Estudo da penetração de cloretos na camada de cobrimento do concreto com altos teores de cinza volante

Abstract

The wall effect between the form and the concrete increases the water/cement relation in this interface so that the structural durability piece is in the dependence of the characteristics of this layer that extends from the surface against the form until the reinforcement. To reduce the pores of this layer, supplementary cementing materials have been used to increase the impermeability and decrease the fluids flow between the environment and the interior concrete interior. This investigation presents results on the study of the covercrete prototypes layer (beam) to approach the laboratory test to the one of a real construction, moulded in wooden forms and cured in humid cure for 7 days simultaneously with cast specimens. Portland cement (reference) and with its substitution, in mass, for 50% fly ash, with and without addition of lime were tested. This calcium hydroxide was used to increase the alkaline reserve. The proprieties studied were tested at each 2,5cm of distance of the covercrete, from surface up to 5cm depth, also collected powered samples, with appropriate rotative drilling machines, in identical depths to the previous ones. The analyzed variables were: compression strength, chloride-ion penetration (ASTM C 1202/97), total chloride-ion in acid, Cl-/OH- ratio and specific electric conductivity. The results highlight that the chloride-ion penetration appraised by charge passed in Coulombs in the reference concrete increases from the surface to the depths 2,5 and 5,0 cm. While for the fly ash mixture with or without lime the charge passed is smaller than reference concrete when compared to the corresponding layers each mixture, showing the beneficial effect this supplementary cementing materials offer in terms of protection against chloride-ion peneration and other aggressive substances, protecting the reinforcement more efficiently against corrosion.