Browsing by Author "Brito, Jorge de"
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- Bond of recycled coarse aggregate concrete: model uncertainty and reliability-based calibration of design equationsPublication . Pacheco, João; Brito, Jorge de; Chastre, Carlos; Evangelista, LuisThis paper concerns the design of lap splice lengths for ribbed steel reinforcement bars embedded in concrete produced with coarse recycled concrete aggregates. Recycled aggregates are weaker and typically lead to concrete with lower tensile strength. Both aspects change the model uncertainty of bond strength formulae and a major topic of the paper is the influence of recycled aggregates on the model uncertainty of the bond strength model of fib Bulletin 72. A stochastic model for this model uncertainty is developed from a meta-analysis. The model uncertainty, estimated from analogue specimens made with either natural aggregate concrete or recycled aggregate concrete, is compared and the incorporation of recycled aggregates was indeed found to have a detrimental influence on the model uncertainty. A partial factor for lap splice length design is calibrated through reliability analyses so that the probability of failure of the bond length design of recycled aggregate concrete is equivalent to that of natural aggregate concrete. Two design equations were studied: that of the fib Bulletin 72 and that of the D6 draft of the second generation of Eurocode 2.
- Effect of the maturity of recycled aggregates on the mechanical properties and autogenous and drying shrinkage of high-performance concretePublication . Revilla-Cuesta, V.; Evangelista, Luis; Brito, Jorge de; Ortega-López, Vanesa; Manso, Juan M.The high cement content of high-performance concrete (HPC) results in improved strength, but also in large shrinkage. The substitution of natural aggregates (NA) with recycled aggregates (RA) notably affects these properties in conventional concrete. This study intends to analyse the effect of the content of RA and their maturity (time elapsed between casting and crushing of the parent concrete from which RA are obtained) on these properties of HPC. To this end, five mixes were manufactured with 0%, 25%, and 100% of coarse and fine RA of different maturities, 7 days (early-age RA) and 6 months (matured RA). The mechanical properties and the autogenous, drying, and total shrinkage of all mixes were determined. Both the increase of RA content and the lower stiffness and strength of early-age RA relative to matured RA worsened the mechanical behaviour of HPC. Regarding shrinkage, the lower stiffness and higher water absorption of matured RA compared to NA decreased autogenous shrinkage by 20%, but increased drying and total shrinkage. The lower stiffness of early-age RA and their shrinkage amplified all types of shrinkage of HPC around 10-20%. Nevertheless, the hydration of their unhydrated cement particles during the mixing process reduced those increases from what was expected. Total shrinkage of early-age recycled aggregate HPC could be estimated from the shrinkage of both a HPC mix of identical composition but with matured RA and the parent concrete. Overall, it can be concluded that RA's maturity affects the mechanical performance and, especially, the shrinkage of HPC, so it should be considered when using this type of aggregate.
- Eurocode shear design of coarse recycled aggregate concrete: reliability analysis and partial factor calibrationPublication . Pacheco, João; Brito, Jorge de; Chastre, Carlos; Evangelista, LuisThis paper contributes to the definition of design clauses for coarse recycled aggregate concrete. One of the main reasons for scepticism towards recycled aggregate concrete is the perceived notion that the heterogeneity of recycled aggregates may increase the uncertainty of the behaviour of concrete. Therefore, the paper uses structural reliability concepts to propose partial factors for recycled aggregate concrete's design for shear failure. The paper builds upon a previous publication by the authors, in which the model uncertainty of recycled aggregate concrete elements designed for shear, with and without shear reinforcement, was compared with that of natural aggregate concrete elements. In that paper, the statistics of the model uncertainty for recycled aggregate concrete shear design were indeed found to be less favourable than those of natural aggregate concrete. Therefore, a partial factor for recycled aggregate concrete design is needed to ensure safety. This paper presents partial factors calibrated with explicit reliability analyses for different cases of design concerning beams (in the case of shear design of elements with shear reinforcement) and slabs (for the design of elements without shear reinforcement). For full incorporation of coarse recycled concrete aggregates and the design of elements without shear reinforcement, the calibrated partial factor reduces the design value of shear resistance by 10% (design with EN1992) or 15% (design with prEN1992) in comparison to natural aggregate concrete's design. For the shear design of elements with shear reinforcement, the partial factor decreases resistance by 5% but a sensitivity analysis showed that the reduction might be, under pessimistic expectations, of up to 20%.
