An effective approach to improve the performance of PC-based superplasticizer in alkali-activated slag

The lack of workability has hindered the industriallisation of alkali-activated slag (AAS) - a novel, low carbon cementitious building material. In order to address this main barrier, adding superplasticiser (SP) is essential. The main reason causing the dysfunction of current commercial SP in AAS has been identified as competitive adsorption between the SPs and the activators. The separate SP addition methods (adding SP and activator separately) offers the potentials to tackle the above issue. In this paper, the effects of separate addition methods of 134 lignosulfonate superplasticiser (LS) in AAS activated by NaOH were investigated. The adsorption between the LS and the slag was examined to understand the interaction between the SP and the slag. The workability and rheological properties of fresh NaOH-activated slag and the compressive strength of hardened NaOH-activated slag were also investigated. The results indicated that the separate addition methods reduced the competitive adsorption between the SPs and the NaOH activator, leading to a higher adsorption of the SPs on the slag. Consequently, the workability and rheological properties of NaOH-activated slag was enhanced by separate addition methods without reducing the compressive strength of hardened NaOH-activated slag