A sustainable bottom ash-based alkali-activated materials and geopolymers synthesized by using activator solutions from industrial wastes

Abstract

This research focused on a 100% using of industrial wastes to produce alkali-activated materials (AAMs) and geopolymers which are sustainable environmentally friendly materials having properties like a cement. Two different sources of lignite and bituminous coal-fired bottom ashes were used as starting materials. Two types of alkaline solutions from wastes, namely, NaOH solution waste discharged from anodize process in aluminum industry (AS1) and alkaline solution prepared from boiling rice husk ash in that NaOH solution waste (AS2), were used instead of commercial alkaline activator solution. Solid/liquid ratios of the samples were studied between 75:25, 70:30, 65:35, and 60:40. Forming by casting method, after curing 28 days, mechanical and physical properties, including XRF, XRD and SEM analysis were investigated. AAMs and geopolymers from wastes with low-cost of raw materials showed good enough properties to use for construction materials such as bricks, tiles, or cement substitution. The best properties were found from the sample using lignite bottom ash as precursor synthesized with AS1 solution at 75:25 solid/liquid ratio, it showed compressive strength of 28.91 ± 2.16 MPa, bulk density 1.77 ± 0.03 g/cm3, water absorption 17.23 ± 0.13%, and apparent porosity 30.46 ± 0.19%. The samples synthesized from lignite bottom ash exhibited better properties than bituminous bottom ash. Depending on SiO2 and Al2O3 contents in raw materials, the lignite bottom ash with lower Si/Al ratio resulted in the better compressive strength. In addition, the higher calcium content in lignite bottom ash significantly affecting increased compressive strength of the samples.