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Ajouter le résultat dans votre panierConcrete modelling for expertise of structures affected by alkali aggregate reaction / E. Grimal in Cement and concrete research, Vol. 40 N° 4 (Avril 2010)
Titre : Concrete modelling for expertise of structures affected by alkali aggregate reaction Type de document : texte imprimé Auteurs : E. Grimal, Auteur Année de publication : 2012 Article en page(s) : pp. 502–507 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali Aggregate Reaction Durability Modeling Structure Expertise Résumé : Alkali aggregate reaction (AAR) affects numerous civil engineering structures and causes irreversible expansion and cracking. In order to control the safety level and the maintenance cost of its hydraulic dams, Electricité de France (EDF) must reach better comprehension and better prediction of the expansion phenomena. For this purpose, EDF has developed a numerical model based on the finite element method in order to assess the mechanical behaviour of damaged structures. The model takes the following phenomena into account: concrete creep, the stress induced by the formation of AAR gel and the mechanical damage. A rheological model was developed to assess the coupling between the different phenomena (creep, AAR and anisotropic damage). Experimental results were used to test the model. The results show the capability of the model to predict the experimental behaviour of beams subjected to AAR. In order to obtain such prediction, it is necessary to take all the phenomena occurring in the concrete into consideration. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002476
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 502–507[article] Concrete modelling for expertise of structures affected by alkali aggregate reaction [texte imprimé] / E. Grimal, Auteur . - 2012 . - pp. 502–507.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 502–507
Mots-clés : Alkali Aggregate Reaction Durability Modeling Structure Expertise Résumé : Alkali aggregate reaction (AAR) affects numerous civil engineering structures and causes irreversible expansion and cracking. In order to control the safety level and the maintenance cost of its hydraulic dams, Electricité de France (EDF) must reach better comprehension and better prediction of the expansion phenomena. For this purpose, EDF has developed a numerical model based on the finite element method in order to assess the mechanical behaviour of damaged structures. The model takes the following phenomena into account: concrete creep, the stress induced by the formation of AAR gel and the mechanical damage. A rheological model was developed to assess the coupling between the different phenomena (creep, AAR and anisotropic damage). Experimental results were used to test the model. The results show the capability of the model to predict the experimental behaviour of beams subjected to AAR. In order to obtain such prediction, it is necessary to take all the phenomena occurring in the concrete into consideration. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002476 Exemplaires
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Titre : Micro-mechanical modelling of alkali–silica-reaction-induced degradation using the AMIE framework Type de document : texte imprimé Auteurs : Cyrille F. Dunant, Auteur ; Karen L. Scrivenerb, Auteur Année de publication : 2012 Article en page(s) : pp. 517–525 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali-Aggregate Reaction (ASR) XFEM (out category) Long-Term Performance Mechanical Properties Modelling Résumé : AMIE, a finite element/extended finite element framework, has been designed to provide the tools to run detailed microstructural simulations; this paper demonstrates the possibility of simulating the mechanisms underlying the alkali–silica-reaction (ASR). The numerical model presented provides a better understanding of experimental observations. Macroscopic free expansion and degradation of mechanical properties have been previously linked to the extent of reaction. The connection between microscopic and macroscopic measurements, simulated by the model, supports the hypothesis that damage is induced by growing gel pockets in the aggregates. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001847
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 517–525[article] Micro-mechanical modelling of alkali–silica-reaction-induced degradation using the AMIE framework [texte imprimé] / Cyrille F. Dunant, Auteur ; Karen L. Scrivenerb, Auteur . - 2012 . - pp. 517–525.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 517–525
Mots-clés : Alkali-Aggregate Reaction (ASR) XFEM (out category) Long-Term Performance Mechanical Properties Modelling Résumé : AMIE, a finite element/extended finite element framework, has been designed to provide the tools to run detailed microstructural simulations; this paper demonstrates the possibility of simulating the mechanisms underlying the alkali–silica-reaction (ASR). The numerical model presented provides a better understanding of experimental observations. Macroscopic free expansion and degradation of mechanical properties have been previously linked to the extent of reaction. The connection between microscopic and macroscopic measurements, simulated by the model, supports the hypothesis that damage is induced by growing gel pockets in the aggregates. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001847 Exemplaires
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Titre : Effects of aggregate size and alkali content on ASR expansion Type de document : texte imprimé Auteurs : Stéphane Multon, Auteur Année de publication : 2012 Article en page(s) : pp. 508–516 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Particle size distribution Alkali-aggregate reaction Alkalis Modeling Pessimum of aggregate Résumé : Attempts to model ASR expansion are usually limited by the difficulty of taking into account the heterogeneous nature and size range of reactive aggregates. This work is a part of an overall project aimed at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. The paper gives measurements in order to provide experimental data concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Results show that no expansion was measured on the mortars using small particles (under 80 µm) while the coarse particles (0.63–1.25 mm) gave the largest expansions (0.33%). When two sizes of aggregate were used, ASR-expansions decreased with the proportion of small particles. Models are proposed to study correlations between the measured expansions and parameters such as the size of aggregates and the alkali and reactive silica contents. The pessimum effect of reactive aggregate size is assessed and the consequences on accelerated laboratory tests are discussed. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002038
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 508–516[article] Effects of aggregate size and alkali content on ASR expansion [texte imprimé] / Stéphane Multon, Auteur . - 2012 . - pp. 508–516.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 508–516
Mots-clés : Particle size distribution Alkali-aggregate reaction Alkalis Modeling Pessimum of aggregate Résumé : Attempts to model ASR expansion are usually limited by the difficulty of taking into account the heterogeneous nature and size range of reactive aggregates. This work is a part of an overall project aimed at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. The paper gives measurements in order to provide experimental data concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Results show that no expansion was measured on the mortars using small particles (under 80 µm) while the coarse particles (0.63–1.25 mm) gave the largest expansions (0.33%). When two sizes of aggregate were used, ASR-expansions decreased with the proportion of small particles. Models are proposed to study correlations between the measured expansions and parameters such as the size of aggregates and the alkali and reactive silica contents. The pessimum effect of reactive aggregate size is assessed and the consequences on accelerated laboratory tests are discussed. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002038 Exemplaires
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Titre : Influence of lithium hydroxide on alkali–silica reaction Type de document : texte imprimé Auteurs : D. Bulteel, Auteur ; E. Garcia-Diaz, Auteur ; P. Dégrugilliers, Auteur Année de publication : 2012 Article en page(s) : pp. 526–530 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali-silica reaction Reactive aggregate Reaction degree Lithium Inhibitor Résumé : Several papers show that the use of lithium limits the development of alkali–silica reaction (ASR) in concrete. The aim of this study is to improve the understanding of lithium's role on the alteration mechanism of ASR.
