Pressed lightweight fly ash-OPC geopolymer concrete containing recycled lightweight concrete aggregate

In this paper, the density and strength of lightweight fly ash-OPC geopolymer concrete containing recycled lightweight concrete aggregate (RLCA) were studied. Waste lightweight concrete was crushed and used as lightweight aggregate. Geopolymer cement was produced from the blend of high calcium fly ash and ordinary Portland cement (OPC), sodium hydroxide and sodium silicate. The fly ash was replaced with OPC at the dosages of 0, 5, 10 and 15% by weight. The results showed that lightweight geopolymer concretes with densities between 1200 and 1500 kg/m3 and 28-day compressive strengths between 4.5 and 17.5 MPa could be fabricated. The incorporation of RLCA reduced both density and strength of lightweight concrete. The addition of OPC enhanced the strength development of geopolymer concrete but also increased the density. The optimum OPC content for strength development was 10%. The NaOH concentration of 10 M, sodium silicate/NaOH ratio of 1.0, OPC content of 10% by weight of fly ash, liquid/solid binder ratio of 1.4, RLCA/solid binder ratio of 1.8 and curing temperature of 60 °C were recommended for the lightweight fly ash-OPC geopolymer concrete.