Marcelo Henrique Farias de Medeiros

Service life of concrete structures considering the effects of temperature and relative humidity on chloride transport

Chloride is one of the main factors responsible for damages related to the corrosion of the concrete reinforcement in marine environments. It is known that this mechanism of degradation is directly related to environmental variables. Within this context, it can be inserted the global climate change. This paper deals with the effects of temperature and relative humidity changes on the service life of concrete structures affected by chloride attack. This way, three situations of environmental aggressiveness were simulated: past, current, and future. Then, models for predicting the chlorides penetration were analyzed to the three selected situations. So, a practical methodology is presented, and the results are consistent with the literature data. Among the results, it can be noted that changes in temperature and relative humidity identified in a period of 100 years were responsible for a reduction from 7.8 to 10.2 years of service life. Most standards provide a design service life of 50 years for reinforced concrete structures.

Durabilidade de concretos com agregados reciclados: uma aplicação de análise hierárquica

A preocupacao com a destinacao dos residuos de demolicao de construcoes e a escassez de materiais naturais para a producao de agregados tem motivado a realizacao de estudos sobre o reaproveitamento dos residuos da construcao em diferentes paises. O presente trabalho discute o uso combinado de agregados reciclados de construcao e demolicao e agregados naturais, para se obter resistencias adequadas do concreto, enfatizando a durabilidade dos elementos estruturais executados. A contribuicao principal deste estudo foi o emprego da Analise Hierarquica (AHP), para comparar o nivel de desempenho das opcoes consideradas. Essa tecnica baseia-se na identificacao dos elementos-chave para a tomada de decisao na definicao de prioridades e na consistencia logica do modelo de priorizacao construido. Foram incluidos no estudo treze tracos de concreto (um de referencia mais doze variacoes de teores de agregados reciclados) para cada um dos tres niveis de resistencia a compressao de dosagem considerados (20, 30 e 40 MPa), totalizando 39 proporcionamentos de concretos. Essas variacoes foram avaliadas utilizando-se oito parâmetros, e o emprego da AHP teve o objetivo de proporcionar uma avaliacao global dos casos estudados. A Analise Hierarquica mostrou-se eficaz no auxilio a tomada de decisoes na dosagem do concreto com agregados reciclados.

Certificação ambiental de habitações: comparação entre LEED for Homes, Processo Aqua e Selo Casa Azul

Visando incentivar mudancas no setor da construcao civil para adequacao as agendas de sustentabilidade, foram desenvolvidos, em varios paises, sistemas de certificacao ambiental de edificacoes. Voltadas principalmente para questoes relativas ao consumo de recursos naturais e impactos ao meio ambiente; essas ferramentas tambem sao denominadas selos verdes para edificios. Com o intuito de identificar a certificacao de melhor desempenho a ser utilizada para edificacoes residenciais no Brasil, usou-se uma analise comparativa. Foram selecionados tres sistemas de certificacao, por se tratarem dos mais usuais no pais, sendo eles o LEED for Homes, o Processo AQUA e o Selo Casa Azul. Para a investigacao utilizou-se da ferramenta Analise Hierarquica (Analytic Hierarchic Process, AHP), que permite a avaliacao de multiplos criterios, com dados que podem ser tanto qualitativos como quantitativos. Este estudo demonstrou que o selo desenvolvido para a realidade brasileira, Selo Casa Azul, tem melhor desempenho para avaliar as edificacoes habitacionais do pais.

Análise hierárquica para escolha entre agregado natural e areia de britagem de rocha para confecção de argamassas de revestimento

Muitas vezes as tomadas de decisao na industria da construcao sao complexas, pois envolvem muitas variaveis, sendo trabalhoso agrupa-las e realizar uma avaliacao global do problema. O metodo de analise hierarquica (AHP) e uma ferramenta que auxilia na tomada de decisao em problemas de engenharia, nos quais diversos fatores devem ser levados em conta na escolha de metodos, produtos ou materiais. O objetivo principal deste artigo e mostrar a forma de aplicacao do metodo de analise hierarquica para sistematizar tomadas de decisoes na industria de argamassas industrializadas. E apresentado um roteiro para verificar o traco de argamassa que apresenta melhor desempenho, considerando determinados resultados de ensaios e um conjunto de criterios previamente estabelecidos. A aplicacao da AHP para esse problema resulta em um indice global que caracteriza o desempenho dos materiais com relacao ao conjunto de criterios utilizado. O resultado apontou que a tecnica de analise hierarquica pode ser eficaz apara apoiar a tomada de decisoes na escolha de argamassas industrializadas. Na analise hierarquica realizada neste estudo, concluiu-se que, para os materiais envolvidos neste trabalho, a substituicao da areia natural por areia de britagem e vantajosa em 78% dos casos.

Reactivity Assessment of Residual Rice-Husk Ashes

AbstractThe production of rice-husk ash without controlled burning results in pozzolans with different physicochemical characteristics. The amorphous content of residual rice-husk ash (RRHA) is rel...

