Assessment of Durability of Reactive Powder Concrete Using Oxygen Permeability Index
-Durability of concrete is very important parameter for using natural resources effectively and reducing the cost of reconstruction, maintenance and repair of structure. This paper focuses on need of much of the need for concrete repair can be eliminated, if sufficient consideration and attention is given to control of surface quality of concrete at the construction stage. A South African approach is used to measure the oxygen permeability index testing and concluded that the method is applicable to actual project and is durability index is a parameter to evaluate the durability of RPC and cover zone concrete. RPC shows a good OPI value indicating impermeable concrete and its use can be justified for special purpose.
THE USE OF FLY ASH, SILICA FUME, SLAG AND OTHER MINERAL BY-PRODUCTS IN CONCRETE
Portland cement is a highly energy-intensive product, and therefore, in an energy-hungry world considerable efforts are being made to find substitute materials for the partial replacement of cement in concrete. Some of the most promising substitutes or supplementary cementing materials are high- and low-calcium fly-ashes, ferrous- and non-ferrous slags and condensed silica fume. This paper presents a state-of-the-art review on the use of these mineral by-products in concrete, and the role of these materials in the less developed countries. The physical and possolanic properties of the supplementary cementing materials are outlined, and their effect on the properties of fresh and hardened concrete discussed. Particular emphasis is placed on the use of condensed silica fume, a relatively new addition to the family of supplementary cementing materials. The contribution of superplasticizers to achieving high-strength concrete incorporating fly-ash and silica fume is mentioned. Reference is made to the currently available specifications for these materials both in North America and Europe, and their limitations discussed. The advantages and limitations in the use of supplementary cementing materials as separately batched ingredients at a ready-mixed concrete plant, versus the use of blended cements are discussed, and North American trends in this field are mentioned briefly. It is emphasized that additional quality control measures are needed when fly-ash, slag and silica fume are incorporated in ready-mixed concrete. This is especially so when chemical admixtures are also incorporated in concrete made with supplementary cementing materials. (Author/TRRL)
A two-chamber vacuum cell for measuring the coefficient of permeability to air of the concrete cover on site
A new testing technique, suitable for on-site, non-destructive measurement of the permeability to air of the concrete cover is presented. The method is based upon applying a vacuum inside a cell placed on the concrete surface and on measuring the rate at which the pressure returns to the atmospheric value. Distinctive features of the method are a two-chamber cell and a regulator that balances the pressure in the inner (measuring) chamber and in the outer (quard-ring) chamber. Thus, unidirectional air flow into the inner chamber is achieved, eliminating any spurious lateral air flow. A simple model is proposed to calculate the coefficient of permeability and the depth affected by the test. Preliminary results fit very well to earlier measurements of the coefficient of permeability to oxygen by the Cembureau method.ResumeOn présente une nouvelle méthode d'essai non destructive, utilisable sur site, pour la mesure de la perméabilité à l'air de l'enrobage du béton. Cette méthode consiste à faire le vide à l'intérieur d'une cellule fixée sur le béton et à mesurer la vitesse à laquelle la pression revient à la valeur atmosphérique. La méthode se distingue notamment par une cellule à deux compartiments et un régulateur de pression entre le compartiment (de mesure) intérieur et le compartiment extérieur (anneau de garde). Ainsi, l'écoulement unidirectionnel d'air dans le compartiment intérieur est obtenu par élimination de tout écoulement latéral parasite. On propose un modèle simple de calcul du coefficient de perméabilité et de la profondeur concernés par l'essai. Les essais préliminaires concordent très bien avec les mesures précédentes du coefficient de perméabilité par la méthode Cembureau.