Contribution to the development of performance specifications for concretes containing blast furnace slag

Orientador: Vanessa Gomes da Silva, Maristela Gomes da SilvaAcompanha 1 CD-ROM de Apendices e AnexoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e UrbanismoResumo: A produção anual de aço em 2008 foi de cerca de 31 milhões de toneladas O processo siderúrgico gera em média 500 kg de resíduos e co-produtos por tonelada de aço produzido. Desse total, 70% correspondem à geração das escórias. Investigar a possibilidade de moagem da escória de alto-forno para atender às usinas de concreto e indústrias afins é de vital importância como estratégia de sustentabilidade sócioambiental para a cadeia produtiva do aço e do concreto. No entanto, as atuais normas e especificações brasileiras de concreto se apresentam como um obstáculo para isso. Atualmente, a maioria das especificações de concreto é predominantemente prescritiva com alguns aspectos de desempenho. As especificações prescritivas impedem o uso de soluções mais inovadoras que potencialmente podem resultar em produtos com desempenho comparável ou até melhor do que aqueles que são produzidos de acordo com as especificações prescritivas. A solução para o avanço tecnológico é o uso de especificações por desempenho. As especificações por desempenho tratam do que se requer do produto e não prescreve como esse produto deve ser produzido. Em outras palavras, ao invés de partirem dos materiais que compõem o concreto, partem do desempenho desejado, deixando a seleção dos materiais, a dosagem e os métodos construtivos a cargo daqueles que contratualmente devem atender às especificações. Há uma necessidade crescente da inclusão de requisitos de desempenho nas especificações e normas, referentes à durabilidade do concreto, especialmente no que concerne a capacidade de proteção do concreto contra a corrosão da armadura. Isso requer que o desempenho da estrutura, ao longo da sua vida útil, possa ser estimado. Para isso, são necessários modelos de previsão de vida útil que correlacionem os requisitos e subrequisitos de durabilidade, medidos em laboratório por meio de ensaios acelerados, e o desempenho em serviço, obtido por meio de dados nas condições reais. Este trabalho apresenta um estudo laboratorial em concretos com escória de alto-forno, avalia suas principais propriedades, principalmente as relativas à deterioração referente à armadura. Foram avaliados: a retração, a absorção capilar, a resistência à compressão axial, o módulo de deformação, a carbonatação tanto natural quanto acelerada, a carga passante, a resistividade elétrica e o efeito sinérgico da carbonatação e da penetração de cloretos sobre a corrosão da armadura. Este efeito sinérgico foi avaliado por meio de ensaios cíclicos e a medida da profundidade de penetração de cloretos, da profundidade de carbonatação, da resistividade elétrica e do potencial de circuito aberto. Com os resultados obtidos neste estudo, verificou-se que a utilização de elevados teores de escória de alto forno, de maneira geral, ou não teve nenhuma influência ou exerceu uma influência positiva sobre as propriedades estudadas, com exceção da retração e da carbonatação acelerada. Os ensaios cíclicos apresentaram uma maneira de avaliar-se o efeito sinérgico da carbonatação e dos cloretos. Quando todos os resultados de ensaios acelerados cíclicos são comparados observa-se que, de maneira geral, as misturas com CP III-32-RS apresentaram o melhor desempenho no que concerne à corrosão das armaduras. Já os ensaios naturais não foram conclusivos. Além disso, este trabalho avalia a vida útil potencial desses concretos por meio da aplicação de modelos de previsão de vida útil. Independentemente do modelo utilizado para a previsão da despassivação por cloretos, a vida útil prevista aumentou com o aumento do teor de escória de alto-forno. De maneira geral, vida útil das misturas cresceu na ordem CPII-E-32, CP III-32-RS e CP III-32-RS + escória e com o aumento da classe de resistência. No entanto, observou-se que as recomendações da NBR 6118/2003 nem sempre garantem que a durabilidade da estrutura seja necessariamente atingida e não diferenciam misturas cujos desempenhos mostraram-se bem diferentes. As recomendações da NBR 6118/2003 mostraram-se inadequadas para a que uma vida útil mínima aceitável seja atingida. A partir desta avaliação de desempenho, apresentam-se sugestões para a modificação das especificações e normas brasileiras a fim de que sigam a tendência mundial e passem de prescrição ao desempenho. Diretrizes para a criação de especificações por desempenho de concretos com escória de alto-forno, incluindo sugestões para os requisitos e subrequisitos de desempenho, bem como os aspectos estratégicos, táticos e operacionais de sua implementação no Brasil também são apresentadosAbstract: 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 wellDoutoradoArquitetura e ConstruçãoDoutor em Engenharia Civi

