Improvement in compatibility of polycarboxylate superplasticizer with poor-quality aggregate containing montmorillonite by incorporating polymeric ferric sulfate

Clay minerals are ubiquitous in nature and are, therefore, difficult to be avoided in mined aggregates. Since aggregate occupies more than 70% weight ratio of the concrete, it is easy to bring more than 0.5 wt% montmorillonite (Mt) in concrete. It is this small dosage of Mt that can result in fast loss of fluidity of fresh concrete, being referred to as poor clay tolerance, which seriously restricts the application of polycarboxylate superplasticizer (PCE) in real concrete. In this study, an attempt to improve the clay tolerance by incorporating polymeric ferric sulfate (PFS) has been made. The effect of PFS on adsorption behavior and dispersion of PCE was investigated, and the mechanism behind was revealed with X-ray diffractometry, Fourier-transform infrared spectroscopy and atomic force microscopy. The results of fluidity indicate that the presence of PFS in PCE system can obviously improve the 60 min fluidity, showing the improvement in clay tolerance. The results of adsorption illustrate that the presence of PFS can affect the adsorption behavior of PCE, with an increase in adsorption amount on cement particles but a decline on Mt particles. The results of XRD and FTIR demonstrate that in Mt suspension, PFS can increase the surficial adsorption of PCE but completely hinder the intercalation of PCE to avoid the interlayer adsorption, resulting in decline in total adsorption amount. The main reason for this is due to the formation of layer on the surface of Mt particles, and strong evidence for this was obtained with AFM. It is this layer that hinders intercalation of PCE over time, which is responsible for the improvement in clay tolerance. Such results suggest an effective method to hinder the intercalation of PCE into Mt layer, and the findings would be expected to provide guidance on improvement in poor clay tolerance of PCE in practical engineering.