The Effect Of Sulfate On The Durability Of Preloaded Reactive Powder Concrete

Reactive powder concrete has ultra-high strength and remarkable durability. It is especially suitable for the structures that have high demand on durability.Research on the durability of reactive powder concrete after the multi-factor couplingeffects has important significance. In this paper,the durability of preloaded reactive powder concrete after the coupling effects of sulfate dry-wet and freeze-thaw cycles were studied, the types of cement, contents of fly ash and mineral powder are chosen as main parameters. The relative dynamic elastic modulus, mass loss rate, compressive strength and compressive strength corrosion factor are the main evaluation indexes.Combined with SEM analysis the change of microstructure of reactive powder concrete,it explores the damage mechanism of reactive powder concrete under the coupling effect of sulfate dry-wet and freeze-thaw cycles.(1)After the coupling effects of sulfate dry-wet and freeze-thaw cycles, the durability of reactive powder concrete is good. Compressive strength and compressive strength corrosion factor should be preferred as its durability evaluation index, followed by the relative dynamic elastic modulus; the mass loss rate is unfavorable as its durability evaluation index, because the mass loss rate of change is small.(2)After the coupling effects of sulfate dry-wet and freeze-thaw cycles, the ability to resist corrosion of preload reactive powder concrete was obviously higher than that of corrosion resistance of high performance concrete.The ability of reactive powder concrete to resist the coupling effect of sulfate dry-wet and freeze-thaw cycles can be improved while fly ash replace silica fume. Mineral powder replace silica can improve the durability of reactive powder concrete. After the coupling effects of sulfate dry-wet and freeze-thaw cycles, high resist-sulfate cement of reactive powder concrete resistance abilityis better than that of Portland cement of reactive powder concrete.(3)The coupling effects of sulfate dry-wet and freeze-thaw cycles have great impact of the microstructure of concrete.Observed by SEM-EDS:C50high performance concrete after the coupling effect,Ca(OH)2content decreases, produces a large number of AFm and CaSO4·2H2O. After the coupling effect, reactive powder concrete generates a small quantity of AFm and CaSO4·2H2O, but because of the dense structure of the reactive powder concrete itself was not observed the existence of Ca(OH)2; After coupling cycles, hydrate garnet is found in resist-sulfate cement of reactive powder concrete, hydrate garnet generation compacts concrete,reduces the possibility of reaction SO4"with Ca2+and inhibits the formation of gypsum crystals expandable, thereby improves the durability of reactive powder concrete.