Clay-based geopolymer cement with industrial additives for improved rheological thermal and microstructural performance

This study investigates the rheological, thermal, and microstructural performance of clay-based geopolymer cement for geotechnical and oil well cementing applications. Kuala Rompin Clay (KRC) was used as the primary aluminosilicate precursor and activated with potassium hydroxide extracted from empty fruit bunch ash (EFBA) combined with sodium silicate. Bauxite, magnesium oxide (MgO), and calcium carbonate (CaCO3) were incorporated as functional additives at replacement levels ranging from 0 to 100%. Rheological parameters, including shear stress, apparent viscosity, yield stress, and plastic viscosity, were measured using a rotational viscometer under water-to-binder (w/b) ratios of 0.8–2.5 across varying shear rates. Results showed that increasing the w/b ratio consistently reduced shear stress and viscosity. Most mixtures exhibited dilatant behavior, while Bingham and pseudoplastic responses were obtained depending on additive type and dosage; KRC systems with 0–40% additives were predominantly dilatant, whereas CaCO3 contents above 30–40% produced shear-thinning behavior. Bauxite and MgO reduced rheological resistance relative to pure KRC, while CaCO3 increased yield stress and plastic viscosity beyond 40%. Thermogravimetric analysis (ambient 900 °C) confirmed good thermal stability, and SEM revealed that rheological transitions were governed by particle dispersion and gel continuity. Optimal performance occurred at 30% bauxite or MgO and 40% CaCO3, demonstrating the suitability of KRC-based geopolymers as sustainable cementing materials.