Hydration reactions in pastes C3S+C3A+CaSO4.2aq+water at 25°C. II

Variation of C₃A/C₃S ratio in pastes if C₃S+C₃A+CaSO₄.2aq+water influences the hydration reactions in a way compatible with retardation of C₃A hydration by amorphous Al (OH)₃, but not compatible with retardation by dissolved ions or by a “C₄AH₁₃” retarding layer.     

Tetracalcium aluminoferrite hydration in the presence of lime and gypsum

The influence of lime and/or gypsum on the C₄AF hydration was examined and the results were compared with those obtained for the C₃A hydration. Gypsum is more effective than CH in retarding the hydration of C₄AF. Ettringite produced in the C₄AF hydration in the presence of C$\text{S}$·H₂ seems to be more stable than that produced in the C₃AC$\text{S}$·H₂H₂ system. The consumption of gypsum, the transformation of ettringite into monosulfate and the hydration of C₄AF in the C₄AFC$\text{S}$·H₂H₂O system are much slower than those in the C₃AC$\text{S}$·H₂H₂O system. The retardation of hydration of C₄AF or C₃A in the presence of C$\text{S}$·H₂ is further increased by the add$\text{i}$tion of CH.     

Changes in C3S hydration in the presence of cellulose ethers

The influence of cellulose ethers (CE) on C₃S hydration processes was examined in order to improve our knowledge of the retarding effect of cellulose ethers on the cement hydration kinetics. In this frame, the impacts of various cellulose ethers on C₃S dissolution, C-S-H nucleation-growth process and portlandite precipitation were investigated. A weak influence of cellulose ethers on the dissolution kinetics of pure C₃S phase was observed. In contrast, a significant decrease of the initial amount of C-S-H nuclei and a strong modification of the growth rate of C-S-H were noticed. A slowing down of the portlandite precipitation was also demonstrated in the case of both cement and C₃S hydration. CE adsorption behavior clearly highlighted a chemical structure dependence as well as a cement phase dependence. Finally, we supported the conclusion that CE adsorption is doubtless responsible for the various retarding effect observed as a function of CE types.     

Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems

The impact of cellulose ethers (CE) on C₃A hydration was examined to support the understanding of the retarding effect of CE on cement hydration. In this sense, we successively studied the CE adsorption on ettringite and calcium hydroaluminates, and then the CE influence during C₃A hydration in presence or absence of calcium sulphate. We emphasized a phase-specific adsorption of CE depending on CE chemistry. Besides, in addition of CE, we highlighted a gradual slowing down of C₃A dissolution as well as ettringite and calcium hydroaluminates precipitation. Again, a great impact of CE chemistry and CE adsorption behaviour were noticed. Thus, HECs induce always a stronger adsorption on calcium hydroaluminates and a longer C3A hydration delays than HPMCs.     

Tricalcium aluminate hydration in the presence of lime,gypsum or sodium sulfate

The influence of Ca(OH)₂, CaSO₄·2H₂O and Na₂SO₄ on the C₃A hydration was examined in order to study the retardation mechanism of C₃A hydration caused by lime and/or gypsum additions. When C₃A hydrates in the presence of gypsum, the results do not confirm the retardation mechanism based on sulfate ions adsorption or C₄AH_x impervious coating. They substantially confirm the mechanism based on ettringite crystals coating C₃A grains. In the absence of gypsum C₃A hydration is retarded by C₄AH_x formation coating C₃A grains.     

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.     

Hydration reactions in pastes C3S + C3A + CaSO4 .2aq. + water at 25°C.III

Influences exerted by various additives, by changes in the water/solids ratio and by variations in C₃S/C₃A ratio at constant CaSO₄.2aq./C₃A ratio, are consistent with a retardation of the hydration of C₃A by local precipitation of amorphous Al(OH)₃.     

Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes

The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C₃S, C₂S, C₃A and C₄AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental ²⁹Si and ²⁷Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.     

Influence of the availability of calcium on the hydration of tricalcium aluminate (C3A) in seawater-mixed C3A–gypsum system

This work examined the effects of seawater (SW) on the hydration of tricalcium aluminate (C₃A) in C₃A–gypsum and C₃A–gypsum–Ca(OH)₂ systems through the characterization of hydration heat release, the evolution of aqueous phase composition and hydration products with the hydration time. It was found that SW increased the dissolution driving force of C₃A and solubility of gypsum, which accelerated the early hydration of C₃A and the formation of ettringite (AFt), leading to a higher hydration degree of C₃A at an early age compared with the deionized (DI) water–mixed pastes. After gypsum depletion to form AFt, and in the absence of Ca(OH)₂, the formation of chloroaluminate hydrates was slower due to the insufficient Ca resulted in an accumulation of Al in solution. This would delay the subsequent transformation of AFt to monosulfate (SO₄–AFm) and the formation of hydrogarnet (C₃AH₆), which would further reduce the hydration degree of the C₃A at the later ages. However, in the presence of Ca(OH)₂, the hydration degree of C₃A–gypsum–Ca(OH)₂ at later ages was increased, which was similar to that of the corresponding DI pastes. This can be inferred that the amount of Ca available in SW-mixed cement concrete can affect the hydration degree of C₃A in cement.     

