Loading...
37 results
Search Results
Now showing 1 - 10 of 37
- Permeabilidade e microestrutura de BAC com incorporação de fíler calcárioPublication . Milho, Raquel M. B. Jorge; Azevedo, Ana Cristina G. R. Borges; Raposeiro Da Silva, PedroA durabilidade do betão está diretamente relacionada com o transporte de fluídos no seu interior que, por sua vez, está condicionado pela microestrutura do mesmo. Dadas as diferenças da estrutura porosa do betão auto-compactável (BAC) quando comparada com a de um betão convencional (BC), serão expectáveis algumas diferenças na durabilidade do primeiro. Um dos principais elementos diferenciadores entre ambos é a necessidade de quantidades significativas de material ultra fino (cimento e adições) por parte do BAC, essencialmente de modo a garantir os seus requisitos de comportamento no estado fresco. A utilização de adições, como o fíler calcário (FC), pode melhorar não só o comportamento do BAC no estado fresco como também influenciar a resistência mecânica e a durabilidade, através de uma microestrutura mais densa. Nesse sentido, o objetivo do presente trabalho é avaliar o efeito da utilização de FC na permeabilidade e na microestrutura do BAC. De modo a comprovar as referidas relações, foram efetuados estudos sobre a correlação entre as propriedades da microestrutura e os mecanismos de transporte, através da produção de misturas de BAC com 0%, 30%, 45% e 60% de substituição de cimento por FC. A caracterização físico-química das amostras de BAC foi realizada por difracção de raios-x e por microscopia eletrónica de varrimento (MEV), sendo esta última técnica também um método de caracterização morfológica. Para analisar as propriedades de transporte do BAC foram executados ensaios de absorção por imersão e absorção capilar. A análise dos resultados obtidos permitiu concluir que os betões em estudo apresentam características satisfatórias ao nível da microestrutura e propriedades de transporte. Salienta-se que em todas as amostras foi encontrada uma microestrutura densa, não tendo sido encontrada uma zona de transição entre o agregado e a pasta com características que a diferenciem da restante da pasta. Estas observações complementam os valores encontrados no estudo das propriedades de transporte, fazendo prever que as amostras apresentam uma baixa porosidade.
- Using graphene oxide as means of improvement of concrete: a brief reviewPublication . Raposeiro Da Silva, Pedro; Evangelista, LuisNowadays, the use of nanomaterials (NM) to improve the performance of cement and concrete matrixes constitutes a potential alternative to the exclusive use of Portland cement (PC). Similarly, there is currently no doubt in the construction industry (CI) about the pressing need to reduce the consumption of PC. The CI represents the world's third-largest industrial energy consumer, and the component related to the production of PC alone represents 7% of the carbon dioxide (CO2) emissions globally (OECD, 2018). PC is undoubtedly the most used material in construction in terms of its relative volume. Raw materials for PC production are generally plentiful and they are also available throughout the world. It is possible to state that, , at this moment, there is no other material with the same availability as the PC, which might be able to fulfil the construction’s technical requirements as the concrete’s main component. In this sense, it is imperative that the cement industry obtains viable technical solutions that allow the reduction of PC consumption. That reduction can be achieved either by its direct replacement with another material (e.g. using fly ash), or by improving the cement and concrete matrix performance with the addition of new materials, such as NM. This second option is quite interesting, since it allows u s to maintain the cement and concrete matrix properties/characteristics, reducing PC consumption by adding a tiny amount of a NM.
- Fresh-state and mechanical properties of high-performance self-compacting concrete with recycled aggregates from the precast industryPublication . Barroqueiro, Tiago; Raposeiro Da Silva, Pedro; De Brito, JorgeThe urgent need to change the less positive impacts of the construction industry on the environment, and more specifically the production and use of concrete, is the main motivation for the research for more efficient and environmentally sustainable solutions. This paper presented the results of an experimental campaign whose ultimate goal was to produce high-performance self-compacting concrete (SCC) using recycled aggregates (RA) from the precast industry. The results of the fresh-state and mechanical properties tests performed on six concrete mixes (using RA from the precast industry) were presented. The first concrete mix is a reference mix using natural aggregates only (100% NA), and the remaining five mixes had various contents of fine (FRA) and coarse (CRA) recycled aggregates in concrete's composition: (2) 25/25% (25% RA); (3) 50/50% (50% RA); (4) 100/100% (100% RA); (5) 0/100% (100% CRA); (6) 100/0% (100% FRA). The results showed that the high-performance concrete mixes with RA from the precast industry performed worse than the reference mix. However, taking into account all the mechanical properties studied, it can be concluded that RA from precast concrete elements are of very good quality and can be incorporated in the production of high-performance SCC. The potential demonstrated by the combined use of fine and coarse recycled aggregates was also emphasized. This type of work is expected to effectively contribute to raise awareness among the various players in the construction industry, particularly in the precast concrete industry, to the feasibility of using RA in significant quantities (notably coarse aggregates) and to the safety needed to assume structural functions, even for applications where high performance is required.