The approach used is a chemical method which allowed a quantitative measurement of the specific degree of reaction of ASR. The chemical concrete sub-system used, called model reactor, is composed of the main ASR reagents: reactive aggregate, portlandite and alkaline solution. Different reaction degrees are measured and compared for different alkaline solutions: NaOH, KOH and LiOH.
Alteration by ASR is observed with the same reaction degrees in the presence of NaOH and KOH, accompanied by the consumption of hydroxyl concentration. On the other hand with LiOH, ASR is very limited. Reaction degree values evolve little and the hydroxyl concentration remains about stable.
These observations demonstrate that lithium ions have an inhibitor role on ASR.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002233
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 526–530[article] Influence of lithium hydroxide on alkali–silica reaction [texte imprimé] / D. Bulteel, Auteur ; E. Garcia-Diaz, Auteur ; P. Dégrugilliers, Auteur . - 2012 . - pp. 526–530.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 526–530
Mots-clés : Alkali-silica reaction Reactive aggregate Reaction degree Lithium Inhibitor Résumé : Several papers show that the use of lithium limits the development of alkali–silica reaction (ASR) in concrete. The aim of this study is to improve the understanding of lithium's role on the alteration mechanism of ASR.
The approach used is a chemical method which allowed a quantitative measurement of the specific degree of reaction of ASR. The chemical concrete sub-system used, called model reactor, is composed of the main ASR reagents: reactive aggregate, portlandite and alkaline solution. Different reaction degrees are measured and compared for different alkaline solutions: NaOH, KOH and LiOH.
Alteration by ASR is observed with the same reaction degrees in the presence of NaOH and KOH, accompanied by the consumption of hydroxyl concentration. On the other hand with LiOH, ASR is very limited. Reaction degree values evolve little and the hydroxyl concentration remains about stable.
These observations demonstrate that lithium ions have an inhibitor role on ASR.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002233 Exemplaires
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Titre : ASR pessimum behaviour of siliceous limestone aggregates Type de document : texte imprimé Auteurs : E. Garcia-Diaz, Auteur Année de publication : 2012 Article en page(s) : pp. 546–549 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Aggregate Alkali-Aggregate Reaction ,Calcium Silicate Hydrate (C-S-H) Concrete Pessimum effect Résumé : Siliceous limestone aggregates have “pessimum” behaviours similar to those observed for pure siliceous aggregates such as flint or opal. For high alkali contents concretes based on fine and coarse reactive siliceous limestone aggregates swell less than concretes based on fine reactive siliceous limestone aggregates and non-reactive coarse aggregates. The reduction of the swelling is more significant for a “micritic” limestone containing highly reactive free silica than for a “sparitic” limestone containing less reactive free silica. The consumption of a part of the alkalis by non-expansive processes such as chemical sorption on silanol sites of reactive silica and pozzolanic C–S–H is expected to explain the reduction of the swelling. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002221
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 546–549[article] ASR pessimum behaviour of siliceous limestone aggregates [texte imprimé] / E. Garcia-Diaz, Auteur . - 2012 . - pp. 546–549.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 546–549
Mots-clés : Aggregate Alkali-Aggregate Reaction ,Calcium Silicate Hydrate (C-S-H) Concrete Pessimum effect Résumé : Siliceous limestone aggregates have “pessimum” behaviours similar to those observed for pure siliceous aggregates such as flint or opal. For high alkali contents concretes based on fine and coarse reactive siliceous limestone aggregates swell less than concretes based on fine reactive siliceous limestone aggregates and non-reactive coarse aggregates. The reduction of the swelling is more significant for a “micritic” limestone containing highly reactive free silica than for a “sparitic” limestone containing less reactive free silica. The consumption of a part of the alkalis by non-expansive processes such as chemical sorption on silanol sites of reactive silica and pozzolanic C–S–H is expected to explain the reduction of the swelling. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002221 Exemplaires
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Titre : The current state of the accelerated concrete prism test Type de document : texte imprimé Auteurs : Jason H. Ideker, Auteur Année de publication : 2012 Article en page(s) : pp. 550–555 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Pore solution Alkali–aggregate reaction Durability Alkalis Accelerated concrete prism test Résumé : Expansions due to alkali–silica reaction (ASR) in the accelerated concrete prism test (ACPT–60 °C) show a significant reduction at 13 weeks compared to 52 week testing in the standard concrete prism test (CPT–38 °C). Previous work indicated that increased leaching, higher mass loss and a reduction in the pH were observed when temperature was increased from 38 to 60 °C. After further investigation the authors have revealed that non-reactive fine aggregate from certain sources combined with the same reactive coarse aggregate exhibited further reduction in expansion in the ACPT. Expansion data for a wide range of reactive coarse aggregates in 38 and 60 °C testing regimes is shown. Data investigating the Spratt reactive coarse aggregate combined with seven different non-reactive sands will be shown to demonstrate the dramatic effect of the non-reactive sand. Selected pore solution analyses will be given to further elucidate this issue. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002245