The hydration of synthetic brownmillerite in presence of low Ca-sulfate content and calcite monitored by quantitative in-situ-XRD and heat flow calorimetry

We present here experimental data of the hydration of C₄AF in a Portland cement environment with low sulfate content. Calorimetric data indicate a distinct two-step main reaction of C₄AF, which was successfully deconvoluted by laboratory scale in-situ-XRD in combination with the G-factor method and a quantitative approach by mass balance estimation with normalized peak areas of hydrate phases. The presented data here suggest a rapid unhindered dissolution of C₄AF after depletion of sulfate in the pore solution, which is then rapidly leading to an oversaturation with respect to sulfate-AFm-16 (C₄A$H₁₆). Since the sulfate content of the mixture is low, a second acceleration of C₄AF dissolution, due to precipitation of hydroxy-AFm-19 (C₄AH₁₉) was observable after the decline in ettringite (C₆A$₃H₃₂) content and the subsequent conversion to sulfate-AFm-16 (C₄A$H₁₆).     

Influence of quartz surfaces on the reaction C3A + CaSO4.2H2O + water

Quartz surfaces counteract the retarding action of SO₄²- on the hydration of C₃A, by presenting additional sites for ettringite crystallization. Strong retardation requires the presence of ettringite near the C₃A, influencing the local concentrations there.     

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.     

Physicochemical effects of nanosilica on C3A/C3S hydration

In this paper, C₃A-gypsum and C₃A-C₃S-gypsum model cement systems with and without nanosilica were studied. The effects of nanosilica on the early stage cement hydration, particularly C₃A hydration, were assessed through the heat of hydration (isothermal calorimetry), phase assemblage (quantitative X-ray diffraction), zeta potential, ion concentration measurements, and morphology (scanning electron microscopy) examinations. The results indicate that while promoting C₃S hydration, nanosilica retarded C₃A hydration in both the systems studied. The retardation was caused by the adsorption and coverage of nanosilica on C₃A surfaces through the electrostatic interaction, thus decreasing the C₃A dissolution rate and hindering the precipitation of hydration products. Consequently, the reduced gypsum consumption rate and the seeding effect of nanosilica further promoted C₃S hydration. These findings suggest that nanosilica and other silica-based nanoparticles can physicochemically influence hydration of cement-based materials, and a better understanding of these influencing mechanisms can help optimize performances of nanoparticle-modified cement-based materials.     

Hydration of tetracalcium aluminoferrite in presence of lime and sulfates

The first part of the paper describes conduction calorimetric and SEM studies of the initial first hour hydration of C₄AF and C₃A with water and saturated solutions of lime, gypsum and gypsum with lime. Lime accelerates while gypsum and gypsum with lime strongly retard the hydration of C₄AF. In case of C₃A, the effect is less pronounced. The second part deals with the hydration of C₄AF at later stages in presence of various additives and the same results as above are obtained. Anhydrite has very little influence while the presence of C₃A reduces the effect of gypsum and hemihydrate on hydration of C₄AF. A detailed investigation of the hydration process by means of X-RD, DTA, SEM and calorimetry has also been made.     

Tricalcium aluminate hydration in the presence of calcium sulfite hemihydrate

This article reports on the study to evaluate the potential possibility of regulating the tricalcium aluminate (C₃A) hydration process by the addition of calcium sulfite hemihydrate. The kind and the form of hydration products were studied in the system: C₃A-CaSO₃·0.5H₂O-H₂O and C₃A-CaSO₃·0.5H₂O-Ca(OH)₂-H₂O by use of XRD, DTA and SEM/EDS methods as well as the kinetics of hydration along with chemical composition development of the liquid phase. The results thus obtained were compared to the hydration process of C₃A with the addition of natural gypsum. The results show that the reaction rate of C₃A with the addition of calcium sulfite hemihydrate differs from the analogous hydration process of C₃A in the presence of calcium sulfate dihydrate. Also, the kind of hydration products obtained in the presence of CaSO₃·0.5H₂O is different.     