- A influência da porosidade na durabilidade do betão auto-compactável (BAC)Publication . Silva, Pedro; Brito, Jorge dePretende-se, neste artigo, apresentar um resumo sobre o estado actual do conhecimento relativo ao comportamento do BAC em termos de durabilidade, mais especificamente sobre o efeito da sua porosidade. Apesar das exigências dos BAC em termos de propriedades no estado endurecido serem as mesmas de um betão convencional (BC), as quantidades de amassadura utilizadas bem como as proporções nas quais os diversos componentes se combinam são diferentes. As diferenças referidas entre os BAC e os BC assentam na diminuição da relação entre as quantidades de agregado grosso e de argamassa com o consequente aumento do volume de pasta através da utilização de maiores volumes de material ultra fino (cimento + adições) e adjuvantes (tipo superplastificantes e/ou moduladores de viscosidade) e no adequado controlo da máxima dimensão de agregado. Apesar das razões, tanto de carácter técnico e económico, como até ecológicas (utilização dos recursos de modo a garantir um crescimento sustentável) para a utilização de maiores quantidades de adições, se estas forem demasiadamente elevadas, tal pode afectar substancialmente a durabilidade do BAC. Tal como acontece com um BC, para obter uma maior durabilidade, o BAC terá de dificultar a penetração dos agentes agressivos para o seu interior. A referida penetração ocorre por difusão ou absorção capilar devido à maior ou menor permeabilidade do BAC à água e aos gases. Desse modo, um conjunto de fluidos poderá penetrar no BAC e deteriorá-lo, tais como a água pura ou com iões agressivos, o CO2 e o oxigénio (como elemento regulador de todas as reacções de corrosão do aço embebido no betão). Com recurso à análise da estrutura dos poros de um betão, é possível prever a sua durabilidade uma vez que esta análise possibilita o conhecimento do modo como os agentes agressivos se difundem ou penetram na massa do betão.
- Mechanical behaviour of concrete made with fine recycled concrete aggregatesPublication . Evangelista, Luís; Brito, Jorge deThis paper concerns the use of fine recycled concrete aggregates to partially or globally replace natural fine aggregates (sand) in the production of structural concrete. To evaluate the viability of this process, an experimental campaign was implemented in order to monitor the mechanical behaviour of such concrete. The results of the following tests are reported: compressive strength, split tensile strength, modulus of elasticity and abrasion resistance. From these results, it is reasonable to assume that the use of fine recycled concrete aggregates does not jeopardize the mechanical properties of concrete, for replacement ratios up to 30%.
- Mechanical evaluation of timber conservation processes by bending testsPublication . Henriques, Dulce Franco; Nunes, Lina; Brito, Jorge deThis paper presents the laboratory work performed with the purpose of understanding the mechanical performance of 340x20x20 mm maritime pine wood samples degraded by rot fungi when treated with a biocide product followed by consolidation through impregnation with a polymeric product. Four commercially available products were used: a water-based biocide, BC, a solvent-based biocide, X, an acrylic consolidant, PB (PB 72), and an epoxy-based consolidant, E. Seven sets of specimens each one having a varied range of fungal degradation were prepared. Then the product combinations were applied by brush to six sets of specimens (E, X-E, BC-E, PB, X-PB, BC-PB) of which one was left untreated for control, 0-0. Finally all sets were subjected to static bending strength test until rupture. Results showed that the acrylic and epoxy-based products lead to increased mechanical capacity of the consolidated wood up to 100% in some cases in specimens with 70% of MOE loss. The results presented the same order of magnitude for both wood consolidants. The previous application of biocide did not have a significant impact in the behavioral pattern of the consolidant: a marked improvement of the bending strength of the degraded specimens after treatment and consolidation. These results demonstrated the feasibility of combining biocide/consolidation products, and provide indications of interest to the application of this technique to extend the lifespan of wood elements moderately degraded by fungi in old buildings.
- Mechanical performance and autogenous and drying shrinkage of MgO-based recycled aggregate high-performance concretePublication . Revilla-Cuesta, V.; Evangelista, Luis; Brito, Jorge de; Skaf, Marta; Ortega-López, VanesaThe high strength and durability of high-performance concrete (HPC) may be significantly reduced by shrinkage cracking. The use of reactive magnesium oxide (MgO) can reduce shrinkage of cement-based materials due to its expansive properties. This study intends to analyse the validity of MgO as shrinkage-reducing agent in recycled aggregate HPC. To do so, ten HPC mixes with 0%, 25%, and 100% of both early-age (7-days air curing) and matured (6-month air curing) RA were produced. In half of the mixes, 10% ordinary Portland cement was replaced with MgO. The use of MgO slightly worsened the mechanical behaviour of HPC, especially when combined with large amounts of RA. On the other hand, the expansion of MgO fully offset the autogenous shrinkage of HPC and reduced total shrinkage by around 20-40%. Water storage of RA, and its deferred release over time, produced a more efficient hydration of MgO, which in turn led to a further reduction of autogenous shrinkage. However, the increase of drying shrinkage caused by RA was greater than this decrease of autogenous shrinkage due to MgO, so the higher the RA content of HPC the lower the total shrinkage reduction when adding MgO. Thus, the decrease of total shrinkage caused by MgO was compensated by the shrinkage increase because of RA when adding amounts above 35% early-age RA and 42% matured RA. Therefore, despite the suitability of MgO as shrinkage-reducing agent in recycled aggregate HPC, its effectiveness was reduced with increasing amounts of RA.
