Shrinkage action mechanism of shrinkage-reducing admixtures based on the pore solution

The low molecular polyether shrinkage-reducing admixture (SRA) is widely used, but the shrinkage mechanism is still unclear. In this study, an investigation was carried out with four SRAs from the view point of molecular structure and property, while the pore solution was used as the research object. It was shown from the shrinkage performance experiments that the addition of 2% dipropylene glycol (SRA2), diethylene glycol-monobutyl ether (SRA3) and diethylene glycol-tert-butyl ether (SRA4) reduced the drying shrinkage by up to 19·2%, 44·4% and 28·5%, respectively, and reduced the autogenous shrinkage by up to 23·8%, 65·1%, 68·8% respectively. However, diethylene glycol (SRA1) did not show any shrinkage-reducing performance. The results of the surface tension, ion concentration and SRA concentration tests showed that the shrinkage-reducing ability is closely related to the molecular structures of SRAs. The shrinkage-reducing abilities of the amphiphilic SRAs are proportional to the surface tension of the pore solution, but inversely proportional to the potassium (K⁺) and sodium (Na⁺) ion concentrations. However, the surface tension reduction is not the main action mechanism for the hydrophilic SRAs. The shrinkage-reducing abilities of hydrophilic SRAs are related to their molecular diameters and the K⁺ and Na⁺ concentrations of the pore solution.