Design,Preparation And Deterioration Mechanism Of Ultra-high Frost Resistant Concrete

Crumb rubber concrete(CRC)has wide application prospect in plateau and cold regions for its excellent properties,such as frost resistance,impact resistance and fatigue resistance.However,the mix proportion and freeze-thaw mechanism of CRC have not been systematically researched.Therefore,it is significant to promote the application of CRC in plateau and alpine regions by optimizing the mix proportion design of CRC,further improving its frost resistance,mastering its destruction process and exploring microscopic mechanism under the freeze-thaw cycle.Based on the relationship between the mix proportion and frost resistance of CRC,the design of high frost resistant CRC was achieved,and the ultra-high frost resistant CRC was prepared.The deformation behavior of CRC during freeze-thaw cycle was online characterized by vibrating wire strain acquisition system.The freeze-thaw deterioration process of CRC was recorded in the same system,and the temperature response mechanism of CRC deformation was revealed.The main conclusions are as follows:(1)Based on the correlation between CRC mix design and freezing resistance,a model of crumb rubber spacing was established,and a mix design method of high frost resistant CRC was proposed.20～40 mesh crumb rubber was used to prepare concrete,and the proposed design method was verified from frost resistance of CRC.It was found that the freezing resistance of CRC increased first and then decreased with the expand of crumb rubber spacing.When the crumb rubber spacing was between 0.3mm and 0.4mm(The amount of crumb rubber:194kg/m~3～134kg/m~3),the frost resistance of CRC was the best.After 400freeze-thaw cycles,the mass loss rate of CRC was less than 5%,the relative dynamic elastic modulus maintained 80%,the high frost resistance of CRC was demonstrated.(2)With the principle of the ultra-high frost resistance pavement engineering application index(compressive strength>30MPa,flexural strength>5MPa,freeze-thaw resistance times>600),to ensure the crumb rubber uniformly dispersed in the mortar of the premise,the effects of aggregate gradation,crumb rubber spacing and particle size to concrete performance were studied.The results indicated that aggregate gradation optimization slightly improved compressive and flexural strength of concrete,but had little effect on frost resistance of concrete.And with the decrease of crumb rubber spacing,the compressive and flexural strength of concrete decreased gradually but frost resistance of concrete increased gradually.When the crumb rubber spacing was 0.25 mm and the particle size was 40-60mesh(0.36mm),the ultra-high frost resistance(freeze-thaw resistance times>800)was realized,which achieved the design requirements.(3)The strain change behavior of concrete during freeze-thaw cycles was monitored in situ by strain acquisition system.Combined with the changes of mass loss rate,relative dynamic elastic modulus and microstructure,the freeze-thaw deterioration regular of concrete was explained.The results show that the strain change of concrete in each freeze-thaw cycle had experienced four stages:big pores freezing,small pores freezing,water absorption resistance and ice-thawing.Crumb rubber in freeze-thaw cycle can not only reduce the frost heaving pressure in the process of freezing,but also inhibit the external water intrusion in the process of thawing,which plays a role of regulating valve.