The Experts below are selected from a list of 40896 Experts worldwide ranked by ideXlab platform
J De Brito - One of the best experts on this subject based on the ideXlab platform.
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structural Concrete with simultaneous incorporation of fine and coarse recycled Concrete aggregates mechanical durability and long term properties
Construction and Building Materials, 2017Co-Authors: D Pedro, J De Brito, Luis EvangelistaAbstract:Abstract This investigation intends to analyse the effects of the variation of different types of recycled Concrete aggregates (RCA) on structural Concrete. For this purpose, two source Concrete (SC) mixes, one produced in the laboratory and another in a precasting plant, were considered. The experimental campaign included mechanical, durability and long-term tests: compressive strength in cubes; splitting tensile strength; modulus of elasticity; abrasion resistance; water absorption by immersion and by capillarity; resistance to carbonation; resistance to chloride ion penetration; shrinkage and creep. The recycled aggregate Concrete (RAC) mixes were compared with a Reference Concrete (RC) produced solely with natural aggregates (NA). Concerning the replacement percentages for fine and coarse recycled Concrete aggregates (FRCA/CRCA%), the following were considered: 25/25; 50/50; 100/0; 0/100 and 100/100%. The results show that it is possible to achieve similar performances using RCA from different SC but with similar compressive strengths. In fact, RAC mixes achieved results comparable to RC in several properties.
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use of coarse recycled aggregates from precast Concrete rejects mechanical and durability performance
Construction and Building Materials, 2014Co-Authors: D Soares, J De Brito, J Ferreira, J PachecoAbstract:Abstract This paper presents the results of an experimental campaign developed with the aim of evaluating the effect of the incorporation in Concrete of recycled aggregates from crushed elements produced by the precasting Concrete industry. The specific purpose was to study the use of the coarse fraction of these aggregates. This was done by studying various replacement ratios of the coarse fraction of the aggregates. The possibility/need to correct the composition of Concrete mixes with recycled aggregates was also investigated, by testing various contents of a superplasticizer, intending to replicate the characteristics of a Reference Concrete, i.e. a mix with an analogous composition but where all aggregates are natural. An extensive set of tests was performed to evaluate the mechanical and durability properties of all Concrete mixes. The results prove that the Concrete mixes with recycled aggregates have an equivalent performance to that of the Reference Concrete in most of the properties. In the others, where a performance loss was registered, that loss was lower than the one reported in the literature review performed. This was expected since the quality of the coarse aggregates recycled from precast elements is very good and totally fit for the production of new Concrete, originating Concrete compositions with good quality, namely in terms of hardened state properties. As expected the use of a superplasticizer is beneficial for Concrete performance in all properties analysed.
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the effect of superplasticisers on the workability and compressive strength of Concrete made with fine recycled Concrete aggregates
Construction and Building Materials, 2012Co-Authors: Pedro Pereira, Luis Evangelista, J De BritoAbstract:Abstract 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.
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Post-fire residual mechanical properties of Concrete made with recycled Concrete coarse aggregates
Cement and Concrete Research, 2011Co-Authors: J.p.b. Vieira, João R. Correia, J De BritoAbstract:Abstract This paper presents results of an experimental study on the residual mechanical performance of Concrete produced with recycled coarse aggregates, after being subjected to high temperatures. Four different Concrete compositions were prepared: a Reference Concrete made with natural coarse aggregates and three Concrete mixes with replacement rates of 20%, 50% and 100% of natural coarse aggregates by recycled Concrete coarse aggregates. Specimens were exposed for a period of 1 h to temperatures of 400 °C, 600 °C and 800 °C, after being heated in accordance with ISO 834 time–temperature curve. After cooling down to ambient temperature, the following basic mechanical properties were then evaluated and compared with Reference values obtained prior to thermal exposure: (i) compressive strength; (ii) tensile splitting strength; and (iii) elasticity modulus. Results obtained show that there are no significant differences in the thermal response and post-fire mechanical behaviour of Concrete made with recycled coarse aggregates, when compared to conventional Concrete.
Luis Evangelista - One of the best experts on this subject based on the ideXlab platform.
