Fly ash changes the microstructure of paste and can increase concrete durability. Calcium hydrated lime was added to concrete with 50% of the cement, by weight, substituted with fly ash, with the intent of replacing some of the calcium hydroxide consumed by the pozzolanic activity. Three proportions of mixes were studied: concrete with high early strength cement (HESC), concrete with 50% HESC and 50% fly ash, and concrete with 50% HESC, 50% fly ash and an additional 20% of hydrated lime. They were then tested according to ASTM C1202, but with the application of a voltage of 30 V during 35 h. Results revealed that concretes containing fly ash and hydrated lime presented a lower accumulated charge density and coefficient of chloride diffusion than the HESC concrete used as a reference.

The hydration process of Portland cement triggers reactions of stabilization of minerals from the contact of the clinker with water, which is the Hydrated Calcium Silicate (C-S-H), the Etringite (3CaO.Al2O3.3CaSO4.32H2O) and the Portlandite (Ca(OH)2). In order to understand the effects of the evolution of hydration in cement, it is possible to apply non-destructive tests. In this context, the objective of this work is to evaluate the influence of the type of cement, the curing age, of the format and humidity of the test specimens of concrete in the ultrasonic pulse velocity (UPV). In order to do that, 36 cylindrical test specimens (10 x 20 cm) and 9 cubic ones with 25 cm of edges, with mix proportion of 1:2,7:3,2 (cement/sand/gravel), water/cement ratio of 0.58 and three types of Portland cement (CP II-Z-32, CP IV-32 RS and CP V-ARI) were molded. With data obtained it was possible to correlate the increase of concrete strength along time (at ages of 7, 14, 28, 70 and 91 days) with the increase of the ultrasonic pulse velocity. Besides, it was possible to prove the direct influence of the concrete moisture and of the degree of hydration in the UPV. The shape of the test specimen generally had no influence on the results, except in the case of cement CP V ARI.

ResumoThe corrosion potential technique is used as an electrochemical method to support the monitoring of reinforcement corrosion in reinforced concrete structures. The corrosion potential ranges and its correlation with corrosion's likelihood (recommended by ASTM C 876:2015) are usually employed as an evaluation criterion of the results. The thermodynamic state of corrosion in the structure or specimen (laboratory) can be established if these criteria are well used. However, the method is infl uenced by numerous factors related to the concrete, environment and the procedures adopted at the time of the test. In order to provide useful information to technical and scientifi c community for the correct use of this type of non-destructive evaluation technique, the aim of this article is to evaluate some of the possible factors of infl uence on the corrosion potential measures, such as concrete moisture content, water-cement ratio, thickness of the concrete cover and degree of chloride contamination. The results indicate that moisture and the degree of chloride contamination tend to make more electronegative corrosion potential. Furthermore, the infl uence of concrete cover is diff erent for concrete contaminated (1% of chloride by weigh of cement) and not contaminated by chlorides: the infl uence of the cover thickness in the concrete contaminated with chlorides was reverse because the greater the cover thickness, the least electronegative corrosion potential value; on the other hand, in the concrete without contamination by chlorides, the eff ect of the cover thickness in corrosion potential readings was irrelevant. All these statements were proven with 95% statistical signifi cance.Keywords: corrosion potential, concrete moisture content, water-cement ratio, chloride, concrete cover.O método de medida de potencial de corrosão é utilizado como uma ferramenta eletroquímica de auxílio ao monitoramento da corrosão das armaduras de estruturas de concreto armado. Como critério de avaliação dos resultados, é comum que sejam adotados os intervalos de potencial de corrosão e sua correlação com a probabilidade de corrosão, preconizadas pela ASTM C 876:2015. Com este critério é possível estabelecer um panorama da situação termodinâmica de corrosão na estrutura ou no corpo de prova em laboratório. Porém, o método é infl uenciado por inúmeros fatores relacionados ao concreto, ao ambiente e aos procedimentos adotados no momento da realização das leituras. Visando fornecer informações para orientar o meio técnico e científi co ao uso correto deste tipo de método de avaliação não destrutiva, o objetivo deste trabalho é avaliar alguns dos possíveis fatores de infl uência nas medidas de potencial de corrosão, tais como: teor de umidade do concreto, relação água/cimento, espessura do cobrimento das armaduras e grau de contaminação por cloretos. Os resultados indicaram que a umidade e o grau de contaminação do concreto por íons cloretos tenderam a tornar o potencial de corrosão mais eletronegativo. Além disso, foi verifi c...

To estimate the compressive strength of concrete is necessary in many reinforced concrete structures inspection works. In Brazil, the standard tests for this purpose are: Compressive test in drilled cores, rebound hammer test and ultrasonic test. In the United States and Europe are also regulated other techniques. The aim of this paper is to analyze the use of Pull Off test as an inspection tool of concrete and also disclose the possibility of use of complementary techniques to the standard ones in Brazil. The results show that the Pull Off test results in high correlation (R²> 0.93) with the compressive strength, measured in cylindrical and prismatic specimens. The rebound hammer test did not show satisfactory correlation (R²≅0.6) for the case of cylindrical specimens. The ultrasonic test showed high correlation (R²> 0.98), but behaves differently with the shape changing of the specimens.

RESUMOO objetivo deste estudo é analisar como o tipo de aço, o pH do meio e a proteção superficial da barra de aço são capazes de alterar as propriedades eletroquímicas deste metal. Para isso, foi aplicada a técnica de polarização linear em barras de aço para avaliar a corrosão das amostras. No estudo foram avaliados os aços CA-50, CA-60 e CP-175-RB, com e sem proteção superficial. Estudos como este são essenciais para o aprimoramento das técnicas de leitura, em especial para o entendimento dos resultados obtidos em reparos já realizados. A partir dos resultados foi possível observar como as três variáveis analisadas influenciaram os resultados da densidade de corrente e da taxa de corrosão. Palavras-chave: taxa de corrosão, durabilidade, pH, polarização linear. ABSTRACTThe aim of this study is to analyze how the steel type, the environment pH and surface protection of steel bar are able to change the electrochemical properties of this metal. Therefore it was applied the linear polarization technique to steel bars to assess the corrosion of the samples. The study evaluated the CA-50, CA-60 and CP-175-RB steels bars, with and without surface protection. Studies like this are essential for the improvement of reading techniques, especially for the understanding of the results obtained in repairs already made. From the results, it was possible to observe how the three variables influenced the results of the current density and corrosion rate.