Effect of coupled B/Na and B/Ba doping on hydraulic properties of belite-ye'elimite-ferrite cement

摘要

Belite-ye'elimite-ferrite (BYF) cement was prepared by coupled B/Na and B/Ba doping. X-ray diffractometry (XRD) shows that both of the coupled doping methods stabilized the alpha(H)'-belite, and promoted the formation of the cubic-ye'elimite. The clinkers were then used to prepare cement pastes. Both coupled doping methods improved the compressive strength compared with the cement paste without dopants. Compared with single B doping, coupled B/Na doping decreased the early-age hydration heat and the compressive strength at all the hydration ages; whilst coupled B/Ba doping increased the hydration heat and compressive strength at the early ages, but decreased the strength after 28 d. It can be thus inferred that in addition to the polymorph, the type and amount of the dopants also impact the hydraulic properties of BYF cement. XRD study on the hydrated cement paste reveals that coupled B/Na doping increased the hydration degree of belite, but decreased that of ye'elimite. The total amount of the hydration products represented by the non-evaporable water content decreased, which agrees with the compressive strength. Coupled B/Ba doping increased the hydration degrees of both belite and ye'elimite, contributing to the increase of the compressive strength at the early ages. However, scanning electron microscopy shows that the precipitation of barite formed circles around the unhydrated clinkers at the later ages. The available space outside the circles was not effectively filled. This is probably responsible for the decrease of the compressive strength. (C) 2019 Elsevier Ltd. All rights reserved.