Impact of added water and superplasticizer on early compressive strength of selected mixtures of palm oil fuel ash-based engineered geopolymer composites

This paper investigates and presents a study on the comparative effects of added water and naphthalene-based superplasticizer (SP) on the compressive strength and microstructure of the developed palm oil fuel ash engineered geopolymer composites (POFA-EGC). Three differently prepared 50 mm × 50 mm × 50 mm specimens (with 10% water, with 10% SP and with 5% SP & 5% water) were used to study the synthesis of POFA and alkali-activating solutions (8 M NaOH_(aq) + Na₂SiO₃ [Ms = 3.3]). 2% volume fraction of PVA fibres were added to engineer the cementitious composite mixture. All the specimens were cured in an oven for 24 h at 60 ± 5 °C to accelerate the geopolymer reaction process to generate the binder. After testing, the obtained results showed that while specimens with added water only gave the compressive strength of 29.4 MPa, there was a 19% decrease in compressive strength for samples with SP only at 28 days. The specimens with water and SP combined have the least strength. Microstructural examinations (SEM) and material characterization (XRD, FTIR) of the alkali-activated composite also revealed the superior performance of the specimens with water over SP. The significant finding of this research work is the better performance of POFA-EGC prepared with only water in both fresh and hardened states. It is recommended that water be given precedence over SP in the development of POFA-EGC.