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F Goetzneunhoeffer - One of the best experts on this subject based on the ideXlab platform.
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studies on the early hydration of two modifications of ye elimite with gypsum
Cement and Concrete Research, 2017Co-Authors: Daniel Jansen, J Neubauer, A Spies, D Ectors, F GoetzneunhoefferAbstract:Abstract Two modifications of ye'elimite (namely orthorhombic ye'elimite (stoichiometric C4A3$) and iron-containing cubic ye'elimite (C4A2,7F0,3 S ¯ )) were synthesized and the reactions without additional sulfate and with gypsum were tracked by means of heat flow calorimetry. Without gypsum the reaction differs significantly for both modifications while the addition of gypsum leads to almost comparable reactions. With addition of gypsum two distinct heat flow maxima could be detected while the reaction without gypsum showed only one distinct maximum for both modifications. For the systems with gypsum additional experiments were performed namely in-situ XRD, NMR, thermodynamic modeling, TGA and pore solution composition. It could be shown that the reaction with gypsum shows two steps of Ettringite precipitation for both modifications. The two steps show significant differences. During the first step of Ettringite precipitation gypsum and ye'elimite and free water are consumed forming Ettringite and a highly hydrated AHx. The second Ettringite precipitation is powered by ye'elimite consumption but no further gypsum dissolution. In addition, water is removed from the AHx used up for the second Ettringite precipitation. The two modifications of ye'elimite react comparable with gypsum but show slightly different heats of hydration when reacting with the same calcium sulfate (gypsum) during early hydration; this is due to slightly lower reaction turnover of the cubic, iron-containing modification leading to slightly reduced Ettringite formation.
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a comparative structural study of wet and dried Ettringite
Cement and Concrete Research, 2010Co-Authors: Guillaume Renaudin, J Neubauer, Yaroslav Filinchuk, F GoetzneunhoefferAbstract:Two different techniques were used to compare structural characteristics of "wet" Ettringite (stored in the synthesis mother liquid) and "dried" Ettringite (dried to 35% relative humidity over saturated CaCl 2 solution). Lattice parameters and the water content in the channel region of the structure (site occupancy factor of the water molecule not bonded to cations) as well as microstructure parameters (size and strain) were determined from a Rietveld refinement on synchrotron powder diffraction data. Local environment of sulphate anions and of the hydrogen bonding network was characterized by Raman spectroscopy. Both techniques led to the same conclusion: the "wet" Ettringite sample immersed in the mother solution from the synthesis presents similar structural features as Ettringite dried to 35% relative humidity. An increase of the a lattice parameter combined with a decrease of the c lattice parameter occurs on drying. The amount of structural water, the point symmetry of sulphate and the hydrogen bond network are unchanged when passing from the wet to the dried Ettringite powder. Ettringite does not form a high-hydrate polymorph in equilibrium with alkaline solution, in contrast to the AFm phases that lose water molecules on drying. According to these results we conclude that Ettringite precipitated in aqueous solution at the early hydration stages is of the same chemical composition as Ettringite present in the hardening concrete. © 2009 Elsevier Ltd. All rights reserved.
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refined Ettringite ca6al2 so4 3 oh 12 26h2o structure for quantitative x ray diffraction analysis
Powder Diffraction, 2006Co-Authors: F Goetzneunhoeffer, J NeubauerAbstract:A revised structure model of Ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes. The model is derived from two different existing structure models, both of which are suitable for restricted use but are inferior to the refined Ettringite structure presented. In the first published Ettringite structure proposed by Moore and Taylor [Acta Crystallogr. B 26, 386–393 (1970)], none of the 128 positions for H are given in the unit cell, which results in reduced scattering power for use of this model for quantification purposes. For the precise quantification of Ettringite in samples together with anhydrous phases, the scattering factors of all atoms including the H positions are indispensable. The revised structure model is based on the data of Moore and Taylor, supplemented by the H positions determined by Berliner (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic, Society, 1998, pp. 127–141) on the basis of a neutron diffraction structural investigation of deuterated Ettringite at 20 K. Berliner’s (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic Society, 1998, pp. 127–141) thermal parameter should not, however, be used, since a normal application is at room temperature. In order further to improve the structure model of Ettringite, Rietveld refinement with the rigid body approach for OH and H2O molecules and SO4 tetrahedra was employed. The refined and improved Ettringite structure model was tested for quantitative phase analysis by the determination of actual Ettringite contents in mixtures with an internal standard. Synthesized and orientation-free prepared Ettringite powders were investigated by X-ray powder diffraction analysis and quantified in four different blends with zircon. The quantification results with the new structure model demonstrate the superior quality of the revised Ettringite structure.
