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Showing papers on "Ettringite published in 2012"


Journal ArticleDOI
TL;DR: In this paper, the coupled substitution of metakaolin and limestone in Portland cement (PC) was investigated and the mechanical properties were studied in mortars and the microstructural development in pastes by X-ray diffraction, thermogravimetry analysis, mercury intrusion porosimetry and isothermal calorimetry.

763 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the heat released during the hydration of a commercial Ordinary Portland Cement can be assigned mainly to three mechanisms, the silicate reaction (sum of dissolution of alite and precipitation of C-S-H-phase and portlandite), the dissolution of C3A, and the precipitation of ettringite.

265 citations


Journal ArticleDOI
TL;DR: In this article, three CSAB cements synthesized from reagent-grade chemicals with varied phase compositions were examined for dimensional stability in water and sulfate solutions, and the interdependent effects of C 4 A 3 ε (Ye'elimite) content, calcium sulfate content, water-to-cement ratio, and particle fineness were evaluated.

206 citations


Journal ArticleDOI
TL;DR: In this paper, the phase assemblage, kinetics and microstructural development of C(3)A-gypsum systems with different gypsum additions were investigated in terms of phase assembly, phase formation, and kinetics.

192 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the hydration process and the mortar properties of samples containing calcium sulphoaluminate clinker and gypsum combined with quartz filler or limestone filler.

161 citations


Journal ArticleDOI
TL;DR: In this article, the hydration of a low-alkali cement based on CEM III/B blended with 10% of nanosilica has been studied, and the pore water composition revealed ten times lower alkali concentrations than in Portland cements.

151 citations


Journal ArticleDOI
TL;DR: Sulfate sorption on limestone seems to be an alternative to treating mine waters with sulfate concentrations below the 1200-2000mg/L range, where lime precipitation is not effective, and this approach does not require alkaline pH values, as in the ettringite process.

104 citations


Journal ArticleDOI
01 Aug 2012-Fuel
TL;DR: In this article, the self-cementing process of CFBC fly ash paste is based on three main reactions: (1) generation of Ca(OH)2 micelles by quick slaking of lime, (2) generating of ettringite (AFt), hydrated calcium silicate (CSH), portlandite, and gypsum.

95 citations


Journal ArticleDOI
Abstract: Calcium sulfoaluminate (CSA) cements are currently receiving a lot of attention because their manufacture produces less CO2 than ordinary Portland cement (OPC). However, it is essential to understand all parameters which may affect the hydration processes. This work deals with the study of the effect of several parameters, such as superplasticizer (SP), gypsum contents (10, 20 and 30 wt.%) and w/c ratio (0.4 and 0.5), on the properties of CSA pastes during early hydration. This characterization has been performed through rheological studies, Rietveld quantitative phase analysis of measured X-ray diffraction patterns, thermal analysis and mercury porosimetry for pastes, and by compressive strength measurements for mortars. The effect of the used SP on the rheological properties has been established. Its addition makes little difference to the amount of ettringite formed but strongly decreases the large pore fraction in the pastes. Furthermore, the SP role on compressive strength is variable, as it increases the values for mortars containing 30 wt.% gypsum but decreases the strengths for mortars containing 10 wt.% gypsum.

93 citations


Journal ArticleDOI
TL;DR: In this paper, a method that accelerates the ettringite formation in concrete has been used to study the impact of cement properties on DEF, and the results showed that delayed ettricite formation is likely to lead to swelling and cracking in structures which have undergone eartly age heating to a temperature of over 65°c.
Abstract: Delayed ettringite formation in concrete is likely to lead to swelling and cracking in structures which have undergone eartly age heating to a temperature of over 65°c. Application of a method that accelerates this process has made it possible to study the impact of cement properties on DEF.

92 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of ettringite at lower temperatures in the Portland cement/calcium aluminate cement, and the effect of calcium sulfate variety on the setting time of the ternary system and the strength development of its mortars at 0, 5, 10 and 20°C were investigated.

Journal ArticleDOI
TL;DR: In this article, the self-cementitious properties and pozzolanic reactivity of CFBC desulfurization ashes (CFBCA), modified CFBCAs (MCFBCAs), and pulverized fuel fly ash (PFA) are investigated.

