Civil Engineering

This works intends to analyze, experimentally and numerically, the bond-slip behavior between steel and concrete made with recycled aggregates (RA) from construction and demolition waste (CDW) from several recycling plants in Portugal. Pull-out tests performed in concrete mixes with RA from CDW are described and the main results (bond strength, bond-slip curves and failure modes) are shown and discussed. Additionally, a comparison between experimental and analytical (using equations from the literature) results is made. Afterwards, finite element (FE) models using Abaqus are developed and compared with the experimental results. The interface behavior between steel and concrete follows that prescribed by the CEB-FIP Model Code and uses as input experimental results. After validation, the models show good results when extended to predict the bond-slip behavior of the remaining concrete mixes studied. It is generally concluded that, per each 10% of natural aggregates replaced with RA f...

The majority of worldwide structures use concrete as its main material. This happens because concrete is economically feasible, due to its undemanding production technology and ease of use. However, it is widely recognized that concrete production has a strong environmental impact in the planet. Natural aggregates use is one of the most important problems of concrete production nowadays, since they are obtained from limited, and in some countries scarce, resources. In Portugal, although there are enough stone quarries to cover coarse aggregates needs for several more years, supplies of fine aggregates are becoming scarcer, especially in the northern part of the country. On the other hand, as concrete structures' life cycle comes to an end, an urgent need emerges to establish technically and economically viable solutions for demolition debris, other than for use as road base and quarry fill. This paper presents a partial life cycle assessment (LCA) of concrete made with fine recycled concrete aggregates performed with EcoConcrete tool. EcoConcrete is a tailor-made, interactive, learning and communications tool promoted by the Joint Project Group (JPG) on the LCA of concrete, to qualify and quantify the overall environment impact of concrete products. It consists of an interactive Excel-spreadsheet in which several environmental inputs (material quantities, distances from origin to production site, production processes) and outputs (material, energy, emissions to air, water, soil or waste) are collected in a life cycle inventory, and are then processed to determine the environmental impact (assessment) of the analysed concrete, in terms of ozone layer depletion, smog or "greenhouse" effect.

Research on the use of Construction and Demolition Waste (CDW) as recycled aggregate (in particular crushed concrete) for the production of new concrete has by now established the feasibility of this environmentally-friendly use of otherwise harmful waste. However, contrary to conventional concrete (CC), no large applications of concrete made with recycled concrete have been made and there is still a lack of knowledge in some areas of production and performance of recycled aggregate concrete (RAC). One issue concerns curing conditions: these greatly affect the performance of concrete made on site and some potential users of RAC wonder how RAC is affected by far-from-ideal curing conditions. This paper shows the main results of experiments to determine the influence of different curing conditions on the mechanical performance of concrete made with coarse recycled aggregate from crushed concrete. The properties analyzed include compressive strength, splitting tensile strength, modulus of elasticity, and abrasion resistance. The general conclusion in terms of mechanical performance is that RAC is affected by curing conditions roughly in the same way as CC.

It is considered that using crushed recycled concrete as aggregate for concrete production is a viable alternative to dumping and would help to conserve abiotic resources. This use has fundamentally been based on the coarse fraction because the fine fraction is likely to degrade the performance of the resulting concrete. This paper presents results from a research work undertaken at Institut Superior Tecnico (IST), Lisbon, Portugal, in which the effects of incorporating two types of superplasticizer on the mechanical performance of concrete containing fine recycled aggregate were evaluated. The purpose was to see if the addition of superplasticizer would offset the detrimental effects associated with the use of fine recycled concrete aggregate. The experimental programme is described and the results of tests for splitting tensile strength, modulus of elasticity and abrasion resistance are presented. The relative performance of concrete made with recycled aggregate was found to decrease. However, the same concrete with admixtures in general exhibited a better mechanical performance than the reference mixes without admixtures or with a less active superplasticizer. Therefore, it is argued that the mechanical performance of concrete made with fine recycled concrete aggregates can be as good as that of conventional concrete, if superplasticizers are used to reduce the water-cement ratio of the former concrete.

Fine recycled aggregates are seen as the last choice in recycling for concrete production. Many references quote their detrimental influence on the most important characteristics of concrete: compressive and tensile strength; modulus of elasticity; water absorption; shrinkage: carbonation and chloride penetration. These two last characteristics are fundamental in terms of the long-term durability of reinforced or prestressed concrete. In the experimental research carried out at IST, part of which has already been published, different concrete mixes (with increasing rates of substitution of fine natural aggregates sand-with fine recycled aggregates from crushed concrete) were prepared and tested. The results were then compared with those for a reference concrete with exactly the same composition and grading curve, but with no recycled aggregates. This paper presents the main results of this research for water absorption by immersion and capillarity, chloride penetration (by means of the chloride migration coefficient), and carbonation resistance, drawing some conclusions on the feasibility of using this type of aggregate in structural concrete, while taking into account any ensuing obvious positive environmental impact.

