Influence of migrating inhibitor concentration on corrosion resistance of steel reinforcement in concrete

To increase the service life and durability of reinforced concrete structures, new technologies have been developed, such as cathodic protection, re-alkalinization, chloride extraction, and the use of corrosion inhibitors. This study evaluated the influence of cement type, concrete cover thickness, and the addition of organic migrating corrosion inhibitor (MCI) on the corrosion resistance of the embedded steel in concrete against the induced action of chloride ions. To accomplish this, corrosion tests were carried out using electrode potential techniques simultaneously with acceleration cycles of chloride attack. Four mixtures with two levels of reinforcement cover (25 and 40 mm) were subjected to 30 weekly cycles of chemical attack: a reference mixture (without inhibitor) and three others adopting concentration levels of 0.30%, 0.45%, and 0.60% of MCI in the volume of concrete. The concrete properties (compressive strength, voids, specific gravity, and water absorption by immersion and capillarity) were verified. In the corrosion tests on reinforced concrete with lower cover thickness, the mixture with 0.60% MCI addition showed the best results: corrosion potential values less negative than -200 mV, with less than 10% probability of corrosion.Para aumentar a vida útil e durabilidade das estruturas de concreto armado foram desenvolvidas novas tecnologias como a proteção catódica, re-alcalinização, extração de cloreto, e o uso de inibidores de corrosão. Este estudo avaliou a influência do tipo de cimento, espessura do cobrimento de concreto e adição de inibidor de corrosão orgânico migratório (MCI) na resistência à corrosão do aço embutido no concreto contra a ação induzida de íons cloreto. Para isso, foram realizados ensaios de corrosão utilizando técnicas de potencial de eletrodo simultaneamente com ciclos de aceleração de ataque de cloretos. Quatro misturas com dois níveis de cobertura do aço (25 e 40 mm) foram submetidas a 30 ciclos semanais de ataque químico: uma mistura de referência (sem inibidor) e outras três adotando níveis de concentração de 0,30%, 0,45% e 0,60% de MCI em volume de concreto. As propriedades do concreto (resistência à compressão, índice de vazios, massa específica e absorção de água por imersão e capilaridade) foram verificadas. Nos ensaios de corrosão em concretos armados com menor espessura de cobrimento, a mistura com adição de 0,60% de MCI apresentou os melhores resultados: valores de potencial de corrosão inferiores a -200 mV, com probabilidade de corrosão inferior a 10%

Electronic voting to encourage interactive lectures: a randomised trial

Background: Electronic Voting Systems have been used for education in a variety of disciplines. Outcomes from these studies have been mixed. Because results from these studies have been mixed, we examined whether an EVS system could enhance a lecture's effect on educational outcomes. Methods: A cohort of 127 Year 5 medical students at the University of Adelaide was stratified by gender, residency status and academic record then randomised into 2 groups of 64 and 63 students. Each group received consecutive 40-minute lectures on two clinical topics. One group received the EVS for both topics. The other group received traditional teaching only. Evaluation was undertaken with two, 15-question multiple-choice questionnaires (MCQ) assessing knowledge and problem solving and undertaken as a written paper immediately before and after the lectures and repeated online 8–12 weeks later. Standardised institutional student questionnaires were completed for each lecture and independent observers assessed student behaviour during the lectures. Lecturer's opinions were assessed by a questionnaire developed for this study. Results: Two-thirds of students randomised to EVS and 59% of students randomised to traditional lectures attended. One-half of the students in the EVS group and 41% in the traditional group completed all questionnaires. There was no difference in MCQ scores between EVS and traditional lectures (p = 0.785). The cervical cancer lectures showed higher student ranking in favour of EVS in all parameters. The breast cancer lectures showed higher ranking in favour of traditional lectures in 5 of 7 parameters (p < 0.001). The observed higher-order lecturer-students interactions were increased in the EVS lecture for one lecturer and reduced for the other. Both lecturers felt that the EVS lectures were difficult to prepare, that they were able to keep to time in the traditional lectures, that the educational value of both lecture styles was similar, and that they were neutral-to-slightly favourably disposed to continue with the EVS technology. The 2 lecturers disagreed regarding the ease of preparation of the traditional lecture, their ability to keep to time in the EVS lecture, and personal satisfaction with the EVS lecture. The lecturers felt that EVS encouraged student participation and helped identify where students were having difficulty. Conclusion: In this setting, EVS technology used in large group lectures did not offer significant advantages over the more traditional lecture format.Paul M Duggan, Edward Palmer and Peter Devit

Propriedades de concreto auto-adensável contendo cinzas volantes

Self-compacting concrete is a high performance concrete with excellent rheological properties that can be spread in areas of difficult access. Selfcompacting concrete requires a high consumption of cement production, which has a negative effect on the environmental aspect, since the production of cement releases significant amounts of CO2. This study aims analysis the influence of the substitution (20 and 40% by weight) of Portland cement by fly ash on the selfcompacting concrete properties in the fresh state (spreading, workability, passing ability - J-ring test, viscosity - V-funnel test) and hardened (compressive strength).The passing ability was proved more effective to the mixture with 20% of replacement. To the viscosity, control concrete had lower flow time in V-funnel. The compressive strength results at 28 days showed a reduction of 9.5% for concrete with 20% fly ash and 77.0% for concrete with 40% fly ash compared to the control concrete.Self-compacting concrete is a high performance concrete with excellent rheological properties that can be spread in areas of difficult access. Selfcompacting concrete requires a high consumption of cement production, which has a negative effect on the environmental aspect, since the production of cement releases significant amounts of CO2. This study aims analysis the influence of the substitution (20 and 40% by weight) of Portland cement by fly ash on the selfcompacting concrete properties in the fresh state (spreading, workability, passing ability - J-ring test, viscosity - V-funnel test) and hardened (compressive strength).The passing ability was proved more effective to the mixture with 20% of replacement. To the viscosity, control concrete had lower flow time in V-funnel. The compressive strength results at 28 days showed a reduction of 9.5% for concrete with 20% fly ash and 77.0% for concrete with 40% fly ash compared to the control concrete

Influence of fired clay brick waste additions on the durability of mortars

The use of metakaolin is known to help improve properties of Portland cement-based mortars. The presumed similarities between the characteristics of metakaolin and those of a powdered (<45 mu m) fired clay brick clean waste (CBW) led to the investigation of the effect on the durability of mortars of partial replacement (10, 25 and 40 wt.%) of Portland cement by CBW. Properties such as 28 and 90 days-compressive strength, water absorption, apparent porosity, absorption by capillarity, chloride retention, carbonation depth and sulphate resistance were evaluated. The CBW-containing cured mortars showed improved strength and density, as the result of combined physical and pozzolanic pore filling effect of added CBW. However, CBW-free mortar exhibited larger spreading and, being more porous, higher sulphate resistance and ability to absorb chlorides. Optimum performance was found for the 40 wt.% CBW mortar whose compressive strength can be up to 130% higher than that of the CBW-free mortar. (C) 2015 Elsevier Ltd. All rights reserved