Tailoring the Molecular Weight of APEG-Based Polycarboxylate Superplasticizers: Mechanistic Insights into the Workability and Compressive Strength of Alkali-Activated Circulating Fluidized Bed Fly Ash Materials.

This study aims to investigate the effects and mechanisms of polycarboxylate superplasticizers (PCEs) on alkali-activated circulating fluidized bed fly ash (CFBFA) materials. Two PCEs-APEG-500 and APEG-2400-were synthesized using allyl polyethylene glycol ethers (APEG) with molecular weights of 500 and 2400, respectively. Their water-reducing performance and impact on the compressive strength of alkali-activated CFBFA materials were evaluated. The results show that both PCEs exhibited significant water reduction (up to 28% for APEG-2400) in pure CFBFA paste systems, but their efficacy was largely diminished in alkali-activated systems. Compared to the control group without PCEs, APEG-500 improved compressive strength by 20.37% at 1 day and 33.00% at 28 days, while APEG-2400 exhibited lower early strength but achieved a 10.31% strength increase at 28 days. Mechanistic analyses via XRD and FTIR analyses indicated that there was no significant alteration in reaction products, suggesting that the shorter side chains of APEG-500 facilitated particle adsorption and accelerated early hydration. Mercury intrusion porosimetry revealed that PCEs refined the pore structure by increasing harmless pores and reducing harmful ones, with APEG-2400 showing an 11.11% higher proportion of harmful pores compared to APEG-500. SEM observations supported these findings. This study clarifies the relationship between PCE molecular weight and CFBFA material properties, providing a basis for optimizing CFBFA-based cementitious materials.