Tensile strength and bonding characteristics of self-compacting concrete

Self-compacting concrete, also referred to as self-consolidating concrete, is able to flow and consolidate under its own weight and is deaerated almost completely while flowing in the formwork. It is cohesive enough to fill the spaces of almost any size and shape without segregation or bleeding. This makes SCC particularly useful wherever placing is difficult, such as in heavily-reinforced concrete members or in complicated workforms. The objectives of this research were to compare the Splitting Tensile Strength and Compressive Strength values of self-compacting and normal concrete specimens and to examine the bonding between the coarse aggregate and the cement paste using the Scanning Electron Microscope. Cylinder specimens (8 by 4 ) were tested for Splitting Tensile and Compressive Strength after 28 days of standard curing, in order find out if self-compacting concrete would show an increase in these strengths and a better bonding between aggregate and cement paste, compared to normal concrete. The mix design used for making the concrete specimens was based on previous research work from literature. The water - cement ratios varied from 0.3 to 0.6 while the rest of the components were kept the same, except the chemical admixtures, which were adjusted for obtaining the self-compactability of the concrete. All SCC mixtures exhibited greater values in both splitting tensile and compressive strength after being tested, compared to normal concrete. The splitting tensile strength increased by approximately 30%, whilst the compressive strength was around 60% greater. In addition, the SCC tensile strengths after 7 days were almost as high as those obtained after 28 days for normal concrete. This was possible due to the use of mineral and chemical admixtures, which usually improve the bonding between aggregate and cement paste, thus increasing the strength of concrete. Images taken from concrete samples having water-cement ratios of 0.3, 0.4, and 0.6, using the Scanning Electron Microscope, have shown that the widths of the physical interface microcracks were greater for normal concrete than for self-compacting concrete, which implies that the aggregate-cement bonds were better for SCC than for normal concrete

Concrete Microstructure Characterization and Performance

Microstructural characteristics such as the interfacial transition zone (ITZ) and cracking patterns from compressive strength testing are main features that characterize concrete behavior. Certain materials such as blast furnace slag or fly ash introduced in the concrete mix aid in improving its strength and durability. Others such as nanosilica particles may affect only the microstructure of the paste without making any significant improvement in the strength of the ITZ or paste-aggregate bond. Additionally, in situ investigation of the microstructures of fresh cement paste can greatly enhance knowledge of the development properties of concrete at an early age (e.g., setting and hydration), which can be helpful for improvement of the quality of concrete. Common technologies such as Scanning Electron Microscope (SEM) are currently employed in petrographic analysis of cementitious materials and concrete microstructure

L'adhésion à l'UE, un objectif partagé ou partageant la société moldave?

L'histoire récente de la Moldavie atteste des quelques progrès notables de ce pays en termes de démocratisation, condition préalable à toute intégration européenne. Cependant, les résultats électoraux des scrutins organisés depuis la déclaration d'indépendance, en août 1991, n'expriment pas de manière continue une volonté des citoyens moldaves d'intégrer leur pays à l'Europe. En effet, les partis élus n'ont pas toujours été, loin s'en faut, ceux qui promouvaient une telle intégration

Bilan de la transition démocratique en Moldavie - 1991-2011

Depuis une vingtaine d'années la République de Moldavie indépendante mène des efforts pour consolider son régime démocratique. Même si sa démocratisation a pris un essor assez rapide, avec la mise en place d'un nouveau réseau d'institutions constitutionnelles, inspirées du modèle occidental, les leaders moldaves n'ont su soutenir ce processus de démocratisation constamment. Le passé soviétique se lit encore aisément surtout dans le comportement des leaders politiques formés durant l'époque précédente. Leur incapacité de dépasser la condition de dirigeant absolu, à prérogative de prendre des décisions incontestables, vicie beaucoup leur image de dirigeants démocratisés