Influência da pozolanicidade e do efeito fíler na resistividade elétrica volumétrica e superficial do concreto

Abstract

Reinforcement corrosion is one of the most frequent pathological manifestations in concrete structures. The corrosion rate is directly related to the moisture inside the concrete, the interconnection of the pores and the movement and concentration of ions within the cementitious composite. This mobility of ions in aqueous solution can modify the ohmic resistance of the material and promote the acceleration of the corrosion process of the reinforcement. In this context, electrical resistivity can be considered an important parameter to assess the risk of the occurrence of a corrosive process in the reinforcement, in addition to assessing the quality of the concrete. There are two types of methods used to measure the electrical resistivity of concrete: bulk and superficial. The electrical resistivity of the cementitious composite, whether bulk or superficial, it depends on the chemical composition, the specific mass, the porosity, the presence of moisture, the temperature of the concrete, among other aspects. The surface electrical resistivity, used as an indicator of the risk of reinforcement corrosion, is the subject of several current scientific studies, while there are few studies on the use of bulk electrical resistivity to evaluate the quality of concrete. Thus, this work proposes to evaluate the influence of the nature of mineral additions and the dimension of the specimens in the two types of electrical resistivity. Mineral additions with characteristics of filler (limestone filler and red mud) and pozzolan (rice husk ash and metakaolin) were used. Mineral additions were evaluated for their chemical composition and their level of pozzolanic activity, to later be added to the concrete to replace 10% of the cement mass. The concretes formed were characterized in terms of bulk and surface electrical resistivity, immersion absorption and void indices, elasticity module (static and dynamic) and compressive strength. The results obtained indicated that the dimensions of the specimens do not influence the bulk electrical resistivity, but confirmed that they interfere with the surface electrical resistivity, due to the relationship between the height of the specimens and the distance between the four electrodes used in the measurement equipment. In addition, it can be concluded that cementitious composites with pozzolanic mineral additions and fillers showed higher values of electrical resistivity, both bulk and superficial. The compressive strength of concretes with the addition of pozzolans showed a significant increase when compared to reference concrete. On the other hand, the same behavior wasn´t observed in concretes with the addition of fillers, since these concretes showed a small reduction in the results of compressive strength in relation to the reference concrete. In the elastic modulus by resonant frequency, dynamic, and in the static modulus, mineral additions provided significant changes in the results obtained when compared with the reference concrete. Due to the resistivity values obtained, the risk of reinforcement corrosion, using the reference concrete, was classified as “high risk”. The substitution of 10% of Portland cement by the studied pozzolanic and filler mineral additions promoted a reduction in the risk of corrosion of the concretes due to the improvement in the quality of the materials.