Compatibility of Polycarboxylate Ethers with Cementitious Systems Containing Fly Ash: Effect of Molecular Weight and Structure

Substituting cement with mineral additives like fly ash is increasingly essential for sustainable production. While replacement rates largely depend on fresh-state properties, the interaction between fly ash and polycarboxylate ether (PCE) molecular structures remains underexplored. In this regard, this study investigates the effect of PCE molecular structures and weight on the rheology, setting, and strength of cementitious systems containing up to 45% fly ash additions. Seven distinct PCE possessing different molecular weights (27,000–78,000 g/mol) as well as backbone and side chain lengths are synthesized. The interaction between PCE and solid particles was explored through total organic carbon, dynamic light scattering, and gel permeation chromatography. Test results showed that the adsorption rates of the cement and fly ash particles within the cementitious composites improved by up to 90% with fly ash replacement and upon using PCE with a medium molecular weight of 56,000 g/mol, backbone length of 21 k, and short side chain length of 1000 g/mol. This has resulted in a 75% reduction in the material’s apparent viscosity, delayed setting times of up to 38%, and improved early- and late-age compressive strengths of up to 123%. Such data can interest cement and admixture producers in proposing suitable PCEs for superior fly ash concrete performance.