Contribution to the development of performance specifications for concretes containing blast furnace slag / Contribuição ao desenvolvimento de especificações por desempenho para concretos com escoria de alto-forno

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

In 2008 alone, the annual steel production in Brazil was around 31 million tons. The steel production process generates an average of 500 kg of residues and co-products per ton of steel. From this total, 70% corresponds to the slags. Although investigating the increase of blast furnace slag use is of extreme importance for the concrete and steel industries socio-environmental sustainable strategy, the current Brazilian standards and specifications represent a barrier. Currently, most concrete specifications are predominantly prescriptive with some performance requirements. Prescriptive specifications prevent the use of innovative solutions that can potentially result in products with comparable or even better performance than those produced according to prescriptive specifications. The solution for the technology progress is the use of performance specifications. Performance specifications stipulate what is required from the product and do not prescribe how the product should be produced. In other words, they focus on the desired performance rather than on the concrete ingredients, materials selection, proportioning or construction methods. These are the responsibility of those individuals who contractually have to comply with the specifications. There is an increasing need to include performance requirements related to durability in specifications and standards, especially those related to reinforcement deterioration. It requires the performance of the structure to be estimated during its service life. It also requires service life prediction models which can correlate the durability requirements, measured through laboratory testing, and the performance in service, obtained from real exposure condition data. The present thesis presents a laboratory study on concretes containing blast furnace-slag, evaluates their main properties, especially those related to reinforcement deterioration. The following properties were evaluated: shrinkage, capillary absorption, compressive strength, modulus of elasticity, natural and accelerated carbonation, charge passed, electrical resistivity and the synergic effect of carbonation and chloride penetration on the reinforcement corrosion. This synergic effect was evaluated through cyclic testing and the measurement of chloride penetration, carbonation depth, electrical resistivity and open circuit potential. The results of this study showed that the use of high blast furnace slag contents generally either did not have an impact or had a beneficial impact on the properties studied, with exception of shrinkage and accelerated carbonation. The cyclic testing presented a way to evaluate the synergic effect of carbonation and chlorides. When all the accelerated cyclic test results are compared, it can be observed that in general the mixtures containing CP III-32-RS presented a better performance regarding reinforcement corrosion. On the other hand, the natural tests did not present any conclusive results. In addition, this thesis evaluated the potential service life of these concretes through mathematical models. No matter which model was used to predict corrosion initiation due to chloride ingress, the predicted service life increased with the increase of the blast furnace slag content. Generally, the service life of the mixtures increased in the order CPII-E-32, CP III-32- RS e CP III-32-RS + slag and with the increase of the compressive strength. Nevertheless, it was observed that NBR 6118/2003 recommendations do not always guarantee the structure durability and do not differentiate mixtures that performed considerably differently. NBR 6118/2003 recommendations were identified as inadequate to assure an acceptable service life. Based on the performance evaluation of the mixtures, changes to the Brazilian specifications and standards were suggested in order to follow the international trend and to move from prescription to performance. Guidelines to develop performance specifications for concretes containing blast furnace slag were presented, including suggestions for the performance requirements and sub-requirements. The strategic, tactic and operational aspects for their implementation in Brazil were presented, as well

ASSUNTO(S)

concrete durability (engineering) concreto escoria slag durabilidade (engenharia) durability of building materials materiais de construção - durabilidade

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