The Influence of Physical Properties on the Durability and Compressive Strength of Fly Ash-Based Geopolymer Mortar under Tidal Acidic Exposure

Abstract

The rising demand for cement and electricity has increased carbon emissions and produced large volumes of Fly Ash (FA) waste from coal power plants. Converting this waste into geopolymer mortar provides a sustainable alternative to conventional cement. This study used FA from the Asam-Asam Power Plant, activated with sodium silicate (Na2SiO3) and 8M sodium hydroxide (NaOH) in ratios of 1:1, 1.5:1, 2:1, and 2.5:1, with superplasticizer (SP) dosages from 0.1 to 0.3%. Mortar specimens were evaluated for water absorption, porosity, and sorptivity at 28 days and for compressive strength at 28 days and after up to three months of exposure to tidal acidic exposure. At 28 days, compressive strength reached 12.61 MPa. Secondary sorptivity was 0.0008–0.0023 mm s-1/2 for the geopolymer mixes (minimum at SP3–R1.5) and 0.00071 mm s-1/2 for the cement mortar; the initial 1–6 h segment satisfied the linearity criterion (r ≥ 0.98) only for the cement mortar (Si=0.049 mm s-1/2), indicating a divergence between mechanical strength and capillary transport. Geopolymers showed greater resistance to strength loss under tidal acidic exposure.