John H. Sharp - One of the best experts on this subject based on the ideXlab platform.
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Delayed Ettringite formation in heat-cured Portland cement mortars
Cement and Concrete Research, 1999Co-Authors: Renhe Yang, C.d. Lawrence, Cyril J. Lynsdale, John H. SharpAbstract:Abstract A Portland cement mortar was subjected to elevated temperature curing at 100°C for 12 h and then stored under water at room temperature. Expansions, attributable to delayed Ettringite formation, were found to develop over a period of 1 year. Sulfate ions released to the pore fluid at elevated temperatures, and partly sorbed by C-S-H gel, evidently formed Ettringite in the outer products and the paste–aggregate transition zones during subsequent water storage at room temperature. The results of X-ray microanalyses implied that a potential for Ettringite band formation had been established in the mortar. Investigations of microstructural features by backscattered electron imaging indicated that the expansion was caused by generation and extension of these Ettringite bands. No evidence in support of an alternative mechanism based on a homogeneous expansion of the cement paste could be found.
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delayed Ettringite formation in 4 year old cement pastes
Cement and Concrete Research, 1996Co-Authors: Renhe Yang, C.d. Lawrence, John H. SharpAbstract:Abstract Cement paste prisms (40 × 40 × 160 mm) made from portland cement have been cured at 100 °C for 3 hours, followed by extended water storage at room temperature. Large expansions have been observed after 2 1 2 years for prisms made with a certain portland cement. Backscattered electron imaging (bse) in a scanning electron microscope (SEM), combined with x-ray microanalysis and quantitative x-ray diffraction analysis, was employed to examine the microstructure, the distribution and the quantity of Ettringite formed. Bands of Ettringite could be readily observed in a heat cured prism near one of its long surfaces, but not in the central region of the prism. X-ray microanalysis demonstrated that S and A1 species, initially dispersed in the outer and the inner hydration products around cement grains during heat curing, diffused from these hydration products during the period of 2 1 2 to 3 1 2 years water storage at room temperature to form the Ettringite bands. Trends between the occurrence of Ettringite bands and paste expansion suggest that a causal relationship may exist between these factors.
Xiao Qin - One of the best experts on this subject based on the ideXlab platform.
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Relationship between delayed Ettringite formation and delayed expansion in massive shrinkage-compensating concrete
Cement and Concrete Composites, 2004Co-Authors: Peiyu Yan, Feng Zheng, Jiang Peng, Xiao QinAbstract:The possibility of delayed expansion induced by delayed Ettringite formation in massive shrinkage-compensating concrete was investigated. Mortars were prepared using ordinary Portland cement and a sulfoaluminate-based expansive agent. They were cured in three different moist conditions at elevated temperature in a temperature match conditioning process to simulate the temperature development in the interior of massive concrete, and then at ambient temperature. Changes in quantity and morphology of Ettringite were examined using semi-quantitative X-ray diffraction and scanning electron microscopy. The time-dependent length change of restrained mortars was also measured. The results show that, in addition to the quantity of Ettringite, the structure of mortar, morphology of Ettringite and curing conditions also influenced expansion of mortars induced by delayed Ettringite formation. The expansion mechanism of delayed Ettringite formation and the relationship between curing conditions and length change, delayed expansion and damage to concrete structure are discussed.
Paulo J.m. Monteiro - One of the best experts on this subject based on the ideXlab platform.
