Elizamary Otto Ferreira

The determination of the optimum amount of constituents, for UHPC production still needs studies, because in many cases this definition is empirical. This work aims to present a methodology for determining the amount of silica fume and to establish a water/binder ratio based on laboratory tests. To define the quantity of constituents necessary for the formation of the paste, the wet packaging method was used and the concentration of solids, the volume of voids and the excess of water were determined. The results indicated that the adopted methodology is adequate, leading to commonly used values.

The diversity of the types of cement manufactured, driven by the extensive use of additions, has given cementitious composites properties that can directly interfere in the durability and useful life of concrete. Considering the interaction of sulfate ions with cement hydration products, in order to understand it becomes essential for the proper choice of materials in order to protect the structures from this aggressor agent. In order to verify the influence of the choice of cement type on the resistance to attack by sulfates, this article analyzes the compressive strength; sulfate content, electron microscopy and energy dispersive spectroscopy of mortars made with cements CP II-F-32, CP IV-32 and CP V-ARI submitted to calcium, sodium and magnesium sulfate solutions for 4 months. The specimens exposed to calcium and sodium sulfate solutions showed increased compressive strength at early ages due to the formation of ettringite in the pores. On the other hand, CP II-F-32 cement showed the greatest deterioration due to magnesium sulfate attack.

Among the pathological manifestations associated with reinforced concrete, corrosion of the reinforcement is one of the most serious issues since it is related to the durability of the structures and the safety of the users. Although the reinforcement in the structural components is protected by a covering layer, carbonation or the presence of chlorides in the concrete generates necessary conditions for corrosion of the reinforcement. This causes a reduction in the cross section and the generation of products that, due to their volumetric expansion, cause cracks in the interior of the concrete. This work evaluates the effects of corrosion on mechanical properties of corroded reinforcements through accelerated conditions in the laboratory. Steel bars installed inside cylindrical concrete specimens are subjected to accelerated corrosion, immersed in a saline solution with the application of an electric current for periods of 1, 3, 5 and 7 d. After corrosion, the steel bars are removed and their weight loss, degree of corrosion and tensile strength are evaluated. The results demonstrate an increased degree of corrosion with exposure time to the saline solution and the non-uniform reduction of the tensile strength of the bars due to the formation of corrosion pits with varying depth along the bar.