Effects of Nanomaterials on the Hydration Kinetics and Rheology of Portland Cement Pastes

In this paper, effects of nanomaterials on the hydration kinetics and rheology of ordinary Portland cement pastes were investigated. Three nanomaterials, nano-limestone, nano-silica, and nano-clay (a highly purified magnesium aluminosilicate), were added to a cement paste at the levels of 0.0 %, 0.5 %, 1.0 %, and 1.5 % (by mass) of cement. The heat of cement hydration of the paste was measured using isothermal calorimetry. Rheological behavior of the paste was characterized using a rotational rheometer. The rheology measurements were performed at 10, 30, 60, 90, and 120 min after the cement was mixed with water. Set times of the paste were measured according to ASTM C191 [Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA]. The experimental results indicate that the addition of nano-limestone and nano-silica accelerated cement early hydration, the maximum heat flow increased, whereas the time to reach the heat-flow peaks decreased. The initial and final set times were also reduced. These effects were enhanced with increased nano-addition level. The addition of nano-clay also significantly increased the intensity of the heat flow peaks, and, especially, the peak corresponding to the renewed reaction of the aluminate phase. Addition of these nanomaterials generally increased yield stress and viscosity of the cement paste, especially after 60 min when cement hydration started to accelerate. Nano-clay considerably influenced the rheological behavior of the cement paste. Significantly higher shear stresses were required to initiate the flow.This article is published as Wang, Xin, Kejin Wang, Jussara Tanesi, and Ahmad Ardani. "Effects of nanomaterials on the hydration kinetics and rheology of Portland cement pastes." Advances in Civil Engineering Materials 3, no. 2 (2014): 142-159. DOI: 10.1520/ACEM20140021. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

A Cementitious Long-Life Wearing Course to Reduce Frequency of Maintenance Works on High-Traffic Roads

Under the framework of OECD/CEMT JTRC, an international team of road research laboratories worked together in order to evaluate technical solutions for long-life pavement. As a matter of fact, there are in many countries highly trafficked road sections where any traffic disruption brings high external costs. For such a case, the aim was to study wearing courses that could last several decades with no maintenance. The paper briefly presents an innovative technical solution, called HPCM (High-Performance Cementitious Material), consisting of a thin layer of ultra-high performance fibre-reinforced mortar with calcined bauxite aggregate embedded in the surface when in a fresh state. Many laboratory and two full-scale tests were carried out, dealing with surface resistance (abrasion, wear, shocks, freeze-and-thaw, acid attacks), cracking under restrained shrinkage and fatigue resistance due to heavy traffic loading. Although this material still requires some additional research to be implemented on scale-1 road sites, there are good expectations of its potential durability

Multi-scale investigation of the performance of limestone in concrete

Limestone (calcium carbonate, CaCO3) has long been a critical component of concrete, whether as the primary raw material for cement production, a fine powder added to the binder component, or a source of fine and/or coarse aggregate. This paper focuses on the latter two of these examples, providing a multi-scale investigation of the influences of both fine limestone powder and conventional limestone aggregates on concrete performance. Fine limestone powder in the form of calcite provides a favorable surface for the nucleation and growth of calcium silicate hydrate gel at early ages, accelerating and amplifying silicate hydration, and a source of carbonate ions to participate in reactions with the aluminate phases present in the cement (and fly ash). Conversely, the aragonite polymorph of CaCO3 exhibits a different crystal (and surface) structure and therefore neither accelerates nor amplifies silicate hydration at a similar particle size/surface area. However, because these two forms of CaCO3 have similar solubilities in water, the aragonite does contribute to an enhancement in the reactivity of the aluminate phases in the investigated systems, chiefly via carboaluminate formation. In 100% ordinary Portland cement (OPC) concretes, 10% of the OPC by volume can be replaced with an equivalent volume of limestone powder, while maintaining acceptable performance. A comparison between limestone and siliceous aggregates indicates that the former often provide higher measured compressive strengths at equivalent levels of hydration, even when the two aggregate types exhibit similar elastic moduli. This suggests that the interfacial transition zone in the limestone-based concretes exhibits a higher degree of bonding, likely due to the favorable physical (texture) and chemical nature of the limestone surfaces. These observations reinforce the value of utilizing limestone to increase the performance and sustainability of 21st century concrete construction.Peer reviewed: YesNRC publication: Ye