Research Of Dechlorination Soda Residue Used As Internal Curing Materials On Concrete Performance Influence And Mechanism

Soda residue is a kind of waste in soda manufacturing by solvay process,and the comprehensive utilization is difficult.For high performance concrete,shrinkage cracking has been a universal problem due to low water-cement ratio.Through internal curing materials timely release water to enhance internal relative humidity and reduce autogenous shrinkage,the internal curing has been an effective way to solve concrete shrinkage crack.In this paper,dechlorination soda residue was used as internal curing materials to join in concrete after appropriate dispose.Then gives a comprehensive study on the properties of anti-chloride concrete(W/B=0.35)and ultra-high performance concrete(W/B=0.15),including the working and mechanical performance,autogenous shrinkage deformation,then the mechanism was discussed in this paper by scanning electron microscope,mercury intrusion poremeasurement and thermal analysis technology.The main work and results of this paper are summarized as following:First of all,the preparation technology and performance of soda residue internal curing materials was given a detailed study.When soda residue was grinded separately,it's easy to appear sticky phenomenon,mixing with fly ash can be a good way to solve this problem.As grinding time extended,the particle size of soda residue changed to be fine and pore structure was damaged severely,the capacities of absorbing water also will decrease.Optimization of the fina preparation technology of soda residue internal curing materials: dechlorination soda residue mixed with fly ash according to the mass ratio of 2:1 after drying,then added to the ball mill grinding 3 min.Combining with hydration activity and water absorbency,finally choose X3 as the internal curing materials.The water absorbent rate can reach about 1.2 times as its own quality,and about 80% of the adsorption water can be released eventually under the two different 94.6% and 59.1% relative humidity environment,the absorbing and releasing water performances meet the requirement of concrete internal curing materials.Then studied the effect of soda residue internal curing materials on the performance and mechanism of anti-chloride concrete,which substituted not more than 15% binding materials(isometric substitute fly ash and mineral power).The results show that: it will reduce the workability of concrete mixture when incorporated with soda residue,therefore need to be used with additional water or increase the dosage of water reducing agent.And it also will have an adverse effect on the mechanical property of concrete,so need to control soda residue content as not to cause great influence to the strength.It can obviously improve the internal relative humidity and reduce autogenous shrinkage of concrete.As the content of soda residue is 10% and 15%,the autogenous shrinkage reduction ratio is over 31.1% and 78.1% in 3d.Causeing secondary expansion by ettringite formation at the early age and reduceing the capillary contraction stress through internal curing are the two principle of reducing autogenous shrinkage.After mixed with soda residue,it will cause expansion within the cement stone at the early age along with ettringite crystal formation,and also will have an impact on the whole hydration process of cement;it changes the distribution of concrete's pore structure,increasing the quantity of gel pores and decreasing the large pores;it will increase the internal porosity of concrete,so the drying shrinkage value of concrete increase slightly and the anti-chloride ion permeability decline slightly.Finally studied the effect of soda residue internal curing materials on the performance and mechanism of ultra-high performance concrete,which substituted not more than 10% binding materials(isometric substitute fly ash and mineral power).The results show that: similar to the anti-chloride concrete,the working and mechanical performance of concrete will decline as the dosage of soda residue increase,but the development rate of autogenous shrinkage and total deformation value will significantly lower.As the content of soda residue is 5% and 10%,the autogenous shrinkage reduction ratio is over 31.61% and 59.7% in 3d,and in 7d it's over 32.7% and 51.4%.The activity of mineral admixtures and hydration degree can be greatly improved under the condition of high temperature steam curing,the more gels will further fill the pore system,result in the decline of porosity and average pore diameter.The different distribution of free mixing water and internal curing water in time and space,then affect the hydration process and pore structure,which is the main reason of the change of concrete performance.The much higher inner relative humidity compared with blank group of the same age is the main reason for soda residue to reduce concrete shrinkage.