Development of High-Quality and Water-Resistant PBG Through H-PDMS Modification: from Experiments to Molecular Dynamics Simulation

The effective treatment and high-value application of phosphogypsum (PG) are of critical importance for the sustainable development of this construction material. However, its poor water-resistance property has limited its application in the construction field. In order to expand the application potential of phosphorous-building gypsum (PBG) as a durable material, potassium hydroxide (KOH) and hydroxyl-terminated polydimethylsiloxane (H-PDMS) were used as the activating agent, and the water-resistant modifying agent in this study, respectively, to develop a high-quality and water-resistant PBG product. In addition, molecular dynamics was used to reveal the modification mechanism of H-PDMS and the water-resistance mechanism of KOH activating PBG. The study results show that H-PDMS can significantly improve the water-resistance performance of PBG test blocks. KOH can increase the surface activity of PBG by introducing -OH radicals, promote the reaction between H-PDMS and PBG, and form a dense hydrophobic layer on PBG, thus effectively improving its water-resistance performance. The number of surface active -OH radicals in PBG, the clustering effect of H-PDMS, and impurities in PBG can all result in different experimental and simulation outcomes. Meanwhile, the electrostatic force is an important factor influencing the adsorption of water droplets on the surface of PBG, and the reaction of H-PDMS with PBG normally occurs between Si-O and S-O. This study has systematically interpreted the working mechanism of water-resistant PBG, presenting an important significance in the utilization of PG resources.