No description available.

第23回名古屋大学年代測定総合研究センターシンポジウム平成22(2010)年度報告

No description available.

La carbonatation est l’un des processus initiateurs de la corrosion des armatures du béton armé. Sa cinétique est souvent utilisée pour modéliser la durabilité des ouvrages. La carbonatation résulte de la réaction en présence d’eau entre le dioxyde de carbone contenu dans l’air et les phases hydratées de la pâte de ciment. Elle donne du carbonate de calcium et provoque une baisse du pH qui induit la dépassivation des armatures et leur corrosion. La carbonatation des matériaux à base de ciment a été largement étudiée ces dernières années mais les données de la littérature sont extrêmement contradictoires sur la plupart des évolutions qu’elle engendre tant au niveau microstructural qu’à l’échelle macroscopique. Notre travail a eu pour objectif d’étudier les conséquences microscopiques et macroscopiques de la carbonatation sur deux mortiers standards simples à base de ciment CEM I et CEM II. Nous avons mené une étude expérimentale approfondie sur deux mortiers normalisés à base de ciment CEM I et CEM II pour comprendre les mécanismes physico-chimiques de la carbonatation. Nous avons utilisé les techniques suivantes pour examiner les conséquences de la carbonatation sur les caractéristiques microstructurales de la matrice cimentaire : analyse thermogravimétrique, diffraction de rayons X, pycnométrie à l’hélium, adsorption – désorption d’azote et de vapeur d’eau. Comme ces modifications observées au niveau de la microstructure induisent à leur tour des évolutions significatives au niveau des propriétés macroscopiques d’usage et des indicateurs de durabilité, nous avons examiné les conséquences de la carbonatation sur la perméabilité au gaz, la vitesse de propagation des ondes ultrasonores, la conductivité thermique et la résistivité électrique de surface. Notre étude a également porté sur la contribution de la carbonatation à la cicatrisation des mortiers endommagés thermiquement. Enfin, nos résultats expérimentaux ont été utilisés comme base de données pour élaborer un modèle sur la propagation de CO2 dans la matrice cimentaire. / Carbonation is one of the most important factors that initiate the corrosion of steel bars in reinforced concrete. Its kinetics are often used to model the durability of structures. Under the action of carbon dioxide from the air and with the presence of water in the pores, several hydrated phases of the cement paste are carbonated and form calcium carbonate. This process causes a decrease in pH of the pore water, which subsequently induces the depassivation and corrosion of the rebars. Although the carbonation of cementitious materials has been extensively studied in recent years, results in literature about changes in both micro and macroscopic levels are extremely contradictory. The aim of this work is to study the micro and macroscopic effects of carbonation on two standard cement mortars CEM I and CEM II. A wide experimental campaign was conducted on two standard mortars CEM I and CEM II in order to apprehend the physicochemical mechanisms of the carbonation. The following techniques were used to examine the impacts of carbonation on the microstructural characteristics of the cementitious matrix : thermogravimetric analysis, X-ray diffraction, helium pycnometry, nitrogen and water vapor adsorption-desorption. As changes observed in the microstructure could consequently induce significant modifications in the macroscopic properties and the sustainability indicators, we examined the effects of carbonation on the gas permeability, the ultrasonic waves velocity, the thermal conductivity and electrical resistivity. Our work also studied the self-healing effect caused by carbonation of thermally damaged mortars. Finally, our experimental results were used as a database to elaborate a model of the propagation of CO2 in the cementitious matrix.

The chloride-induced corrosion of reinforcing steel in concrete structures has become a widespread durability problem throughout the world. When concrete structures come in contact with chloride sources, the chloride ions will diffuse through the body of the concrete and ultimately reach the steel. Not all of the chloride ions which penetrate the concrete remain free in the pore solution. Some of the ions become bound to the hydration products in a chemical reaction to form calcium chloroaluminate hydrate (Friedel' salt). It is also well known that only the portion of the chloride ions that remains free is responsible for causing damage to the concrete structures by corroding steel rebar. Thus, the chloride binding capacity of the cementitious matrix plays a major role in controlling chlorides ingress and, consequently, the corrosion of steel reinforcement in concrete. The chloride binding capacity is affected by cement composition, environmental factors, and by the source of the chlorides ( vs. ). To quantify the durability of new and existing structures, a clear understanding of the mechanisms of chloride penetration into the concrete cover is required.<p> Currently, most of the models available in the published literature for calculating free chloride ions in concrete use Ficks law for chloride transport and chloride binding isotherms to account for bound chlorides. Binding isotherms are cement and environment specific. Thus, the existing models cannot be used for all types of cement and variable general environmental exposure conditions such as temperatures, pH levels, and chloride sources. A general mechanistic approach that can overcome those limitations is proposed in this thesis based on the concepts of ion-exchange theory for an accurate determination of chloride ingress in concrete under variable environmental conditions.<p> Some of the model input parameters, such as exchange capacity and the equilibrium constant for the exchange reaction, were not easy to determine directly from experiments and were determined through an inverse modeling procedure. Verification experiments were carried out by varying different environmental parameters and making comparisons with the simulated results using the corresponding parameters.<p> The experimental results showed that the proposed procedure is able to predict the amount of free chlorides in concrete, including predictions of chloride binding as a function of pH, temperature, chloride sources, and the presence of other ions such as carbonate. The proposed model was also used to clarify some unresolved issues such as the effect of chloride sources on binding and the effect of pH on the release of bound chlorides in the presence of carbonation.

