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Showing papers on "Ettringite published in 1987"


DOI
01 Apr 1987
TL;DR: In this article, a series of parameters have been examined as to their influence on the durability of heat treated concretes, including the threshold temperature of damage, the so3 content of the cement, the humidity of storage, and the w/c.
Abstract: In the last years, precast units made of high strength concrete, and having been heat treated during production, have shown partly damaged structure related to loss of strength. This damage always occurred in those building components which, for several years, had been subjected to open-air weathering (e.g. Front panels and sleepers). The damage has often been characterized by crack formation emerging from the edges of the building components, as well as by a loss of bond between the cement paste and the coarse aggregate. In order to clarify this damage, a series of parameters have been examined as to their influence on the durability of heat treated concretes. Beside others, the investigation concentrated on the following subjects: the threshold temperature of damage, the so3 content of the cement, the humidity of storage, and the w/c. (Author/TRRL)

62 citations


Patent
19 Nov 1987
TL;DR: In this article, the CaO and alumina contents of the waste products are adjusted as necessary to enable them to combine with a sulphate additive at elevated pH and so couple the faster reactions of the mineral Ettringite with the slower ones of the calcium silicates.
Abstract: Methods for producing cementitious compositions from waste products, such as non-ferrous slags, or fossil fuel combustion residue, or ferrous slags, whereby the CaO and alumina contents of the waste products are adjusted as necessary to enable them to combine with a sulphate additive at elevated pH and so couple the faster reactions of the mineral Ettringite with the slower ones of the calcium silicates.

50 citations


Patent
09 Dec 1987
TL;DR: In this article, a process for the formation of hydraulic binders and building elements comprising from 70% ettringite and up to 30% calcium silicate hydrates is disclosed.
Abstract: HYDRAULIC BINDERS AND BUILDING ELEMENTS FORMED OF NON-TRADITIONAL MATERIALS A process is disclosed for the formation of hydraulic binders and building elements comprising from 70% ettringite and up to 30% calcium silicate hydrates. Ettringite is a very strong mineral and the product may be at least the equal in terms of mechanical properties of Portland cement while not suffering shrinkage and expansion problems. The process comprises mixing powdered source materials of reactive CaSO4, CaO and Al2O3 with or without SiO3 with or without SiO2 and hydrating the intimate mixture at a ratio in the range of 1 part powdered source materials to 0.35-1 part water. Most conveniently, impure source material such as industrial by-products are used as they have been found to catalyse the hydration reaction. Further if gypsum is a powdered source material, in a natural, pure or chemical form, it is preferably calcined since such material sets quickly and gives early mechanical strength. A clinker of calcium sulphoaluminate may be produced for use as a powdered source material.

29 citations


Journal ArticleDOI
TL;DR: The seawater leachability of cadmium and lead sludges solidified in portland cement paste was investigated in this article, which showed that the total amount of lead leached from the stabilized waste over a 50-day period was about 1.0% of the total lead added to the paste.
Abstract: The seawater leachability of cadmium and lead sludges solidified in portland cement paste was investigated. The leachates of the wastes containing cadmium and lead were analyzed for metal contents using flame atomic absorption spectrophotometry (AAS) as well as pH and alkalinity. A control sample containing only portland cement paste was also leached to serve as a comparison. Results show that the total cadmium leached from the stabilized waste over a 50-day period was about 1.0% of the total cadmium added to the paste. Lead was not detected in the leachate, however, this could be due to physical and analytical interferences associated with lead. The pH and alkalinity data show that initially, hydroxide is leached from the waste and calcium carbonates are formed on the particle surfaces. After a 50-day period, the pH and alkalinity of the waste leachates approach that of the seawater leachant. The microstructure of the waste samples was investigated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and powder X-ray diffraction (XRD). The presence of lead did not appear to have an effect on the hydrated structure of the portland cement paste, whereas cadmium seemed to create a more porous microstructure with abundant colloidal ettringite (a calcium sulfoaluminate compound often found in hydrated portland cement paste). Results show that the fixation of cadmium in portland cement paste accelerates sulfate attack on the paste by seawater, which in turn leads to destructive cracking of the paste. It appears that cadmium release is related to the physical destruction of the portland cement paste.

