Showing papers on "Ettringite published in 1999"
TL;DR: In this article, the thermal behavior of hydration products in ordinary Portland cement as a function of age was investigated using differential scanning calorimeter (DSC) and X-ray diffraction analysis.
228 citations
TL;DR: Calcium sulfoaluminate, C4A3S or CSA, often known as Klein s compound, can be readily synthesized as a single phase at about 1300°C and is also formed along with belite and a ferrite phase when limestone is reacted with various minerals or waste products at 1200°C as discussed by the authors.
Abstract: Calcium sulfoaluminate, C4A3S or CSA, often known as Klein s compound, can be readily synthesized as a single phase at about 1300°C. It is also formed along with belite and a ferrite phase when limestone is reacted with various minerals or waste products at 1200–1300°C. The presence of CSA can lead to early strength development, and such systems may be regarded as low-energy cements, providing environmental benefits, notably emission of less carbon dioxide than in the production of Portland cement. Under controlled, specified conditions, usually including addition of gypsum, the hydration of CSA gives acceptable setting times and good strength development. These properties are based on the rapid formation of ettringite and variable quantities of an amorphous gel phase. These characteristics have already led to the formulation of various commercial products taking advantage of these special properties for applications in building chemistry and mining. Further systematic research is required leading to grea...
203 citations
TL;DR: In this paper, the authors investigated the release of mineral nutrients and other species from untreated and stabilised wood ash, and found that the short-term release of these salts, as simulated in laboratory experiments, was not reduced by the stabilisation methods applied.
Abstract: The release of mineral nutrients and other species from untreated and stabilised wood ash has been investigated. Stabilisation is applied with the aim to modify the solubility of ash components and the ash particle size, i.e. to form dense ash particle agglomerates. This process induces the formation of several secondary minerals. The most important reaction is the transformation of Ca(OH) 2 into CaCO 3 which lowers the calcium leaching rate significantly. A significant fraction of the alkali metals, K and Na, is present in salts which are rapidly released. The short-term release of these salts, as simulated in laboratory experiments, was not reduced by the stabilisation methods applied. Generally, low leaching rates were observed for the important plant nutrients P and Mg as well as for Fe and other metals from both untreated and agglomerated ashes. Thermodynamic equilibrium modelling of the hardening process showed that in addition to the transformation of Ca(OH) 2 to CaCO 3 , formation of the mineral ettringite is possible at a high pH. Experimental results have confirmed this. As the pH in the pore solution decreases during long-term leaching ettringite will be transformed into calcium carbonate and gypsum. In accordance with the experimental results, no formation of secondary solubility controlling potassium or sodium minerals was indicated by the modelling results.
196 citations
TL;DR: The use of ground granulated blastfurnace slag (GGBS), an industrial byproduct, is well established as a binder in many cement applications where it provides enhanced durability and high resistance to sulphate attack.
173 citations
TL;DR: In this article, it was shown that thaumasite can form at low temperatures, particularly 0-5 °C, as a non-binding calcium carbonate silicate sulphate hydrate under conditions of destructive sulphate attack.
Abstract: Thaumasite has been shown to form at low temperatures, particularly 0–5 °C, as a non-binding calcium carbonate silicate sulphate hydrate under conditions of destructive sulphate attack. Formation of thaumasite arises generally from calcium silicate hydrate CSH and Ca2+, CO2−3, SO2−3, CO2 and water, or from ettringite in the presence of CSH, carbonate and/or carbon dioxide and water. It basically resembles a carbonated ettringite, with which it has often been confused in the past. Conversion of the main cementitious binder CSH into the non-binder thaumasite is a destructive form of sulphate attack. Greater awareness of the potential problems that thaumasite can cause has arisen with the increased use of limestone fillers in cements, the common employment of limestone aggregates in concrete and the introduction of Portland limestone cements, together with the realisation that structural foundations of buildings are, on average, below ambient temperature and (more often than not with on- and above-ground construction) are within the optimum temperature range for thaumasite to be formed. Instances have been found in specific studies of large quantities of thaumasite being formed in foundation concretes with no evidence for any structural damage above ground level. It is important to be aware of the propensity of thaumasite to form at low temperatures for mix designs, so as not to encourage any destructive sulphate attack by thaumasite to arise. This means utilising low water cement ratios for workable mortars and concretes, so as to give reduced permeability. This will prevent, or at least suitably hinder, ingress of destructive ions and water, so that the potential for destructive sulphate attack by formation of thaumasite is not actually realised in practice.
