The retention of flowability and rheological properties in one-part alkali activated materials

Alkali activated materials (AAMs) are increasingly recognised as a sustainable alternative to Ordinary Portland Cement (OPC) due to their use of industrial by-products and favourable mechanical and chemical properties. However, the adoption of high-volume slag-based AAMs is impeded by challenges such as rapid setting and limited workability, primarily driven by the interaction of high-concentration alkalis with precursors. One-part AAMs, consisting of a dry mix of precursors and activators that only need water addition to start the reaction, offer improved control over fresh properties compared to traditional two-part systems. However, there are limited studies available on the impact of the retarding/superplasticising admixtures on the fresh properties of one-part AAMs. This study explores the potential of borax, ZnO, and fumaric acid as admixtures in one-part AAMs to address these issues. This research reveals that borax admixture, serving as both a superplasticiser and retarder, notably enhances initial flowability, reduces yield stress and slightly improves the strength. The strength reduction was observed when borax was used to replace the activator. Additionally, ZnO delays the setting, thereby improving flowability retention, although it does not affect mechanical strength after 28 days. Fumaric acid enhances flowability at 5 min by retarding the reaction. However, due to the high viscosity, flow diameter of fumaric acid-based specimens is lower than that of ZnO-based specimens. The study reveals that admixtures, used up to an optimum limit (5 wt% borax, 1 wt% ZnO, and 1 wt% fumaric acid), effectively improve flowability and extend workable time in AAMs while maintaining mechanical strength. • Impact of admixtures on flowability and rheological properties of one part AAMs were studied. • Borax, ZnO, and fumaric acid extend the retention of flowability in one-part AAMs by delaying the setting process. • Borax acts as both a superplasticiser and retarder, increasing initial flowability and reducing yield stress. • ZnO forms intermediate reaction products and delays the setting of AAMs. • Fumaric acid initially enhances flowability but slightly lowers mechanical strength of AAM.