- A pressão exercida pelo betão auto-compactável (BAC) nas cofragensPublication . Silva, Pedro; Brito, Jorge dePretende-se, neste artigo, apresentar um resumo sobre o estado actual do conhecimento relativamente à avaliação da pressão que o betão auto-compactável (BAC) exerce sobre as paredes das cofragens. Com o início de uma utilização mais generalizada do BAC, tanto na construção de edifícios e obras de arte, como na pré-fabricação (indústria que tem sabido aproveitar as mais valias desta nova tecnologia), alterou-se significativamente o processo de colocação do betão nas cofragens. Tais alterações aparecem associadas essencialmente às diferenças de comportamento no estado fresco entre um betão convencional (BC) e um BAC. Este último apresenta-se como uma mistura, em suspensão, de partículas com uma extensão em termos de dimensões que pode ir desde o mícron até a 2 cm, com a capacidade de, sem precisar de qualquer tipo de vibração, conseguir preencher completamente as cofragens, envolvendo de forma adequada as armaduras sem deixar vazios nem ocorrer qualquer fenómeno de segregação tanto durante a colocação como durante o tempo em que permanece fluido. A possibilidade de eliminar a fase de vibração, entre outras, permite uma betonagem em contínuo. Não obstante a possibilidade de betonar em contínuo ter claras vantagens em termos do tempo associado à tarefa, a pressão que o BAC irá exercer, essencialmente nas cofragens de elementos verticais, pode, em alguns casos, ser comparável à pressão hidrostática de um líquido com a massa volúmica do betão. Contudo, logo numa fase inicial de implementação do BAC e depois de analisados alguns resultados práticos de cofragens monitorizadas, chegou-se à conclusão de que, em alguns desses casos, os pressupostos iniciais não eram verificados, tendo mesmo sido observados resultados em que a pressão exercida por um BAC seria igual à de um BC ou até inferior. Por outras palavras, a tixotropia do BAC será um factor importante na pressão do mesmo sobre as cofragens.
- Reabilitação urbana em Portugal. Especificidades e fundamentos para um plano estratégicoPublication . Henriques, Dulce Franco; Brito, Jorge de; Pinho, Fernando F. S.; Freitas, V. P. deA reabilitação do património edificado constitui uma prioridade atual do setor da Arquitetura, Engenharia e Construção (AEC) em Portugal, decorrente do nível de degradação de muitos edifícios e outras construções, e da redução de investimento na construção de novas infraestruturas. Esta situação reflete a mudança de paradigma em curso: passagem da construção nova para a reabilitação. Neste contexto, um grupo de mais de 30 especialistas, oriundos de 15 instituições e empresas, no âmbito do Grupo de Trabalho “Reabilitação”, da Plataforma Tecnológica Portuguesa da Construção (PTPC), elaborou o “Caderno de Síntese Tecnológica - Reflexão sobre a estratégia para a Reabilitação em Portugal” (CST), publicado no final de 2015, visando sensibilizar os decisores e atores da construção para a temática da reabilitação. Nesta comunicação, cujos autores são os membros da Comissão Editorial do CST, constituída por Dulce Henriques (ISEL), Fernando F. S. Pinho (DEC FCT UNL), Jorge de Brito (IST UL), Maria João Falcão (LNEC), Rita Moura (TEIXEIRA DUARTE, SA) e Vasco Peixoto de Freitas (FEUP; Coordenador do CST), são apresentadas as principais linhas orientadoras do CST que, enquanto documento de reflexão no âmbito da reabilitação do património edificado, procura contribuir para a definição de um plano estratégico Nacional de reabilitação do património.
- Seismic resistance of earth construction in PortugalPublication . Gomes, Maria Idália; Lopes, Mário; Brito, Jorge deThis paper presents an assessment of the potential seismic performance of new earth construction in Portugal. Results of a parametric study on a properly designed rammed earth construction, considering several strengthening solutions, are presented and discussed. It is concluded that single storey houses can have acceptable seismic performance even in high seismicity areas, provided that the structure is adequately strengthened by reinforced concrete columns and beams. Improvement of the characteristics of the structural material (earth) may be necessary to reduce damage.