- Binary mixes of self-compacting concrete with municipal solid waste incinerator bottom ashPublication . Simões, Joel R.; Raposeiro Da Silva, Pedro; Silva, Rui V.With the objective of establishing a viable alternative to the use of cement, the main objective of this study is to verify the possibility of using municipal solid waste incinerator bottom ash (MIBA) as a partial cement replacement, thereby reducing the environmental impact associated with the use of concrete as a building material. To this end, self-compacting concrete (SCC) binary mixes of cement and MIBA were evaluated in their fresh and hardened state (i.e., self-compactability, mechanical and durability related performance). Four SCC mixes were produced to cover a wide range of replacement levels of cement with MIBA, namely: 20%, 30%, 40% and 50%. A fifth SCC mix, without MIBA, was produced with 30% fly ash to carry out a comparative analysis with composites with well-established performance. The results showed that the use of bottom ash from municipal solid waste incinerators caused an overall decline in the performance of self-compacting concrete. Apart from the smaller number of reactive phases in the bottom ash when compared with fly ash, which led to a slower rate of strength development, the decline was also caused by the increased porosity from the oxidation of aluminium particles. Nevertheless, the results showed promising indicators regarding the durability of mixes with 20% MIBA, with values very similar to those of reference concrete.
- Safe use of electric arc furnace dust as secondary raw material in self compacting mortars productionPublication . Lozano-Lunar, Angelica; Raposeiro Da Silva, Pedro; De Brito, Jorge; Fernandez Rodriguez, Jose Maria; Jimenez, Jose RamonThis research contributes to the development of the Circular Economy concept by managing waste through its use as a construction material. A novel process in which two samples of industrial waste Electric Arc Furnace Dust collected from two different steelwork plants are used as secondary raw material in the production of self-compacting mortars is proposed. At a previous stage, a characterisation of mortar material components was carried out. Then, self-compacting mortars with replacement ratios of 25%, 50% and 100% of siliceous filler with Electric Arc Furnace Dust were designed. The feasibility of Electric Arc Furnace Dust use was analysed by means of the study of mechanical strength, mineralogical, capillary properties and leaching behaviour in monolithic and granular state. The environmental classification of mortars, according to their leaching behaviour, was carried out in accordance with European Directive 2003/33/EC (2003). Electric Arc Furnace Dust incorporation modified the self-compactability and common hydration reactions. Mechanical strength decreased with Electric Arc Furnace Dust incorporation, although the mortar with 25% of replacement with one of the Electric Arc Furnace Dust's showed a negligible loss compared to the self-compacting reference mortar. Water absorption by capillarity increased with Electric Arc Furnace Dust content, consistently with the mortars' mechanical behaviour. The leaching behaviour analysis in a monolithic state revealed that all mortar releases were below the permitted limit. In a granular state, the mortar with the best mechanical behaviour was environmentally safe, leaving all the elements encapsulated by the self-compacting matrix. The results of this study contribute to Electric Arc Furnace Dust management through its valorisation as secondary raw material in the production of self-compacting mortars, addressing an unprecedented line of research.
- Experimental study of the mechanical properties and shrinkage of self-compacting concrete with binary and ternary mixes of fly ash and limestone fillerPublication . Raposeiro Da Silva, Pedro; De Brito, JorgeSelf-compacting concrete’s (SCC’s) particular need for self-compacting, i.e. to achieve a high passing and filling ability, deformability capacities and a high resistance to segregation, necessarily requires the reduction of the volume of coarse aggregate and the increase of the volume of ultrafine materials and admixtures (mainly superplasticisers). The increase in the volume of ultrafine materials mentioned, achieved exclusively at the cost of the cement, would have, as main effects, the significant increase of the overall cost of SCC, of its hydration heat and potential effects on properties such as shrinkage and cracking. Consequently, significant amounts of mineral additions are usually incorporated, in replacement of part of the cement to improve the workability properties, reduce the production of hydration heat and reduce the overall cost. Mainly because it needs to incorporate significant quantities of ultrafine materials (cement and mineral additions), SCC has great potential for the use of these sub-products, such as fly ash (FA), or other commercial products, such as limestone filler (LF), as partial replacement of cement. However, the use of significant quantities of mineral additions (also necessary to ensure self-compactability), with the consequent increase in the paste volume and decrease in the coarse aggregate, will alter the SCC’s microstructure and lead to a change in shrinkage and mechanical properties. It is therefore essential to investigate and demonstrate the applicability of large quantities of these additions (in both binary and ternary mixes), mainly due to the existing regulation limitations related to their use in blended cements and as direct replacement of cement in the production of concrete mixes. To this end, an experimental programme was conducted to evaluate the effect of large quantities of FA and LF in binary and ternary mixes on the mechanical properties and shrinkage of SCC. This study focuses essentially on the evaluation of compressive strength in cubic and cylindrical moulds, splitting tensile strength, the secant and dynamic elastic modulus and, finally, shrinkage. A detailed analysis of the results and their comparison with both reference values and with results of other authors is performed. For that purpose, a total of 11 SCC mixes were produced: 1 with cement (C) only; 3 with C + FA in 30, 60 and 70% replacement by volume (fad); 3 with C + LF in 30, 60 and 70% fad; and finally, 4 mixes with C + FA + LF in combinations of 10–20, 20–10, 20–40 and 40–20% fad.
