The influence of supplementary cementing materials on the water retaining ability of hydrated lime and Portland cement mortars

Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Sorptivity (S) defines the liquid absorption ability of a porous substrate such as brick, stone or concrete block by capillarity. Transfer sorptivity (A), a function of sorptivity and desorptivity, defines the ability of the substrate to withdraw water from the wet mix. 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 is determined by a modified American Petroleum Institute pressure cell. 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). The presence of 50% FA in CL90 mortars causes a dramatic increase in desorptivity which is quantitatively equivalent to the most water releasing PC mortars. On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). It is concluded that desorptivity and hence transfer sorptivity increases as the volume fraction of GGBS and FA increases in CL 90 mortars and decreases with increased volume fraction addition of SF in PC mortars. Since the time taken to dewater a mortar joint (tdw) is inversely proportional to the transfer sorptivity, tdw can be dramatically altered by the addition of SCMs to both CL90 and PC mortars.