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N Thaulow - One of the best experts on this subject based on the ideXlab platform.
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delayed ettringite formation in swedish concrete railroad ties
Cement and Concrete Research, 2004Co-Authors: Sadananda Sahu, N ThaulowAbstract:Since the 1970s, failures of a number of precast concrete products manufactured at elevated temperatures have been reported. This article reports on a case where a petrographic examination of cracked Swedish concrete railroad ties identified delayed ettringite formation (DEF) as the damaging mechanism. This was unexpected because the concrete railroad ties were steam-cured with a maximum concrete temperature below 60 deg C. The authors discuss the influence of various parameters on DEF, in light of this case. They note that DEF is not only influenced by the curing temperature, but also by various other factors, such as Cement Composition (alkalis, C3S, C3A, SO3, and MgO), fineness, etc. The authors conclude that if an unfavorable combination of these parameters exists, delayed ettringite may occur at lower temperatures than 70 deg C. The conditions that confer risk include the use of high alkali Cement with high surface area, high C3S content, concrete with low water-to-Cement ratio, and high Cement content.
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DELAYED ETTRINGITE FORMATION IN SWEDISH CONCRETE RAILROAD TIES
Cement and Concrete Research, 2004Co-Authors: Sadananda Sahu, N ThaulowAbstract:Abstract A petrographic examination of cracked Swedish concrete railroad ties identified delayed ettringite formation (DEF) as the damaging mechanism. This was unexpected because the concrete railroad ties were steam-cured with a maximum concrete temperature below 60 °C. The consensus in the published literature is that DEF only occurs in concrete subjected to heat curing above 70 °C. However, DEF is not only influenced by the curing temperature, but also by various other factors, such as Cement Composition (alkalis, C3S, C3A, SO3, and MgO), fineness, etc. If an unfavorable combination of these parameters exists, delayed ettringite may occur at lower temperatures than 70 °C. In this paper, the influence of various parameters on DEF is discussed with reference to the investigated concrete.
Sadananda Sahu - One of the best experts on this subject based on the ideXlab platform.
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delayed ettringite formation in swedish concrete railroad ties
Cement and Concrete Research, 2004Co-Authors: Sadananda Sahu, N ThaulowAbstract:Since the 1970s, failures of a number of precast concrete products manufactured at elevated temperatures have been reported. This article reports on a case where a petrographic examination of cracked Swedish concrete railroad ties identified delayed ettringite formation (DEF) as the damaging mechanism. This was unexpected because the concrete railroad ties were steam-cured with a maximum concrete temperature below 60 deg C. The authors discuss the influence of various parameters on DEF, in light of this case. They note that DEF is not only influenced by the curing temperature, but also by various other factors, such as Cement Composition (alkalis, C3S, C3A, SO3, and MgO), fineness, etc. The authors conclude that if an unfavorable combination of these parameters exists, delayed ettringite may occur at lower temperatures than 70 deg C. The conditions that confer risk include the use of high alkali Cement with high surface area, high C3S content, concrete with low water-to-Cement ratio, and high Cement content.
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DELAYED ETTRINGITE FORMATION IN SWEDISH CONCRETE RAILROAD TIES
Cement and Concrete Research, 2004Co-Authors: Sadananda Sahu, N ThaulowAbstract:Abstract A petrographic examination of cracked Swedish concrete railroad ties identified delayed ettringite formation (DEF) as the damaging mechanism. This was unexpected because the concrete railroad ties were steam-cured with a maximum concrete temperature below 60 °C. The consensus in the published literature is that DEF only occurs in concrete subjected to heat curing above 70 °C. However, DEF is not only influenced by the curing temperature, but also by various other factors, such as Cement Composition (alkalis, C3S, C3A, SO3, and MgO), fineness, etc. If an unfavorable combination of these parameters exists, delayed ettringite may occur at lower temperatures than 70 °C. In this paper, the influence of various parameters on DEF is discussed with reference to the investigated concrete.
