![]() Cement and Concrete Research 39, 1111-1121. Physical and microstructural aspects of sulfate attack on ordinary and limestone blended Portland cements. Schmidt, T., Lothenbach, B., Romer, M., Neuenschwander, J., Scrivener K., 2009. How to identify carbonate rock reactions in concrete. Dietmar Kruger currently lives in Los Angeles, CA in the past Dietmar has also lived in Santa Monica CA and Spokane Valley WA. Instrument having Wienand, Karlheinz Klammer, Marc Dietmann. Dolomite dissolution under alkaline condition is a dynamic process of dissolution and precipitation stimulated by high Ca2+ content, high ionic strength, low temperature and high pH with the consequence of low Mg2+ concentration. Weitzel, Dietmar : SeeWestinghouse Electric Corporation : SeePfeifer, Thomas. Brucite and calcite were detected insitu by Raman spectroscopy surrounding partially dissolved dolomite grains. pH > 11 further accelerate the process of dedolomitization by the removal of Mg2+ as brucite (Mg(OH)2) precipitates. In consequence dolomite solubility increases with increasing ionic strength. It is believed that solutions can even reach thenardite saturation as efflorescences are found on the tunnel walls. Some interstitial solutions are dominated mainly by Na+ and SO42- and reach concentrations up to 30 g/l TDS. Portlandite acts as an additional Ca2+ source and is much more abundant than the alkalies. Furthermore it is more likely that Portlandite (Ca(OH)2) plays a more important role than Na and K in the cement. Interacting ground water is enriched in Ca2+and saturated with respect to gypsum as marine evaporites are found in situ rocks. Modelling approaches by PhreeqC show a thermodynamically possibility in the alkaline range when additional Ca2+ in solution causes dolomite to become more and more undersaturated as calcite gets supersaturated. In addition a series of batch experiments is set up. Werner Piller Head of Doctoral School Earth Sciences at. 27-31, D-35578 Wetzlar telex 483 867 grun telefax (064 41) 20 06-40 Production. Dietmar Klammer Head of Doctoral School Geosciences (Class of Earth Sciences) at TU Graz. Petrological analysis such as microprobe, SEM and Raman spectroscopy as well as a hydrochemical analysis of interstitial solutions and ground water and modelling with PhreeqC (Parkhurst and Appelo, 1999) are carried out. Dietmar Klammer indust56 misc23 Grn-Optik Wetzlar GmbH Industriestr. Therefore we investigated concrete samples from Austrian tunnels that show partially dissolved dolomite aggregates. In this study we are trying to gain new insides about the conditions that can lead to the dissolution of dolomite in concrete. Due to very low solubility of dolomite in alkaline solutions this reaction seems doubtful. It is believed that dolomite aggregates can react with the alkalis from the cement, dissolve and form calcite and brucite (Katayama, 2004). Much less is known about the so called alkali carbonate reaction (ACR). Abstract reprinted with permission from Elsevier.Chemical alteration of concrete has gained much attention over the past years as many cases of deterioration due to sulphate attack, thaumasite formation (TSA) or alkali silica reactions (ASR) have been reported in various constructions (Schmidt et al, 2009).Find a library where document is available. ![]() ![]() In this contribution, the reaction mechanisms and environmental controls of de-dolomitization are discussed in relation to the durability of concrete under sulfate attack. Infiltration of Ca–SO₄–type ground water into the de-dolomitization zone facilitated calcite and brucite neo-formations at 13 > pH > 10.5 during advanced states of concrete deterioration and subsequently resulted in thaumasite precipitation at pH ~ 8.7. Leaching of hydrated cement phases resulted in IS with a pH ~ 12-13, which promoted incongruent dolomite dissolution. During the initial stage of sulfate attack, ettringite and gypsum formation weakened the concrete's microstructure and initiated ACR. A conceptual reaction model for the portlandite–calcium silicate hydrate (CSH) phases–dolomite–calcium sulfate–calcite–brucite–thaumasite system was developed based on experimental data, hydrochemical modelling, IS chemistry and apparent concrete compositions. Environmental controls and reaction pathways of coupled de-dolomitization and thaumasite formationĭeteriorated concrete and interstitial solutions (IS) were collected from Austrian tunnels to elucidate potential connections between de-dolomitization caused by coupled alkali carbonate reactions (ACR) and thaumasite form of sulfate attack (TSA).
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