Evaluation of Slag-Blended Alkaline-Activated Palm Oil Fuel Ash Mortar Exposed to the Sulfuric Acid Environment

The performance of alkaline activated ground slag/ultrafine palm oil fuel ash (AAGU) mortars upon their exposure to 6% of H2SO4aq (acid) for 60 days was investigated. The mortars were prepared with NaOHaq of varied concentrations and Na2SiO3aq (Ms-SiO2/Na2O=3.3) activators and then cured at a temperature of 60°C for 24 h. The findings through strength, microstructural examination, and product characterization revealed that sulfuric acid attack could cause the disintegration of microstructure through the removal of the key elements—Ca, Mg, Na and Al—which resulted in the formation of gypsum, expansive shrinkage cracks, and a reduction in strength retention. Maintaining the slag content, concentration of NaOHaq, Na2SO3aq/NaOHaq ratio, and the mixing water content in the range of 20–40 wt.%, 8–10 M, 1.0–2.5, 5–10 wt.% of the pozzolanic materials (PMs), respectively could enhance the resistance of AAGU mortar subjected to sulfuric acid attack.