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Hjh Jos Brouwers – One of the best experts on this subject based on the ideXlab platform.

  • a method for predicting the Alkali concentrations in pore solution of hydrated slag cement paste
    Journal of Materials Science, 2011
    Co-Authors: Wei Chen, Hjh Jos Brouwers
    Abstract:

    The Alkalinity of the pore liquid in hardened cement paste or concrete is important for the long-term evaluation of Alkalisilica reaction (ASR) expansion and corrosion prevention of steel bar in steel reinforced structures among others. It influences the reactivity of supplementary cementitious materials as well. This paper focuses on the Alkali binding in hydrated slag cement paste and a method for predicting the Alkali concentrations in the pore solution is developed. The hydration of slag cement is simulated with a computer-based model CEMHYD3D. The amount of Alkalis released by the cement hydration, quantities of hydration products, and volume of the pore solution are calculated from the model outputs. A large set of experimental results reported in different literatures are used to derive the Alkali-binding capacities of the hydration products and practical models are proposed based on the computation results. It was found that the hydrotalcite-like phase is a major binder of Alkalis in hydrated slag cement paste, and the C–S–H has weaker Alkali-binding capacity than the C–S–H in hydrated Portland cement paste. The method for predicting the Alkali concentrations in the pore solution of hydrated slag cement paste is used to investigate the effects of different factors on the Alkalinity of pore solution in hydrated slag cement paste.

  • Alkali binding in hydrated portland cement paste
    Cement and Concrete Research, 2010
    Co-Authors: Wei Chen, Hjh Jos Brouwers
    Abstract:

    The Alkali-binding capacity of C–S–H in hydrated Portland cement pastes is addressed in this study. The amount of bound Alkalis in C–S–H is computed based on the Alkali partition theories firstly proposed by Taylor (1987) and later further developed by Brouwers and Van Eijk (2003). Experimental data reported in literatures concerning thirteen different recipes are analyzed and used as references. A three-dimensional computer-based cement hydration model (CEMHYD3D) is used to simulate the hydration of Portland cement pastes. These model predictions are used as inputs for deriving the Alkali-binding capacity of the hydration product C–S–H in hydrated Portland cement pastes. It is found that the relation of Na+ between the moles bound in C–S–H and its concentration in the pore solution is linear, while the binding of K+ in C–S–H complies with the Freundlich isotherm. New models are proposed for determining the Alkali-binding capacities of C–S–H in hydrated Portland cement paste. An updated method for predicting the Alkali concentrations in the pore solution of hydrated Portland cement pastes is developed. It is also used to investigate the effects of various factors (such as the water to cement ratio, clinker composition and Alkali types) on the Alkali concentrations.

Barbara Lothenbach – One of the best experts on this subject based on the ideXlab platform.

  • Alkali binding by magnesium silicate hydrates
    Journal of the American Ceramic Society, 2019
    Co-Authors: Ellina Bernard, Barbara Lothenbach, Isabelle Pochard, Celine Cauditcoumes
    Abstract:

    The binding of Na+, K+, and Li+ by magnesium silisilicate hydrate (M–S–H) was investigated in batch sorption experiments. Sorption isotherms and cation exchange measurements indicated the binding of Alkalis in cation exchange sites compensating the negative surface charge of M–S–H. Higher pH values led to further deprotonation of the silanol groups and a higher Alkali uptake by M–S–H. No significant incorporation of Alkalis in the main silica or magnesium oxide sheets was observed. However, the silica sheets were less polymerized in the presence of higher Alkali hydroxide concentrations.