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structural Concrete with simultaneous incorporation of fine and coarse recycled Concrete aggregates mechanical durability and long term properties
Construction and Building Materials, 2017Co-Authors: D Pedro, J De Brito, Luis EvangelistaAbstract:Abstract This investigation intends to analyse the effects of the variation of different types of recycled Concrete aggregates (RCA) on structural Concrete. For this purpose, two source Concrete (SC) mixes, one produced in the laboratory and another in a precasting plant, were considered. The experimental campaign included mechanical, durability and long-term tests: compressive strength in cubes; splitting tensile strength; modulus of elasticity; abrasion resistance; water absorption by immersion and by capillarity; resistance to carbonation; resistance to chloride ion penetration; shrinkage and creep. The recycled aggregate Concrete (RAC) mixes were compared with a Reference Concrete (RC) produced solely with natural aggregates (NA). Concerning the replacement percentages for fine and coarse recycled Concrete aggregates (FRCA/CRCA%), the following were considered: 25/25; 50/50; 100/0; 0/100 and 100/100%. The results show that it is possible to achieve similar performances using RCA from different SC but with similar compressive strengths. In fact, RAC mixes achieved results comparable to RC in several properties.
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the effect of superplasticisers on the workability and compressive strength of Concrete made with fine recycled Concrete aggregates
Construction and Building Materials, 2012Co-Authors: Pedro Pereira, Luis Evangelista, J De BritoAbstract:Abstract 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.
Yohannes L Yaphary - One of the best experts on this subject based on the ideXlab platform.
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reduction in cement content of normal strength Concrete with used engine oil ueo as chemical admixture
Construction and Building Materials, 2020Co-Authors: Yohannes L YapharyAbstract:Abstract In this study, the coupling effects of admixing a used engine oil (UEO) and reducing the cement paste content on the properties of a normal strength Concrete were investigated. Initially, various tests were performed to determine the effect of the admixed UEO on the properties (i.e. workability, air content, setting times, strengths, drying shrinkage, and freezing and thawing (F–T) durability) of the Reference Concrete (formed in accordance with ASTM C494). Based on the acquired knowledge regarding the aforementioned effects, the chemical-admixture type of the UEO was evaluated. The UEO largely complies with the ASTM C494 type A water-reducing admixture specifications. The admixed UEO can facilitate the production of Concrete with 9.4% less cement content than that in the Reference Concrete, but with comparable properties. This study provides a basis for realizing a more economical and eco-friendly production of Concrete by both reducing its cement content and admixing UEO.
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reduction in cement content of normal strength Concrete with used engine oil ueo as chemical admixture
Construction and Building Materials, 2020Co-Authors: Yohannes L YapharyAbstract:Abstract In this study, the coupling effects of admixing a used engine oil (UEO) and reducing the cement paste content on the properties of a normal strength Concrete were investigated. Initially, various tests were performed to determine the effect of the admixed UEO on the properties (i.e. workability, air content, setting times, strengths, drying shrinkage, and freezing and thawing (F–T) durability) of the Reference Concrete (formed in accordance with ASTM C494). Based on the acquired knowledge regarding the aforementioned effects, the chemical-admixture type of the UEO was evaluated. The UEO largely complies with the ASTM C494 type A water-reducing admixture specifications. The admixed UEO can facilitate the production of Concrete with 9.4% less cement content than that in the Reference Concrete, but with comparable properties. This study provides a basis for realizing a more economical and eco-friendly production of Concrete by both reducing its cement content and admixing UEO.
Konstantin Kovler - One of the best experts on this subject based on the ideXlab platform.
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can superabsorent polymers mitigate autogenous shrinkage of internally cured Concrete without compromising the strength
Construction and Building Materials, 2012Co-Authors: Marianne Tange Hasholt, Ole Mejlhede Jensen, Konstantin Kovler, Semion ZhutovskyAbstract:Abstract The paper “Super absorbing polymers as an internal curing agent for mitigation of early-age cracking of high-performance Concrete bridge decks” deals with different aspects of using superabsorbent polymers (SAP) in Concrete to mitigate self-desiccation. The paper concludes that “Addition of SAP leads to a significant reduction of mechanical strength”. The experimental results are in contradiction with several publications and question the appropriateness of using SAP as internal curing agent. However, the observed strength loss – and possibly also other observations – seems to be caused by overestimation of SAP water absorption. This results in an increase in water/cement ratio (w/c) for Concrete with SAP. It is misleading to conclude on how SAP influences Concrete properties, based on comparison of Concrete mixes with SAP and Reference Concrete without SAP, if SAP mixes have higher w/c than the Reference mix.
