Combined effect of lignosulfonate and carbonate on pure portland clinker compounds hydration. V. Hydration of dicalcium silicate alone and in the presence of tricalcium aluminate

The effect of sodium carbonate and/or sodium lignosulfonate on the hydration of C₂S alone and in the presence of C₃A has been examinated by DTG and TG curves and by zeta potential measurements. The combined addition of sodium carbonate and lignosulfonate retards the C₂S hydration to a lower extent than that observed for the C₃S hydration. The retarding effect on the C₂S hydration is significantly lower in the presence of 20% C₃A. On the other hand, the early C₃A hydration is completely blocked by admixtures simultaneously added. Addition of 0.9% sodium carbonate without lignosulfonate blocks the early hydration of both C₃A and C₂S. This effect was not found in the C₃SC₃A system.     

Combined effect of lignosulfonate and carbonate on pure portland clinker compounds hydration. IV. Hydration of tricalcium aluminate-sodium oxide solid solution

The combined effect of lignosulfonate and sodium carbonate on the hydration of C₃A and C₃ANa₂O solid solution was examined by DTG and TG curves, by XRD analysis and by zeta potential measurements. It is confirmed that the simultaneous addition of lignosulfonate and carbonate completely blocks the C₃A hydration with an induction period whose length is proportional to the percentage of admixtures. On the other hand, no induction period was observed in the hydration of C₃ANa₂O solid solution in the presence of both lignosulfonate and carbonate. The effect of the admixtures on the zeta potential is substantially the same for C₃A and C₃ANa₂O solid solution. The liquefying effect of NC and lgs combined addition seems to be more pronounced on C₃A than on C₃ANa₂O solid solution.     

Combined effect of lignosulfonate and carbonate on pure portland clinker compounds hydration II. Tricalcium aluminate hydration

The effect of the combined addition of sodium lignosulfonate and sodium carbonate on the C₃A hydration was studied. XRD analysis, zeta potential measurements, DTG and TG curves were carried out. The influence of the combined presence of lignosulfonate and carbonate on the C₃A hydration is very similar to that found for the C₄AF hydration examined in a previous paper. The liquefying effect of the admixtures could be ascribed to both a strong retarding action and a dispersing effect caused by the change in the zeta potential.     

Combined effect of lignosulfonate and carbonate on pure portland clinker compounds hydration. I. Tetracalcium aluminoferrite hydration

The combined effect of sodium lignosulfonate and sodium carbonate on the C₄AF hydration was examined by DTG and TG curves and by zeta potential measurements. In the presence of lignosulfonate-carbonate systems the C₄AF hydration is completely blocked. The higher the percentage of admixtures, the longer is this induction period. Moreover a strong change in the zeta potential is caused by the simultaneous addition of lignosulfonate and carbonate. Both the strong retarding action and the dispersing effect caused by the change in the zeta potential could explain the liquefying effect of the admixtures. After the induction period the C₄AF hydration is strongly accelerated by the lignosulfonate-carbonate system.     

The influence of an ion-exchange resin on the kinetics of hydration of tricalcium silicate

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 growth of C-S-H hydrates and/or portlandite far away from the surface of the C₃S grains. This consequently increases the quantity of hydrates that can precipitate before a continuous hydrate layer forms over the surfaces of C₃S particles.     

