Study On The Durability Of Red Mud Concrete For Pile In Salt Soil

Salt soil,a kind of soil with high salt content,has a strong erosion on concrete pile foundation and greatly reduces the service life.At the same time,red mud discharged by aluminum smelting industry is a kind of solid waste with high water and alkaline contents.The mud has reached a very great amount and caused a great harm on the environment.How to reasonably deal with and utilize red mud has become a global problem.In this paper,the alkali activity of red mud and the alkali fixation in fly ash or slag cement system was studied.A salt solution simulated the salt soil was made,and the mechanical properties,salt freezing and salt erosion of red mud concrete were also studied to meet the requirements of pile foundation concrete and to realize the effective utilization of red mud.The results are as follows:(1)Alkali activity and alkali fixation effect of red mud.The effects of different steaming curing temperature and time on the strength,hydration degree and accumulation of salt on the surface in fly ash or slag cement hardened mortar were studied.Steaming curing increased the reaction of alkali in red mud and fly ash or slag,hydration degree,strength of hardened mortar.Accumulation of salt is also effectively eliminated.More suitable steam curing temperature and time is 100℃ and 18 h.(2)Mechanical properties of red mud concrete for pile foundation.The strength of red mud concrete at 7 days and 28 days is studied.When the amount of red mud is less than 20%,the strengths of fly ash or slag concrete are above 40 MPa at 28 days which meets the strength design requirement of C40 concrete.Compared with fly ash red mud concrete,slag red mud concrete is a higher strength at 7 days,but their difference becomes small at 28 days.(3)Durability of concrete pile foundation in salt soil environment.The losses of mass,strength or dynamic modulus of pile foundation concrete in a simulated salt erosion and freezing environment were studies.It is found that red mud concrete can well resist salt erosion and freezing.Under the condition of salt erosion,when the amount of red mud is 10%,salt erosion cycles for slag concrete and fly ash concrete are 220 and 180 respectively.However,the salt corrosion resistance is decreased with increasing amount of red mud.Underthe condition of salt freezing,the salt freezing cycles for slag concrete and fly ash concrete are240 and 210 respectively.When the amount of red mud is the same,slag concrete has a better durability than fly ash concrete in salt soil environment.In a word,red mud slag or fly ash concrete suit to prepare precast pile has a good durability in the salt soil environment by adding an appropriate amount of red mud(within20%).Accumulation of salt on the surface of the concrete is also well eliminated by steaming curing and introducing active mineral admixture,provide a way for the utilization of red mud resources,and provide theoretical reference for the structural durability design in Northwest China.