The Influence of Water-Repellent Admixtures on the Hydration Process, Water Absorption, and Mechanical Properties of Cement Paste: An NMR Study Combined with Additional Methods

Abstract

Water repellent (WR) has been widely used to improve the durability of cementitious materials (CMs) by reducing the absorption of water and aggressive ions. In this study, cement pastes were prepared with three types of WR, namely, waterborne pure nanosilicone emulsion (NS), isobutyltriethoxysilane (IS), and octyltriethoxysilane (OCT). The effects of WR on setting time, compressive strength, and water absorption were investigated. The influence of WR on the transverse relaxation time spectrum from 0 min to 28 days during the hydration process was monitored with a low-field nuclear magnetic resonance (LF-NMR). In addition, X-ray diffraction (XRD) and heat flow were employed to study the effect of WR on hydration characteristics. The results showed that the WR specimens exhibited a limited reduction of compressive strength compared with the control sample at 28 days. The use of WR reduced the water absorption of cement paste when compared to that of the control specimens. The results showed that the WR exhibited a retarding effect on hydration reactions, and the capillary and gel pores of the cement paste increased compared with that of the reference sample. XRD analysis showed that the formation of hydration products had been restricted with the addition of WR. The heat flow results showed that the retardation effect was enhanced as the WR dosages increased.