertheless,some problems have arisen.As the density of the rubber particles is lower,rubber particles are prone to float up in cement-based materials during the molding and transportation,resulting in uneven distribution of rubber particles in cement-based materials and seriously affecting the performance of rubber cement-based materials,which restricts the development of rubber cement-based materials and applications.In this paper,the fluid mechanics theory is used to analyze the reason why rubber particles are prone to float up in cement-based materials,and some methods are put forward to avoid up-floating phenomenon.Based on the weakest chain model,the failure probability of cement concrete and crumb rubber concrete and the effect of rubber particles' up-floating phenomenon on the compressive strength of concrete and the crack distribution during the compression have been analyzed.It is proposed to improve the up-floating condition in rubber cement-based materials by using a method of adding Super Absorbent Polymer and cryogenic rubber particles.Moreover,the R2 V vectorization software and the area statistical function in the AutoCAD software were used to count the rubber particles' distribution in each area of the cross-section of the specimen.Based on the theoretical and experimental results,the following conclusions could be drawn:(1)According to the principle of fluid mechanics,the speed of upward movement of rubber particles is proportional to the square of the rubber particle size;Under static conditions,it is necessary to consider the density difference between the rubber particles and the cement paste and the rubber particle size as the two important factors in controlling the rubber particles floating in the rubber cement-based material;As for dynamic conditions,the viscosity and density of cement paste are two important factors;(2)The rubber particles' up-floating phenomenon in the concrete will increase the failure probability of crumb rubber concrete,thereby reducing the material strength,and cracks will first appear in the rubber particle concentrated distribution area and finally develop into through-cracks;(3)Addition of super absorbent polymer can improve the rubber particles' up-floating situation in cement-based materials,and the super absorbent polymer can also improve the strength,cracking resistance and shrinkage resistance of cement-based materials.In addition,super absorbent polymer can shorten the initial setting time of cement;(4)Drying the surface of the rubber particles and placing them in an environment at-15 ° C for a period of time can improve the rubber particles up-floating condition in the cement-based material because the density of the rubber particles is greatly increased by the freezing treatment,meanwhile,the effect of frozen rubber on flexural strength and compressive strength of rubber cement-based materials is slight.