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 550–555[article] The current state of the accelerated concrete prism test [texte imprimé] / Jason H. Ideker, Auteur . - 2012 . - pp. 550–555.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 550–555
Mots-clés : Pore solution Alkali–aggregate reaction Durability Alkalis Accelerated concrete prism test Résumé : Expansions due to alkali–silica reaction (ASR) in the accelerated concrete prism test (ACPT–60 °C) show a significant reduction at 13 weeks compared to 52 week testing in the standard concrete prism test (CPT–38 °C). Previous work indicated that increased leaching, higher mass loss and a reduction in the pH were observed when temperature was increased from 38 to 60 °C. After further investigation the authors have revealed that non-reactive fine aggregate from certain sources combined with the same reactive coarse aggregate exhibited further reduction in expansion in the ACPT. Expansion data for a wide range of reactive coarse aggregates in 38 and 60 °C testing regimes is shown. Data investigating the Spratt reactive coarse aggregate combined with seven different non-reactive sands will be shown to demonstrate the dramatic effect of the non-reactive sand. Selected pore solution analyses will be given to further elucidate this issue. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002245 Exemplaires
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Titre : Is alkali–carbonate reaction just a variant of alkali–silica reaction ACR = ASR? Type de document : texte imprimé Auteurs : P.E. Grattan-Bellew, Auteur Année de publication : 2012 Article en page(s) : pp. 556–562 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Reaction Characterization Alkali–aggregate reaction Alkali–carbonate Résumé : The mechanism of the alkali–carbonate reaction (ACR) has been recognized as being different from that of the more common alkali–silica reaction (ASR). However, the identification of alkali–silica gel in ACR concrete from Cornwall, Ontario, Canada by Katayama, in 1992 raised the possibility that ASR was at least playing a role in the ACR reaction. The acid insoluble residues of the ACR aggregate from Kingston, along with two other aggregates were analyzed to determine what might be contributing to the reaction. The acid insoluble residue of the ACR Kingston rock contains 96% quartz of high solubility in NaOH. Good correlation was found between the amount of quartz and expansion of concrete prisms indicating that the expansion was due mainly to an alkali–silica reaction. This conclusion is supported by observations, in 2008, by Katayama of gel in thin sections of concrete made with the Kingston aggregate. It is concluded that ACR = ASR. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002427
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 556–562[article] Is alkali–carbonate reaction just a variant of alkali–silica reaction ACR = ASR? [texte imprimé] / P.E. Grattan-Bellew, Auteur . - 2012 . - pp. 556–562.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 556–562
Mots-clés : Reaction Characterization Alkali–aggregate reaction Alkali–carbonate Résumé : The mechanism of the alkali–carbonate reaction (ACR) has been recognized as being different from that of the more common alkali–silica reaction (ASR). However, the identification of alkali–silica gel in ACR concrete from Cornwall, Ontario, Canada by Katayama, in 1992 raised the possibility that ASR was at least playing a role in the ACR reaction. The acid insoluble residues of the ACR aggregate from Kingston, along with two other aggregates were analyzed to determine what might be contributing to the reaction. The acid insoluble residue of the ACR Kingston rock contains 96% quartz of high solubility in NaOH. Good correlation was found between the amount of quartz and expansion of concrete prisms indicating that the expansion was due mainly to an alkali–silica reaction. This conclusion is supported by observations, in 2008, by Katayama of gel in thin sections of concrete made with the Kingston aggregate. It is concluded that ACR = ASR. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002427 Exemplaires
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Titre : Effects of seawater on AAR expansion of concrete Type de document : texte imprimé Auteurs : A. Shayan, Auteur Année de publication : 2012 Article en page(s) : pp. 563–568 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Concrete AAR Expansion Curing temperature Seawater Résumé : Recently, AAR was identified in submerged piles of some bridges in tidal waters. Microstructural examination detected chloroaluminate salts in some cracks. To clarify whether seawater had influenced the deterioration an experimental program was planned to examine the effects of sodium chloride on AAR under various curing conditions.
Concrete prisms containing either of highly-reactive, slowly-reactive or nonreactive aggregate, and either low or high alkali contents, were stored in saltwater (representing seawater) or at 100% RH, at temperatures of 38, 60 and 80 °C, for expansion measurement over 600 days, after which the temperature for those stored in saltwater was lowered to 23 °C, to check its effect on further expansion, which could be attributed to precipitation of ettringite and/or Ca-chloroaluminate.
