Search results for "Portlandite"
showing 5 items of 5 documents
A new view on the kinetics of tricalcium silicate hydration
2016
Abstract C3S hydration is an interesting example of chemical coupling between C3S dissolution, C–S–H and portlandite precipitation. It occurs because Ca2 +, OH− and silicate ions are present in C3S, in both hydration products and in the surrounding solution. Various experimental data sets reveal that the undersaturation with respect to C3S always increases when C3S hydration enters into the deceleratory phase, leading to the conclusion that C3S dissolution is at the origin of this deceleration, not C–S–H growth. In addition, as soon as portlandite precipitates, the dissolution limits the hydration already in the acceleratory hydration step. The evolution of the undersaturation cannot accoun…
The influence of an ion-exchange resin on the kinetics of hydration of tricalcium silicate
2010
The addition of a finely-ground ion-exchange resin makes it possible to modify the hydration kinetics of C3S pastes. Analyses of the liquid phase in pastes and more dilute suspensions show that the resin exchanges calcium ions for sodium ions very rapidly during the early stage of hydration and therefore the concentration of silica in solution increases. The resin impacts the hydration of C3S by other mechanisms which depends on the resin quantity added. For a high resin quantity, the induction period is very short, but the longer-term hydration is enhanced compared to a reference sample without resin. We hypothesize that the surface of the resin can provide sites for the nucleation and gro…
Aqueous Solubility Diagrams for Cementitious Waste Stabilization Systems. 4. A Carbonation Model for Zn-Doped Calcium Silicate Hydrate by Gibbs Energ…
2002
A thermodynamic Gibbs energy minimization (GEM) solid solution-aqueous solution (SSAS) equilibrium model was used to determine the solubility of Zn from calcium silicate hydrate (CSH) phases doped with 0, 0.1, 1, 5, and 10% Zn at a unity (Ca+Zn)/Si molar ratio. Both the stoichiometry and standard molar Gibbs energy (G(o)298) of the Zn-bearing end-member in the ideal ternary Zn-bearing calcium silicate hydrate (CZSH) solid solution were determined by a "dual-thermodynamic" (GEM-DT) estimation technique. The SSAS model reproduces a complex sequence of reactions suggested to occur in a long-term weathering scenario of cementitious waste forms at subsurface repository conditions. The GEM model …
Improvements in aggregate-paste interface by the hydration of steelmaking waste in concretes and mortars
2019
[EN] The objective of the experimental work is to study the mechanical properties in self-compacting concretes (SCC) in which part of the limestone aggregate has been replaced by granulated blast furnace slag (GBFS) in different percentages ranging from 0% to 60%. The results show that at early ages the SCC with the largest content in slag tend to have lower compressive strengths due to the poor compacting of the aggregates, although in the long-term their strength increases due to the reactivity of the slag. In fact, at the age of 365 days, the mortars made with the substitution of 50% of cement by ground GBFS reach compressive strength similar to that of the mortar made with 100% of cemen…
Portlandite solubility and Ca 2+ activity in presence of gluconate and hexitols
2021
The current paper investigates the impact of gluconate, D-sorbitol, D-mannitol and D-galactitol on calcium speciation at high pH values by i) solubility measurements of portlandite (Ca(OH)2) and ii) potentiometric titration measurements of calcium salt solutions. Thermodynamic modeling was used to fit the chemical activities of Ca2+ and OH- ions and thus to determine the strength and kind of the different Ca-organic-hydroxide complexes. The strength of complex formation with Ca decreases in the order gluconate >> sorbitol > mannitol > galactitol, which follows the same order as sorption on portlandite. Heteropolynuclear gluconate complexes with calcium and hydroxide dominate the…