New insights into tricalcium silicate hydration in paste

The knowledge of the aqueous phase composition during the hydration of tricalcium silicate (C₃S) is a key issue for the understanding of cement hydration. A new in situ method of computing calcium ion concentration from the measurement of the electrical conductivity on paste was coupled to isothermal calorimetry and BET measurements to get new insights on the early hydration of C₃S. Ion concentrations of the aqueous phase are mainly dependent on the degree of hydration and the water to C₃S ratio. In the case of C₃S paste, the calcium and silicon concentrations determined at low degrees of hydration can be related to the equilibrium curve of C-S-H having C/S = 1.27 and named C_1.27SH_y. It is expected that C_1.27SH_y thermodynamically controls the aqueous phase composition at this early stage. Indeed, the formation of C_1.27SH_y is quasi-immediate when C₃S is in contact with water inducing a very rapid increase of the specific surface area that remains constant during the induction period. At higher degrees of hydration, the aqueous phase composition departs from the C_1.27SH_y equilibrium curve. C_1.27SH_y appears to be a metastable C-S-H that could be related to an intermediate phase previously reported. The quasi-immediate precipitation of C_1.27SH_y on C₃S surface explains why calcium and silicon concentrations remain low during early hydration even though C₃S is strongly undersaturated. This also agrees with the control of the end of the induction period by the nucleation and growth of more stable C-S-H.     

Early hydration of cement constituents with organic admixtures

The hydration of C₂S, C₃S, C₃A, C₄AF and type 1 portlant cement in the presence of calcium lignosulfonate and salicylic acid was studied at a high(20/1) water-cement ratio. The effect of these admixtures on the development, microstructure and surface area of the hydration products was investigated.     

Early hydration of tricalcium silicate II. The induction period

The initial hydration of C₃S was found to be stimulated by adding to the paste prehydrated C₃S and by lowering the Ca⁺⁺ concentration of the liquid phase with oxalic acid. An addition of crystalline calcium hydroxide did not alter the duration of the induction period. Based on these findings the origin of the induction period in C₃S hydration is discussed.     

Combined hydration of tricalcium silicate and β-dicalcium silicate

The mutual interaction of tricalcium silicate (C₃S) and β-dicalcium silicate (β-C₂S) in their combined hydration was studied. The rate of β-C₂S hydration was accelerated significantly in the presence of C₃S. The rate of C₃S hydration was retarded, but only in the presence of large amounts of β-C₂S. The stoichiometric composition and the pore structure of the hydrates formed was altered only unsignificantly when both compound hydrated simultaneously.     

Effect of barium on the formation of tricalcium silicate

The effect of barium carbonate on the kinetics of tricalcium silicate formation has been studied. Burnability study of mixes of calcium carbonate and quartz in 3:1 ratio and barium carbonate equivalent to 0.5 to 4% BaO by weight showed accelerated rate of clinkerisation through mineralising action. The addition of BaCO₃ significantly reduced the time and temperature of formation of C₃S. At 1450°C up to 1.85% BaO could be assimilated in forming solid solution of C₃S. With up to 2% BaO triclinic form and 4% BaO, monoclinic form of C₃S was stabilised. The solubility of BaO in C₃S at 1450°C was investigated using chemical analysis (estimation of free lime) and energy dispersive analysis of X-rays. The limit of solubility is found to be 1.85% (by weight) at 1450°C. Above the solubility limit, BaO formed Ba₃SiO₅ at 1450°C.     

Hydration of tricalcium silicate

Results of following the quantities of free Ca(OH)₂ and of tricalcium silicate (C₃S) during the hydration of C₃S, and also the influence of the presence of free CaO on this reaction are in accordance with the hypothesis of Stein & Stevels with regard to the hydration of C₃S. at the first contact between C₃S and water, a surface hydrate, invisible by electron microscope methods, is considered to be formed and to retard the reaction strongly. This hydrate is thought to change into one which retards the hydration reaction less and changes later into a third hydrate, tobermorite gel.     

Hydrothermal stability of vinyl-type polymer concrete containing tricalcium silicate (C3S)

Infrared analysis (IR) studies and measurements of the mechanical and physical properties of vinyl-type polymer concrete (PC) containing tricalcium silicate (C₃S) as a constituent of the inorganic phase were performed after exposure of the composite to a 25% simulated geothermal brine at 240°C. The purpose of the study was to determine the physical effects and the chemical reaction mechanism produced by the apparent interactions between the vinyl-type polymers, C₃S, and the hydration products of C₃S. Infrared analysis indicated that ionic bonding between carboxylate anion (?COO^θ) groups in the polymer produced by the hydrothermal reaction and Ca²⁺ ions of C₃S occurred. The addition of silica flour, calcium carbonate, and calcium hydroxide to the filler system did not produce results similar to those produced by the C₃S.     