Journal ArticleDOI
TL;DR: Stress-strain simulations are performed to find that Ca-O bonds are responsible for failure of the calcium sulfate and tricalcium aluminate column in ettringite during uniaxial compression and tension and that hydrogen bond re-formation during compression induces an increase in plastic strain beyond the material's stress-strains proportionality limit.
Abstract: Ettringite is a hexacalcium aluminate trisulfate hydrate mineral that forms during Portland cement hydration. Its presence plays an important role in controlling the setting rate of the highly reactive aluminate phases in cement paste and has also been associated with severe cracking in cured hardened cement. To understand how it forms and how its properties influence those of hardened cement and concrete, we have developed a first-principles-based ReaxFF reactive force field for Ca/Al/H/O/S. Here, we report on the development of this ReaxFF force field and on its validation and application using reactive molecular dynamics (RMD) simulations to characterize and understand the elastic, plastic, and failure response of ettringite at the atomic scale. The ReaxFF force field was validated by comparing the lattice parameters, pairwise distribution functions, and elastic constants of an ettringite crystal model obtained from RMD simulations with those from experiments. The predicted results are in close agreement with published experimental data. To characterize the atomistic failure modes of ettringite, we performed stress–strain simulations to find that Ca–O bonds are responsible for failure of the calcium sulfate and tricalcium aluminate (C3A) column in ettringite during uniaxial compression and tension and that hydrogen bond re-formation during compression induces an increase in plastic strain beyond the material’s stress–strain proportionality limit. These results provide essential insight into understanding the mechanistic role of this mineral in cement and concrete degradation, and the ReaxFF potential developed in this work serves as a fundamental tool to further study the kinetics of hydration in cement and concrete.

Journal ArticleDOI
TL;DR: In this article, a one-dimensional differential equation related to the diffusion reaction behavior of sulfate ions in concrete is presented, and based on chemical reactions between sulfate and calcium aluminates in concrete, the expansive volume strain caused by ettringite growth is analyzed.

Journal ArticleDOI
TL;DR: The chemical evolution of two hydrated low pH binders prepared from binary or ternary mixtures was characterized over one year at 20°C, 50°C and 80°C as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the effect of limestone and calcium sulfate content on sulfate resistance of ground granulated blast furnace slag (GGBS) blended cement was evaluated using ASTM C 1012, and a variety of mechanisms of the sulfate resilience of GGBS blended cement were revealed by the analyses of hydration products and sulfate ion ingress.

Journal ArticleDOI
TL;DR: In this paper, an investigation was performed on the improvement of properties for commercial hemihydrate by means of low additions of granulated blast furnace slag and pozzolanas like silica fume or fly ash.

Journal ArticleDOI
TL;DR: Results show that higher water/binder (W/B) is required to keep the consistency when increasing the percentage of FGD gypsum, and Scanning electron microscopy and X-ray diffraction results indicate that massive ettringite crystals and C-S-H gels exist in the hydration products.

Journal ArticleDOI
TL;DR: In this article, pore solution expression test was conducted to squeeze pore solutions of different parts of cement paste partially exposed to Na 2 SO 4 solution, and the sulfate concentration and pH value of pore mixture were measured.

Journal ArticleDOI
TL;DR: In this paper, a laboratory study on the deterioration of blended cement combinations of plain Portland cement (PPC) with red brick dust (RBD) and ground basaltic pumice (GBP) is presented.
Abstract: This paper presents a laboratory study on the deterioration of blended cement combinations of plain Portland cement (PPC) with red brick dust (RBD) and ground basaltic pumice (GBP). One type of clinker, same Blaine values and two different proportions of additive by mass of clinker, were employed. In addition to these blends, Portland cements without additives were prepared as control specimens. The compressive strength and the sulphate resistance of cements have been experimentally studied in this paper. A series of laboratory tests were undertaken on all specimens. A large quantity of sheet-like C–S–H was found in the mortars incorporating RBD and GBP. The results indicated that the increase in the additive content caused a significant increase in the sulphate resistance of the mortars. Hence, the studied RBD and GBP can be recommended for use as admixtures in cement production. The development of the particular microstructure including the secondary minerals in the plain and blended cements were studied via SEM analysis. SEM images revealed the presence of ettringite and Portlandite minerals, where the former was most probably responsible for the increase (together with the gypsum roses) as well as a decrease of strength based on its formation at different sites and crystal form. Portlandite was responsible for an increase in the specimen strength.

Journal ArticleDOI
TL;DR: In this article, the sulfate resistance of white Portland cement (WPC) containing 0, 50% or 70% granulated blast-furnace slag as a partial cement replacement was investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the resistance of Triclinic-C3S, grey and white Portland cement paste to decalcification induced by accelerated leaching in concentrated ammonium nitrate solutions.
Abstract: This study compared the resistance of Triclinic-C3S, grey (OPC) and white (WOPC) Portland cement paste to decalcification induced by accelerated leaching in concentrated ammonium nitrate solutions. Paste microstructure was studied with scanning and backscattering electron microscopy (SEM and BSEM) and nitrogen BET surface area techniques. Ca2+ leached content was quantified by ICP, XRD and FTIR techniques were used to study phase mineralogy. The conclusions drawn from the findings were that calcium leaching-induced decay in the cementitious materials studied (C3S, OPC and WOPC), accelerated by immersion in ammonium nitrate, affected the main calcium phases in the samples (CH, C–S–H gel and ettringite), i.e., both the anhydrous and the hydrated phases. The present study showed that the Ca/Si ratio of C–S–H gels declines on a gradient from the sample core outward. Specimen surface area and nanoporosity rose in cementitious materials after Ca leaching-induced decay and subsequently declined as a result of the collapse of the structure of the hydrated cement, and in particular of the C–S–H gel. C3S paste was impacted more quickly and intensely by leaching than the WOPC and OPC pastes. Further to the findings of this study, the leaching resistance of these three materials, in descending order, is: OPC > WOPC > C3S.