20 citations


Journal ArticleDOI
TL;DR: In this article, the properties of LFA, ground to highlight its hydraulic properties, have been investigated by means of strength and other tests on mortars and pastes, with various levels of replacement of OPC by LFA.
Abstract: Synopsis Lignite fly ashes (LFA) often have self-cementing as well as pozzolanic properties, due to their high lime content. LFA is compatible with Portlandcement and can replace a significant percentage of cement in concrete in order to save energy and reduce costs. The properties of LFA, ground to highlight its hydraulic properties, have been investigated by means of strength and other tests on mortars and pastes, with various levels of replacement of OPC by LFA. Analysis by X-ray diffraction, differential thermal analysis-thermogravimetry and electron microscope-selected area electron diffraction methods indicated that the strength of OPC/LFA mortars is due to compounds of C-S-H gel formed by the reaction of free lime with silica, and from the hydration of dicalcium silicate which may exist in LFA. The early strength is attributed to hydrated calcium aluminate compounds and ettringite.

19 citations


01 Jan 1987
TL;DR: In this article, the effects of temperature and relative humidity on reactive concretes from three UK structures are investigated in a series of long-term experiments, and interim findings are presented here.
Abstract: The effects of temperature and relative humidity on alkali-silica reactive concretes from three UK structures are being investigated in a series of long-term experiments, and interim findings are presented here. Preliminary indications are that temperature has both the opposite and a far more significant effect on expansion behaviour than previously recognised. Expansion rate is initially proportional to temperature, but falls off more rapidly at higher temperatures than at lower temperatures. Maximum expansion is inversely proportional to temperature, and final expansion at lower temperatures may be more than twice that at 38 deg c. The cutoff humidity (defined as that below which expansion due to asr (alkali silica reaction) does not occur) is higher at elevated temperatures, and expansion variability between concretes is most apparent at lower temperatures and higher humidities. Petrological examination of test samples reveals moderate alkali contents but only small quantities of gel, and concretes from one structure contain an abundance of ettringite. In the absence of external sulphate it is concluded that the ettringite formed by recrystallization of primary sulphate minerals, and was stabilised by reaction of the limestone aggregate. This was probably facilitated by asr, and it is proposed that the resulting pressures contributed to concrete distress. The accepted model of alkali-silica reaction is reviewed in the light of these findings. It is proposed that temperature has a direct effect on both reactant transport and aggregate attack processes. Moisture availability is considered fundamental to expansion of the reaction product, but its effect is thought to be modified by temperature which alters the gel structure, and hence its swelling properties. It is observed that other factors may interact with asr to cause deterioration, and that secondary processes may continue after asr is exhausted. The implications of these findings to the management of affected structures are discussed.(a) for the covering abstract of the conference see IRRD 811982.

16 citations


Patent
30 Jun 1987
TL;DR: In this article, a hydraulic mixture of a hydraulic cement mixture consisting of a major amount of a first portland cement constituent and a minor amount of an expansive ettringite sulfoalumina component, an aggregate component, and an accelerator component is used for grouting repair of concrete surfaces.
Abstract: A dry cementitious composition which is shrinkage compensating and fast-setting for use in grouting repair of concrete surfaces. The cementitious composition comprises a hydraulic cement mixture of a major amount of a first portland cement constituent and a minor amount of a second expansive ettringite sulfoalumina cement constituent, an aggregate component, and an accelerator component. The accelerator component is a polyvalent metal salt of formic acid, specifically an alkaline earth metal formate such as calcium formate. Specific formulations include a mixture of Type I, Type IP, or Type III cement as a first constituent with Type K, Type M, or Type S cement as a second constituent, with the ratio of the first to the second constituent within the range of 2-3. The material may be employed to affect a grouting repair by mixing the dry formulation with water to provide a cementitious slurry which sets to provide a compressive strength of at least 4000 psi at 24 hours and a positive volume change of no more than 0.1% at 14 days curing.

