Numerical Study On Chloride Resistance Of Recycled Aggregate Concrete

To preserve natural resources and alleviate the burden on landfill areas,one efficient way to utilize increasing amounts of construction and demolition waste is to form recycled coarse aggregates(RCA)for the production of recycled aggregate concrete(RAC).With the utilization of RAC in building construction,the durability of this material requires particular attention,especially in terms of chloride penetration.This paper presents a numerical study on the chloride diffusion mechanism within RAC.Considering the random distribution of RCA,a five-phase RAC model – including new mortar,adherent old mortar,new interfacial transition zone(ITZ),old ITZ and original natural coarse aggregates – is proposed to predict the effective diffusion coefficient of chlorides in RAC.The parametric studies,based on a series of critical factors(i.e.volume fraction of RCA,adhesive ratio of old mortar,chloride diffusivity of adherent old mortar,thicknesses of old and new ITZs and chloride diffusivity of old and new ITZs),reveal the properties of each phase and their individual impact on the effective diffusion coefficient of chlorides in RAC.The results obtained indicate that,interestingly,the effective diffusion coefficient tends to vary in terms of its relationships with high-quality adherent old mortar,lower adhesive ratio of old mortar,smaller thickness of ITZs and relatively superior chloride penetration resistance of ITZs,which cannot be found from existing models and experiments.The research results provide a theoretical basis and reference value for the development and application of recycled aggregate concrete.