Improved evidence for the existence of an intermediate phase during hydration of tricalcium silicate

Abstract

Tricalcium silicate (Ca 3 SiO 5 ) with a very small particle size of approximately 50 nm has been prepared and hydrated for a very short time (5 min) by two different modes in a paste experiment, using a water/solidratio of 1.20, and by hydration as a suspension employing a water/solid-ratio of 4000. A phase containing uncondensed silicate monomers close to hydrogen atoms (either hydroxyl groups or water molecules) was formed in both experiments. This phase is distinct from anhydrous tricalcium silicate and from the calciumsilicate-hydrate (C-S-H) phase, commonly identified as the hydration product of tricalcium silicate. In the paste experiment, approximately 79% of silicon atoms were present in the hydrated phase containing silicate monomers as determined from 29 Si{ 1 H} CP/MAS NMR. This result is used to show that the hydrated silicate monomers are part of a separate phase and that they cannot be attributed to a hydroxylated surface of tricalcium silicate after contact with water. The phase containing hydrated silicate monomers is metastable with respect to the C-S-H phase since it transforms into the latter in a half saturated calcium hydroxide solution. These data is used to emphasize that the hydration of tricalcium silicate proceeds in two consecutive steps. In the first reaction, an intermediate phase containing hydrated silicate monomers is formed which is subsequently transformed into C-S-H as the final hydration product in the second step. The introduction of an intermediate phase in calculations of the early hydration of tricalcium silicate can explain the presence of the induction period. It is shown that heterogeneous nucleation on appropriate crystal surfaces is able to reduce the length of the induction period and thus to accelerate the reaction of tricalcium silicate with water.

Research review of cement clinker chemistry

“…5 gives an overview on the principles of the different theories. According to the protective layer theory the surface of C 3 S is covered by a product layer that is claimed to be an intermediate phase in the precipitation process of C-S-H phases [44][45][46][47]. The overall reaction process is believed to be controlled by that layer.…”

Morpho-topological investigation of the mechanisms and kinetic regimes of alite dissolution

“…Despite those efforts and the large collection of new data generated, no conclusive assessment could emerge to discriminate the divergent points of view, debated now for several decades in the cement chemistry community, on what happens within the first 10-15 minutes upon mixing of cement and water and what causes the induction/dormant period. Whether a protective membrane [5,6] forms or not, whether cement surface undergoes a superficial protonation as originally proposed by Barret [7] or a superficial hydration as more recently proposed by Gartner [8] or whether precipitation/growth of hydrates governs completely the overall hydration kinetics [2,9,10] remains unanswered with certitude, although all various hypotheses are generally supported with extensive series of data or thermodynamic considerations.…”

Calorimetric study on the influence of redispersible E/VC/VL terpolymer on the early hydration of Portland cement

“…The length of the induction period is controlled by the slow dissolution of various ions, and the onset of the acceleration period is triggered by achieving the supersaturated concentration of ions, especially Ca 2? ions, and producing stable nuclei for hydrates [24][25][26][27]. Some researches contributed the length prolongation of the induction period and the delayed onset of the acceleration period to the adsorption of polymer particles on cement particles and the complexation effect of Calorimetric study on the influence of redispersible E/VC/VL terpolymer on the early… 1231 organic groups released by polymers with Ca 2?…”

“…Therefore, the delay of E/VC/VL on the onset of the acceleration period can be attributed to the adsorption of E/VC/VL particles on cement particles and the viscosity increase in liquid phase of fresh cement paste due to the slow dissolution of PVA (the protective colloid of E/VC/ VL). It is widely approved that during the acceleration period, the CSH gels and portlandite (Ca(OH) 2 ) mainly form from C 3 S hydration controlling the hydration evolution rate [24,25]. Accordingly, the E/VC/VL inhibits the hydration of C 3 S in cement paste during the acceleration period.…”