Journal ArticleDOI
TL;DR: In this paper, a petrographic examination of concrete core samples was carried out using a combination of tools including: stereomicroscopic evaluation, polarized light microscopy, scanning electron microscopy and X-ray diffraction and electron microprobe analysis.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the microstructures of adobes, manufactured with clayey soil containing an important amount of quartz and stabilised with cement up to 12% by weight, with X-ray diffraction, infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometric.
Abstract: Microstructures of adobes, manufactured with clayey soil containing an important amount of quartz and stabilised with cement up to 12% by weight, were investigated with X-ray diffraction, infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometry. The water absorption and mechanical (compressive and flexure strengths) characteristics of specimens elaborated with these mixtures were also measured. Cement additions resulted in the formation of calcium silicate hydrate (CSH) type tobermorite, portlandite, ettringite, iron oxyhydroxide and calcite. The CSH was formed through the hydration of anhydrous cement compounds (alite and belite). The formation of CSH through pozzolanic reaction, requiring kaolinite (unique clay minerals) and tiny quartz (obtained with the same material mixed of quicklime) is negligible. Moreover, CSH marked crystallisation with curing time contributed to the improvement of mechanical properties. The cement stabilised adobes comprised of 4–12% by weight cement, immersed for 4 days, were still suitable as building materials according to the required standards. This study concludes that for cement stabilised adobes, clayey soils containing an important amount of quartz were suitable soils for manufacturing resistant and durable adobes.

Journal ArticleDOI
TL;DR: In this paper, solid sorbents containing ettringite, Ca6Al2(SO4)3(OH)12·26H2O, were prepared from concrete sludge by adding various amounts of aluminum sulfate to enhance ettricite formation.

Journal ArticleDOI
TL;DR: In this article, the carbonation processes of ettringite and calcium aluminate hydrates phases developed by hydration of calcine cement, fly ash and calcium sulphate ternary mixtures have been studied.
Abstract: The carbonation processes of ettringite and calcium aluminate hydrates phases developed by hydration of calcium aluminate cement, fly ash and calcium sulphate ternary mixtures have been studied. The hydrated samples were submitted to 4% of CO2 in a carbonation chamber, and were analysed, previous carbonation and after 14 and 90 days of carbonation time, by infrared spectroscopy and X-ray diffraction; the developed morphology was performed with the 14 days carbonated samples. The results evidenced that ettringite reacts with CO2 after 14 days of exposition time and evolves totally at 90 days; the developed hydrated phases C3AH6 in samples with major CAC content, also reacts with CO2. Due to carbonation, calcium carbonate – mainly vaterite but also aragonite-, depending on the initial formulation, aluminium hydroxide and gypsum were detected.

Journal ArticleDOI
TL;DR: In this article, a novel aluminate 12CaO⋅7Al2O3 was prepared as accelerator in order to improve the performance of cement-based solidification/stabilization (S/S).

Journal ArticleDOI
TL;DR: In this paper, the effect of C 3 A content on sulfate resistance of limestone incorporated cements has been investigated within the scope of a study, and it was shown that increasing C 3A content propagate the deterioration rate of limestone blended cement mortars exposed to both Na 2 SO 4 and MgSO 4 solutions.

Journal ArticleDOI
TL;DR: In this paper, the pore structure of concrete incorporating metakaolin (MK) was characterized when exposed to two types of curing conditions, seawater and fresh water, respectively, and the influence of MK, carbonation and curing conditions on thermodynamic stability of hydrate phases were further investigated.

Journal ArticleDOI
TL;DR: In this paper, the crystal structure and properties of ettringite under pressure were modeled using density functional theory and a change in slope was predicted for all the lattice parameters versus pressure at about 2.5 GPa.
Abstract: Ettringite is a rare mineral with high-water content, more than half of its weight, and a relevant secondary product in Portland cement. Using density functional theory, we simulate the crystal structure and properties of ettringite under pressure. Our calculations predict a change in slope for all the lattice parameters versus pressure at about 2.5 GPa. Above such pressure, the elastic properties show a drastic increase of nearly 80% in the bulk modulus. This finding is explained in terms of a concurrent amorphization and densification of the hydrogen bond network. At low pressures, ettringite can be compressed substantially without significant repulsion in the hydrogen bond network. At high pressures, the hydrogen bonds become stiff, and their contribution to the total repulsion is then important. These changes are also supported by the evolution on the electronic density of ettringite with pressure.