The results indicate that the type of aggregate and concrete alkali content had the greatest effect on AAR expansion. Exposure to saltwater did not have any significant effect on the AAR expansion.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002488
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 563–568[article] Effects of seawater on AAR expansion of concrete [texte imprimé] / A. Shayan, Auteur . - 2012 . - pp. 563–568.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 563–568
Mots-clés : Concrete AAR Expansion Curing temperature Seawater Résumé : Recently, AAR was identified in submerged piles of some bridges in tidal waters. Microstructural examination detected chloroaluminate salts in some cracks. To clarify whether seawater had influenced the deterioration an experimental program was planned to examine the effects of sodium chloride on AAR under various curing conditions.
Concrete prisms containing either of highly-reactive, slowly-reactive or nonreactive aggregate, and either low or high alkali contents, were stored in saltwater (representing seawater) or at 100% RH, at temperatures of 38, 60 and 80 °C, for expansion measurement over 600 days, after which the temperature for those stored in saltwater was lowered to 23 °C, to check its effect on further expansion, which could be attributed to precipitation of ettringite and/or Ca-chloroaluminate.
The results indicate that the type of aggregate and concrete alkali content had the greatest effect on AAR expansion. Exposure to saltwater did not have any significant effect on the AAR expansion.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002488 Exemplaires
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Titre : The role of alkali content of Portland cement on the expansion of concrete prisms containing reactive aggregates and supplementary cementing materials Type de document : texte imprimé Auteurs : Medhat H. Shehata, Auteur ; Michael D.A. Thomas, Auteur Année de publication : 2012 Article en page(s) : pp. 569–574 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali–aggregate reaction Alkalis Fly ash Pore solution Modified accelerated mortar bar test Résumé : This paper presents results covering the effects of alkali content of Portland cement (PC) on expansion of concrete containing reactive aggregates and supplementary cementing materials (SCM). The results showed that the alkali content of PC has a significant effect on expansion of concrete prisms with no SCM. When SCM is used, the expansion was found to be related to both the chemical composition of the SCM and, to a lesser extent, the alkali content of the PC. The concrete expansions were explained, at least partly, on the basis of the alkalinity of a pore solution extracted from hardened cement paste samples containing the same cementing blends. An empirical relation was developed correlating the chemical composition (Ca, Si and total Na2Oe) of the cementing blend (PC + SCM) and the alkalinity of the pore solution. Results from accelerated mortar bar test (ASTM C 1260) and a modified version thereof are also presented. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002075
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 569–574[article] The role of alkali content of Portland cement on the expansion of concrete prisms containing reactive aggregates and supplementary cementing materials [texte imprimé] / Medhat H. Shehata, Auteur ; Michael D.A. Thomas, Auteur . - 2012 . - pp. 569–574.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 569–574
Mots-clés : Alkali–aggregate reaction Alkalis Fly ash Pore solution Modified accelerated mortar bar test Résumé : This paper presents results covering the effects of alkali content of Portland cement (PC) on expansion of concrete containing reactive aggregates and supplementary cementing materials (SCM). The results showed that the alkali content of PC has a significant effect on expansion of concrete prisms with no SCM. When SCM is used, the expansion was found to be related to both the chemical composition of the SCM and, to a lesser extent, the alkali content of the PC. The concrete expansions were explained, at least partly, on the basis of the alkalinity of a pore solution extracted from hardened cement paste samples containing the same cementing blends. An empirical relation was developed correlating the chemical composition (Ca, Si and total Na2Oe) of the cementing blend (PC + SCM) and the alkalinity of the pore solution. Results from accelerated mortar bar test (ASTM C 1260) and a modified version thereof are also presented. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002075 Exemplaires
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Titre : Reactivity of reclaimed concrete aggregate produced from concrete affected by alkali–silica reaction Type de document : texte imprimé Auteurs : Medhat H. Shehata, Auteur Année de publication : 2012 Article en page(s) : pp. 575–582 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali–Aggregate Reaction Reclaimed concrete aggregate Fly Ash Lithium Compound SEM Résumé : This paper presents results from a research program that focused on studying the reactivity of reclaimed concrete aggregate (RCA) produced from concrete affected by alkali–silica reaction (ASR). The results showed that RCA produced from ASR-affected concrete causes significant expansion when used in new concrete. The expansion was similar to that produced in concrete containing the reactive aggregate used originally in the old concrete. It is believed that crushing the old concrete exposed fresh faces of the reactive aggregate which causes renewed reaction and expansion in the new concrete. The alkalis contributed from the RCA are also believed to contribute to the expansion. The amount of supplementary cementing materials required to mitigate the expansion in new concrete containing ASR-affected RCA was higher than those normally needed in concrete containing the virgin reactive aggregate. The results showed a good agreement between the 14-day expansion of accelerated mortar bars and the expansion of concrete prisms. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002087
