Utilization of recycled fine powder as an activator in fly ash based geopolymer mortar

• Published in: Construction & building materials 2022-03, Vol.323, p.126581, Article 126581
• Main Authors: Sharma, Abhishek, Singh, Paramveer, Kapoor, Kanish
• Format: Article
• Language: English
• Subjects: Compressive strength; Dry shrinkage; Fly ash; Geopolymer mortar; Recycled fine powder
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2022.126581

•The RFP could be used as an activator for FA based geopolymers specially in ambient curing conditions.•The addition of RFP in FA based geopolymers enhance their compressive strength at early stages of curing.•The presence of un-hydrated cement particles in RFP provides additional hydration products in the form of C-A-S-H/N-A-S-H gel along with geopolymer matrix.•The utilization of concrete waste in the form of RFP as an activator for FA based geopolymers helps to attain sustainability. The paper discusses the potential of recycled fine powder as an activator in fly ash based geopolymer mortar. In current study, the recycled fine powder was used as partial substitute of fly ash at different replacement levels i.e., 10%, 20%, 30%, 40% and 50%. The sodium hydroxide and sodium silicate solutions were used as an alkaline solution for geopolymer mortar. The alkali/binder ratio of 0.45, sodium hydroxide of 12 molarity, sodium silicate / sodium hydroxide ratio of 2 and water/solid ratio of 0.35 kept constant for all geopolymer mortar mixes. The fresh properties of geopolymer mortar were evaluated in terms of slump flow and setting time. Further, the compressive strength and durability properties were assessed in terms of water absorption, porosity and dry shrinkage for all geopolymer mortar mixes at both ambient and heat curing. The observed results show that up to 30% substitution of recycled fine powder enhances the strength and durability properties of geopolymer mortar mixes. The recycled fine powder shows prominent results for compressive strength at early stage of ambient curing. The microstructure analysis validates the presence of calcium content in recycled fine powder provides additional Na2O–Al2O3–SiO2–H2O / CaO–Al2O3–SiO2–H2O gel with geopolymer matrix and densify the microstructure to enhance all properties of geopolymer mortar.