Influence Of Shrinkage-reducing Agent And Polypropylene Fiber On Shrinkage Of Ceramsite Concrete

Ceramsite concrete has been accepted widely by engineering field for its lightweight,designable strength,good insulation and other advantages.However,due to the volume stability of lightweight aggregate is not as good as that of ordinary concrete,the early micro expansion and contraction are larger,which will cause a series of problems such as structure leakage,corrosion,low strength and so on,thus weakening its durability,the shrinkage is one of the main problems restricting the application of ceramsite concrete.Shrinkage Reducing agent(SRA)can reduce capillary stress mainly by cutting down the surface tension of the solution in the capillary.Polypropylene fiber(PPF)can reduce concrete shrinkage by improving the uniformity,reducing water loss and increasing the toughness,at the same time can control the early micro expansion by bonding with the cement matrix.Overall considering both the advantage and shortage of two kinds of materials above in mechanism,effect and application scope,it's difficult to just make use of single existing reduction technology to ensure other performances of ceramsite concrete no degradation and minimize its shrinkage simultaneously.In order to achieve excellent effect,this paper mainly studied the influence of SRA and/or PPF on autogenous shrinkage,drying shrinkage,compressive strength and microscopic structure.The results were as follows:(1)Adding SRA alone can greatly improve the autogenous shrinkage of ceramsite concrete,With the increase of SRA content,the early micro expansion increases largely,autogenous shrinkage are reduced greatly.Adding PPF alone can the improve the autogenous shrinkage of ceramsite concrete to some extent.With the increase of PPFcontent,the early micro expansion and autogenous shrinkage reduces,the early microexpansion reduced greatly,and the autogenous shrinkage reduces slowly,the effect ofSRA is better than that of PPF on the whole.Through making a comparison with theSRA and PPF mixed group,SRA and PPF reducing the autogenous shrinkage of ceramsite concrete not only show good compatibility,but also produce a good"Overlay" effect.(2)Adding SRA alone can greatly improve the drying shrinkage of ceramsiteconcrete,With the increase of SRA content,the early micro expansion increases largely while that of drying shrinkage firstly increases then decreases.Adding PPF alone canthe improve the drying shrinkage of ceramsite concrete to some extent.With the increase of PPF content,the early micro expansion and drying shrinkage reduces,the early micro expansion reduced greatly,and the drying shrinkage reduces slowly,the effect of SRA is better than that of PPF on the whole.Through making a comparison with the SRA and PPF mixed group,SRA and PPF reducing the drying shrinkage of ceramsite concrete not only show good compatibility,but also produce a good"Overlay" effect.(3)Adding SRA alone can affect the early compressive strength of ceramsite concrete,With the increase of SRA content,the early compressive strength decreases greatly.Adding PPF alone has little effect on the early compressive strength of ceramsite concretecan,but PPF under the high content will increase the intensity slightly.Through making a comparison with the SRA and PPF mixed group,and the same SRA group under same content,the addition of PPF can improve the reduction of compressive strength caused by SRA content.(4)Adding SRA alone can improve the degree of ceramsite concrete pore refining,part of the capillary tension disappear,but will increase the ceramsite concrete porosity,and with the increase of dosage of SRA,the higher the degree of refinement.Adding PPF alone can improve the uniformity of the ceramsite concrete,toughness,are attached to the PPF produce hydration products and concrete matrix has good bonding effect.Through making a comparison with the SRA and PPF mixed group,ceramsite concrete structure is more compact,the degree of pore refining,more uniform distribution of pore,SRA and PPF density of ceramsite concrete structure development with excellent compatibility and overlay.