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Does the utilization of coal fly ash in Concrete construction present a radiation hazard
Construction and Building Materials, 2012Co-Authors: Konstantin KovlerAbstract:Abstract The advantages of utilization of coal fly ash in Concrete construction, as well as the technological and environmental problems caused by an elevated content of chemical/radioactive contaminants, are discussed. The paper deals with the question whether the utilization of coal fly ash in Concrete construction presents a radiation hazard. The analysis of the experimental studies shows that although radon exhalation rate of Concrete containing coal fly ash can be sometimes slightly higher, than that of the Reference Concrete, radon emanation coefficient is lower. In view of this, the standards regulating radioactivity of building materials, but not addressing the decrease of radon emanation coefficient properly could be detrimental to the utilization of fly ash in Concrete construction. Drawing direct comparisons between results presented in different papers is challenging because of varying methodologies, sample sizes, material properties, such as age, moisture and porosity, and experimental goals. The need in the systematic study considering different factors, which can influence the radon release of a Concrete, is emphasized.
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legislative aspects of radiation hazards from both gamma emitters and radon exhalation of Concrete containing coal fly ash
Construction and Building Materials, 2011Co-Authors: Konstantin KovlerAbstract:Abstract Utilization of coal fly ash in Concrete construction has clear environmental, technological and economical advantages. At the same time, fly ash is known to have enhanced concentrations of Naturally Occurring Radioactive Materials (NORM). Legislative issues related to the utilization of coal fly ash in Concrete construction are analyzed. Different approaches implemented in standards regulating gamma radiation and radon emanation of Concrete and other building materials are reviewed. Although radon exhalation rate of Concrete containing coal fly ash can be sometimes slightly higher than that of the Reference Concrete, radon emanation coefficient is usually lower. In view of this, the standards regulating radioactivity of building materials, but not addressing radon emanation properly could be detrimental to the utilization of fly ash in Concrete. At the same time, the evaluation of the excess dose caused by building materials for the radon pathway is complicated, and much more research work is required to justify the assumptions of the physical models in the future standards.
Ahmed Loukili - One of the best experts on this subject based on the ideXlab platform.
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Drying of Recycled Aggregate Concrete: Plastic Shrinkage, Cracking Sensitivity, and Durability
Key Engineering Materials, 2016Co-Authors: Ahmed Z. Bendimerad, Emmanuel Roziere, Ahmed LoukiliAbstract:This paper presents the results of experimental research on recycled Concrete at early age and long term. It consists in studying the effect of initial water saturation of recycled Concrete gravel (RG). Five mixtures were investigated, one mixture with natural aggregates only (Reference Concrete) and the second with 100% of RG using four initial water saturations: 30%, 70%, 100% and 120% of saturated surface dried (SSD) state. A stress/strength approach was used to quantify the risk of cracking at early age. It is based on experimentally assessed parameters. At long term the effect of initial water saturation on the ultimate drying shrinkage was investigated. The drying shrinkage was correlated with drying depth and the natural carbonation was also studied. At early age the results indicate RG affected the properties of the recycled Concrete. However, the Concrete with oversaturated RG showed a behavior close to Reference Concrete in terms of cracking sensitivity. At long term, the drying shrinkage is weakly depending of initial water saturation, but the durability of Concrete can be affected by the drying depth. A good correlation between compressive strength at one day and the carbonation depth at 18 months was observed
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Influence of paste volume on shrinkage cracking and fracture properties of self-compacting Concrete
Cement and Concrete Composites, 2007Co-Authors: Emmanuel Roziere, Sébastien Granger, Ph Turcry, Ahmed LoukiliAbstract:Self-compacting Concrete (SCC) mixtures are usually designed with higher volumes of paste than vibrated Concrete mixtures. The results reported in this paper come from a study of nine SCC Concrete mixtures. Volume of paste was varied between 291 and 457 l/m3. One of the mixtures had already been used in a large scale test, and the others were designed by varying several parameters of the Reference Concrete mixture. Mechanical properties, shrinkage, fracture parameters and fracture process zone (FPZ) size were measured. Fracture behavior was characterized by means of three-point bending tests and acoustic emission analysis. From the experimental results, increasing the volume of paste has a restricted effect on strength, unless water content varies. Strength, elastic modulus and fracture resistance slightly decrease with an increase in paste content. Volume of paste causes an increase in shrinkage and cracking due to shrinkage. Fracture and acoustic emission analysis show that increasing the volume of paste tends to make SCC more brittle.
