Effect of the optimized triple mixing method on the ITZ microstructure and performance of recycled aggregate concrete

Due to the existence of two weaknesses in the ITZ, the performance of recycled aggregate concrete (RAC) is much lower than that of natural aggregate concrete. An optimized triple mixing (OTM) method was developed to strengthen the ITZ in the RAC in this paper. It was found that OTM could dramatically improve the compressive strength, freezing and thawing resistance and water impermeability of the RAC. The reason is that supplementary cementitious materials (SCMs) filled the ITZ in the RAC prepared by OTM. Additionally, SCMs formed a thin and dense layer to coat the recycled aggregate, which was beneficial in terms of strengthening the ITZ structure of the RAC. In addition, OTM was beneficial for the dispersion of SCMs in the ITZ, even if the amount of the mixing water was not sufficient. (C) 2019 Elsevier Ltd. All rights reserved.