Mechanism Study On The Influence Of Rubber On Mortar Properties

Rubber cement based material is a new type of green material.Adding rubber in cement material,not only improves the brittleness of the material,but also provides a way of disposal solution.Now,some qualitative conclutions have been drawn on the influences of rubber on the properties of cement based material.For example,the strength and elasticity modulus of cement based material decrease,while the property of cracking resistance is improved when rubber is added in.But the mechanism analysis on how the rubber function on cement based material is relatively limite.Crumb rubber mortar was chosen as the object of my study.In order to study the rubber function on cement based material,microscopic,mesoscopic and macroscopic study was combined in the research.On the micro level,scanning electron microscopy test was conducted to study the interface transition zone of rubbercement paste,and mercury intrusion porosimetry was conducted to study the pore structure of crumb rubber mortar.On the meso level,based on the existing elastic module model of composite materials,the study took the effect of rubber volume and porosity into account.On the macro level,compressive strength,flexural strength,splitting strength,elasticity modulus,drying shrinkage and cracking resistance of rubberized mortars were tested,and relevant theory analysis on rubberized mortars was done.The research findings and conclusions of this paper are as follows:(1)Rubber size has great influence on the workability of rubberized mortars.The consistency and fresh density of rubberized mortars decreases as the size of rubber decreases.The water-absorption increases as rubber size decreases.Rubber particle size has a great influence on the interface transition zones of rubber-cement paste,as observed by the scanning electron microscope.(2)The pore volume of rubberized mortars increase as rubber size decrease,and rubber mainly increase the porosity of pores whose aperture is less than 50 nm or more than 1000 nm.Fractal dimension D of rubberized mortar decreases as rubber size decreases,as calculated in the paper.(3)The compressive strength,flexural strength and splitting strength of rubberized mortars decrease as rubber size decrease,for rubber of smaller size can introduce more pores in mortar.Based on test rusults,reduction factor of compressive strength,flexural strength and splitting strength is calculated taking into account rubber content and additional porosity.Elasticity modulus formula of rubberized mortars is established,based on the existing elasticity modulus formula for binary complex.The derivation process of rubberized mortar elasticity modulus formula is divided into three steps based on the perspective of mesoscopic.Finally,via comparison between test and the calculated results,the elasticity modulus formula calculation model is verified(4)The drying shrinkage of rubberied mortar increases as rubber size decreases.Mechanism of rubberized mortar is studied based on the theory of capillary tube tension.The results show that two factors that are responsible for the rubber effect on drying shrinkage of mortar.On the one side,rubber especially that of smaller size can increase the micropore(<50nm),which increase the stress of drying shrinkage;on the other side,rubber especially that of smaller size can decrease the elasticity modulus of mortar,which decrease the ability of mortar to resist deformation.The coefficient of ruber effect on drying shrinkage of rubberied mortar is fitted considering the two aspects discussed above.(5)Both traditional restrained ring shrinkage test and new restrained squared eccentric ring shrinkage test were conducted to study the cracking resistance of rubberized mortars in the paper.The results show that material with lower dring shrinkage not necessarily results in better cracking resistance.Rubber can improve the cracking resistance of mortar mainly because that the reduction effect of rubber on mortar restraint stress is greater than that on mortar strength.The new restrained squared eccentric ring shrinkage test can shorten the test period for it can increase the restraint stress,and the intensification factor is calculated through test results.