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- The effect of multi-recycling on the mechanical performance of coarse recycled aggregates concretePublication . Abreu, Vilson; Evangelista, Luis; De Brito, JorgeThis paper presents the mechanical performance results obtained to evaluate the effect of incorporating coarse recycled aggregates from various recycling cycles. These aggregates were obtained from crushing elements of concrete of controlled origin, which were mixed to have the same performance in each cycle. The specific purpose was to study the mechanical performance of concrete designed with incorporation of coarse recycled aggregates from three successive recycling cycles at two replacement ratios, 25% and 100%, comparing it with that of a reference concrete, a mix with the same composition but where all aggregates are natural. An experimental campaign was carried out: to obtain all the necessary coarse recycled aggregates; to produce the concrete mixes that were the source of the recycled coarse aggregates; to produce the concrete mixes that were studied and; to perform all the necessary tests to evaluate the mechanical properties of these concrete mixes. Compressive strength, modulus of elasticity, tensile strength and abrasion resistance were tested. The results prove that, with the increase of the number of recycling cycles of the coarse aggregates, there is a decrease of its quality that affects the mechanical performance of concrete. That mechanical performance decreases asymptotically with the number of recycling cycles, tending towards a final value representative of the property’s stabilization, and linearly with the increase in the ratio of incorporation of recycled coarse aggregates. It is concluded that, by knowing the final value, concrete with incorporation of coarse recycled aggregates from any recycling cycle can be designed for the most diverse applications with a good safety level.
- Performance of concrete made with recycled aggregates from Portuguese CDW recycling plantsPublication . Bravo, Miguel; De Brito, Jorge; Pontes, Jorge; Evangelista, LuisThe objective of this research is the production of concrete with recycled aggregates (RA) from various CDW plants around Portugal. The influence of the RA collection location and consequently of their composition on the characteristics of the concrete produced was analysed. In the mixes produced in this research RA from five plants (Valnor, Vimajas, Ambilei, Europontal and Retria) were used: in three of them coarse and fine RA were analysed and in the remaining ones only coarse RA were used. The experimental campaign comprised two tests in fresh concrete (cone of Abrams slump and density) and eight in hardened concrete (compressive strength in cubes and cylinders, splitting tensile strength, modulus of elasticity, water absorption by immersion and capillarity, carbonation and chloride penetration resistance). It was found that the use of RA causes a quality decrease in concrete. However, there was a wide results scatter according to the plant where the RAs were collected, because of the variation in composition of the RA. It was also found that the use of fine RA causes a more significant performance loss of the concrete properties analysed than the use of coarse RA. © (2015) Trans Tech Publications, Switzerland.
- Influence of the crushing process of recycled aggregates on concrete propertiesPublication . Pedro, Diogo; De Brito, Jorge; Evangelista, LuisThis work intends to evaluate the (mechanical and durability) performance of concrete made with coarse recycled concrete aggregates (CRCA) obtained using two crushing processes: primary crushing (PC) and primary plus secondary crushing (PSC). This analysis intends to select the most efficient production process of recycled aggregates (RA). The RA used here resulted from precast products (P), with strength classes of 20 MPa, 45 MPa and 65 MPa, and from laboratory-made concrete (L) with the same compressive strengths. The evaluation of concrete was made with the following tests: compressive strength; splitting tensile strength; modulus of elasticity; carbona-tion resistance; chloride penetration resistance; capillary water absorption; and water absorption by immersion. These findings contribute to a solid and innovative basis that allows the precasting industry to use without restrictions the waste it generates. © (2015) Trans Tech Publications, Switzerland.
- Performance of concrete made with aggregates recycled from precasting industry waste: influence of the crushing processPublication . Pedro, Diogo; De Brito, Jorge; Evangelista, LuisThe aim of this paper is to evaluate the influence of the crushing process used to obtain recycled concrete aggregates on the performance of concrete made with those aggregates. Two crushing methods were considered: primary crushing, using a jaw crusher, and primary plus secondary crushing (PSC), using a jaw crusher followed by a hammer mill. Besides natural aggregates (NA), these two processes were also used to crush three types of concrete made in laboratory (L20, L45 e L65) and three more others from the precast industry (P20, P45 e P65). The coarse natural aggregates were totally replaced by coarse recycled concrete aggregates. The recycled aggregates concrete mixes were compared with reference concrete mixes made using only NA, and the following properties related to the mechanical and durability performance were tested: compressive strength; splitting tensile strength; modulus of elasticity; carbonation resistance; chloride penetration resistance; water absorption by capillarity; water absorption by immersion; and shrinkage. The results show that the PSC process leads to better performances, especially in the durability properties.