The chloride-induced corrosion of reinforcing steel in concrete structures has become a widespread durability problem throughout the world. When concrete structures come in contact with chloride sources, the chloride ions will diffuse through the body of the concrete and ultimately reach the steel. Not all of the chloride ions which penetrate the concrete remain free in the pore solution. Some of the ions become bound to the hydration products in a chemical reaction to form calcium chloroaluminate hydrate (Friedel' salt). It is also well known that only the portion of the chloride ions that remains free is responsible for causing damage to the concrete structures by corroding steel rebar. Thus, the chloride binding capacity of the cementitious matrix plays a major role in controlling chlorides ingress and, consequently, the corrosion of steel reinforcement in concrete. The chloride binding capacity is affected by cement composition, environmental factors, and by the source of the chlorides ( vs. ). To quantify the durability of new and existing structures, a clear understanding of the mechanisms of chloride penetration into the concrete cover is required.<p> Currently, most of the models available in the published literature for calculating free chloride ions in concrete use Ficks law for chloride transport and chloride binding isotherms to account for bound chlorides. Binding isotherms are cement and environment specific. Thus, the existing models cannot be used for all types of cement and variable general environmental exposure conditions such as temperatures, pH levels, and chloride sources. A general mechanistic approach that can overcome those limitations is proposed in this thesis based on the concepts of ion-exchange theory for an accurate determination of chloride ingress in concrete under variable environmental conditions.<p> Some of the model input parameters, such as exchange capacity and the equilibrium constant for the exchange reaction, were not easy to determine directly from experiments and were determined through an inverse modeling procedure. Verification experiments were carried out by varying different environmental parameters and making comparisons with the simulated results using the corresponding parameters.<p> The experimental results showed that the proposed procedure is able to predict the amount of free chlorides in concrete, including predictions of chloride binding as a function of pH, temperature, chloride sources, and the presence of other ions such as carbonate. The proposed model was also used to clarify some unresolved issues such as the effect of chloride sources on binding and the effect of pH on the release of bound chlorides in the presence of carbonation.

No description available.

The carbonation of the building materials based on the ordinary Portland cement is relatively well-known and extensively studied phenomenon. Conversely mechanism, reaction products and factors affecting the carbonation of the alkali activated materials are still not sufficiently clarified. In this work, the progression of the carbonation of the alkali activated materials under different conditions was investigated. The reaction products and the microstructural changes were determined by XRD respectively SEM-EDX analysis. The corrosive conditions due to the decreasing of the pH of the binders by the carbonation were observed by XPS analysis of the steel fibers. The carbonation of the alkali activated samples was compared with the reference samples based on the Portland composite cement. Besides these analyzes, the mechanical properties of the binders were monitored.