The reuse of structural concrete elements to produce new concrete aggregates is accepted as an alternative to dumping them and is favourable to the sustainability of natural reserves. Even though the construction sector is familiar with the use of coarse recycled concrete aggregates, the recycled concrete fines are classified as less noble resources. This research sets out to limit the disadvantages associated with the performance of concrete containing fine recycled concrete aggregates through the use of superplasticisers. Two types of latest generation superplasticisers were used that differ in terms of water reduction capacity and robustness, and the workability, density and compressive strength of each of the compositions analysed were then compared: a reference concrete, with no plasticisers, and concrete mixes with the superplasticisers. For each concrete family mixes with 0%, 10%, 30%, 50% and 100% replacement ratios of fine natural aggregates (FNA) by fine recycled concrete aggregates (FRA) were analysed. Concrete with incorporation of recycled aggregates was found to have poorer relative performance. The mechanical performance of concrete with recycled aggregates and superplasticisers was generally superior to that of the reference concrete with no admixtures and of conventional concrete with lower performance superplasticisers.

The construction industry keeps on demanding huge quantities of natural resources, mainly minerals for mortars and concrete production. The depletion of many quarries and environmental concerns about reducing the dumping of construction and demolition waste in quarries have led to an increase in the procuring and use of recycled aggregates from this type of waste. If they are to be incorporated in concrete and mortars it is essential to know their properties to guarantee the adequate performance of the end products, in both mechanical and durability-related terms. Existing regulated tests were developed for natural aggregates, however, and several problems arise when they are applied to recycled aggregates, especially fine recycled aggregates (FRA). This paper describes the main problems encountered with these tests and proposes an alternative method to determine the density and water absorption of FRA that removes them. The use of sodium hexametaphosphate solutions in the water absorption test has proven to improve its efficiency, minimizing cohesion between particles and helping to release entrained air.

Conservation of natural resources, shortage of waste land and the high cost associated to treatment prior to disposal are driving growing interest in the recycling of construction and demolition waste materials (CDW). A challenging application for recycled CDW is the replacement of natural aggregates in the production of structural concrete. In the past few years several studies have examined the viability of this substitution. Although recycled aggregates are mostly heterogeneous, less dense and more porous than natural aggregates, satisfactory results have been attained by several authors regarding concrete workability, mechanical properties and durability. However, a systematic microstructural characterization of recycled aggregate concrete is still unaccomplished.In this context, the use of fine recycled concrete aggregates to replace natural fine aggregates in the production of structural concrete was tested, and attained microstructures are reported. The recycled aggregates we...

This research aims at analysing the mechanical performance of concrete with recycled aggregates (RA) from construction and demolition waste (CDW) from various locations in Portugal. First the characteristics of the various aggregates (natural and recycled) used in the production of concrete were thoroughly analysed. The composition of the RA was determined and several physical and chemical tests of the aggregates were performed. In order to evaluate the mechanical performance of concrete, compressive strength (in cubes and cylinders), splitting tensile strength, modulus of elasticity and abrasion resistance tests were performed. Concrete mixes with RA from CDW from several recycling plants were evaluated, in order to understand the influence that the RA's collection point, and consequently their composition, has on the characteristics of the mixes produced. The analysis of the mechanical performance allowed concluding that the use of RA worsens most of the properties tested, especially when fine RA are used. On the other hand, there was an increase in abrasion resistance when coarse RA were used. In global terms, the use of this type of aggregates, in limited contents, is viable from a mechanical viewpoint.

h i g h l i g h t s The use of FRCA significantly increased the shrinkage and creep deformation. The FRCA's effect on rheological behaviour is influenced by the curing age. Superplasticizers increase early-age shrinkage but decrease it in the long-term. High-performance superplasticizer decreases creep deformation. The incorporation of FRCA partially hindered the effectiveness of the superplasticizers.

