Morphology and microstructure of hydrating portland cement and its constituents III. Changes in the hydration of a mixture of C3S,C3A and gypsum with and without triethanolamine and calcium lignosulphonate present

Systematic sequential observations with the electron microscope were made of the morphological changes which occurred during the hydration of a paste mixture of C₃S, C₃A and gypsum. It was found that this system produced hydration products similar in nature to those produced by the monomineral systems with gypsum present. The two organic admixtures studied had some effect on changes in morphology and microstructure of the hydrating mixture, but they showed a pronounced influence on the rate of the hydration processes.     

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. III. Hydration of tricalcium silicate alone and in the presence of tricalcium aluminate

The effect of carbonate and/or lignosulfonate on the hydration of C₃S alone and in the presence of C₃A has been examined by DTG and TG curves and by zeta potential measurements. The combined addition of sodium carbonate and lignosulfonate strongly retards C₃A hydration. However by mixing 20 % C₃A with C₃S the retarding effect is significantly lower. On the other hand the early C₃A hydration is completely blocked by sodium carbonate and lignosulfonate simultaneously added. It seems that the fluidifying effect of the combined addition of those admixtures could be ascribed to both the dispersing action and the completely blocking effect on the early C₃A hydration.     

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.     

Influence of lignosulphonate,glucose and gluconate on the C3A hydration

The influence of desugarized sodium lignosulphonate, glucose and sodium gluconate on the C₃A hydration has been examined using DTG analysis. At relatively low concentration levels of admixtures in the aqueous phase (1 to 3 g/l), such as those practically used for concrete mixes, lignosulphonate and glucose retard only slightly the C₃A hydration. Sodium gluconate is significantly more efficient in retarding C₃A hydration than lignosulphonate and glucose.     

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.     

Alkaline Hydration Of C2S and C3S

This study analyzed the behavior of two laboratory‐synthesized calcium silicates, C₃S and C₂S, after hydration in 8‐M NaOH and in water as a control. Two‐ and 28‐d mechanical strength values were determined and the products were characterized with XRD, TEM, and ²⁹Si and ²³Na MAS NMR. The results showed that hydrating C₃S in a highly alkaline medium had no significant effect on the mechanical development of the material, whereas in C₂S hydration, that medium hastened hydration substantially, impacting setting and hardening times. This finding has technological implications, given the low early‐age reactivity of dicalcium silicate under normal hydration conditions.     

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.     

The mechanism of the hydration in the system C3S-pozzolana

A mixture of five kinds of Japanese pozzolanas and synthesized pure C₃S were hydrated. The hydration mechanism in the system C₃S-pozzolana was investigated. The hydration of C₃S was accelerated by the addition of pozzolanas. The reasons for the acceleration increase of the precipitation sites of hydrates and the increase of the dissolution speed of C₃S caused by the depression of Ca²⁺ ionic concentration in the liquid phase was due to the addition of pozzolanas. The reaction between pozzolana and formed Ca(OH)₂ is pronounced after 1 to 3 days. Zonal hydrates existing between C₃S and pozzolana grains have Ca ionic concentration gradient from C₃S to pozzolana. It was often observed that in intact pozzolana grains which had no precipitated hydrates, there was clearance between pozzolanas and hydrates, and cast of trace. That tendency was pronounced in pozzolanas which had substantial alkalies. The mechanism of the hydration in the system C₃S-pozzolana was considered from those results.     

The influence of mineral admixtures on sulfate resistance of limestone cement pastes aged in cold MgSO4 solution

The influence of slag (S), fly ash (FA) and silica fume (SF) on the sulfate resistance of limestone cements was evaluated. Hardened pastes were exposed to MgSO₄ solution at 5 °C. Visible changes of the samples during the exposure were followed. Absorption of sulfate was measured and changes in mineralogical composition were evaluated by thermogravimetric analysis and X-ray diffraction (XRD). It was found that among admixtures used, only the addition of silica fume to limestone cement significantly improved its sulfate resistance. Cement with lower contents of C₃A and C₃S also showed favorable performance compared to cement having higher contents of these minerals.     

Effect of Temperature on C3S and C3S + Nanosilica Hydration and C–S–H Structure

This study aimed to monitor the effect of temperature and the addition of nanosilica on the nanostructure of the C–S–H gel forming during tricalcium silicate (C₃S) hydration. Two types of paste were prepared from a synthesized T₁ C₃S. The first consisted of a blend of deionized water and C₃S at a water/solid ratio of 0.425. In the second, a 90 wt% C₃S + 10 wt% of nanosilica blend was mixed with water at a water/solid ratio of 0.7. The pastes were stored in closed containers at 100% RH and 25°C, 40°C, or 65°C. The hydration reaction was detained after 1, 14, 28, or 62 d with acetone, and then pastes were studied by ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR).The main conclusion was that adding nSA expedites C₃S hydration at any age or temperature and modifies the structure of the C–S–H gel formed, two types of C–S–H gel appear. At 25°C and 40°C, more orderly, longer chain gels are initially (1 d) obtained as a result of the pozzolanic reaction between nSA and portlandite (CH) (C–S–H_II gel formation). Subsequently, ongoing C₃S hydration and the concomitant flow of dimers shorten the mean chain length in the gel.     

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.     