15 citations


Journal Article
TL;DR: In this article, the authors investigated the effect of calcium sulfate impurities in deicing salts on the durability of portland cement mortar and reported significant losses in pore volume for the treated samples as compared to samples frozen and thawed in water only.
Abstract: Research on the topic of calcium sulfate impurities in deicing salts adversely affecting the durability of portland cement mortar is covered in this paper. Natural rock salt may contain as much as 4.0 percent calcium sulfate. When combined with chloride solutions the solubility of calcium sulfate increases by as much as 3.5 times; hence, the calcium sulfate impurities contained in rock salt brine become highly detrimental, causing attack on cement mortar samples. These impurities can collect in pavement joints and cracks, reaching high concentrations through evaporation and the repeated use of deicing salts. Such a destructive mechanism may account for premature field failure of pavements that passed durability tests in the laboratory. Durability studies using brines containing differing amounts of gypsum in proportion to the sulfates occurring in natural rock salts have been conducted. To model field conditions, samples were concurrently subjected to brines and rapid freeze-thaw testing. Deterioration proved so rapid that testing was stopped at 88 cycles. Tensile tests showed strength losses up to 40 percent for samples subjected to brine solutions containing gypsum impurities. Mercury intrusion porosimetry showed significant losses in pore volume for the treated samples as compared to samples frozen and thawed in water only. X-ray diffraction tests discovered increased amounts of ettringite and Friedel's salt, a tricalcium aluminate chloride hydrate.

11 citations


Journal ArticleDOI
TL;DR: In this article, the compressive strength, pore size distribution and Ca(OH)2 content were determined on water-cured cement mortar and paste specimens, and the results show all BF-LD-PC and BF-LCD cements to be “sulfate resistant which correlates well with their decreased capillary pore volume and low Ca(O)2 contents.

11 citations


01 Jan 1987
TL;DR: In this paper, the mineralogical and micromorphological changes occuring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture.
Abstract: The mineralogical and micromorphological changes occuring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture. Compacted fly ash, fly ash-lime, bentonite-1ime, bentonite-fly ash, and bentonite-fly ash-lime mixtures were prepared and cured at 23°C and 50°C, for 1, 28, 90 and 180 days. The development of microstructure and cementitous crystals were observed by a scanning electron microscoi in energy dispersive spectrum analyzer and a X-Ray diffractometer. The elastic moduli and strengths were obtained from unconsolidated undrained triaxial and unconfined compressive strength tests. The physical test results were compared with changes observed by scanning electron microscopy and X-Ray diffraction. CSH gel Type I, II and III, ettringite, afwillite and tetracalcium aluminate thirteen hydrate crystals were identified in the cured specimens. The elastic modulus of the fly ash-lime stabilized bentonite was higher than the untreated bentonite and the increase in elastic modulus corresponded to the curing times when new cementitious crystals were observed. Acicular crystals (CSH Type I and II) and ettringite crystals spanned the pores and increased the contact points where blocky aggregates of equant crystals (CSH III) engulfed the fly ash grains providing support. The compressive strength increased, and the strain at failure decreased resulting in an increase in the elastic modulus. Some fly ash grains providing support for montmorillonite aggregates dissolved and created weak spots in the matrix, causing a decrease in elastic modulus at longer curing periods. At 50°C curing temperature the same cementitious crystals were observed as at 23°C. However, the rate of the reactions increased considerably.