A presente comunicação tem como objectivo apresentar o trabalho experimental a desenvolver acerca do desempenho de betões com agregados finos provenientes da reciclagem de betão. Presentemente, os documentos normativos relativos à utilização de agregados reciclados em betões prevê a utilização da sua fracção grossa, com diferentes taxas de incorporação, dependendo do fim a que o betão final se destina, mas apontam para a não inclusão da fracção fina dos mesmos. Genericamente, apontam-se como principais problemas para a inclusão destes materiais a sua elevada porosidade, que conduz a uma estrutura do betão menos compacta, com consequentes reduções de desempenho. No entanto, alguns trabalhos anteriormente desenvolvidos apontam para que a inclusão da fracção fina dos agregados reciclados possa não ser tão prejudicial como se julga, podendo ser um substituto eficaz dos agregados naturais, em especial se se tiver em atenção as condicionantes ambientais inerentes ao processo extractivo. O trabalho pretende obter mais informação sobre o desempenho de betões com agregados finos reciclados de betão, comparando-os com betões convencionais, executados exclusivamente com agregados naturais pétreos.

The Portuguese construction sector is currently ruled by new buildings, responsible for 95% of the annual investment in this sector. Formal aspects and initial costs are the primary design concerns, using current long lifespan construction, with little consideration given to future maintenance or future needs. This situation represents a tremendous waste of resources (present and future), and there is a growing perception of the need to address these issues. One of the possible change trends lies in a revision of current design practices to increase building adaptability accommodating current construction logics, but there is a lack of examples bridging the gap between current (international) theory and (Portuguese) practice. The Lisbon EXPO 98 World Exhibition was the largest example of urban regeneration in Portugal, in which several buildings addressed the need for adaptability according to different design logics, since their original uses would cease or change upon the exhibition's closure. This paper will present the case study of an EXPO 98 building, Portugal's Pavilion by Pritzker Winner Architect Álvaro Siza, as an example of the use of design strategies to provide adaptability (at structural, spatial and material levels) within an institutional building, using current Portuguese construction possibilities.

This paper evaluates the influence of two superplasticizers (SP) on the durability properties of concrete made with fine recycled concrete aggregate (FRCA). For this purpose, three families of concrete were tested: concrete without SP, concrete made with a regular superplasticizer and concrete made with a high-performance superplasticizer. Five volumetric replacement ratios of natural sand by FRCA were tested: 0%, 10%, 30%, 50% and 100%. Two natural gravels were used as coarse aggregates. All mixes had the same particle size distribution, cement content and amount of superplasticizer. The w/c ratio was calibrated to obtain similar slump. The results showed that the incorporation of FRCA increased the water absorption by immersion, the water absorption by capillary action, the carbonation depth and the chloride migration coefficient, while the use of superplasticizers highly improved these properties. The incorporation of FRCA jeopardized the SP's effectiveness. This research demonstrated that, from a durability point of view, the simultaneous incorporation of FRCA and high-performance SP is a viable sustainable solution for structural concrete production.

Bu çalışmada Bayburt İli sınırları içinde bulunan kireçtaşı, doğal dere agregası, serpantine ve Bayburt taşı kullanılarak geleneksel betonlar üretilmiştir. Deneysel çalışmada çimento dozajı ve işlenebilirlik sabit tutulmuştur. Çalışmada çökme, Ve-Be, birim hacim ağırlık ve ilk 2 saat içinde oluşan en yüksek taze beton sıcaklıkları ölçülmüştür. Hazırlanan beton örneklerden Bayburt taşı ile üretilen betonlar 90 gün, diğerleri 28 gün süreyle kirece doygun su içinde küre tabi tutulmuştur. Sertleşmiş haldeki betonların 7 ve 28 gün yaşlarında basınç dayanımı deneyi sırasında alınan deformasyon ve gerilme kayıtları sayesinde gerilme-deformasyon bilgileri edinilmiş ve su emme oranları ölçülmüştür. Sonuçlara göre beton numunelerin 28 günlük basınç dayanımı sonuçları; kireçtaşı, doğal dere ve serpantin agregası için sırasıyla 40, 35 ve 5 MPa olarak elde edilmiştir. Bayburt taşı agregası ile üretilen betonlarda basınç dayanımları 28 günde 16 MPa ve 90 günde 22 MPa değerine ulaşmıştır.

This paper investigates the effect of recycled coarse aggregate incorporation on the relationship between 150 mm cubic and Փ 150 mm cylindrical compressive strength (the reference strength of standards) by comparing data from recycled and natural aggregate concrete compositions in which both cubes and cylinders were tested. A conversion factor from cubic to cylindrical strength is proposed in two versions: A deterministic and a probabilistic one. Such factor has not been studied before and researchers have been converting cubic data as if natural aggregate concrete were tested. The probabilistic factor is intended for reliability analyses on the structural behaviour of recycled aggregate concrete using data from laboratory cube tests. It was found that the incorporation of recycled coarse aggregates sourced from concrete waste significantly decreases the expected value of the factor but the factor’s scatter is relatively unaffected.

