Tailoring the sequence structure of polycarboxylate superplasticisers to improve the sulfate ion sensitivity

Polycarboxylate polymers (PCPs) with different sequence structures are synthesised using free radical polymerisation and reversible addition–fragmentation chain transfer polymerisation. Incompatibility between PCP and sulfate ion is well known and the dispersion ability of PCP has been known to degrade by sulfate ion in a solution of fresh cement paste. Flowability and rheology studies have revealed that block PCP or gradient PCP is less sensitive to sulfate ion than random PCP when the density of side chains is 1:1. Total organic carbon and dynamic light scattering are used to reveal this difference. Results for total organic carbon illustrate that the adsorption amount of block PCP and gradient PCP is much larger than for random PCP at the same PCP concentration, because the density of exposed carboxylic groups with block distribution is higher than in random PCP, therefore there is a larger adsorption amount. Results of dynamic light scattering show the conformation of random PCP in synthetic solution is unchanged with the concentration of sulfate ion, whereas that of block PCP or gradient PCP shows shrinkage in a high sulfate ion concentration. These findings offer guidance for research and development of PCP to improve its sensitivity to sulfate competitive adsorption and subsequently its compatibility with cement.