8 citations


01 Jan 1987
TL;DR: In this paper, a concrete tunnel lining affected by dissolved calcium sulphate in water due to the oxidation and the solubility of the pyrites contained in the rock was found.
Abstract: Some different degrees of alteration have been found in a concrete tunnel lining affected by dissolved calcium sulphate in water due to the oxidation and the solubility of the pyrites contained in the rock: in some cases the damage has been of such an extent that the concrete has changed into a plastic mass. Measurements taken inside the tunnel over many years showed a range of temperature from 4 deg to 6 deg c. The chemical analysis of the concrete, the diffractometric analysis and the scanning electron microscope analysis performed on some alteration products all clearly showed the presence of thaumasite and calcite, while no ettringite was found. The recorded thermal conditions, the presence of silica due to feldspar alteration and the free carbon dioxide in the water lead to the conclusion that the ettringite has been transformed completely into thaumasite. In order to understand this transformation, some laboratory tests were carried out on mortar immersed in a water mixture containing calcium sulphate, calcium carbonate, calcium hydroxide and amorphous silica in an environment rich in carbon dioxide, at the temperature of 5 deg and 20 deg c respectively. (Author/TRRL)

ReportDOI
01 Mar 1987
TL;DR: In this article, the suitability of masonry cement for the solidification of sodium sulfate wastes produced at boiling water reactors (BWR's) was investigated, and it was determined by x-ray diffraction that in the presence of water, themore-» sulfate reacts with hydrated calcium aluminate to form calcium aluminum sulfate hydrate (ettringite). This reaction involves a volume increase resulting in failure of the waste form.
Abstract: Portland cements are widely used as solidification agents for low-level radioactive wastes. However, it is known that boric acid wastes, as generated at pressurized water reactors (PWR's) are difficult to solidify using ordinary portland cements. Waste containing as little as 5 wt % boric acid inhibits the curing of the cement. For this purpose, the suitability of masonry cement was investigated. Masonry cement, in the US consists of 50 wt % slaked lime (CaOH/sub 2/) and 50 wt % of portland type I cement. Addition of boric acid in molar concentrations equal to or less than the molar concentration of the alkali in the cement eliminates any inhibiting effects. Accordingly, 15 wt % boric acid can be satisfactorily incorporated into masonry cement. The suitability of masonry cement for the solidification of sodium sulfate wastes produced at boiling water reactors (BWR's) was also investigated. It was observed that although sodium sulfate - masonry cement waste forms containing as much as 40 wt % Na/sub 2/SO/sub 4/ can be prepared, waste forms with more than 7 wt % sodium sulfate undergo catastrophic failure when exposed to an aqueous environment. It was determined by x-ray diffraction that in the presence of water, themore » sulfate reacts with hydrated calcium aluminate to form calcium aluminum sulfate hydrate (ettringite). This reaction involves a volume increase resulting in failure of the waste form. Formulation data were identified to maximize volumetric efficiency for the solidification of boric acid and sodium sulfate wastes. Measurement of some of the waste form properties relevant to evaluating the potential for the release of radionuclides to the environment included leachability, compression strengths and chemical interactions between the waste components and masonry cement. 15 refs., 19 figs., 9 tabs.« less

Patent
25 Feb 1987
TL;DR: In this paper, a mixture of ready-for-use mortar mixture for rapidly hardening plaster of insulation systems, containing binders, standard additions and additives, characterised by a content of a.m.of EP02111941.
Abstract: of EP02111941. Mortar mixture, preferably ready-for-use mortar mixture for rapidly hardening plaster of insulation systems, containing binders, standard additions and additives, characterised by a content of a. 10 to 40 parts by weight reactive calcium silicates, b. 3 to 7 parts by weight reactive aluminates, calculated as CA, c. 1 to 7 parts by weight calcium hydroxide, d. 0.2 to 2 parts by weight calcium sulphate hemihydrate and/or calcium sulphate anhydrite-III, e. 0.4 to 4 parts by weight calcium sulphate anhydrite-II, f. 0.03 to 0.5 parts by weight organic setting retarders inhibiting the formation of nuclei and the growth of calcium aluminium sulphate hydrate, with the ratio of the components b:c being smaller than or equal to 5, in such a manner that a reaction chain runs across the following reaction products : primary ettringite, monophases (calcium aluminate monosulphate), secondary ettringite and calcium hydrosilicates.