This paper presents a literature review on the Fresh state properties of selfcompacting concrete with fine and coarse recycled aggregates. The growing environmental awareness of today's society causes greater concern with the high consumption of natural resources and the waste originated by the activities of the various industries. In particular, the construction industry consumes a large part of those resources and is, currently, the main responsible for the production of waste in Europe, whose dumping and treatment results in severe environmental and economic consequences. Given that concrete is the most commonly used material in the construction activity, it becomes a significant portion of the construction and demolition waste. In this context, the work developed intends to present a literature review on the incorporation of recycled aggregates (RA) in the production of self-compacting concrete (SCC). For each concrete property, the following information was collected: type and physical characteristics of the materials used for SCC production; mix composition; tests results; discussion and conclusions on those tests. A description of the experimental campaigns performed is first presented. Next, each fresh state property of the SCC is analyzed based on the results obtained by the various authors. The concrete's properties analyzed in the fresh state are: slump-flow diameter and slump flow time, V-funnel time, L-box, J-ring and sieve segregation. The theme of SCC with RA is of great relevance to society since this increasingly requires the construction industry to adopt new processes that minimize the negative impacts on the environment.

An investigation on the scatter of code-type constitutive models that relate compressive strength (c f) with tensile strength (ct f) and Young's modulus (c E) of standard concrete specimens is presented. The influence of the mix design on the accuracy of the c f vs. ct f and c f vs. c E relationships is discussed, with emphasis on the lithological type and morphology of the coarse aggregates. The uncertainty of the constitutive models is analysed in probabilistic terms and random variables that model the uncertainty of the c f vs. ct f and c f vs. c E relationships are proposed for reliability analyses of serviceability limit states. The suitability of the models proposed is assessed through preliminary conservative estimates of their design values. 2. Reesearch goals and significance This paper intends to investigate whether different mix designs and strength ranges will result in different accuracy and precision of the θ of the c c t f vs f and c f vs. c E relationships. The main objective of the paper is the proposal of probability distributions of E θ and fct θ intended for serviceability limit-state (SLS) reliability analyses. Coefficients E θ and fct θ are calculated as shown in

This paper presents a literature review concerning the characteristics of MgO (magnesium oxide or magnesia) and its application in cementitious materials. It starts with the characterization of MgO in terms of production processes, calcination temperatures, reactivity, and physical properties. Relationships between different MgO characteristics are established. Then, the influence of MgO incorporation on the properties of cementitious materials is investigated. The mechanical strength and durability behaviour of cement pastes, mortars and concrete mixes made with MgO are discussed. The studied properties of MgO–cement mixes include compressive strength, flexural strength, tensile strength, modulus of elasticity, water absorption, porosity, carbonation, chloride ion penetration, shrinkage, expansion, and hydration degree. In addition, microscopic analyses of MgO-cement mixes are also assessed. Summarizing the results of different studies, it is concluded that MgO incorporation in cem...

The possibility of using recycled aggregates from construction and demolition waste (CDW) in concrete is rather widely agreed upon when it comes to the use of coarse recycled aggregates. However, this is not the case when fine recycled aggregates (FRA) are considered, as it is deemed that these seriously impair the behaviour of concrete. Hence, this work presents a technical specification proposal for the use of FRA from CDW in concrete, to attempt to fill this gap in legislation. The specification is based on a wide collection of experimental results, from which it is shown that for low incorporation ratios (up to 25%), the properties of concrete with FRA from CDW are comparable to those of a reference concrete. The intended international scope of the specification is ensured by the fact that FRA from CDW are typified by composition (percentage of concrete, masonry, glass, etc.) rather than by geographical origin or construction type. It is shown that, after typifying the FRA and a...

This research evaluates the fracture behavior of concrete with reactive magnesium oxide (MgO). Replacing cement with MgO is an attractive option for the concrete industry, mainly due to sustainability benefits and reduction of shrinkage. Four different MgO’s from Australia, Canada, and Spain were used in the concrete mixes, as a partial substitute of cement, at 5%, 10%, and 20% (by weight). The fracture toughness (KI) intensity factor and the stress–strain softening parameters of the wedge split test were evaluated after 28 days. The experimental results showed that the replacement of cement with MgO reduced the fracture energy between 13% and 53%. Moreover, the fracture energy was found to be correlated with both compressive strength and modulus of elasticity. A well-defined relationship between these properties is important for an adequate prediction of the non-linear behavior of reinforced concrete structures made with partial replacement of cement with MgO.