Recycling and sustainability of geopolymer concretes are crucial for both the environment and the economy. For this purpose, the usability of recycled geopolymer concrete aggregates (RGAs) obtained by crushing geopolymer concrete produced from different aluminosilicate sources (perlite, blast furnace slag, red mud, volcanic ash, etc.) in the production of portland cement concrete was investigated. RGAs were used instead of normal aggregates as fine, coarse, and coarse+fine aggregates in concrete produced with CEM I cement. In the mixtures produced with CEM II cement, only coarse aggregates were replaced with RGAs. Compressive, flexural, and bond strength (pull-out test); restrained shrinkage (ring test); and drying shrinkage, ultrasonic pulse velocity, water absorption, and bulk density tests were performed. Additionally, the properties of the mixtures after exposure to high temperatures (300°C and 600°C) were investigated. The results showed that, with the incorporation of RGAs into concrete, regardless of the size of the RGA grains, compressive, flexural, and bond strength decreased. However, this decrease was more visible in compressive strength (14%–32% for 28 days). Drying shrinkage, water absorption, and permeable void volume increased, but cracking potential decreased. At high temperature (300°C), strength loss was 26% in reference mixture with CEM I cement (RCI) and 14% in reference mixture with CEM II cement (RCII), while RGA mixtures showed 12%–18% (CEM I) and 4%–5% (CEM II) loss. Although fine RGAs had lower compressive and flexural strength than coarse RGAs, drying shrinkage, water absorption, and permeability were lower. Mixtures of CEM II exhibited higher drying shrinkage than mixtures of CEM I. However, there was no significant difference between them in other properties.
Anis et al. (Wed,) studied this question.