Influence of precuring on high pressure steam hydration of tricalcium silicate II. Effect of fineness of tricalcium silicate

C₃S samples of different fineness were precured at room temperature and subsequently autoclaved. It was found that, as the fineness is increased: 1) the effect of precuring on the hydration rate of C₃S in autoclave is less evident; 2) the precuring time corresponding to the highest amount of C₃SH_1.5 becomes longer; 3) particularly for short precuring times, the quantity of C₃SH_1.5 decreases and the formation of α-C₂SH is favored; 4) the amounts of the two crystalline hydrated silicates are reduced while the formation of CSH is favored.     

Influence of tricalcium aluminate on the microstructure evolution of CaO specimen during hydration

C₃A-containing CaO specimen was prepared and the evolution of its microstructure during hydration process was investigated to clarify the protective mechanism of tricalcium aluminate (C₃A) on hydration resistance of CaO specimen. The slit-shaped micropores were formed on the grain boundary of CaO due to the stacking of lamellar C₄AH₁₃ formed by the hydration of C₃A. The contact area of residual C₃A with the moisture was reduced by the porous C₄AH₁₃ layer at the original site, which resulted in a slower dissolution rate of C₃A grain through the porous layer. In addition, the crack propagation and the formation of macropores were inhibited by the pinning effect of C₄AH₁₃, which was beneficial to the improvement of hydration resistance.     

Influence of size-classified and slightly soluble mineral additives on hydration of tricalcium silicate

Early-age hydration of cement is enhanced by slightly soluble mineral additives (ie, fillers, such as quartz and limestone). However, few studies have attempted to systematically compare the effects of different fillers on cementitious hydration rates, and none have quantified such effects using fillers with comparable, size-classified particle size distributions (PSDs). This study examines the influence of size-classified fillers [ie, limestone (CaCO₃), quartz (SiO₂), corundum (Al₂O₃), and rutile (TiO₂)] on early-age hydration kinetics of tricalcium silicate (C₃S) using a combination of experimental methods, while also employing a modified phase boundary and nucleation and growth model. In prior studies, wherein fillers with broad PSDs were used, it has been reported that between quartz and limestone, the latter is a superior filler due to its ability to partake in anion-exchange reactions with C-S-H. Contrary to prior investigations, this study shows that when size-classified and area matched fillers are used—which, essentially, eliminate degrees of freedom associated with surface area and agglomeration of filler particulates—the filler effect of quartz is broadly similar to that of limestone as well as rutile. Results also show that unlike quartz, limestone, and rutile—which enhance C₃S hydration kinetics—corundum suppresses hydration of C₃S during the first several hours after mixing. Such deceleration in C₃S hydration kinetics is attributed to the adsorption of aluminate anions—released from corundum's dissolution—onto anhydrous particulates’ surfaces, which impedes both the dissolution of C₃S and heterogeneous nucleation of C-S-H.     

Time dependent driving forces and the kinetics of tricalcium silicate hydration

Simulations of tricalcium silicate (C₃S) hydration using a kinetic cellular automaton program, HydratiCA, indicate that the net rate depends both on C₃S dissolution and on hydration product growth. Neither process can be considered the sole rate-controlling step because the solution remains significantly undersaturated with respect to C₃S yet significantly supersaturated with respect to calcium silicate hydrate (C–S–H). The reaction rate peak is attributed to increasing coverage of C₃S by C–S–H, which reduces both the dissolution rate and the supersaturation of C–S–H. This supersaturation dependence is included in a generalized boundary nucleation and growth model to describe the kinetics without requiring significant impingement of products on separate cement grains. The latter point explains the observation that paste hydration rates are insensitive to water/cement ratio. The simulations indicate that the product layer on C₃S remains permeable; no transition to diffusion control is indicated, even long after the rate peak.     

