Chemistry of the Aqueous Phase of Ordinary Portland Cement Pastes at Early Reaction Times

Abstract

The chemistry of the aqueous phase of ordinary portland cement paste at early ages (<2 h) has been analyzed in terms of the concentrations of the elemental components in the pore fluid. The concentrations of calcium, sulfur, aluminum, and silicon are rationalized by plotting the data on ''phase diagrams.'' To simplify the analysis, the portland cement system is described using two subsystems: (i) CaOAl 2 O 3 -CaSO 4 -H 2 O, modified by the presence of sodium and potassium, and (ii) CaO-SiO 2 -H 2 O. During the first 10 min of hydration, the calcium, sulfur, and aluminum concentrations all decrease, roughly in proportion, which suggests a precipitation process, a conversion of calcium sulfate hemihydrate to gypsum, and the initial formation of ettringite. The CaO-Al 2 O 3 -CaSO 4 -H 2 O subsystem seems to move from a phase assemblage of gypsum, Al 2 O 3 ⅐3H 2 O, and ettringite to an assemblage of gypsum, calcium hydroxide, and ettringite during the first 15-30 min after the water and the cement are mixed. The silicate equilibrium is approached more slowly. The intensity of mixing has relatively little effect on the concentrations beyond the first few minutes.

Influence of aluminium inclusions on dielectric properties of three-phase PZT–cement–aluminium composites

“…This figure also shows the possible formation of ettringite structures (micron scale), which are needle-like crystals formed during the curing and hydration of cement. These structures are similar to those described by Kelzenberg et al (1998), Rothstein et al (2002) and Thomas et al (2003), who describe the formation of ettringite during early hydration of Portland cement. Ettringite is typically formed in hydrated Portland cement as a result of the reaction of calcium aluminate with calcium sulfate, which are both present in Portland cement.…”

“…In general, ettringite usually forms during the early hydration step and then converts to calcium aluminate monosulfate relatively quickly. If the relative concentration of calcium sulfate to tri-calcium aluminate is moderate to high, ettringite will coexist with calcium aluminate monosulfate or minimally convert (Kelzenberg et al, 1998;Rothstein et al, 2002;Thomas et al, 2003).…”

Effects of alkali metal hydroxides on alkali-free accelerators

“…All these anhydrous and hydrated phases were in equilibrium with the ionic species in the pore solution such as Ca 2þ , SO 4 2À , Na þ , Al 3þ and SiO 2 2À (Table 8; Kelzenberg et al (1998)). The results in Table 8 cannot be directly transferred to the pore solution (being the samples of cement/water slurries), nevertheless a similarity of the observed trends could be expected.…”

“…The results in Table 8 cannot be directly transferred to the pore solution (being the samples of cement/water slurries), nevertheless a similarity of the observed trends could be expected. Immediately upon contact of cement with water, a rapid dissolution of ionic species into the liquid phase occurs (Kelzenberg et al, 1998). The hydration of C 3 S and C 2 S is associated with the increase of Ca 2þ : Owing to the rapid dissolution of alkalis, the OH À concentration of the mixing water increases speedily in contact with cement.…”

Surface Chemistry of Ground Granulated Blast Furnace Slag in Cement Pore Solution and Its Impact on the Effectiveness of Polycarboxylate Superplasticizers

“…The term “pore solution” (PS) generally describes the aqueous phase loaded with electrolytes which occurs between cement, slag, or other particles when dispersed in water at specific water‐to‐solids ratios. The SCPS used in this work was composed based on characteristic ion concentrations found in the pore solutions of a common Portland cement (CEM I) . It contained (g/L) Ca 2+ 0.4, K + 7.1, Na + 2.25, and SO 4 2− 8.29.…”