Lightweight geopolymer fly ash sand: an alternative to fine aggregate for concrete production

The current study is aimed at evaluating and critically analyzing the properties of Light Weight Geopolymer Fly Ash Sand (LWGFAS). LWGFAS has been prepared by geopolymerization of fly ash. A liquid solution of 4M NaOH, with Na₂SiO₃/NaOH=2, was used as an activator, and post-set heat treatment of 1 hour at 100 °C was applied for the preparation of LWGFAS. The LWGFAS sample was analyzed for various physical and chemical parameters, along with studies on mineralogy and alkali silica reactivity. The molar concentration of the activator solution and the duration of post-set heat treatment play a vital role in the physical and mechanical properties, particularly specific gravity, bulk density, and water absorption, of the geopolymer fly ash sand. The specific gravity and water absorption of LWGFAS were 1.57 and 17.85%, respectively. Experimental concrete mixes made with LWGFAS as a replacement for natural sand were evaluated for compressive strength and various durability properties of concrete. The study indicates that LWGFAS can be suitable for a wide range of applications in concrete, from lightweight to normal weight concrete, based on the physical and chemical characteristics of Geopolymer Fly Ash Sand.