The influence of supplementary cementing materials on water retaining characteristics of hydrated lime and cement mortars in masonry construction

Abstract

The purpose of this paper is an investigation of the possible role of supplementary cementing materials (SCMs) on the water retaining ability of hydrated lime (CL90) and Portland cement (PC) mortars. Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Transfer sorptivity (A) defines the ability of the substrate to withdraw water from the wet mix. The time to dewater (t dw), is an expression derived from the sharp front theory, and enables calculation of the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The results show that the very water retaining CL90 mortars become progressively more water releasing with increased volume fraction replacement levels of both ground granulated blast-furnace slag (GGBS) and fly ash (FA). On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). Results also show that transfer sorptivity increases as the volume fraction replacement levels of GGBS and FA increases in CL90 mortars and decreases with increased volume fraction replacement levels of SF in PC mortars. Since the time taken to dewater a mortar joint (t dw) is inversely proportional to the squared transfer sorptivity, t dw can be dramatically altered by the addition of SCMs in both CL90 and PC mortars. These parameters have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material. The ability to manipulate the water retaining properties can also allow construction time to be reduced.