Barbara Lothenbach - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic modelling of short and long term hydration of ternary binders influence of portland Cement Composition and blast furnace slag content
Construction and Building Materials, 2018Co-Authors: A Fernandez, Barbara Lothenbach, M C Alonso, Jose Luis Garcia CalvoAbstract:Abstract Ternary blends are currently used to improve the properties of Portland Cement (PC). In this paper, thermodynamic modelling has been used to analyze the influence of the PC Composition on the hydrates formed, in binary and ternary blends with blast furnace slag (BFS), and limestone filler (LF) or fly ash (FA) in order to complement experimental results. Thermodynamic modelling shows that contents of 40–50% of BFS can be optimal in ternary blends with low LF or FA content, and modelling also shows the significant effect of the Composition of the PC used in the hydration process of the blends.
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the role of calcium carbonate in Cement hydration
Cement and Concrete Research, 2007Co-Authors: Thomas Matschei, Barbara Lothenbach, F P GlasserAbstract:Limestone, mainly consisting of calcite, is a permitted additive to Portland Cements often up to a 5 wt.% limit. It is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated Cement pastes. Calcite affects the mineralogical variant of the AFm phase(s). Calcite additions affect the amount of free calcium hydroxide as well as the balance between AFm and AFt phases, although C–S–H is unaffected in much of the range of Compositions. Generic data are shown in graphical form to quantify these mineralogical changes as functions of Cement Composition and amount of added calcite. Calculations of the specific volume of solids as a function of calcite addition suggest that the space-filling ability of the paste is optimised when the calcite content is adjusted to maximise the AFt content. However, before the calculated data can be used uncritically, certain kinetic constraints on reactivity also need to be assessed. Progress towards the quantification of paste mineralogy suggests that (i) elucidation of the mineralogy of pastes, particularly blended Cement pastes, is facilitated by using both theoretical and experimental approaches and (ii) that the ultimate goal, of calculating paste mineralogy from the bulk chemistry, is attainable.
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thermodynamic modelling of the hydration of portland Cement
Cement and Concrete Research, 2006Co-Authors: Barbara Lothenbach, Frank WinnefeldAbstract:A thermodynamic model is developed and applied to calculate the Composition of the pore solution and the hydrate assemblage during the hydration of an OPC. The calculated hydration rates of the individual clinker phases are used as time dependent input. The modelled data compare well with the measured Composition of pore solutions gained from OPC as well as with TGA and semi-quantitative XRD data. The thermodynamic calculations indicate that in the presence of small amounts of calcite typically included in OPC Cements, C-S-H, portlandite, ettringite and calcium monocarbonates are the main hydration products. The thermodynamic model presented in this paper helps to understand the interactions between the different components and the environment and to predict the influence of changes in Cement Composition on the hydrate assemblage.
Frank Winnefeld - One of the best experts on this subject based on the ideXlab platform.
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hydration of calcium sulfoaluminate Cements experimental findings and thermodynamic modelling
Cement and Concrete Research, 2010Co-Authors: Frank Winnefeld, Arbara LothenbachAbstract:Abstract Calcium sulfoaluminate Cements (CSA) are a promising low-CO 2 alternative to ordinary Portland Cements and are as well of interest concerning their use as binder for waste encapsulation. In this study, the hydration of two CSA Cements has been investigated experimentally and by thermodynamic modelling between 1 h and 28 days at w / c ratios of 0.72 and 0.80, respectively. The main hydration product of CSA is ettringite, which precipitates together with amorphous Al(OH) 3 until the calcium sulfate is consumed after around 1–2 days of hydration. Afterwards, monosulfate is formed. In the presence of belite, stratlingite occurs as an additional hydration product. The pore solution analysis reveals that stratlingite can bind a part of the potassium ions, which are released by the clinker minerals. The microstructure of both Cements is quite dense even after 16 h of hydration, with not much pore space available at a sample age of 28 days. The pore solution of both Cements is dominated during the first hours of hydration by potassium, sodium, calcium, aluminium and sulfate; the pH is around 10–11. When the calcium sulfate is depleted, the sulfate concentration drops by a factor of 10. This increases pH to around 12.5–12.8. Based on the experimental data, a thermodynamic hydration model for CSA Cements based on Cement Composition, hydration kinetics of clinker phases and calculations of thermodynamic equilibria by geochemical speciation has been established. The modelled phase development with ongoing hydration agrees well with the experimental findings.