159 citations
TL;DR: The chemical characteristics of fly ash samples from combustion of three fuels: coal, peat and wood chips, have been studied in this paper, where they were collected in the 12MW CFB at Chalmers University of Technology during full load combustion with similar standard combustion parameters.
150 citations
TL;DR: In this article, the formation of ettringite and the expansion associated with it were studied on pastes made from an Al-bearing compound, gypsum, and tricalcium silicate.
122 citations
TL;DR: In this paper, the Anstett test is used to assess the chemical compatibility of a repairing cementitious material with the presence of gypsum or sulphate salts inside historic buildings.
Abstract: Thaumasite and ettringite can be found among the deterioration products of cementitious materials exposed to sulphate attack. This can occur in concrete structures, as well as in masonry walls of historic buildings erected before the advent of Portland cement. Masonry walls of historic buildings may contain gypsum or other sulphate salts for different reasons. When they need to be repaired, CSH and CAH, formed by the hydration of hydraulic binders used for restoration, can react with water and gypsum or sulphate salts and produce thaumasite and ettringite. Due to these reactions, degradations of the repaired historic buildings can occur causing expansion, cracking, spalling and strength loss. In order to assess preliminarily the chemical compatibility of a repairing cementitious material with the presence of gypsum or sulphate salts inside historic buildings, the Anstett test can be adopted. Alternatively, protection measurements, based on the hindrance of water to penetrate the walls, should be adopted since in the absence of water both thaumasite and ettringite cannot be produced, even in the presence of gypsum, or other sulphate salts inside the historic buildings.
105 citations
TL;DR: In this article, the authors describe the mechanisms by which ground granulated blastfurnace slag (ggbs) prevents sulphate attack of lime-stabilized kaolinite.
99 citations
TL;DR: In this paper, a detailed characterization of six high-calcium fly ashes derived from Powder River Basin coal have been carried out and the hydration products formed in pastes made from fly ash and water were investigated.
Abstract: High-calcium Class C fly ashes derived from Powder River Basin coal are currently used in many parts of the U. S. as supplementary cementing materials in portland cement concrete. These fly ashes tend to contain significant amounts of sulfur, calcium, and aluminum, thus they are potential sources of ettringite. Detailed mineralogical characterizations of six high-calcium fly ashes originating from Powder River Basin coal have been carried out. The hydration products formed in pastes made from fly ash and water were investigated. The principal phases produced at room temperature were found to be ettringite (C6AS¯3H32), monosulfate (C4AS¯H12), and stratlingite (C2ASH8). The relative amounts formed varied with the specific fly ash. Three fly ashes were selected for further study. Portland cement /fly ash pastes made with the selected fly ashes were investigated to evaluate ettringite and monosulfate formation. Each of the three fly ashes were mixed with five different Type I portland cements exhibiting a range of C3A and sulfate contents. The pastes had 25% fly ash by total weight of solids and a water: cement + fly ash ratio of 0.45. After mixing, the samples were sealed and placed in a curing room (R.H. = 100%, 23°C) for 28 days and were then analyzed by X-ray diffraction (XRD) and differential scanning calorimetry ( DSC) to determine the principal hydration products. The hydration products identified by XRD were portlandite, ettringite (an AFt phase), monosulfate, and generally smaller amounts of hemicarboaluminate and monocarboaluminate (all AFm phases). Although the amount of ettringite formed varied with the individual cement, only a modest correlation with cement sulfate content and no correlation with cement C3A content was observed. DSC analyses showed that the cement/fly ash pastes generally formed less ettringite than the cement control pastes, but they formed more of the AFm phases (mainly monosulfate). It appears that the addition of high-calcium fly ash reduces the SO4/Al2O3 ratio in the system thus favoring Afm formation.
81 citations
TL;DR: In this paper, the formation of ettringite and monosulfate from tricalcium aluminate/gypsum mixtures with a molar ratio of 1:1 sulfate-to-aluminate was investigated by isothermal calorimetry and X-ray diffraction analyses.
TL;DR: In this paper, a Portland cement mortar was subjected to elevated temperature curing at 100°C for 12 hours and then stored under water at room temperature for a period of 1 year, and the results of X-ray microanalyses implied that a potential for ettringite band formation had been established in the mortar.
TL;DR: Sulfate can occur in Portland cement clinkers as alkali sulfates, potassium calcium sulfate (calcium langbeinite), anhydrite, and as a substituent in the major phases, especially alite and belite as mentioned in this paper.
TL;DR: In this article, it was shown that gypsum is a major source of sulfate that produces sulfate-induced heave in lime-treated soils beneath roads and other paved structures.
