Effects Of Shrinkage Reducing Admixtures And Superabsorbent Polymers On Shrinkage Of High Performance Concrete

High Performance Concrete(HPC) has attracted a lot of attention for its exceptional advantage in workability, mechanical property and durability performance. However, due to the high cement content in its mixture pro portions and the relatively low water-binder ratio, initial shrinkage of HPC is greater than ordinary concrete, which increases the risk of early-age cracking and hinders its further application in the engineering field. Shrinkage Reducing Agent(SRA) can r educe capillary stress mainly by cutting down the surface tension of the solution in the capillary. Super Absorbent Polymer(SAP) is always considered as an ideal curing material that restrain shrinkage of HPC via keeping internal relative humidity. Overal l considering both the advantage and shortage of two kinds materials above in mechanism, effect and application scope, it’s difficult to just make use of single existing reduced technology to ensure other performances of HPC and minimize its shrinkage. In order to achieve excellent effect, this paper mainly studied the influence of SRA and/or SAP on autogenous shrinkage, drying shrinkage, compressive strength and microscopic structure. The results were as follows:(1)Adding SRA alone reduced drying shrinkag e of HPC significantly and decreased autogenous shrinkage slightly meanwhile. However, increasing the amount of SAP not only decreased the shrinkage effect apparently, but also caused lots of adverse impacts on strength.(2)Adding SAP alone reduced autogenous shrinkage of HPC significantly compared to adding SRA alone. The drying shrinkage of HPC can be reduced as well in this situation which wasn’t as good as adding SRA alone. These two effects also increased with the amount of SAP. So the effect of SAP wa s better than that of SRA on the whole. The amount of SAP in this paper has little influence on the reduction of compressive strength.(3)In term of decreasing autogenous shrinkage of HPC, mutual blending of SAP and SRA not only displayed superior compat ibility, but also formed a good "superposition" effect which was better in the case of increasing the amount of SAP only in comparison with increase that of SRA only.(4)In term of decreasing drying shrinkage of HPC, mutual blending SAP and SRA indicated that it was better than the corresponding SAP alone added but was worse than the corresponding SRA alone added. These groups also reflected that SAP and SRA displayed superior compatibility in the aspect of reducing shrinkage.However, increasing the amoun t of SAP is inferior to increasing the amount of SAP.(5)Increasing the amount of SAP showed a lower discount on compressive strength compared with SRA in the case of mutual blending SAP and SRA.