Performance evaluation of superplasticizers in one part geopolymer mortar

The widespread adoption of one-part geopolymer cement (OPGC) is constrained by its intrinsically low workability, which limits handling, casting, and field implementation. This study introduces a dry-mix technological strategy in which powdered superplasticizers (SPs) are directly pre-blended with the geopolymer binder, thereby eliminating on-site liquid admixture dosing and enhancing practical constructability. Powdered sulfonated naphthalene formaldehyde (SNF) and polycarboxylate ether (PCE) were incorporated at 0.5-2.5% by binder weight into an OPGC mortar composed of ground granulated blast furnace slag (GGBS), diatomite, and feldspar, activated using solid sodium hydroxide and anhydrous sodium silicate. Fresh performance, mechanical behavior, and in-situ quality indicators were evaluated through flowability, setting time, compressive, flexural, and split tensile strengths, ultrasonic pulse velocity, and rebound hammer testing. Chemical stability and microstructural evolution were examined via zeta potential, ATR-FTIR, XRD, SEM, and EDS analyses. The incorporation of 1% SNF yielded a 272.9% increase in relative slump and a 15.44% enhancement in 28-day compressive strength compared with the control, achieving a peak strength of 53.8 MPa. In contrast, PCE produced marginal workability gains (< 15%) and caused substantial strength reductions (up to 47%) to higher dosages. Spectroscopic and zeta potential analyses confirmed the chemical robustness of SNF under highly alkaline conditions, whereas PCE exhibited structural degradation and adverse dispersion behavior. Microstructural observations revealed denser and more homogeneous geopolymer gel matrix in SNF-modified systems. All SNF-based mortars exceeded 43 MPa at 28 days, matching the performance benchmark of 43-grade Ordinary Portland Cement while delivering an estimated 16-25% cost reduction. These findings demonstrate that the dry incorporation of SNF provides a scalable and industry-compatible pathway for producing high-performance, user-friendly one-part geopolymer binders, advancing their viability for practical construction applications.