Strength Characteristics of Geopolymer Synthetic Sand Using Fly Ash

Sand is a naturally available resource that has numerous applications in civil engineering. Due to a rapid increase in construction activities and exploitation of natural resources, there has been a scarcity of natural river sand (NRS), causing environment related issues such as erosion of riverbanks and the lowering of the water table. Hence, there is a need to identify and process sustainable alternative granular materials such as geopolymer synthetic sand (GPSS). In this connection, an attempt has been made for the effective utilization of fly ash in the synthesis of granular materials through geopolymerization. Geopolymer synthetic sand was prepared using 12 M NaOH solution at 100°C for 1 h and the granules produced were used as an alternative for natural river sand. The granulated materials were characterized by their physical properties [specific gravity, water absorption, grain size distribution, specific surface area, and scanning electron microscope (SEM)], chemical properties [pH, electrical conductivity (EC), total dissolved solids (TDS), and cation exchange capacity (CEC)], engineering properties (cohesion, angle of shearing resistance, optimum moisture content and maximum dry density, and hydraulic conductivity), mineralogical properties [X-ray diffraction (XRD)], and thermal properties [thermogravimetric analysis (TGA) and differential thermal analysis (DTA)]. In addition, compressive strength tests were performed on GPSS and NRS mortar. It was noted that GPSS mortar attained similar strength as NRS mortar. Based on the experimental investigations and microanalysis, it can be concluded that GPSS granules have the potential for use as an alternative to natural river sand.

In the present study, an attempt has been made to prepare and characterize geopolymer synthetic sand with effective utilization of fly ash by using alkaline solutions of sodium hydroxide and sodium silicate. The optimized geopolymer solution was used for the synthesis of granules and the GPSS prepared was analyzed for various physical, chemical, engineering, mineralogical, and thermal properties and the results obtained for GPSS were compared with natural river sand. Geopolymer synthetic sand produced similar results as that of natural river sand. Thus, GPSS is a promising candidate as an alternative to NRS in various construction activities such as embankment material, subgrade material, underground pipe back filling material, construction of partition walls, construction of panel walls, heat insulation on roofs, filter material in retaining walls, light weight concrete blocks, and so forth. Hence, geopolymer synthetic sand is an effective alternative to fine aggregate in natural river sand. Using GPSS would bring down the exploitation of NRS and also reduce rapid depletion of NRS through human activities.