Abstract: Gypsum is a major source of sulfate that produces sulfate-induced heave in lime-treated soils beneath roads and other paved structures. This deformation of pavement subgrade is known to result from the growth of the basic hydrous calcium aluminum sulfate mineral, ettringite, or a silica-bearing analog, thaumasite. The problem occurs in soils that have been treated with lime (CaO) for subgrade stabilization. Gypsum is a common sulfate mineral in sedimentary rocks and soils, and in north Texas it is present in soils developed on the montmorillonitic Eagle Ford Group shales (Upper Cretaceous). Because these soils are highly unstable the conventional treatment for road subgrade includes the addition of lime (CaO) or some other cementitious material such as fly ash or Portland cement.
The pyrite-bearing Eagle Ford shale contains gypsum (CaSO4 • 2H2O) produced by reaction of calcium carbonate in the shale with acid sulfate from oxidation weathering of pyrite (FeS2). Sulfate movement upward in the soils can occur by capillarity, and it can be carried downward by infiltration, an often incomplete or interrupted event that leaves gypsum stranded as a soil evaporite. Once formed, the moderately soluble gypsum is retained in the clay-rich soils because of their low hydraulic conductivities, which makes them, in essence, reservoirs of gypsum.
Experiments performed for this study confirm that gypsum in a lime-treated subgrade soil can supply sulfate for the growth of the expansive mineral ettringite. No sulfate external to the subgrade of the road is necessary for the reaction to occur.
Gypsum is widely distributed in soils and surface outcrops in the western U.S. and should be the first mineral suspected where sulfate-induced heave has been diagnosed. Although gypsum is a moderately soluble mineral, it may be abundant in soils in regions with humid climates if its sulfate is derived from pyritic black shales by oxidation during soil formation.
Eagle Ford soils do not produce sulfate-induced heave everywhere that road base has been lime-treated, but the problem is observed most frequently where roads follow streams, or run across low-lying areas or hillside slopes. Other studies have documented a correlation between deformation and major precipitation events. Ground water, soil water, and surface drainage regimes appear to control the specific sites at which severe deformation may take place within the stratigraphically-controlled belts of gypsum-bearing soils.
Soluble sulfate tests currently in use to identify soils with the potential for sulfate-induced heave are known for inconsistent results. Total sulfate in a soil is a better predictor of the problem, and when gypsum is the sulfate mineral it can be determined quantitatively by existing laboratory methods.
Stratigraphy is a first-order guide to where sulfate-induced heave may occur in the north Texas region, thus geologic maps of the Eagle Ford shale outcrop belt are also indicators of areas of possible sulfate-induced deformation.
TL;DR: In this article, the effect of silica fume on corrosion resistance to sulphate attack of Na 2 SO 4 and MgSO 4 solutions has been studied in Portland cement mortars containing limestone and no limestone.
TL;DR: ICP/OES, AES, ETAAS, TXRF, IC, XRPD, XPS, SEM/EDX, FT-IR, Raman, Mossbauer and ESR have been used to characterize inorganic components in a fly ash sample.
Abstract: ICP/OES, AES, ETAAS, TXRF, IC, XRPD, XPS, SEM/EDX, FT-IR, Raman, Mossbauer and ESR have been used to characterize inorganic components in a fly ash sample. It has been possible to determine silicates and aluminium silicates (gehlenite, gismondine and cabasite) in addition to many inorganic compounds (halite, sylvite, anhydrite, bassanite, gypsum, syngenite, ettringite, haematite, calcite and rutile).
TL;DR: In this paper, the results of a test program to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described.
Abstract: The results of a test programme to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described. The mortars were prepared from four cements; a Portland cement, a sulfate-resisting Portland cement and two Portland limestone cements containing 15% by mass of an oolitic limestone and a carboniferous limestone. The mortar specimens were subject to BS 5328 Class 4A and 4B sulfate exposure conditions. These are the highest classes for concretes prepared using sulfate-resisting Portland cement (SRPC) before surface protection is required and are two and three classes higher than those recommended for concretes prepared using Portland cement (PC) and Portland limestone cement (PLC), respectively. Two free water-cement ratios were used, 0.5 and 0.75. Performance was monitored by visual assessment, expansion and changes in flexural and compressive strengths. At a free water-cement ratio of 0.75, the PC mortars and PLC mortars exhibited visually very severe attack with the former showing expansion and reductions in strength, and the latter mainly reductions in strength. At a free water-cement ratio of 0.50 both the PC mortars and PLC mortars showed slight/moderate to severe visual attack, the degree of deterioration appearing slightly greater in the PLC mortars, more especially those made with oolitic limestone. The PLC mortars also exhibited reductions in compressive failure load. The SRPC mortars exhibited little visual deterioration, no expansion, a small increase in flexural strength and no significant reductions in compressive strength. At a free water-cement ratio of 0.75 substantial amounts of thaumasite, together with ettringite was present in the surface layers of the deteriorated PLC mortars whilst ettringite was present in the surface layers of the deteriorated PC mortars. It is concluded that mortars made with a PC with a C 3 A content of about 10% by mass were broadly similar in their vulnerability to sulfate attack at 5 °C as PLC mortars containing 15% limestone by mass, although the mode of attack was different.