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 575–582[article] Reactivity of reclaimed concrete aggregate produced from concrete affected by alkali–silica reaction [texte imprimé] / Medhat H. Shehata, Auteur . - 2012 . - pp. 575–582.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 575–582
Mots-clés : Alkali–Aggregate Reaction Reclaimed concrete aggregate Fly Ash Lithium Compound SEM Résumé : This paper presents results from a research program that focused on studying the reactivity of reclaimed concrete aggregate (RCA) produced from concrete affected by alkali–silica reaction (ASR). The results showed that RCA produced from ASR-affected concrete causes significant expansion when used in new concrete. The expansion was similar to that produced in concrete containing the reactive aggregate used originally in the old concrete. It is believed that crushing the old concrete exposed fresh faces of the reactive aggregate which causes renewed reaction and expansion in the new concrete. The alkalis contributed from the RCA are also believed to contribute to the expansion. The amount of supplementary cementing materials required to mitigate the expansion in new concrete containing ASR-affected RCA was higher than those normally needed in concrete containing the virgin reactive aggregate. The results showed a good agreement between the 14-day expansion of accelerated mortar bars and the expansion of concrete prisms. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002087 Exemplaires
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Titre : Experimental investigation of the mechanisms by which LiNO3 is effective against ASR Type de document : texte imprimé Auteurs : C. Tremblay, Auteur Année de publication : 2012 Article en page(s) : pp. 583–597 Langues : Anglais (eng) Mots-clés : Alkali-silica reaction Concrete expansion testing Lithium nitrate inhibition mechanisms Reaction products Résumé : Various series of experiments were carried out on cements pastes, concretes made with a variety of reactive aggregates, composite specimens made of cement paste and reactive aggregate particles, and a variety of reactive natural aggregates and mineral phases immersed in various Li-bearing solutions. The main objective was to determine which mechanisms(s) better explain(s) the effectiveness of LiNO3 against ASR and variations in this effectiveness as well with the type of reactive aggregate to counteract. The principal conclusions are the following: (1), the pH in the concrete pore solution does not significantly decrease in the presence of LiNO3; (2), the concentration of silica in the pore solution is always low and not affected by the presence of LiNO3, which does not support the mechanism relating to higher solubility of silica in the presence of lithium; (3), the only reaction product observed in the LiNO3-bearing concretes looks like classical ASR gel and its abundance is proportional to concrete expansion, thus is likely expansive while likely containing lithium; this does not support the mechanisms relating to formation of a non or less expansive Si–Li crystalline product or amorphous gel; (4), early-formed reaction products coating the reactive silica grains or aggregate particles, which could act as a physical barrier against further chemical attack of silica, were not observed in the LiNO3-bearing concretes, but only for a number of reactive materials after immersion in 1 N LiOH at 350 °C in the autoclave (also at 80 °C for obsidian); (5), higher chemical stability of silica due to another reason than pH reduction or early formation of a protective coating over the reactive phases, is the mechanism among those considered in this study that better explains the effectiveness of LiNO3 against ASR. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002750
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 583–597[article] Experimental investigation of the mechanisms by which LiNO3 is effective against ASR [texte imprimé] / C. Tremblay, Auteur . - 2012 . - pp. 583–597.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 583–597
Mots-clés : Alkali-silica reaction Concrete expansion testing Lithium nitrate inhibition mechanisms Reaction products Résumé : Various series of experiments were carried out on cements pastes, concretes made with a variety of reactive aggregates, composite specimens made of cement paste and reactive aggregate particles, and a variety of reactive natural aggregates and mineral phases immersed in various Li-bearing solutions. The main objective was to determine which mechanisms(s) better explain(s) the effectiveness of LiNO3 against ASR and variations in this effectiveness as well with the type of reactive aggregate to counteract. The principal conclusions are the following: (1), the pH in the concrete pore solution does not significantly decrease in the presence of LiNO3; (2), the concentration of silica in the pore solution is always low and not affected by the presence of LiNO3, which does not support the mechanism relating to higher solubility of silica in the presence of lithium; (3), the only reaction product observed in the LiNO3-bearing concretes looks like classical ASR gel and its abundance is proportional to concrete expansion, thus is likely expansive while likely containing lithium; this does not support the mechanisms relating to formation of a non or less expansive Si–Li crystalline product or amorphous gel; (4), early-formed reaction products coating the reactive silica grains or aggregate particles, which could act as a physical barrier against further chemical attack of silica, were not observed in the LiNO3-bearing concretes, but only for a number of reactive materials after immersion in 1 N LiOH at 350 °C in the autoclave (also at 80 °C for obsidian); (5), higher chemical stability of silica due to another reason than pH reduction or early formation of a protective coating over the reactive phases, is the mechanism among those considered in this study that better explains the effectiveness of LiNO3 against ASR. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002750 Exemplaires