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thermodynamic modelling of the hydration of portland Cement
Cement and Concrete Research, 2006Co-Authors: Barbara Lothenbach, Frank WinnefeldAbstract:A thermodynamic model is developed and applied to calculate the Composition of the pore solution and the hydrate assemblage during the hydration of an OPC. The calculated hydration rates of the individual clinker phases are used as time dependent input. The modelled data compare well with the measured Composition of pore solutions gained from OPC as well as with TGA and semi-quantitative XRD data. The thermodynamic calculations indicate that in the presence of small amounts of calcite typically included in OPC Cements, C-S-H, portlandite, ettringite and calcium monocarbonates are the main hydration products. The thermodynamic model presented in this paper helps to understand the interactions between the different components and the environment and to predict the influence of changes in Cement Composition on the hydrate assemblage.
Kimberly E Kurtis - One of the best experts on this subject based on the ideXlab platform.
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influence of portland Cement Composition on early age reactions with metakaolin
Cement and Concrete Research, 2007Co-Authors: Fabien Lagier, Kimberly E KurtisAbstract:Abstract The reactivity of two metakaolins, which vary principally in their surface area, and Portland Cements of varying Composition were examined via isothermal calorimetry for pastes at water-to-Cementitious materials ratio of 0.50 containing 8% Cement replaCement by weight of metakaolin. Both metakaolins examined appear to have a catalysing effect on Cement hydration. Calorimetry showed accelerated hydration, a slight increase in cumulative heat evolved during early hydration, and – for some Cements examined – apparently an increased intensity of the heat evolved, particularly during the period typically associated with hydration of calcium aluminates. The higher surface area metakaolin had a greater effect. It is proposed that the presence of metakaolin may enhance dissolution of Cementitious phases and/or provide additional, well-dispersed sites for nucleation of hydration products, in addition to increasing the early age concentration of solubilized aluminium (due to metakaolin dissolution). The increased intensity of some of the calorimetry data also suggests that some additional exothermic reactions are occurring, which may be related to an increased reactivity of calcium aluminate phases in the Cement as well as the reaction of the metakaolin. This effect is apparently increased as the Cement equivalent alkali content increases.
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time to failure for concrete exposed to severe sulfate attack
Cement and Concrete Research, 2003Co-Authors: Paulo J M Monteiro, Kimberly E KurtisAbstract:Abstract In the 1940s, the U.S. Bureau of Reclamation (USBR) began a long-term, nonaccelerated laboratory test program to determine the influence of a variety of concrete-mix parameters on resistance to severe sulfate exposure conditions. This paper reports the time of failure of these samples as influenced by their water-to-Cement (w/c) ratio, Cement Composition, and percent replaCement of Cement with fly ash. The analysis indicates that there is a “safe zone” for concrete made with w/c ratio lower than 0.45 and Cement with unhydrated tricalcium aluminate (C 3 A) content lower than 8% where failure did not occur within the 40-year exposure period. As expected, concrete samples cast with high amount of C 3 A failed after a relatively short time of sulfate exposure. Expansion tests indicated that Cements containing high amounts of C 3 S may lead to premature failure of concrete, even when moderate w/c ratios are used. Samples prepared with 25% and 45% replaCement of Cement with fly ash showed significantly less expansion than comparable mixtures containing no pozzolans.