Effectiveness of rice husk ash-derived alkali activator in fresh, mechanical, and microstructure properties of geopolymer mortar at ambient temperature curing

AbstractConventional geopolymers are proven to be eco-friendly compared to Portland cement-based concrete (PC). However, the used alkali activator, i.e. sodium silicate is associated with high carbon emission and cost, making the geopolymers not really a sustainable alternative to PC. This experimental investigation was carried out to understand the potential of rice husk ash (RHA)-based alkali activator in the synthesis of fly ash-blast furnace slag (FA-GGBFS)-based geopolymers at ambient temperature. Three different concentrations of sodium hydroxide (by wt. %) solutions, i.e. 20%, 24%, and 27%, were used to synthesize an RHA-based alkali activator. A commercial-grade sodium silicate solution was used to compare the results of geopolymer mortars (GPM) with the prepared RHA-based alkali activator. Fresh, mechanical, and microstructural investigations were carried out for both the RHA and commercial-grade alkali activator-based FA-GGBFS GPM specimens. The compressive strength of RHA-based optimum GPM was found to be 41 MPa at 28 days of the curing period, which was close to the control sample made with the commercial activator; similar observations were found for the flow table test. Microstructural investigation (XRD and SEM) confirmed that the GPM prepared with the RHA-based alkali activator has a similar microstructure as the GPM with the commercial-grade alkali activator.Keywords: Geopolymeralkali-activated materialsrice husk ashalternative alkali activatormicrostructure and mechanical properties Authors’ contributionsS.K. Das: Conceptualization, Formal analysis, Visualization, Investigation, Writing—original draft preparation, Writing—review and editing, and Supervision; N. Behera: Investigation, Methodology, Formal analysis, Writing—original draft preparation; S.K. Patro: Conceptualization, Visualization, Supervision, and Writing—review and editing; S.M. Mustakim: Resources, Writing—review and editing; Y. Suda: Formal analysis, Writing—review and editing; N. Leklou: Validation and Writing—review and editing.AcknowledgmentsThe authors acknowledge the experimental support of CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, India, for this research. The authors also thank Mr. Manoj Nayak and Mr. Pradyumna Kumar Sahu of the Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla, Odisha, India, for their help during the experimental investigation. Grøn Tek Concrete and Research, Bhubaneswar, India, is also acknowledged for the support provided during this research.Disclosure statementNo potential conflict of interest was reported by the authors.