Research Of Soda Residue Internal Curing Agent On Low Water-binder Ratio Concrete Autogenous Shrinkage And Cracking Behaviors Influence

In recent years,the state has vigorously developed and promoted high performance concrete and ultra-high performance concrete,which have the characteristics of low waterbinder ratio.The cracking problem caused by the excessive early autogenous shrinkage of low water-binder ratio concrete is a major problem affecting its popularization and application.Internal curing agent can effectively reduce the autogenous shrinkage of low water-binder ratio concrete,which is an important means to solve this problem.The alkali residue of industrial waste residue after soda-soda process is a kind of porous powder containing a large number of micro-pore.After treatment,it can be prepared to be used as internal curing agent,the main components of which are calcium carbonate and a small amount of calcium sulfate.Previous studies have shown that the self-shrinkage of concrete with low water-binder ratio can be reduced by adding internal curing agent of alkali residue(co-grinding with fly ash),but there is still a 28-day compressive strength of concrete.Therefore,it is necessary to further optimize the preparation and application of alkali slag curing agent in order to reduce the autogenous shrinkage and early cracking risk of concrete without reducing the 28-day compressive strength of concrete.In this paper,a series of comparative tests on three groups of soda residue(from NANFANG SODA ASH INDUSTRIAL COMPANY)internal curing agents are carried out,and the evaluation methods of three kinds of soda residue internal curing agents are put forward.Then,the mechanical properties,autogenous shrinkage properties,cracking properties and mechanism analysis of high performance concrete with water-cement ratio of 0.35 and 0.25 and ultra high performance concrete with water-cement ratio of 0.18 that use soda residue internal curing agent are systematically studied,and summarize the method of use soda residue internal curing agents without reducing the 28-day compressive strength of concrete.The main work and results of this paper are summarized as following:The evaluation method of soda residue internal curing agents was summarized.Through this method,choose the soda residue internal curing agent for the study on mechanical properties,autogenous shrinkage and early crack resistance of low water-binder ratio concrete.The result shows that on the premise that the 28-day compressive strength will not be adversely affected and the soda residue internal curing agent will be used reasonably.The results show that at 0.35 water-cement ratio,reduce the autogenous shrinkage value of 3 days by about 25%.,the tensile stress of concrete decreases by20% in 3 days,15% in 15 days under restraint conditions,and the crack resistance of concrete can be improved.At 0.25 watercement ratio,reduce the autogenous shrinkage value of 3 days by about 40%,the tensile stress of concrete decreases by 20% in 3 days,20% in 15 days under restraint conditions,and the crack resistance of concrete can be improved.In ultra-high performance concrete with 0.18 water-binder ratio,reduce the autogenous shrinkage value of 3 days by about 40%.Under the restrained conditions,cracks appear in 3 days,compared with the control group within 8 hours,which can significantly improve the crack resistance of ultra-high performance concrete.The usage methods of soda residue internal curing agent are summarized.For high performance concrete,soda residue internal curing agent takes over cement;for ultra high performance concrete,soda residue internal curing agent takes over silica fume.The content of soda residue internal curing agent is about 5% of the total amount of cementitious materials,and the ratio of additional water should be 0~50%.The lower the water-cement ratio,the higher the ratio of additional water should be.The analysis shows that the principle of reducing autogenous shrinkage of concrete with soda residue internal curing agent is:firstly,there are many pores in soda residue internal curing agent,and it has good water absorption and release performance.It slows down the hydration process of cementitious materials,slows down the decline rate of relative humidity in concrete,and reduces the power of autogenous shrinkage;secondly,calcium sulfate in soda residue internal curing agent can promote the formation of ettringite,causes volume expansion and compensates part of self-shrinkage value.