Properties of geopolymer concrete produced with surface-improved recycled concrete aggregates

Due to the high energy consumption and carbon dioxide emissions caused by cement production, geopolymer concretes (GPC) have emerged as an alternative to ordinary concretes. In order to make the concrete industry more environmentally friendly and sustainable, ways to reduce the use of natural resources are used. Aggregates, which make up approximately 70% of the concrete, consume natural resources. Recycling concrete is the most effective method of reducing construction waste. In addition to the use of industrial wastes as binders in GPB production, it is also possible to use recycled aggregates (RCA) instead of natural aggregates (NA). However, it is important to eliminate the negative effects of these aggregates on concrete properties. In this study, the properties of GPCs produced using pozzolanic slurry impregnated RCAs were investigated. In the production of GPC, fly ash (FA), blast furnace slag (BFS) and metakaolin (MK) were used as binders, sodium silicate and sodium hydroxide solutions were used as alkali activators. RCAs were impregnated with cement slurry and FA, silica fume (SF), MK and BFS slurries. All pozzolanic slurries improved the properties of RCAs. The slurry containing SF was the most effective slurry, reducing the water absorption of RCA by 55%, abrasion and impact resistance by 33%. Strength and durability properties of slurry impregnated RCA GPCs were compared with NA and unimpregnated RCA GPCs. Among the binders used in GPC production, the highest performance was obtained with BFS. Strength and durability properties of GPCs impregnated with SF slurry were the best. Compared to GPCs with untreated RCA, improvements in compressive strength by 56%, in splitting tensile strength by 35%, in water absorption by 38%, in capillary water absorption by 54%, and in chloride permeability were achieved by 39%.