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A hydration study of various calcium sulfoaluminate cements
Cement and Concrete Composites, 2014Co-Authors: Antonio Telesca, Milena Marroccoli, M. L. Pace, Michele Tomasulo, Gian Lorenzo Valenti, Paulo J.m. MonteiroAbstract:Abstract The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) Ettringite when combined with lime and calcium sulfate, (ii) Ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) Ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate Ettringite cluster was observed.
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Ettringite strengthening at high pressures induced by the densification of the hydrogen bond network
Journal of Physical Chemistry C, 2012Co-Authors: Paulo J.m. Monteiro, Antonio Telesca, Hegoi Manzano, Andres Ayuela, Jorge S DoladoAbstract: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.
R. Talero - One of the best experts on this subject based on the ideXlab platform.
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co precipitation of Ettringite of rapid and slow formation consequence expansive synergic effect its demonstration by mortars and concretes
Materiales De Construccion, 2011Co-Authors: R. TaleroAbstract:Several prior papers have shown that enough pozzolans can bring about rapid formation Ettringite (from its Al 2 O 3 r- ). It has likewise been found that the formation rate of this Ettringite is higher than the of slower forming Ettringite originating from OPC (from its C 3 A). In this context: What type of effect will they ultimately produce? Addition? Synergism? Antagonism? or perhaps Inversion of final expansive action?. To reply to these questions, 4 PC and 12 blended cements containing 20%, 30% or 40% metakaolin, were tested using the ASTM C 452-68, EN 196-1 and RT-86:ΔL tests and also concrete specimens. The experimental results have shows that the joint precipitation in a common sulfate medium, of Ettringite from pozzolan and from OPC, was always more synergic than additive , and the technical consequences of the Expansive Synergic Effect may be classified as beneficial, adverse or indifferent according to its sulfates content in excess is more or less adequate.
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Performance of Metakaolin and Portland Cements in Ettringite Formation as Determined by ASTM C 452-68: Kinetic and Morphological Differences
Cement and Concrete Research, 2005Co-Authors: R. TaleroAbstract:Abstract In this study, the results of prior XRD and Le Chatelier–Ansttet test experiments were re-verified in terms of a relative parameter, the Length Growth Rate, Vcl(=Δ L (%)/day). For this purpose ASTM C 452-68 testing was conducted for 2 years on 40 cements, 10 Portland cements–6 OPCs and 4 SRPCs–and 30 blended cements containing 20%, 30% and 40% metakaolin (M pozzolan). ASTM C 452-68 specimens were manufactured with all cements and their daily length growth rate was calculated by dividing the measured increase in length, Δ L (%), by the number of days lapsing since the preceding measurement. Additional experiments were also run: chemical analysis, XRD and SEM analysis of Ettringites and tests to determine specific properties of some cements tested. The results have once again borne out that: (a 1 ) The formation rate of the Ettringite deriving from the reactive alumina, Al 2 O 3 r − , present in pozzolans is considerably higher than the rate for Ettringite forming from the C 3 A (and, logically, much higher than for C 4 AF Ettringite) present in OPC. Owing to this, these Ettringites were termed: “rapid formation” ( ett-rf ), “slow formation” ( ett-lf ) and “very slow formation” ( ett-vlf ʺ) Ettringites, respectively. (b 1 ) The foregoing directly affects the size of the respective crystals, which are much smaller in ett-rf than in ett-lf . These results have also shown that: (a 2 ) In a gypsum and water environment (ASTM C 452-68 specimens), the pozzolanic reactions involving the reactive alumina, Al 2 O 3 r − , present in pozzolans take place during the first 28 days of age–and, sometimes, even during the first 7 days (this occurred for most POZCs prepared with this M pozzolan and PC)–, and Ettringite from both, Al 2 O 3 r − and C 3 A, origin, are the reaction products in all cases. (b 2 ) Ett-rf and ett-lf formation does not take place independently from one another, but inter-dependently or in a joint way or interactive way. Consequently, both Ettringites appear, to a greater or lesser extent, when dealing with gypsum and water environments. Nevertheless, the reaction products are closer to ett-rf than to ett-lf , when more M pozzolan is added (40%) and vice versa (20%), and in any case, topochemical mechanism with prior dissolution must be preponderant over through-solution mechanism. (b 3 ) According to ASTM C 150-95 standard, the optional physical requirement to characterize SRPCs is Δ L 14 days ≤0.040%. Unlike the requirement formerly used, i.e., Δ L 28 days ≤0.054%, this requirement “predicts” rather than “assures” the most probable behaviour of a PC under gypsum attack. Moreover, if the results of the tests set out in standards EN 196-1, EN 196-3, EN 196-5 and EN 450 and/or ASTM C 311-94b, mainly, are positive, the ASTM C 452-68 test can be validly used to characterize and differentiate at 28 days, POZCs prepared with M pozzolan–or any other natural or artificial (fly ash) pozzolan–, which would give rise to low, moderate or high sulfate resistance. The only requisite in this regard would be to establish suitable standard and chemical–physical requirements and specifications.