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Titre : Influence of steel fibers on the development of alkali-aggregate reaction Type de document : texte imprimé Auteurs : Maria Rita Pires de Carvalho, Auteur Année de publication : 2012 Article en page(s) : pp. 598–604 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali-aggregate reaction Fiber reinforcement Mortar AAR accelerated test Résumé : This work presents the results of an experimental research concerning the use of fibers in mortar specimens subjected to alkali-aggregate reaction (AAR). Two types of steel fibers (0.16 mm diameter and 6.0 mm length, and 0.20 mm diameter and 13.0 mm length) were used with fiber volume contents of 1% and 2%. Besides the expansion accelerated tests, compressive tests and flexural tests have also been carried out to display the main mechanical characteristics of the fiber-reinforced mortars after being subjected to AAR. Moreover, the microstructure of the specimens was analyzed by scanning electron microscopy and energy dispersive X-ray. The results shown that the addition of steel fibers reduced the expansion due to AAR for the experimental conditions studied in this paper. The most expressive benefit corresponded to the addition of 13.0 mm fibers in the mixture containing 2% fiber content. This fiber volume content also corresponded to the maximum increment in the mechanical properties compared to the reference mortar, mainly for the post-cracking strength and for the toughness in bending. It was observed that the fibers have a beneficial effect on the material, without compromising its main mechanical properties. En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900338X
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 598–604[article] Influence of steel fibers on the development of alkali-aggregate reaction [texte imprimé] / Maria Rita Pires de Carvalho, Auteur . - 2012 . - pp. 598–604.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 598–604
Mots-clés : Alkali-aggregate reaction Fiber reinforcement Mortar AAR accelerated test Résumé : This work presents the results of an experimental research concerning the use of fibers in mortar specimens subjected to alkali-aggregate reaction (AAR). Two types of steel fibers (0.16 mm diameter and 6.0 mm length, and 0.20 mm diameter and 13.0 mm length) were used with fiber volume contents of 1% and 2%. Besides the expansion accelerated tests, compressive tests and flexural tests have also been carried out to display the main mechanical characteristics of the fiber-reinforced mortars after being subjected to AAR. Moreover, the microstructure of the specimens was analyzed by scanning electron microscopy and energy dispersive X-ray. The results shown that the addition of steel fibers reduced the expansion due to AAR for the experimental conditions studied in this paper. The most expressive benefit corresponded to the addition of 13.0 mm fibers in the mixture containing 2% fiber content. This fiber volume content also corresponded to the maximum increment in the mechanical properties compared to the reference mortar, mainly for the post-cracking strength and for the toughness in bending. It was observed that the fibers have a beneficial effect on the material, without compromising its main mechanical properties. En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900338X Exemplaires
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Titre : Selection of an effective ASR-prevention strategy for use with a highly reactive aggregate for the reconstruction of concrete structures at Mactaquac generating station Type de document : texte imprimé Auteurs : Sean Hayman, Auteur Année de publication : 2012 Article en page(s) : pp. 605–610 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali-aggregate reaction Fly ash Granulated lastfurnace slag Pozzolan Résumé : Mactaquac Generating Station was constructed in the mid 1960's and is located in the province of New Brunswick in Eastern Canada. The effect of ASR expansion on the concrete structures of the station were first noticed approximately 10 years after construction and, ASR was conclusively diagnosed in 1986. Since 1985, various remedial measures have been undertaken to mitigate the effects of concrete expansion. Eventually reconstruction of the concrete structures will be necessary and current projections are that replacement should be complete by 2030. Due to the lack of any suitable locally-available non-reactive aggregate, consideration is being given to using the same source of reactive aggregate for reconstruction.
This paper describes a research study to determine the optimum strategy for preventing deleterious ASR expansion with this aggregate. The options being evaluated include the use of pozzolans and slag, limiting the alkali content of the concrete, and the use of chemical admixtures. Methods of evaluation include accelerated laboratory tests and field exposure of large blocks.En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900221X
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 605–610[article] Selection of an effective ASR-prevention strategy for use with a highly reactive aggregate for the reconstruction of concrete structures at Mactaquac generating station [texte imprimé] / Sean Hayman, Auteur . - 2012 . - pp. 605–610.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 605–610
Mots-clés : Alkali-aggregate reaction Fly ash Granulated lastfurnace slag Pozzolan Résumé : Mactaquac Generating Station was constructed in the mid 1960's and is located in the province of New Brunswick in Eastern Canada. The effect of ASR expansion on the concrete structures of the station were first noticed approximately 10 years after construction and, ASR was conclusively diagnosed in 1986. Since 1985, various remedial measures have been undertaken to mitigate the effects of concrete expansion. Eventually reconstruction of the concrete structures will be necessary and current projections are that replacement should be complete by 2030. Due to the lack of any suitable locally-available non-reactive aggregate, consideration is being given to using the same source of reactive aggregate for reconstruction.