TL;DR: The use of sulfite-containing waste materials mainly from flue gas desulfurization causes the formation of new lamellar phases (AFm) in the field of calcium aluminum hydrates.
TL;DR: In this paper, the properties of fly ash, fluorogypsum, and Portland cement were investigated with X-ray diffraction, differential thermal analysis, scanning electron microscopy with energy dispersing spectrum, and mercury intrusion porosimetry.
TL;DR: In this article, three types of concrete were made from granite and quartz sand, coarse and fine flint, and coarse and finelimestone, and they were cast and cured at 95-100°C and subsequently stored at room temperature under water.
Abstract: Portland cement mortars were made from natural quartz and crushed limestone sands, and combinations of thetwo. Three types of concrete were made from granite and quartz sand, coarse and fine flint, and coarse and finelimestone. Mortar and concrete prisms were cast and cured at 95–100°C and subsequently stored at roomtemperature under water. The quartz sand mortars exhibited large expansions within the first year but thelimestone mortars remained stable even after 6 years. The ultimate expansion of those mortars with combinationsof limestone and quartz aggregate had intermediate values. The granite aggregate concretes expanded readily butthe limestone and the flint concretes started to expand only after very long induction periods. X ray diffraction,scanning electron microscopy with back-scattered electron imaging and X ray microanalysis were used to examinethe composition and microstructure of the hydration products. Differences in the features of ettringite bands thatdeveloped in the various heat-cured m...
TL;DR: In this paper, suspension hydration of C3A with gypsum (in the molar ratio of 1:3) was investigated at room temperature and water/solid ratio of 4.
TL;DR: In this paper, the behaviour of Portland cement and Portland cement with 30% fly ash in 10% ammonium-sulphate solution was studied within a comprehensive research program All materials have been chemically analysed and their physico-chemical and mechanical properties have been investigated X-ray diffraction was used for following changes into microstructure after storage of samples in ammonium sulphates solution, and phase composition changes were identified.
01 Jan 1999
TL;DR: In this paper, the effects of heavy metals on the physical and chemical properties of portland-cement based pastes were studied using different types of cement, four metal oxides, and four soluble metal salts.
Abstract: The effects of heavy metals on the physical and chemical properties of portland-cement based pastes were studied using different types of cement, four metal oxides, and four soluble metal salts. Type I (high calcium aluminate content) and Type V (low calcium aluminate content) portland cements were used to study the effects of their chemical differences on paste properties and metal stabilization. Fresh pastes were tested for workability, initial setting times, and heats of hydration. Hardened pastes were tested for strength and leachability by both TCLP (Toxic Characteristic Leaching Procedure) and column leaching with acetic acid. The cement matrix was an excellent stabilization matrix, better than could be projected from pH considerations alone. The investigation also involved examining Type I portland cement paste treated with three metals together - chromium, cadmium and lead, added at very high (1% by mass of cement) and intermediate (1000 ppm by mass of cement) levels. The leaching solutions were acetic acid, "synthetic rain" (pH 3 sulfuric/nitric acid), and deionized water. A Type N masonry cement matrix was also investigated. The leachabilities were very low throughout the pH range of 6-11 for lead and chromium. At very high pH values, the leachabilities of lead and chromium were significantly higher. Cadmium leachability was negligible above pH 10, but became rapid and highly significant below pH 9. At pH values below 6, which generally corresponded to the extraction of nearly all calcium present, all metals were rendered highly leachable. For all the metals, the leachability in masonry cement-stabilized matrix has higher than with Type I during the intermediate leaching steps. A series of tests involved testing of a contaminated soil matrix, both dry and contaminated with aged SAE 10 W oil (without additives). Cement was used at 8% by weight of total mix. The results of leachability vs pH generally were consistent with those obtained in the multiple metals leaching studies; as long as calcium silicate hydrate was present, metals solubility was very low, irrespective of pH. In an attempt to address the early high pH leaching of lead and chromium, a series of experiments was run with silica fume, in an amount calculated to react with all calcium hydroxide generated from hydration of the calcium silicates. The results indicated that leachabilities of lead and chromium were reduced at pH values greater than 11.0, and also at the low pH values obtained after multiple sequential batch leaches. Since ettringite is known to be much less soluble than calcium monosulfoaluminate hydrate, it was also though that a system in which extra sulfate is present might yield even lower leachabilities for those metals which were substituted in the ettringite lattice. The results indicated that at very high pH values, the leachability of chromium was reduced with the lower excess gypsum level, and at low pH values, less than about 5.0, with both high gypsum levels. At intermediate pH values, chromium leachability was minimum for the unaltered matrix.
