Alkali–Silica Reaction: The Influence of Calcium on Silica Dissolution and the Formation of Reaction Products

Swiss Federal Laboratories for Materials Science and Technology, Empa, 8600 Dübendorf, Switzerland
Journal of the American Ceramic Society (Impact Factor: 2.61). 11/2010; 94(4):1243 - 1249. DOI: 10.1111/j.1551-2916.2010.04202.x


In a model system for alkali–silica reaction consisting of microsilica, portlandite (0–40 mass%), and 1M alkaline solutions (NaOH, KOH), the influence of calcium on silica dissolution and on the formation of reaction products is investigated. The reaction and its products are characterized using calorimetry, X-ray diffraction, thermogravimetric analysis, nuclear magnetic resonance, desorption experiments, and pore solution analysis in combination with thermodynamic modeling. Silica dissolution proceeds until portlandite is consumed due to the formation of C–S–H, and subsequently, saturation of dissolved silica in the alkaline solution is reached. As a result, the amount of dissolved silica increases with the increasing portlandite content. Depending on the amount of portlandite added, the reaction products show differences in the relative amounts of Q1, Q2, and Q3 sites formed and in their average Ca/Si ratio. The ability of the reactions products to chemically bind water decreases with the decreasing relative amount of Q3 sites and with the increasing Ca/Si ratio. However, the amount of physically bound water in the reaction products reaches a maximum value at a Ca/Si ratio between 0.20 and 0.30.

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    • "The suggested sequence includes the formation of C–S–H as the first reaction product in the ASR process. The formation of C–S–H continues up to a point of local depletion of Ca(OH) 2 [8] [9] [10] [11] [12]. "
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    ABSTRACT: This paper presents the results of the investigations on the chemistry of pore solutions, the contents of calcium hydroxide, and the expansions in mortars containing both reactive and non-reactive aggregates. In order to examine the effect of the temperature, experiments were performed at three different temperatures (23 °C, 38 °C and 55 °C). The composition of the pore solution were measured at short time intervals for a period of up to 130 days in order to capture the kinetics of chemistry of pore solution. The results showed that the changes in the concentrations of alkali ions can be best explained by the first order reaction. In addition, the proposed rate equation could reasonably simulate the changes in the actual concentrations of alkalis. Finally, the results in this paper suggest that the rate of the alkali-silica reaction in cementitious system containing highly reactive aggregate can be also expressed as the first order reaction.
    Cement and Concrete Research 05/2015; 71. DOI:10.1016/j.cemconres.2015.01.017 · 2.86 Impact Factor
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    • "In the microsilica samples with portlandite addition, the amount of reacted microsilica increases with increasing portlandite content as shown by calorimetry, XRD and NMR results. In these samples the formation of C–S–H removes silicon from the pore solution, enabling further microsilica dissolution [31]. The reaction proceeds until calcium is depleted. "
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    ABSTRACT: The influence of the LiNO3 on the ASR product was studied both in a model system and in mortars. In the model system, the addition of LiNO3 decreases the dissolution rate and the solubility of silica. Lithium changes the 2-dimensional cross-linked (Q3 dominated) network of the ASR product into a less structured, Q2 dominated product, likely by adopting the role of calcium. In the mortar samples the addition of LiNO3 decreases expansion and significantly influences the chemical composition and the morphology of the reaction product. Lithium decreases the calcium, sodium and potassium content and changes the relatively porous plate-like reaction product into a dense one without texture. The findings in the mortars indicate that the ASR-suppressing effect of lithium is caused by the lower potential of the reaction product to swell. Furthermore, it forms a protective barrier after an initial reaction slowing down ASR.
    Cement and Concrete Research 03/2014; 59:73-86. DOI:10.1016/j.cemconres.2014.02.00 · 2.86 Impact Factor
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    ABSTRACT: Alkali silica reaction (ASR) occurs due to chemical reaction between hydroxyl ions in the pore water within the concrete matrix and certain forms of silica. This reaction could lead to strength loss, cracking, volume expansion and potentially failure of the structure. This manuscript reports findings of an experimental investigation of the inter-particle bonding between the reactive aggregates and the geopolymer matrix. Specimens were prepared using two Class F and one Class C fly ash stockpiles. Mechanical testing included the potential reactivity of aggregate and length change measurements as per ASTM standards. Petrographic analysis was conducted using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results suggest that the extent of ASR reactions due to the presence of reactive aggregates in fly ash-based geopolymer concrete is substantially lower than in the case of OPC based concrete, and well below the ASTM specified threshold. The ability to utilize ASR-vulnerable aggregates in the production of geopolymer concrete products would increase the economic and sustainability appeal of this technology, potentially resulting in significant cost savings and reduce carbon footprint by eliminating the need to transport large volumes of high quality aggregates across the country.
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