  • Alkali uptake in calcium alumina silicate hydrate c a s h
    Cement and Concrete Research, 2016
    Co-Authors: E Lhopital, Barbara Lothenbach, Karen Scrivener, Dmitrii A Kulik
    Abstract:

    Abstract Uptake of the Alkalis K and Na by calcium silicate hydrate (C-S-H) and calcium alumina silicate hydrate (C-A-S-H) of molar Ca/Si ratios = 0.6 to 1.6 and molar Al/Si ratio = 0 or 0.05 has been studied at 20 °C. Alkalis are thought to be bound in the interlayer space of C-A-S-H and show preferred uptake by lower Ca/Si ratios and by higher Alkali concentrations. A consequence of Alkali uptake into C-A-S-H is a rearrangement of the C-A-S-H structure. Less calcium is present in the interlayer and shorter silica chains are observed for the same molar Ca/Si ratio. No significant difference was observed between sodium and potassium uptake. Equilibration times of 91 days to 1 year or the solid phase being either C-S-H or C-A-S-H had seemingly no effect on Alkali uptake.

  • composition solubility structure relationships in calcium Alkali aluminosilicate hydrate c n k a s h
    Dalton Transactions, 2015
    Co-Authors: E Lhopital, John L Provis, Rupert J Myers, Barbara Lothenbach
    Abstract:

    The interplay between the solubility, structure and chemical composition of calcium (Alkali) aluminosilicate hydrate (C-(N,K-)A-S-H) equilibrated at 50 °C is investigated in this paper. The tobermorite-like C-(N,K-)A-S-H products are more crystalline in the presence of Alkalis, and generally have larger basal spacings at lower Ca/Si ratios. Both Na and K are incorporated into the interlayer space of the C-(N,K-)A-S-H phases, with more Alkali uptake observed at higher Alkali and lower Ca content. No relationship between Al and Alkali uptake is identified at the Al concentrations investigated (Al/Si ≤ 0.1). More stable C-(N,K-)A-S-H is formed at higher Alkali content, but this factor is only significant in some samples with Ca/Si ratios ≤1. Shorter chain lengths are formed at higher Alkali and Ca content, and cross-linking between (alumino)silicate chains in the tobermorite-like structure is greatly promoted by increasing Alkali and Al concentrations. The calculated solubility products do not depend greatly on the mean chain length in C-(N,K-)A-S-H at a constant Ca/(Al + Si) ratio, or the Al/Si ratio in C-(N,K-)A-S-H. These results are important for understanding the chemical stability of C-(N,K-)A-S-H, which is a key phase formed in the majority of cements and concretes used worldwide.

Benoit Fournier – One of the best experts on this subject based on the ideXlab platform.

  • Effect of Alkali release by aggregates on Alkali-silica reaction
    Construction and Building Materials, 2017
    Co-Authors: C. Drolet, Josée Duchesne, Benoit Fournier
    Abstract:

    Abstract Mortar and concrete specimens were made using one Alkali-bearing reactive aggregate, one Alkali-free reactive aggregate and one Alkali-free non-reactive aggregate in order to determine the effect of an Alkali release by an aggregate into the pore solution on the development of ASR using pore water extraction and direct expansion measurements. The fine fraction of the Alkali-bearing reactive aggregate was found to be able to release up to 3 wt% of its total Na 2 O content (0.73 kg Na 2 O/m 3 ) into the pore solution of mortar at the age of one year for specimens stored at 60 °C. However, there is no evidence that this sodium release influenced the rate of the development of the expansion. Results on mortar specimens also indicated that the amount of Na 2 O bounded into ASR gel is approximately proportional to the progress of expansion. The same proportionality is however not observed for potassium ion. For concrete specimens, it is clear that Na 2 O and K 2 O ions are bound into ASR reaction products, but there is no evidence that the coarse fraction of the Alkali-bearing aggregate released Alkalis into the pore solution of concrete after one year of testing completed in this study.

  • Alteration of Alkali reactive aggregates autoclaved in different Alkali solutions and application to Alkali-aggregate reaction in concrete (II) expansion and microstructure of concrete microbar
    Cement and Concrete Research, 2006
    Co-Authors: Laibao Mei, Mingshu Tang, Benoit Fournier
    Abstract:

    The effect of the type of Alkalis on the expansion behavior of concrete microbars containing typical aggregate with Alkalisilica reactivity and Alkali-carbonate reactivity was studied. The results verified that: (1) at the same molar concentration, sodium has the strongest contribution to expansion due to both ASR and ACR, followed by potassium and lithium; (2) sufficient LiOH can completely suppress expansion due to ASR whereas it can induce expansion due to ACR. It is possible to use the duplex effect of LiOH on ASR and ACR to clarify the ACR contribution when ASR and ACR may coexist. It has been shown that a small amount of dolomite in the fine-grained siliceous Spratt limestone, which has always been used as a reference aggregate for high Alkalisilica reactivity, might dedolomitize in Alkaline environment and contribute to the expansion. That is to say, Spratt limestone may exhibit both Alkalisilica and Alkali-carbonate reactivity, although Alkalisilica reactivity is predominant. Microstructural study suggested that the mechanism in which lithium controls ASR expansion is mainly due to the favorable formation of lithium-containing less-expansive product around aggregate particles and the protection of the reactive aggregate from further attack by Alkalis by the lithium-containing product layer.

Wei Chen – One of the best experts on this subject based on the ideXlab platform.

  • a method for predicting the Alkali concentrations in pore solution of hydrated slag cement paste
    Journal of Materials Science, 2011
    Co-Authors: Wei Chen, Hjh Jos Brouwers
    Abstract:

    The Alkalinity of the pore liquid in hardened cement paste or concrete is important for the long-term evaluation of Alkali-silica reaction (ASR) expansion and corrosion prevention of steel bar in steel reinforced structures among others. It influences the reactivity of supplementary cementitious materials as well. This paper focuses on the Alkali binding in hydrated slag cement paste and a method for predicting the Alkali concentrations in the pore solution is developed. The hydration of slag cement is simulated with a computer-based model CEMHYD3D. The amount of Alkalis released by the cement hydration, quantities of hydration products, and volume of the pore solution are calculated from the model outputs. A large set of experimental results reported in different literatures are used to derive the Alkali-binding capacities of the hydration products and practical models are proposed based on the computation results. It was found that the hydrotalcite-like phase is a major binder of Alkalis in hydrated slag cement paste, and the C–S–H has weaker Alkali-binding capacity than the C–S–H in hydrated Portland cement paste. The method for predicting the Alkali concentrations in the pore solution of hydrated slag cement paste is used to investigate the effects of different factors on the Alkalinity of pore solution in hydrated slag cement paste.

  • Alkali binding in hydrated portland cement paste
    Cement and Concrete Research, 2010
    Co-Authors: Wei Chen, Hjh Jos Brouwers
    Abstract:

    The Alkali-binding capacity of C–S–H in hydrated Portland cement pastes is addressed in this study. The amount of bound Alkalis in C–S–H is computed based on the Alkali partition theories firstly proposed by Taylor (1987) and later further developed by Brouwers and Van Eijk (2003). Experimental data reported in literatures concerning thirteen different recipes are analyzed and used as references. A three-dimensional computer-based cement hydration model (CEMHYD3D) is used to simulate the hydration of Portland cement pastes. These model predictions are used as inputs for deriving the Alkali-binding capacity of the hydration product C–S–H in hydrated Portland cement pastes. It is found that the relation of Na+ between the moles bound in C–S–H and its concentration in the pore solution is linear, while the binding of K+ in C–S–H complies with the Freundlich isotherm. New models are proposed for determining the Alkali-binding capacities of C–S–H in hydrated Portland cement paste. An updated method for predicting the Alkali concentrations in the pore solution of hydrated Portland cement pastes is developed. It is also used to investigate the effects of various factors (such as the water to cement ratio, clinker composition and Alkali types) on the Alkali concentrations.

Ondrej Gedeon – One of the best experts on this subject based on the ideXlab platform.

  • Analysis of Alkali-silicate glasses by electron probe analysis
    Spectrochimica Acta Part B: Atomic Spectroscopy, 2003
    Co-Authors: Karel Jurek, Ondrej Gedeon
    Abstract:

    Abstract The brief review of our previous papers concerning the bombardment of Alkalisilicate glass by electron beam is presented. Phenomena connected with Alkali ions migration are summarized and explained. The paper contributes to a better understanding of glass structure as well as to the achievement of optimum analytical conditions and consequent results in glass containing Alkalis.