This paper describes a research study to determine the optimum strategy for preventing deleterious ASR expansion with this aggregate. The options being evaluated include the use of pozzolans and slag, limiting the alkali content of the concrete, and the use of chemical admixtures. Methods of evaluation include accelerated laboratory tests and field exposure of large blocks.En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900221X Exemplaires
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Titre : The EU “PARTNER” Project — European standard tests to prevent alkali reactions in aggregates: Final results and recommendations Type de document : texte imprimé Auteurs : Jan Lindgård, Auteur Année de publication : 2012 Article en page(s) : pp. 611–635 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Aggregate Alkali-silica reactions Test methods Résumé : This paper presents the main findings in the EU PARTNER Project (2002–2006) providing the basis for a unified European test approach for evaluating the potential alkali-reactivity of aggregates. The project evaluated the tests developed by RILEM and some regional tests for their suitability for use with the wide variety of aggregates and geological types found across Europe. The project had 24 partners from 14 countries, covering most of Europe, from Iceland to Greece. 22 different types of aggregates from 10 different European countries were evaluated. It was found that in most cases the RILEM tests could successfully identify the reactivity of the aggregates tested. They were most successful with normally reactive and non-reactive aggregates, but with aggregates that react very slowly an extended test period may be necessary for some of the RILEM methods. Overall, the accelerated mortar bar test and the accelerated concrete prism test seemed most effective and to have the best precision. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002440
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 611–635[article] The EU “PARTNER” Project — European standard tests to prevent alkali reactions in aggregates: Final results and recommendations [texte imprimé] / Jan Lindgård, Auteur . - 2012 . - pp. 611–635.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 611–635
Mots-clés : Aggregate Alkali-silica reactions Test methods Résumé : This paper presents the main findings in the EU PARTNER Project (2002–2006) providing the basis for a unified European test approach for evaluating the potential alkali-reactivity of aggregates. The project evaluated the tests developed by RILEM and some regional tests for their suitability for use with the wide variety of aggregates and geological types found across Europe. The project had 24 partners from 14 countries, covering most of Europe, from Iceland to Greece. 22 different types of aggregates from 10 different European countries were evaluated. It was found that in most cases the RILEM tests could successfully identify the reactivity of the aggregates tested. They were most successful with normally reactive and non-reactive aggregates, but with aggregates that react very slowly an extended test period may be necessary for some of the RILEM methods. Overall, the accelerated mortar bar test and the accelerated concrete prism test seemed most effective and to have the best precision. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002440 Exemplaires
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Titre : Summary of research on the effect of LiNO3 on alkali–silica reaction in new concrete Type de document : texte imprimé Auteurs : X. Feng, Auteur Année de publication : 2012 Article en page(s) : pp. 636–642 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : SEM EDX Alkali-aggregate reaction Lithium compounds Résumé : This paper summarizes findings from a research study conducted at the University of New Brunswick in collaboration with the University of Texas at Austin, and CANMET-MTL, on the effect of LiNO3 on ASR in new concrete. The studies included expansion testing, silica dissolution measurements and microstructural examinations of cement systems containing glass and two different reactive aggregates (NB and NS). Only a small proportion of the data are presented here for the purpose of highlighting the principal findings of this investigation.
Based on these findings, it is proposed that the inhibiting effect of LiNO3 against ASR in new concrete is attributed to the formation of two reaction products in the presence of lithium, these being a crystalline lithium silicate compound (Li2SiO3) crystal and a Li-bearing, low Ca silica gel. These two phases could serve as a diffusion barrier and protective layer to prevent the reactive silica from further attack by alkalis.
It was found that the reason the two reactive aggregates selected responded differently to LiNO3 was due to the difference in their textural features. The NB aggregate contained reactive volcanic glass particles, the surface of which was immediately and equally available to sodium, potassium and lithium, and thus a Li–Si barrier was able to form quickly. The reactive phase in the NS aggregate was microcrystalline and strained quartz, which was embedded in a dense matrix of a non-reactive predominantly alumino-silicate phase and was not easily accessible to lithium.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002270
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 636–642[article] Summary of research on the effect of LiNO3 on alkali–silica reaction in new concrete [texte imprimé] / X. Feng, Auteur . - 2012 . - pp. 636–642.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 636–642
Mots-clés : SEM EDX Alkali-aggregate reaction Lithium compounds Résumé : This paper summarizes findings from a research study conducted at the University of New Brunswick in collaboration with the University of Texas at Austin, and CANMET-MTL, on the effect of LiNO3 on ASR in new concrete. The studies included expansion testing, silica dissolution measurements and microstructural examinations of cement systems containing glass and two different reactive aggregates (NB and NS). Only a small proportion of the data are presented here for the purpose of highlighting the principal findings of this investigation.
Based on these findings, it is proposed that the inhibiting effect of LiNO3 against ASR in new concrete is attributed to the formation of two reaction products in the presence of lithium, these being a crystalline lithium silicate compound (Li2SiO3) crystal and a Li-bearing, low Ca silica gel. These two phases could serve as a diffusion barrier and protective layer to prevent the reactive silica from further attack by alkalis.
