Investigating the use of bio-derived lignosulfonate admixtures in alkali activated cements

Alkali activated cements have been successfully developed as viable alternatives to conventional Portland cement, attracting a lot of interest in both academic research and industry. This study aims to study the fresh state performance of alkali activated cements and the potential that bio-derived admixtures have in improving their properties. The main challenge faced when using these admixtures is lack of detailed understanding of their behaviour in these cements and their interactions with the precursor particles, to bring about the observed fresh state properties.
This study investigated the behaviour of lignosulfonates in aqueous solutions, increasing pH and ionic strength to determine their chemical stability. The chemical treatment of these admixtures was done with solutions that simulate the activating solution environment of the alkali activated cements. The activator plays a crucial role not only in activating the precursors but also providing an environment in which admixtures must dissolve and interact with the cement particles to induce dispersion. Therefore, it is important to understand how the admixtures behave in such chemical environments presented by alkali activated cements.
In exploring the fresh state behaviour of alkali activated cements, pastes were produced from mix designs formulated and optimised from low calcium fly ash and high calcium ground granulated blast furnace slag, activated with sodium silicate solution. It was demonstrated that an optimum dosage can be achieved for the dispersion efficiency of lignosulfonate admixtures. The effectiveness of the admixtures was determined by the type of lignosulfonate, dosage and cement system it was added to, highlighting that compatibility plays an essential role in admixture selection.
The working mechanisms of lignosulfonate admixtures in alkali activated cements were elucidated. This was achieved through zeta potential and adsorption measurement studies. It was demonstrated that lignosulfonates work primarily through electrostatic interactions, and that these interactions are greatly influenced by the chemical environment and the surface chemistry of the precursor particles.
This study established the potential of lignosulfonates for use as admixtures in alkali activated cements. The understanding gained from this study about the chemical action and stability of lignosulfonates in alkaline media, their interactions in cement systems and effect on the properties of these cements filled gaps in the literature and challenged some long-standing conclusions on these materials.