Hydration of polyphase Ca3SiO5-Ca3Al2O6 in the presence of gypsum and Na2SO4

Alite (Ca₃SiO₅: C₃S^*) and calcium aluminate (Ca₃Al₂O₆: C₃A) are the major phases in Portland cement, which have an essential role in the development of early age properties. The effects of gypsum content, fineness, and Na₂SO₄ addition on the early-stage hydration kinetics are investigated for polyphase (co-sintered) Ca₃SiO₅-Ca₃Al₂O₆ model systems using calorimetry, X- ray diffraction, thermal analysis, and solid-state ²⁷Al and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. The results demonstrate that the hydration of C₃A significantly affects the hydration of C₃S. The C₃S and C₃A hydration is hindered considerably in severely over-sulfated systems (where C₃A hydration is suppressed due to a very high gypsum content) and systems with additional Na₂SO₄. Although there is a considerable amount of Al incorporation in the C-S-H phase, no clear trends with respect to gypsum content, hydration age or Na₂SO₄ addition are observed for the Al_IV/Si ratios of the C-S-H phase determined from ²⁹Si NMR. With the addition of Na₂SO₄, recrystallization of ettringite from the AFm phases is postponed from 1 day to 7 days. *Cement chemistry notation: C-CaO, S-SiO₂, A-Al₂O₃, -SO₃, N-Na₂O.     

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.     

Crystal structure refinement and hydration behaviour of 3CaO·SiO2 solid solutions with MgO,Al2O3 and Fe2O3

In this paper, analytical evidence on crystal structure and hydration behaviour of 3CaO·SiO₂ (C₃S) solid solutions with MgO, Al₂O₃ and Fe₂O₃ is presented. Samples were prepared using an innovative sol–gel process as precursor. The Rietveld refinements of XRDs show significant changes in the crystal structures for C₃S solid solutions with MgO and Al₂O₃, but only small changes for Fe₂O₃. Low concentrations of MgO do not change the hydration of C₃S, but 1.4 wt.% increases the reactivity after some days. With Al₂O₃ the initial and long-term hydration is activated, but the main reaction of C₃S decreases. Fe₂O₃ retards the hydration for several days, the long-term reaction is not affected or even activated. Altogether changes in hydration activity are more dominated by the type of oxide than by the height of changes in lattice parameters. The results can help to interpret the reactivity of different Portland cements and improve the quality control of the cement production.     

Modification of Dicalcium Silicates Phase Composition by BaO, SO3 and MgO

Minor components can affect the hydration activity of dicalcium silicates (C₂S) through the modification of its phase composition. In this paper, the influences of BaO, SO₃ and MgO on burnability and phase composition of belite have been investigated. The results showed that SO₃ could significantly decrease the f-CaO content of C₂S due to the substitution of [SiO₄]^4? by [SO₄]^2?, accelerate the formation of C₂S and effectively stabilize β-C₂S. Different from SO₃, BaO and MgO would increase the f-CaO content due to the substitution of Ca²⁺ by Ba²⁺ or Mg²⁺. Meanwhile, in the aspects of promoting C₂S formation and stabilizing its high activity crystal, the effect of BaO or MgO was lower than SO₃. SEM showed that belite clinker with SO₃ was spherical-shaped and its size was in the range of 2–5 μm.     

Tricalcium silicate (C3S) hydration under high pressure at ambient and high temperature (200 °C)

The hydration of a tricalcium silicate paste at ambient temperature and at 200 °C under high pressure (up to 1000 bar) has been studied. Two high pressure cells have been used, one allows in-situ electrical conductivity measurements during hydration under high pressure. The hydration products were characterized by thermal analysis, X-ray diffraction and ²⁹Si NMR measurements. The pressure has a large kinetic effect on the hydration of a C₃S paste at room temperature. The pressure was seen to affect drastically the hydration of a C₃S paste at 200 °C and this study evidences the competition between the different high temperature phases during the hydration.     

Mineral admixtures in mortars: Quantification of the physical effects of inert materials on short-term hydration

This work is the second part of an overall project, the aim of which is the development of general mix design rules for concrete containing different kinds of mineral admixtures. The first part presented the separation of the different physical effects responsible for changes in cement hydration when chemically inert quartz powders are used in mortars. This second part describes the development of an empirical model, based on semiadiabatic calorimetry measurements, which leads to the quantification of the enhancement of cement hydration due to the heterogeneous nucleation effect at short hydration times. Experimental results show that not all the admixture particles participate in the heterogeneous nucleation process. Consequently, the concept of efficient surface S_eff is introduced in the model. S_eff is the total admixture surface S (m² of mineral admixture/kg of cement) weighted by a function ξ(p). The efficiency function ξ(p) depends only on the replacement rate p and is independent of time, fineness and type of mineral admixture used. It decreases from 1 to 0: Low replacement rates give an efficiency value near 1, which means that all admixture particles enhance the hydration process. An efficiency value near 0 is obtained for high replacement rates, which indicates that, from the hydration point of view, an excess of inert powder does not lead to an increase in the amount of hydrates compared with the reference mortar without mineral admixture. The empirical model, which is mainly related to the specific surface area of the admixtures, quantifies the variation of the degree of hydration induced by the use of inert mineral admixtures. One application of the model, coupled with Powers' law, is the prediction of the short-term compressive strength of mortars.