Resíduo de cerâmica vermelha e fíler calcário em compósito de cimento Portland: efeito no ataque por sulfatos e na reação álcali-sílica

The red-clay waste (RCW) derives from blocks and bricks in their production process and also in the construction industry, when these materials are used in vertical walls. When originated in the production process, the RCW presents a lower degree of impurities, while when originated from construction sites, it contains a greater degree of impurities due to being stored with other residues before its disposal. According to the Brazilian Environmental Council (CONAMA) in its Resolution 307, RCW requires a proper disposal to avoid environmental impacts. The reactive capability of RCW and lime qualifies it to be used as a mineral admixture in Portland cement composition thus avoiding its disposal in landfills for construction waste. The viability of RCW incorporation in Portland cement requires analyses, such as studies of its compressive strength, and moreover of its performance when the hydrated paste is under physical and chemical deleterious interactions. This paper aims to evaluate the influence of milled RCW in Portland cements composition, emphasizing two properties related to concretes durability: its resistance to alkali-silica reaction (ASR) and its resistance to sodium sulfate attack. Therefore, CP V - ARI cement mortars (to be used as reference) and compositions of 10% replacement in cement mass by limestone filler or RCW, in three different fineness, were evaluated for ASR, according to NBR 15.577-5/2008, and for their expansion due to the sodium sulfate attack, according to NBR 13.583/2014. Although, the exposure time was extended aiming a more careful assessment of their degradation. Results showed that RCW increased the expansion caused by ASR, and, in most cases, also increased the expansion due to sodium sulfate attack. On the other hand, a higher comminution of RCW tends to improve the performance of the cementitious matrix when submitted to deleterious action, that is, a greater fineness of RCW has a positive impact on the material behavior under degradation. The limestone filler did not influence the result of expansion by ASR, but caused a reduction of the expansion induced by sodium sulfate attack. The analysis of the extended exposure time (66 days for ASR tests and 210 days for sulfate attack tests) showed that RCW milled for 1.5 hours might potentially be used as a mineral admixture in the binder materials composition, tending to show a similar performance to Portland cement matrix under sodium sulfate attack. Regarding the RAS, and increase in the comminution of RCW milled for 1.5 hours is required to make its particle size distribution similar to the cements, which tends to enhance the mitigation capacity of this mineral admixture

Ataque de matrizes cimentícias por sulfato de sódio:adições minerais como agentes mitigadores

Deterioration of the concrete by sulfates occurs through chemical reactions between the hydrated cement compounds and sulfate ion. As a result of these reactions there is in advanced stages the formation of expansive products that cause cracking and disintegration of concrete. The use of mineral additions in the composition of the binder material to partially replace the clinker causes microstructural changes that interfere in porosity of the hydrated matrix and especially the size distribution and pore interconnectivity. This positively or negatively influences the inflow of water containing sulfate ions into the structure. This paper aims to evaluate the mineral admixtures capacity of reducing the sulfate attack in concrete structures. Dimensional changes of Portland cement mortar bars were determined, as required by ABNT NBR 13.583/2014, and were used to evaluate the mitigatory potential binder material composed by cement CP V - ARI (reference) and compositions with partial replacement of 10% by cement mass using: silica fume; metakaolin; rice husk ash; limestone and quartz filler; and red ceramic residue with different milling times. The reference mortar showed high expansion, as well as mortars containing metakaolin, limestone filler and red ceramic residue, regardless of the milling time. The silica fume, rice husk ash and quartz filler in the composition of the binder material of mortar reduced expansion to acceptable levels, making them resistant to attack by sulphates.

Ensaio de migração de cloretos para concreto: influência do número de fatias extraídas

Chloride migration tests are used to measure the capacity of the concrete to inhibit chloride attack. Many researchers carry through this test in a slice of concrete extracted from the central part of cylindrical specimens, discarding about 75% of the concrete used to mold the specimens. This fact generated the question: would it be possible to extract more slices from a same specimen without losing the confidence in the results? The main purpose of this work is to answer to this question. Moreover, another aim of this study was to show the difference of chloride penetration between finished faces and the formwork surfaces of concrete beams and slabs. The results indicated that it is possible to use more slices of a single specimen for a chloride migration test. Moreover, it was demonstrated that significant difference of chloride penetration exists between the finished surface and the formwork surface of the specimens.

Previsão da vida útil de concreto armado de alta resistência com adição de metacaulim e sílica ativa em ambientes marinhos

In marine environments, the big problem related to concrete durability is a chloride ion attack. Service life prediction in this type of environment is still without consensus by technical and scientific researchers. This work presents advances by proposing a way to interpret data from chloride ions diffusion in high-strength concrete containing metakaolin and silica fume as admixtures. The results showed that metakaolin and silica fume increased service life in a marine environment by 240 per cent and 440 per cent, respectively. This evidenced the high efficiency of the metakaolin and silica fume admixtures as a way of producing more durable concretes for regions highly influenced by saltwater spray.

Repair Mortars Incorporating Multiwalled Carbon Nanotubes: Shrinkage and Sodium Sulfate Attack

AbstractThis study investigates the effect of multiwalled carbon nanotubes (MWCNTs) on the shrinkage and expansion caused by sodium sulfate attack in repair mortars; repair mortar behavior in the f...