The Effects Of Super Absorbent Polymer On The Performance Of Ultra High Performance Concrete

Ultra-High performance concrete (UHPC), as a new type of cement-based materials of excellent performance with high strength, high toughness, high durability, low permeability, is to become a materialof great valuein future.Shrinkage, as an inherent time-varying characteristic of concrete materials, refers to the volume decrease of concrete structures under non-load. Without concideration of the temperature, shrinkage mainly includes chemical shrinkage, autogenous shrinkage, drying shrinkage and carbonation shrinkage. The tensile stress of concrete occurs when the shrinkage happens under internal and external constraints, when the tensile stressof concrete exceeds the ultimate tensile strength,concrete cracks and the performanceofconcrete structuredeteriorates.As for normal concrete, shrinkage stress mainly refers to the stress caused by rying shrinkage. But for ultra-high performance concrete, due torefined aggregate, lowwater-cement ratio and large amount of reactive powder, theautogenous shrinkage plays a leading role in total shrinkage and its impact should be considered. Therefore, it is very important to find a rational approach to reduce drying shrinkage for the application of ultra-high performance concrete.This paper usessuper absorbent polymer(SAP) as ainternal curing agent within the ultra-high performance concrete in order to reduce its shrinkage and improve the performance of crackingresistance. In order to gain better usage of SAP as ainternal curing agent, this paper studied as follows:(1) By measuring the fluidity and fluidity loss of UHPC in different mix proportions, the influence of SAP on the fluidity and fluidity loss of ultra-high performance concrete is founded;(2) By measuring the flexural strength and compressive strength in different proportions, curing conditions and curing age of UHPC, the effects of different particle size, admixturecontent and water absorption amount (additional water-cement ratio) of SAP on the strength of UHPC are founded. And through SEM and XRD, the effect of SAP on the mechanical properties of ultra-high performance concrete is analyzed, from the microstructural prospect of view;(3) By measuring the length of prism in different proportions, curing conditions and curing age of the ultra-high performance concrete, the effects are founded of different particle size, admixturecontent and water absorption amount (additional water-cement ratio) of SAP on the drying shrinkage without constraints of UHPC understandard andhot water curing conditions; By measuring the strain developmentin the UHPCring test; the effects of SAP,santi-cracking performanceon drying shrinkage with constraintsbound of UHPC with and withous steel fibers are investaged;(4)By measuring the volume shrinkage of UHPC in different proportions, the effect of high absorbent resin particle size,admixturecontent and water absorption amount (additional water-cement ratio) of SAP on the autogenous shrinkage of UHPC is researched, Via the theory of capillary tension, the mechanism of decrease of autogenous shrinkage with SAP is analysed.