TL;DR: In this article, the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V were investigated by x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscope.
Abstract: This study investigated the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V. Samples of plain cement and superplasticizer-treated cement have been examined by x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Lignosulfonate has been observed to retard the hydration of cement through specific surface chemical reactions which involve Ca2+ ions in pore solution. The admixture has been found to retard the formation of Ca(OH)2 and stabilize ettringite [Ca6(Al22O6)(SO4)3.32H2O]. The inhibition of the rate of conversion of ettringite to monosulfate [Ca4Al2(OH)12.SO4.6H2O] is attributed to charge-controlled reactions caused by large quantities of Ca2+ ions from initial hydration reactions. Leaching of the admixture doped cement by water-removed lignosulfonate and caused complete hydration of cement. A charge-controlled-reaction model involving the Ca2+ ions is proposed to explain t...
DOI•
01 Jan 1999
TL;DR: Damaging Late Ettringite Formation (DLEF) is caused by a formation, destruction and a later renewed formation of ettringites ocurring preferably after maximum heat treatment (HT) at greater than or equal to 70 degrees C of pastes, mortars and concretes made with high strength Portland cements as mentioned in this paper.
Abstract: For the past 25 to 30 years, preferably heat treated precast concrete members (> 70 degrees C) manufactured with high early strength Portland Cements with higher sulphate contents, under adverse exposure conditions have sometimes exhibited structural damage in the form of map cracking and loss of strength. These damages are characterized as Damaging Late Ettringite Formation (DLEF). DLEF is caused by a formation, destruction and a later renewed formation of ettringite ocurring preferably after maximum heat treatment (HT) at greater than or equal to 70 degrees C of pastes, mortars and concretes made with high strength Portland cements.
TL;DR: In this paper, the effect of hydrothermal alteration on the sorption properties of two cement grouts and Calcium Silicate Hydrogels (CSH-gels) is investigated by using the batch sorption technique.
Abstract: The sorption of radionuclides onto cement materials is a very important parameter when considering the release of radionuclides from radioactive wastes. Once the composition or crystallinity of the constituent minerals of a cement material is changed by alteration in the disposal environment, its sorption ability might be affected. In this study, the effect of hydrothermal alteration on the sorption properties of two cement grouts and Calcium Silicate Hydrogels (CSH-gels) is investigated by using the batch sorption technique. In the case of strontium (a model cation) sorption, the distribution ratio for Ordinary Portland Cement (OPC) and OPC/Blast Furnace Slag blended cement (OPC/BFS) decreased as the alteration temperature increased. This is mainly caused by the decrease of sorption onto CSH-gel which is a constituent of cement materials. In the case of selenium (selenite, a model anion) sorption, the distributionratio decreased as the alteration temperature increased for OPC treated in both distilled water and groundwater, and for OPC/BFS in groundwater. This is attributed to the decomposition of ettringite which sorbs anions. The distribution ratio for OPC/BFS in distilled water increased as the alteration temperature increased, although ettringite decomposed. This is attributed to the formation of monosulphate which also sorbs anions. These results show that the hydrothermal alteration of cement mineral phases in a disposal environment may cause changes which could increase or decrease the sorption of radionuclides onto cements depending on the cement composition and radionuclide speciation.
DOI•
01 Jan 1999
TL;DR: In this article, a mechanism involving hydrates of aluminates and possible unhydrated cement clinker particles is discussed, which results in delayed ettringite formation.
Abstract: Paste, mortar, and concrete cured at temperatures above certain limits may exhibit expansion and cracking during subsequent exposure to varying moist conditions. This phenomenon originally became known as delayed ettringite formation, DEF. DEF results in a typical microstructure which is demonstrated with examples from field samples and laboratory-made samples. The microstructure is compared with examples of internal sulfate attack in laboratory samples. These typical features include gaps around the aggregate where the paste shows an almost perfect replica of the individual aggregate surfaces. Expansion of the paste on a scale which is homogeneous relative to the aggregate would lead to such features. The chemistry in DEF is similar to that of sulfate attack. A mechanism involving hydrates of aluminates and possible unhydrated cement clinker particles is discussed.