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

Aerated concrete has been widely used in the field of building energy conservation,structure reduction and other aspects due to its advantages of light weight,good sound absorption and heat insulation,and shock absorption.Due to the large amount of air bubbles introduced into the aerated concrete,the total porosity can reach 75?80%,the water absorption rate is large,and the interaction between water,water vapor and pore structure will be generated during the water migration,resulting in its strong interaction and larger contraction.There is a case where the strength of the aerated concrete meets the requirements of the national standard and the shrinkage does not meet the requirements,so that the contraction restricts the application of the aerated concrete to a certain degree.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.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 aerated 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 aerated concrete,With the increase of SRA content,the autogenous shrinkage are reduced greatly.Adding PPF alone can the improve the autogenous shrinkage of aerated concrete to some extent.With the increase of PPF content,the autogenous shrinkage reduces,but the autogenous 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 autogenous shrinkage of aerated concrete not only show good compatibility,but also produce a good "Overlay" effect.(2)Adding SRA alone can greatly improve the drying shrinkage of aerated concrete,With the increase of SRA content,while that of drying shrinkage decreases.Adding PPF alone can the improve the drying shrinkage of aerated concrete to some extent.With the increase of PPF content,the drying shrinkage reduces,the effect of SRA is similar to the PPF on the whole.Through making a comparison with the SRA and PPF mixed group,SRA and PPF reducing the drying shrinkage of aerated concrete not only show good compatibility,but also produce a good "Overlay" effect.(3)Adding SRA alone can affect the early compressive strength of aerated 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 aerated concretecan,but PPF under the 2%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 aerated concrete pore refining,part of the capillary tension disappear,but will increase the aerated 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 aerated 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,aerated concrete structure is more compact,the degree of pore refining,more uniform distribution of pore,SRA and PPF density of aerated concrete structure development with excellent compatibility and overlay.