This paper discusses the use of doping technique in the interfacial transition zone (ITZ) between Portland cement paste and lateritic aggregates with the objective of promoting the implementation of structural concrete. Doping technique consists of establishing the initial impregnation of the aggregate with a high performance paste in order to improve its binding to the matrix. A Scanning Electron Microscope (SEM) equipped with an energy dispersive X-ray (EDX) analysis system is used to observe the results of the technique in the ITZ. The results are observed through an analysis of the cement hydration products formed in the ITZ. An ITZ with high concentration of large crystals of calcium hydroxide (CH) is observed in plain concrete, whereas in concrete prepared with doping technique the ITZ is rich in calcium silicate hydrate (CSH). This result confirms the possibility of using this material, which has no commercial value nowadays, as an alternative aggregate for elaborating structural concrete.

Para que as estruturas de concreto alcancem uma vida útil adequada é necessário avaliar a durabilidade e considerar a manutenção das mesmas. Isso tem estimulado o desenvolvimento de tecnologias destinadas a solucionar a problemática de peças deterioradas ou danificadas. Este trabalho analisa o comportamento da zona de interface entre concreto novo e velho após a escarificação do concreto velho (tratamento físico) e o emprego da técnica de dopagem (tratamento químico). A técnica de dopagem consiste na impregnação de pó por via seca ou pasta de alto desempenho, seguida do lançamento de concreto novo, ou no lançamento direto de um concreto novo com características de alto desempenho. O desempenho dessa ligação foi avaliado por meio de ensaios de tração na flexão, até a ruptura, em corpos de prova prismáticos de concreto simples (fck = 20 MPa) e em seguida remoldados. A partir dos resultados, verificou-se que a ruptura dos corpos de prova recuperados ocorreu fora da região de interface e que as resistências à flexão desse concreto foram mantidas tais quais as originais, demonstrando a eficácia do procedimento na ligação entre concreto novo e velho.

In order for concrete structures to have an adequate lifetime it is necessary to assess their durability and also to consider their maintenance. This has encouraged the development of specific technologies to solve problems concerning deteriorated and damaged parts. This study analyses the behavior of the interface zone between fresh and old concrete after scraping the old concrete (physical treatment) and also using the doping technique (chemical treatment). The doping technique consists in dry powder or high performance paste impregnation followed by fresh concrete pouring, or direct pouring of fresh high performance concrete. The performance of that connection was evaluated through flexural tensile tests until failure. The tests were carried out on conventional concrete prismatic specimens (fck = 20 MPa). At the end of the tests the specimens were remolded. The results indicated that the failure in the remolded specimens occurred outside the interface zone and the flexure resistance values were the same when compared to the original values, showing the efficacy of the procedure for connecting fresh and old concrete.

According to some estimates, world's population growth is expected about 50% over the next 50 years. Thus, one of the greatest challenges faced by Engineering is to find effective options to food storage and conservation. Some researchers have investigated how to design durable buildings for storing and conserving food. Nowadays, developing concrete with mechanical resistance for room temperatures is a parameter that can be achieved easily. On the other hand, associating it to low temperature of approximately 35 °C negative requires less empiricism, being necessary a suitable dosage method and a careful selection of the material constituents. This ongoing study involves these parameters. The presented concrete was analyzed through non-destructive tests that examines the material properties periodically and verifies its physical integrity. Concrete with and without incorporated air were studied. The results demonstrated that both are resistant to freezing.

Concrete is defined as a composite material and, in rheological terms, it can be understood as a concentrated suspension of solid particles (aggregates) in a viscous liquid (cement paste). On a macroscopic scale, concrete flows as a liquid. It is known that the rheological behavior of the concrete is close to that of a Bingham fluid and two rheological parameters regarding its description are needed: yield stress and plastic viscosity. The aim of this paper is to present the initial rheological description of high performance concretes using the modified slump test. According to the results, an increase of yield stress was observed over time, while a slight variation in plastic viscosity was noticed. The incorporation of silica fume showed changes in the rheological properties of fresh concrete. The behavior of these materials also varied with the mixing procedure employed in their production. The addition of superplasticizer meant that there was a large reduction in the mixture's yield stress, while plastic viscosity remained practically constant.

Several electrochemical techniques can be used to monitor corrosion, among them are open circuit potential (OCP) and eletrochemical impedance spectroscopy (EIS). Monitoring OCP is the most typical procedure for routine inspection of reinforced concrete structures and can be easily carried out, however it only gives an approximate idea of the corrosion process. EIS is a more complete technique, which supplies information regarding the mechanism and kinetics of reaction electrochemistries, but only used in the laboratory. Based on these two techniques, this study is related to the steel corrosion in high-performance concrete with silica fume and silica from rice husk. The acceleration of the corrosion was carried out using immersion cycles in a 3.5% NaCl solution. As well as high compressive strength values, the addition of silica fume presented low corrosion risks and high impedance module values and significant increases of the concrete resistivity after 22 months of alternate immersion/drying cycles were obtained.