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Kinetochemical and morphological differentiation of Ettringites by metakaolin, Portland cements and the Le Chatelier-Ansttet test. Parameter: Vicat Needle penetration(mm)
Silicates Industriels, 2003Co-Authors: R. TaleroAbstract:In this research, former XRD and Le Chatelier-Ansttet test(Parameter: ΔO(%)) experiments have been also verified by another parameter: Vicat Needle Penetration,VNP,(mm). For this purpose, 28 cements consisting of 7 Portland cements and 21 blended cements containing 20,30 and 40% metakaolin, have been submitted to the L-A test for two years. With all these cements, L-A specimens were manufactured and the parameter Vicat Needle Penetration,-VNP,(mm) was measured for these specimens. Other complementary determinations were: chemical analysis, XDA patterns and SEM of Ettringites and specific properties of some tested cements. These new experimental results have once again borne out that the formation rate of the Ettringite formed from the reactive alumina,Al 2 O 3 r-, present in pozzolans, must be considerably higher than the formation rate of the Ettringite from C 3 A and much higher than the Ettringite from C 4 AF, both present in OPC. Owing to this, these Ettringites were proposed being named: rapid formation(ett-rf),slow formation(ett-lf) and very slow formation(ett-vlf) Ettringites, respectively. On the other hand, these new results have also shown that: (a) For Ettringites formation, the topochemical mechanism,TPQ, must be predominant over the through solution mechanism,TS. (b) The higher the amount of M pozzolan(metakaolin) and C 3 A present in the specimens is, the more similar - qualitatively - is the setting creation, evolution and development of OPC or SRPC, to the setting creation, of 60/40 L-A specimens.
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kinetochemical and morphological differentiation of Ettringites by the le chatelier anstett test
Cement and Concrete Research, 2002Co-Authors: R. TaleroAbstract:Abstract In this research, former XRD experiments have been verified by Le Chatelier–Ansttet (L-A) test. For this purpose, 28 cements consisting of 7 Portland cements and 21 blended cements containing 20%, 30% and 40% metakaolin have been submitted to the Le Chatelier–Anstett (L-A) test for 2 years. With all these cements, L-A specimens were manufactured and a direct parameter was measured for these specimens: increase in diameter, Δ∅, or diameter growth. Other complementary determinations were chemical analysis, XDA patterns and SEM of Ettringites and specific properties of some cements tested. The experimental results have borne out that the formation rate of the Ettringite formed from the reactive alumina, Al2O3r−, present in pozzolans must be considerably higher than the formation rate of the Ettringite from C3A and much higher than the Ettringite from C4AF, both present in OPC. Owing to this, these Ettringites were proposed being named “rapid formation” (ett-rf), “slow formation” (ett-lf) and “very slow formation” (ett-vlf) Ettringites, respectively. On the other hand, these experimental results have also shown that the ett-rf has a much smaller size than the ett-lf (this is a direct consequence of the aforementioned conclusion); that almost all the alumina, Al2O3, present in M pozzolan must be regarded as being “reactive,” Al2O3r−, or at least, the greatest part; that the detrimental effects derived from gypsum attack are shown much earlier in these POZC than in their plain OPC and, to such an extent, that this aggressive action can be described as rapid gypsum attack; and that none of the 21 POZC tested can be described as high nor moderate sulphate resistant cements according to L-A test.