Hydration of tricalcium aluminate in the presence of various amounts of calcium sulphite hemihydrate: Conductivity tests

Hydration of calcium aluminate C₃A (3CaO·Al₂O₃) in the presence of calcium sulphite hemihydrate (CaSO₃·0.5H₂O), with the molar ratio of substrates close to 1, produces the C₃A·CaSO₃·11H₂O calcium monosulphite aluminate phase. Small amounts of calcium sulphite added to calcium aluminate (the ratio of CaSO₃·0.5H₂O / C₃A equalling 0 : 1) change the rate of C₃A hydration and influence the whole reaction. Reaction processes for various ratios of the C₃A-CaSO₃·0.5H₂O mixture were examined in pure distilled water with a considerable amount of liquid W / S = 38-50 (constant W / C₃A). Processes in the liquid phase were monitored with conductivity equipment, and the XRD analysis was used to identify the phases precipitated during the examined reactions.     

Effect of CuO on the formation of clinker minerals and the hydration properties

The purposes of this study are to explore the mechanisms of Cu element in clinker burning and hydration processes and to make effective use of waste containing copper in cement production. The effect of CuO on clinker mineral composition, C₃S polymorph and size, Cu element distribution and state, compressive strengths, hydration products, non-evaporable water quantity and hydration heat release rate was analyzed by XRD, SEM, DTA, isothermal heat-conduction calorimetry, etc. Results show that as the amount of CuO increases the formation and growth of C₃S grain are accelerated, R C₃S is gradually transformed into M₃ and the content of C₄AF increases; a small quantity of CuO increases the 3-day and 28-day strengths and the hydration degree of clinker, but excessive CuO has adverse effects. Those effects of CuO on clinker burning process are attributed to the formation of low-melting Cu₂O and the dissolution of CuO in C₄AF which decrease the formation temperature of liquid phase and increase its quantity. The effects on hydration process result from the combined action of the following factors: the induction period is prolonged; the hydration reactions in the initial and acceleration periods are accelerated.     

The measurement of very early hydration reactions of portland cement clinker by a thermoelectric conduction calorimeter

The heat evolved from very early hydration reactions of portland cement can be measured with the isothermal thermoelectric conduction calorimeter. The cement compounds involved in these reactions are primarily C₃A, NC₈A₃, KC₈A₃, C₄AF, $\text{C}{}_4\text{A}{}_3\text{S}$, CaSO₄, C₃S, and CaO. This paper will describe design, operation and applications of the thermoelectric conduction calorimeter.     

Brownmillerite hydration in the presence of gypsum: The effect of Al/Fe ratio and sulfate ions

The brownmillerite, also known as tetracalcium aluminoferrite (C₄AF), represents a solid solution series of Ca₂(Al_yFe_(2–y))O₅ (0 ≥ y ≤ 1.33), which is one of the most important components in ordinary Portland cement. The hydration of brownmillerite in the presence of gypsum attracts massive attentions, but the hydration mechanism remains controversial nowadays. In particular, the influence of Al/Fe ratio on brownmillerite hydration with gypsum is obscure and out of favor. This paper studies the hydration characteristics of a binary system containing brownmillerite and gypsum with variables including two Al/Fe ratios and gypsum contents in an attempt to interpret the retarding mechanism of sulfate ions. When the molar ratio of brownmillerite to gypsum is 1.0, the hydration process of Ca₂(Al_1.3Fe_0.7)O₅ shows five distinct stages in the conductivity test, while only two stages are observed in the case of Ca₂(Al_1.0Fe_1.0)O₅. A decrease of Al/Fe ratio in brownmillerite leads to severe stagnation of the hydration process. When the molar ratio of Ca₂(Al_1.0Fe_1.0)O₅ to gypsum is increased to 2.7, the hydration is able to proceed and also displays five stages similar to Ca₂(Al_1.3Fe_0.7)O₅. An adsorption layer of sulfate ions on the surface of brownmillerite contributes to the postponement of brownmillerite hydration. In addition, the concentration of aluminum in the solution is the key to break this adsorption layer and dominate the hydration proceeding of brownmillerite.     

Etude de l'effet retardateur du zinc sur l'hydratation de la pate de ciment Portland

The retarding effect of zinc on the hydration of C₃S and C₃A, the two principal Portland cement components, has been investigated by X - ray diffraction. The results show that the C₃S retardation is more important than that of C₃A. This retardation is due to the precipitation of an amorphous layer of zinc hydroxide around the anhydrous grains. The effect of this coating depends on its permeability. The hydration reaction starts again through the transformation of the zinc hydroxide into the crystalline calcium zinc hydroxide Ca Zn₂ (OH)₆, 2H₂ O.