Optimization of alkali-activated fly ash-based geopolymer mortar: Influence of activator composition on strength and workability

Sathia Ramalingam; Vijayalakshmi Ramalingam; Aswin Sriram G

doi:10.62638/ZasMat1420

Authors

Sathia Ramalingam Department of Civil Engineering, Sri Venkateswara College of Engineering, Chennai, India Author https://orcid.org/0000-0002-0851-2145
Vijayalakshmi Ramalingam Department of Civil Engineering, Sri Sivasubramaniya Nadar College of Engineering, Kalavakkam, Chennai , India Author https://orcid.org/0000-0003-4678-2020
Dr Aswin Sriram G Department of Civil Engineering, Sri Sivasubramaniya Nadar College of Engineering, Kalavakkam, Chennai, India Author https://orcid.org/0000-0001-7416-8605

DOI:

https://doi.org/10.62638/ZasMat1420

Abstract

The effect of different combinations of alkali activator compositions, water content and mix proportions on rheology, mechanical properties and microstructure of fly ash-based geopolymer mortars are studied in this paper. Geopolymer mortars were synthesized at a sand-to-fly ash ratio of 2:1, sodium hydroxide (NaOH) molarity varied at 8M, 12M, 14M, 16M, and sodium silicate-to-NaOH ratios of 0·1–2·5. The water content was varied from 1-8% by weight of fly ash for the fixed solution-to-binder ratios of 0.4 and 0.5. Tests for flowability showed a workability between 120 to 140%. The compressive strength was determined at 3, 7, and 28 days. Maximum strength attained was 68 MPa at NaOH 16M and SS/NaOH ratio of 1.5. X-ray diffraction (XRD) analysis showed the formation of a zeolite (hydroxysodalite) phase at higher SS/NaOH ratios, resulting in higher strength. Increasing the ratio of H₂O and Na₂O more than 0.22 decreased strength due to porosity increase. The highest compressive strength was found at Na₂O/SiO₂ ratio of 0.15 to 0.17. The results define important activator ratios which help balance flowability and strength in geopolymer mortar and provide a quantifiable framework for mix optimization of alkali-activated materials.

Keywords:

Geopolymer mortar, Alkali activation, Compressive strength, Rheology and workability, Phase transformation

Supporting Agencies

No funding

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