It was found that the reason the two reactive aggregates selected responded differently to LiNO3 was due to the difference in their textural features. The NB aggregate contained reactive volcanic glass particles, the surface of which was immediately and equally available to sodium, potassium and lithium, and thus a Li–Si barrier was able to form quickly. The reactive phase in the NS aggregate was microcrystalline and strained quartz, which was embedded in a dense matrix of a non-reactive predominantly alumino-silicate phase and was not easily accessible to lithium.En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002270 Exemplaires
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Titre : The so-called alkali-carbonate reaction (ACR) — Its mineralogical and geochemical details, with special reference to ASR Type de document : texte imprimé Auteurs : Tetsuya Katayama, Auteur Année de publication : 2012 Article en page(s) : pp. 643–675 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkali-carbonate reaction (ACR) ASR gel Cryptocrystalline quartz Dedolomitization SEM-EDS Résumé : Typical examples of so-called alkali-carbonate reaction (ACR) in the Canadian field concretes in Ontario, CSA concrete prism, RILEM concrete microbars and RILEM mortar bar containing Pittsburg aggregate, were examined petrographically based on polarizing microscopy, SEM observation and quantitative SEM-EDS analysis of the reaction products. It was revealed that ASR gel was the main product responsible for the crack formation in concretes, and that this gel had a common nature to that in the typical ASR. That is, ASR gel presented distinctive compositional trend lines, passing from low-Ca ASR gel at [Ca/Si] = 1/2–1/6, [Ca]/[Na + K] = 1.0 to the “convergent point” with [Ca/Si] = 1.3–1.8, [Ca]/[Na + K] = 100 at which chemical equilibrium is attained with CSH gel. The so-called ACR is a combination of deleteriously expansive alkali-silica reaction (ASR) of cryptocrystalline quartz, and harmless dedolomitization which produces brucite and carbonate halo. In laboratory specimens, fine dolomitic aggregate undergoes dedolomitization, and brucite and ASR gel react to form non-expansive Mg-silicate gel on the dolomite crystals. This explains why the mortar bar produces smaller expansion than the concrete microbar, and why the reaction products are so minute that they escape attention by optical microscopy. As a crystalline counterpart, mountainite is a candidate for low-Ca ASR gel, while sepiolite is one for Mg-silicate gel. Concealed ASR was detected in ACR-affected field concretes undergoing ingress of deicing salt which formed Friedel's salt and Cl-doped CSH gel. Compositions of ASR products, methods of sample preparation and analysis for correct identification of ACR, and artifacts were critically reviewed. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002737
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 643–675[article] The so-called alkali-carbonate reaction (ACR) — Its mineralogical and geochemical details, with special reference to ASR [texte imprimé] / Tetsuya Katayama, Auteur . - 2012 . - pp. 643–675.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 643–675
Mots-clés : Alkali-carbonate reaction (ACR) ASR gel Cryptocrystalline quartz Dedolomitization SEM-EDS Résumé : Typical examples of so-called alkali-carbonate reaction (ACR) in the Canadian field concretes in Ontario, CSA concrete prism, RILEM concrete microbars and RILEM mortar bar containing Pittsburg aggregate, were examined petrographically based on polarizing microscopy, SEM observation and quantitative SEM-EDS analysis of the reaction products. It was revealed that ASR gel was the main product responsible for the crack formation in concretes, and that this gel had a common nature to that in the typical ASR. That is, ASR gel presented distinctive compositional trend lines, passing from low-Ca ASR gel at [Ca/Si] = 1/2–1/6, [Ca]/[Na + K] = 1.0 to the “convergent point” with [Ca/Si] = 1.3–1.8, [Ca]/[Na + K] = 100 at which chemical equilibrium is attained with CSH gel. The so-called ACR is a combination of deleteriously expansive alkali-silica reaction (ASR) of cryptocrystalline quartz, and harmless dedolomitization which produces brucite and carbonate halo. In laboratory specimens, fine dolomitic aggregate undergoes dedolomitization, and brucite and ASR gel react to form non-expansive Mg-silicate gel on the dolomite crystals. This explains why the mortar bar produces smaller expansion than the concrete microbar, and why the reaction products are so minute that they escape attention by optical microscopy. As a crystalline counterpart, mountainite is a candidate for low-Ca ASR gel, while sepiolite is one for Mg-silicate gel. Concealed ASR was detected in ACR-affected field concretes undergoing ingress of deicing salt which formed Friedel's salt and Cl-doped CSH gel. Compositions of ASR products, methods of sample preparation and analysis for correct identification of ACR, and artifacts were critically reviewed. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002737 Exemplaires
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Titre : Monitoring of an hydraulic structure affected by ASR: A case study Type de document : texte imprimé Auteurs : Patrice Rivard, Auteur Année de publication : 2012 Article en page(s) : pp. 676–680 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Damage Mechanical properties Nondestructive testing Petrography Management Tomography Résumé : Relevant and effective instruments and techniques must be selected for monitoring hydraulic structures affected by Alkali-Silica Reaction (“ASR”). A program aiming at assessing the condition of a hydraulic structure affected by ASR is presented in this paper. The structure has been exhibiting signs of ASR for more than 30 years and shows various levels of damage.
The program encompassed different components, consisting of: (1) stress measurement, (2) evaluation of concrete condition by nondestructive methods without drilling (seismic tomography), (3) the evaluation of the mechanical, physical and petrographic properties of the concrete determined from cores recovered from full-length boreholes.
The results of this case study suggest that ASR may generate relatively little damage in structures and that the concrete mechanical properties do not seem to be significantly affected despite high expansion levels measured in this structure. A major crack was localized with the seismic tomography. The monitoring program will be used to follow the development of ASR in the structure.En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900252X
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 676–680[article] Monitoring of an hydraulic structure affected by ASR: A case study [texte imprimé] / Patrice Rivard, Auteur . - 2012 . - pp. 676–680.
Bibliogr.
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 4 (Avril 2010) . - pp. 676–680
Mots-clés : Damage Mechanical properties Nondestructive testing Petrography Management Tomography Résumé : Relevant and effective instruments and techniques must be selected for monitoring hydraulic structures affected by Alkali-Silica Reaction (“ASR”). A program aiming at assessing the condition of a hydraulic structure affected by ASR is presented in this paper. The structure has been exhibiting signs of ASR for more than 30 years and shows various levels of damage.
The program encompassed different components, consisting of: (1) stress measurement, (2) evaluation of concrete condition by nondestructive methods without drilling (seismic tomography), (3) the evaluation of the mechanical, physical and petrographic properties of the concrete determined from cores recovered from full-length boreholes.
The results of this case study suggest that ASR may generate relatively little damage in structures and that the concrete mechanical properties do not seem to be significantly affected despite high expansion levels measured in this structure. A major crack was localized with the seismic tomography. The monitoring program will be used to follow the development of ASR in the structure.En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900252X Exemplaires
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