Concrete structures have the largest surface area of all human made structures. Large surface area makes concrete capable to absorb CO2 from environment during its lifetime. It is estimated that concrete during its lifetime can absorb about 15-20% of CO2 which had produced in cement production. In Sweden the CO2 uptake by concrete construction is estimated to 300 000 tons annually. This study aims to investigate the influences of fly ash and ground granulated blast furnace slag on carbonation. Accelerated carbonation with 65% relative humidity and 10% CO2 concentration was utilized to simulate the carbonation in cement pastes and cement mortars. Series of experiments have accomplished by collaborating with RISE and university of Borås. In this study cement pastes crushed into three fractions in order to evaluate the impact of particle size and influence of blended cement in CO2 uptake. Lastly, carbonation depth of mortars after 14 days accelerated carbonation were analyzed. Experimental results show that the increasing CO2 uptake induced by adding mineral admixture such fly ash in cement pastes. In this study cement paste with 30% fly ash replacement and fraction lower than 2 mm exhibit the highest CO2 uptake compared to other cement paste in this study. Moreover, carbonation depth of cement mortar was also increased three times more in mortar with 30% fly ash compared with mortar with 100% Portland cement. Therefore, incorporation of mineral admixture in cement pastes can improve the CO2 uptake and moreover, CO2 uptake can be more efficient if more surface area be involved with CO2 by crushing cement paste into lower 2 mm. / Betongkonstruktioner har den största ytan av alla människor gjorda strukturer. Stor yta gör att betong kan absorbera CO2 från luften under betongens hela livstid. Det uppskattas att betong under sin livstid kan absorbera cirka 15–20 % av CO2 som hade producerats i cementproduktionen. I Sverige uppskattas CO2-upptaget till 300 000 ton per år. Denna studie syftar till att undersöka den optimala kombinationen som kan påverka karbonatisering. Accelererad karbonatisering med 65% relativ luftfuktighet och 10% CO2-koncentration utfördes för att kunna simulera upptaget av koldioxid i cementpastor och cementbruk. En rad experiment har genomförts tillsammans med RISE och Högskolan i Borås. I denna studie krossades cementpastor i tre olika fraktioner för att utvärdera effekten av kornstorlek och påverkan av cementpastasinnehål i upptaget av CO2. Slutligen analyserades karboneringsdjupen för cementbruk efter 14 dagar accelererad karbonatisering. De experimentella resultaten från accelererad karbonatisering visar att med ökad halt av flygaska kan CO2-upptaget ökas. Cementpastan med 30 % flygaska och fraktionen lägre än två mm uppvisar det högsta CO2-upptaget jämfört med andra cementpastor med grövre fraktioner i denna studie. Dessutom ökade karbonatiseringsdjupet i cementbruk med 30% flygaska cirka tre gånger mer jämfört med cementbruk med 100% Portlandcement. Utifrån dessa resultat kan det konstateras att inblandning av tillsattmaterial i cementpasta kan förbättra CO2-upptaget och dessutom kan CO2-upptaget sker effektivare om mer kontaktytor blir involverade med CO2 genom att krossa cementpastan i fraktionen 0–2 mm.

Solidification technology can be an effective process for treating a variety of difficult to manage waste materials containing heavy metals prior to reuse or disposal. There are numerous commercial solidification techniques spanning a spectrum of technical complexity and cost. The most common methods include those based on cement or cement/pozzolanic materials. These materials, which are used in many solidification processes, make the technology appear simple and inexpensive. However, there are significant challenges to the successful application of this technique. The morphology and chemistry of the solidified waste forms are complex, specially when the waste streams used contain components other than the metals that are likely to be effectively immobilised. Also, the selection of the binder, depends upon an understanding of the chemistry of both the contaminants and the binder itself, to ensure efficient and reliable results. Nevertheless,a number of complex interactions are known to cause significant retardation on normal hydraulic reactions of cement-based materials, causing numerous and controversial problems. In recent years there has been renewed interest in elucidating the binding mechanisms responsible for the fixation of waste species. Carbonation, which is known to affect a wide range of cementitious materials, is a phenomenon observed by many scientists and has received very little attention. The aim of this work has been to investigate the effects of natural and accelerated carbonation on the development of mechanical and microstructural properties of solidified products as well as on the binding of metallic waste components. Particular emphasis was paid to examine the influence of different binders on the properties of carbonated solidified waste forms. The kinetics of the carbonation reaction was thoroughly examined, particularly when mix parameters such as binder/waste type and water content were varied. An examination of the resulting products showed that carbonated solidified waste materials had improved mechanical properties and increased metal binding capacity, when compared to specimens cured in nitrogen or normal atmospheric conditions. Microstructural analysis showed that large amounts of calcite where characteristics of carbonated samples. The increased formation of calcite as a result of carbonation appeared to be directly linked with the development of strength and enhanced metals fixation. NMR and FTIR spectroscopy indicated that carbonation has a significant influence on the hydration of waste forms by increasing the degree of polymerisation of the silicate hydration phases, with a consequent acceleration of the hydration of the cement paste. Examination by SEM analysis confirmed an acceleration of C3S hydration, typified by a de-calcified hydration rims and a matrix of dense calcite intergrowth infilling porosity. Some metals appeared to be incorporated in the silica-rich rims and others in the calcite rich matrix, suggesting precipitation of metal as both carbonates, silicates and complex double-salts. An examination of the kinetic of the carbonation reaction revealed that the reactivity of the different cements was different in the presence of carbon dioxide, and that when metal wastes were added the susceptibility of the paste to react with carbon dioxide increased. In general the results of this work indicate the potential of carbon dioxide for incorporation into the treatment of wastes during solidification. However, further work is necessary to establish the long-term performance of these carbonated waste forms as well as the behaviour of carbon dioxide upon different waste streams.