Early hydration of tricalcium silicate I. Kinetics of the hydration process and the stoichiometry of the hydration products

The initial hydration of C₃S in paste form at room temperature was studied. The process is initiated by a short lasting rapid hydration in which about 1 – 2% of C₃S is hydrated and a hydrate with low C/S and high H/S ratio is formed. After a subsequent induction period of 4 hours a renewed rapid hydration is observed in which a hydrate of constant stoichiometric composition, independent on the time of hydration is formed. This hydrate has a higher C/S and lower H/S ratio than the one formed initially. The liquid phase stays supersaturated with respect to calcium hydroxide for several hours after the induction period is terminated.     

Influence of triethanolamine on the hydration characteristics of tricalcium silicate

The hydration characteristics of 3CaO.SiO₂ or β2CaO.SiO₂ are studied by an addition of 0.0, 0.1, 0.5 or 1.0% triethanolamine. The amount of Ca(OH)₂ found at 1, 3, 7 or 28 days was in the order C₃S + 0% TEA > C₃S +0.1% TEA > C₃S + 0.5% TEA > C₃S+1.0% TEA, irrespective of whether lime was estimated by X-ray, DTA, TGA or chemical analysis. The rate of hydration, in terms of the disappearance of 3CaO.SiO₂, showed that hydration proceeded faster in the presence of TEA after 1 day. Additions of TEA increase the induction period, promote the formation of a C-S-H with higher CaO/SiO₂ ratio, increase the formation of non-crystalline Ca(OH)₂ and enhance the surface area of the hydrated silicate product.     

Influence of pozzolanic additives on hydration mechanisms of tricalcium silicate

Pozzolanic mineral additives, such as silica fume (SF) and metakaolin (MK), are used to partially replace cement in concrete. This study employs extensive experimentation and simulations to elucidate and contrast the influence of SF and MK on the early age hydration rates of tricalcium silicate (triclinic C₃S), the major phase in cement. Results show that at low replacement levels (i.e., ≤10%), both SF and MK accelerate C₃S hydration rates via the filler effect, that is, enhanced heterogeneous nucleation of the main hydration product (C–S–H: calcium‐silicate‐hydrate) on the extra surfaces provided by the additive. The filler effect of SF is inferior to that of MK because of agglomeration of the fine particles of SF, which causes significant reduction (i.e., up to 97%) in its surface area. At higher replacement levels (i.e., ≥20%), while SF continues to serve as a filler, the propensity of MK to allow nucleation of C–S–H on its surface is substantially suppressed. This reversal in the filler effect of MK is attributed to the abundance of aluminate [Al(OH)₄^?] ions in the solution—released from the dissolution of MK—which inhibit topographical sites for C–S–H nucleation and impede its subsequent growth. Results also show that in the first 24 hours of hydration, MK is a superior pozzolan compared to SF. However, the pozzolanic activities of both SF and MK are limited and, thus, do not produce significant alterations in the early age hydration kinetics of C₃S. Overall, the outcomes of this study provide novel insights into the mechanistic origins of the filler and pozzolanic effects of SF and MK, and their impact on cementitious reaction rates.     

The effect of pressure on tricalcium silicate hydration at different temperatures and in the presence of retarding additives

The hydration of tricalcium silicate (C₃S) is accelerated by pressure. However, the extent to which temperature and/or cement additives modify this effect is largely unknown. Time-resolved synchrotron powder diffraction has been used to study cement hydration as a function of pressure at different temperatures in the absence of additives, and at selected temperatures in the presence of retarding agents. The magnitudes of the apparent activation volumes for C₃S hydration increased with the addition of the retarders sucrose, maltodextrin, aminotri(methylenephosphonic acid) and an AMPS copolymer. Pressure was found to retard the formation of Jaffeite relative to the degree of C₃S hydration in high temperature experiments. For one cement slurry studied without additives, the apparent activation volume for C₃S hydration remained close to ~ ? 28 cm³ mol^? 1 over the range 25 to 60 °C. For another slurry, there were possible signs of a decrease in magnitude at the lowest temperature examined.