Mechanical, shrinkage and chloride ion erosion resistance of concrete prepared with recycled aggregates by heating

This study explored the effects of recycled aggregates (RA) by modifying the shrinkage and chloride penetration resistance of concrete. RA was heated at constant temperatures of 300, 500, and 700 oC for 30 min. Further, the measured shrinkage and chloride penetration resistance of the recycled aggregate concrete (RAC) were also adversely affected by the incorporation of RA. The results indicated that replacing 50% of NA with RA reduced compressive strength by 28.5% at 28 days. Shrinkage values for 100% RA replacement increased by 65.7% at 28 days compared to the reference, while chloride ion penetration (electric flux) doubled. Moreover, when the heating temperature of RA was lower than 500 oC, the compressive strength of RAC increased with increasing temperature and decreased when the temperature exceeded 500 oC. The shrinkage value and chloride ion penetration resistance of the RAC exhibited similar phenomena. The addition of secondary cementitious materials contributed to the compressive strength, shrinkage, and chloride penetration resistance of RAC. Heating RA at 500 oC improved compressive strength by 12.3% compared to untreated RA, reduced porosity to 15.3%, and minimized shrinkage. Incorporating 20% fly ash (FA) and 10% granulated blast-furnace slag (GBFS) enhanced compressive strength by 9.6% and reduced chloride flux by 27% at 120 days. In addition, pore structure characteristics were investigated, and it was found that the pore structure of RAC also improved owing to the heating of RA.