- High-performance self-compacting concrete with recycled aggregates from the precast industry: durability assessmentPublication . Barroqueiro, Tiago; Raposeiro Da Silva, Pedro; De Brito, JorgeThe main objective of this paper is to provide the industry with a simple and practical way of disposing and recovering recycled waste from precast reinforced concrete elements rejected during the quality control process, while minimizing the consumption of natural resources in the production of concrete and, consequently, significantly reducing the environmental impact of both (construction and demolition waste and extracting natural aggregates). In other words, with this work, the intention is to evaluate the feasibility of producing high-performance self-compacting concrete with a less environmental impact, by replacing natural aggregates (NA) with fine and coarse recycled aggregates resulting from the precast industry, which allows the future use of this type of aggregates in the industrial process without reservations concerning the expected durability performance. To achieve these objectives, six types of self-compacting concrete (SCC) were produced incorporating diferente amounts of recycled aggregates. Six replacement ratios for fine recycled aggregates (FRA) and coarse recycled aggregates (CRA) were considered: (FRA/CRA) 0/0; 25/25; 50/50; 100/100; 0/100 and 100/0%. Six di_erent tests were carried out to characterize both the main concrete transport mechanisms and the main concrete degradation mechanisms, namely: the immersion water absorption test, capillary water absorption test, oxygen permeability test, chloride migration test, electrical resistivity test and carbonation test. The obtained results clearly demonstrate that, despite the negative influence of the inclusion of recycled aggregates, it is still possible to produce high-performance self-compacting concrete with perfectly acceptable durability properties.
- Self-compacting concrete with recycled aggregates - A literature reviewPublication . Santos, S.; Raposeiro Da Silva, Pedro; De Brito, JorgeThis paper presents a complete and updated literature review on the properties of self-compacting concrete with fine and coarse recycled aggregates. The subject of self-compacting concrete with recycled aggregates (RASCC) is greatly relevant to Society, since there is an increasing demand from the construction industry to adopt new processes to minimize its negative impacts on the environment. The use of recycled aggregates in concrete production presents a great environmental benefit through savings from the extraction of natural aggregates and the reduction of dumped material. The advantages associated to the use of both concrete with recycled aggregates and self-compacting concrete have boosted an increase in research and a consequent publication of literature in the last few years. Combining these two themes has allowed allying the environmental and economic advantages of each of the materials, leading to an innovative material of great interest to the construction industry in general. Even though RASCC is a relatively recent scientific area, studies on this material have demonstrated its viability, to produce both traditional and non-complex structural elements and highly complex and densely reinforced elements, which hinder the vibration procedures and may influence the final quality.
- Experimental study on chloride migration coefficients of self-compacting concrete (SCC) with binary and ternary mixtures of fly ash (FA) and limestone filler (LF)Publication . Raposeiro Da Silva, Pedro; De Brito, Jorge
- Mechanical performance evaluation of self-compacting concrete with fine and coarse recycled aggregates from the precast industryPublication . Santos, Sara A.; Raposeiro Da Silva, Pedro; De Brito, JorgeThis paper intends to evaluate the feasibility of reintroducing recycled concrete aggregates in the precast industry. The mechanical properties of self-compacting concrete (SCC) with incorporation of recycled aggregates (RA) (coarse recycled aggregates (CRA) and fine recycled aggregates (FRA)) from crushed precast elements were evaluated. The goal was to evaluate the ability of producing SCC with a minimum pre-established performance in terms of mechanical strength, incorporating variable ratios of RA (FRA/CRA%: 0/0%, 25/25%, 50/50%, 0/100% and 100/0%) produced from precast source concretes with similar target performances. This replication in SCC was made for two strength classes (45 MPa and 65 MPa), with the intention of obtaining as final result concrete with recycled aggregates whose characteristics are compatible with those of a SCC with natural aggregates in terms of workability and mechanical strength. The results enabled conclusions to be established regarding the SCC’s produced with fine and coarse recycled aggregates from the precast industry, based on its mechanical properties. The properties studied are strongly affected by the type and content of recycled aggregates. The potential demonstrated, mainly in the hardened state, by the joint use of fine and coarse recycled aggregate is emphasized.