01 Jan 1987
TL;DR: The major alkali aggregate reaction products include siliceous gels either massive or textured gels and crystals in lamellae or fibers as mentioned in this paper, which give rise to secondary minerals such as hydrocalcite, ettringite and thaumasite.
Abstract: The major alkali aggregate reaction products include siliceous gels either massive or textured gels and crystals in lamellae or fibers. Microstructure of cracked concretes, as observed by light and electron microscopy, shows a weak cement paste -aggregate bond. Elemental analysis by epma or edax of this interface reveals ionic diffusion of alkalies but also of calcium carbonate and sulfate which gives rise to secondary minerals as hydrocalcite, ettringite and thaumasite.(a) for the covering abstract of the conference see IRRD 811982.

Book ChapterDOI
01 Jan 1987
TL;DR: In this article, the hydraulic behavior of materials composed from calcined gypsum, fly ash, and portland cement was investigated at 21 and 55°C, using calcined natural gypsuma or phosphogypsum as the source of sulfate.
Abstract: The hydraulic behaviour of materials composed from calcined gypsum, fly ash, and portland cement has been investigated at 21 and 55°C, using calcined natural gypsum or phosphogypsum as the source of sulfate. The effect of added lime has also been studied.

Journal ArticleDOI
TL;DR: In this article, fly ash, lime, bentonite and water mixtures were cured at 23° and 50°C, for 1, 28, 90 and 180 days, and they were observed by scanning electron microscopy, energy dispersive xray spectrometry and x-ray diffractometry.
Abstract: Compacted fly ash, lime, bentonite and water mixtures were cured at 23° and 50°C, for 1, 28, 90 and 180 days. Cementitious products and microstructure were observed by scanning electron microscopy, energy dispersive x-ray spectrometry and x-ray diffractometry. Unconfined compressive strength changes are correlated to the formation of new mineral phases. For bentonite-limefly ash mixtures, strength increased from 1050 kPa (I day) to 2,300 kPa (90 days) and then slightly increased to 2,400 kPa after 180 days at ∼ 230C. Ettringite is the most abundant mineral associated with the increased compressive strength. New minerals identified in the 23°C mixtures include calcium silicate hydrate - Type 1, afwillite and ettringite. Acicular crystals of these and other minerals were formed by the hydration of lime and fly ash in the montmorillonitic clay. The cementitious phases create a rigid framework joining spheres and clay aggregates. Continued reaction dissolves some of the spheres and slightly reduces the rigidity of the cured samples.

Journal ArticleDOI
TL;DR: In this article, the effect of sulphate addition in controlling the flash set is monitored over the critical initial period of hydration and its consequences on the ultimate setting properties of clinker are discussed.

Journal ArticleDOI
TL;DR: In this article, the effect of mixing, age and water/cement ratio on the rheology of non-shrinking cement pastes has been studied using a coaxial cylinders viscometer.
Abstract: Synopsis The effect of mixing, age and water/cement ratio on the rheology of non-shrinking cement pastes has been studied using a coaxial cylinders viscometer. Experiments under steady shear at constant rate, supported by thermogravimetry, gave information on the breakdown of structure. The rheology of non-shrinking cement pastes is broadly similar to that of ordinary Portland cement pastes. However, the rapid formation of ettringite increases the yield value and plastic viscosity. Prolonged mixing results in accelerated formation of ettringite and consequent stiffening of the paste which is also associated with reduced expansion in service. Structural breakdown takes place under continuous shear and the changes can be explained by the effect of shear on the amount of water bound in the ettringite crystals.