Study of Durability of Concrete with Fly Ash as Fine Aggregate under Alternative Interactions of Freeze-Thaw and Carbonation

Abstract

Tostudythedurabilityofconcretewithflyashasfineaggregatesubjectedtoalternativeattacksoffreeze-thawandcarbonation,the appearance, mass loss, relative dynamic modulus of elasticity, relative compressive strength, and carbonation depth of the concrete are investigated using cyclic tests under single carbonation, single freeze-thaw, and alternation of freeze-thaw and carbonation. In addition, microstructural analysis techniques including scanning electron microscope and X-ray diffraction are adopted to reveal the deterioration mechanism of alternating freeze-thaw and carbonation. Results show that carbonation is beneficialforrefiningtheporestructureandincreasingconcretestrengthintheinitialalternativecycle,whichdelaysthedamage from freeze-thaw cycles. Damage from freeze-thaw causes crack propagation in concrete, which leads to carbonation intensification.Comparedwithothertestmodes,concreteunderalternativefreeze-thawandcarbonationcausesthegreatestdegree of deterioration during the initial freeze-thaw cycles. The carbonation depth under alternative freeze-thaw and carbonation is positivelycorrelatedwiththecarbonationtimeandthewater-to-cementratio.However,asthereactantiscontinuouslyconsumed due to the expansion of crystalline ice and CaCO3, alternative cycles result in the appearance of many more new cracks in the concrete.