- Mechanical performance of concrete made with aggregates from construction and demolition waste recycling plantsPublication . Bravo, Miguel; De Brito, Jorge; Pontes, Jorge; Evangelista, LuisThis 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. (C) 2015 Elsevier Ltd. All rights reserved.
- Durability and shrinkage of concrete with CDW as recycled aggregates: Benefits from superplasticizer’s incorporation and influence of CDW compositionPublication . Bravo, Miguel; De Brito, Jorge; Evangelista, Luis; Pacheco, JoãoThe shrinkage and durability properties of a total of 34 concrete mixes with recycled aggregates produced from different untreated construction and demolition waste (CDW) were tested. The effect of a polycarboxylic superplasticizer on the enhancement of these properties is presented, discussed, and compared with the findings of studies on concrete whose recycled aggregates are sourced from concrete. All properties were significantly affected by recycled aggregate incorporation and this effect was strongly dependent on the properties of the recycled aggregates of each specific source. The superplasticizer was less efficient in mixes with CDW than when the recycled aggregates were produced from concrete, the most common source of recycled aggregates in experimental works, despite untreated CDW being more practical and desirable from an industrial and environmental perspective.
- Can we truly predict the compressive strength of concrete without knowing the properties of aggregates?Publication . De Brito, Jorge; Kurda, Rawaz; Raposeiro Da Silva, PedroThis paper is focused on the influence of the geological nature and quality of the aggregates on the compressive strength of concrete and explains why it is important not to ignore the characteristics of aggregates in the estimation of the strength of concrete, even for virgin aggregates. For this purpose, three original (Abrams, American Concrete Institute Manual of concrete practice and Slater) and two modified (Bolomey and Feret) models were used to calculate the strength of concrete by considering results of various publications. The results show that the models do not properly predict the strength of concrete when the characteristics of aggregates are neglected. The scatter between the calculated and experimental compressive strength of concrete, even when made with natural aggregates (NAs) only, was significant. For the same mix composition (with similar cement paste quality), there was a significant difference between the results when NAs of various geological nature (e.g., limestone, basalt, granite, sandstone) were used in concrete. The same was true when different qualities (namely in terms of density, water absorption and Los Angles abrasion) of aggregates were used. The scatters significantly decreased when the mixes were classified based on the geological nature of the aggregates. The same occurred when the mixes were classified based on their quality. For both modified models, the calculated strength of mixes made with basalt was higher than that of the mixes containing other types of the aggregates, followed by mixes containing limestone, quartz and granite. In terms of the quality of the aggregates, the calculated strength of concrete increased (was overestimated) as the quality of the aggregates decreased. The influence of the aggregates on the compressive strength of concrete became much more discernible when recycled aggregates were used mainly due to their more heterogeneous characteristics.
- The effect of superplasticizers on the workability and compressive strength of concrete made with fine recycled concrete aggregatesPublication . Pereira, P.; Evangelista, Luis; De Brito, JorgeThe 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.
- Durability performance of concrete with recycled aggregates from construction and demolition waste plantsPublication . Bravo, Miguel; De Brito, Jorge; Pontes, Jorge; Evangelista, LuisThis research intends to analyse the durability performance of concrete with recycled aggregates (RA) from construction and demolition waste (CDW) from various locations in Portugal. To that effect water absorption by immersion and capillarity, carbonation resistance and chloride ion penetration resistance tests were performed. To better understand the experimental results, the characteristics of the various aggregates (natural and recycled) used in the production of concrete were analysed in detail. The composition of the RA was determined and various physical tests of the aggregates were performed. 33 concrete mixes with RA from different CDW recycling plants were evaluated in order to understand the influence that the RA’s collection point, and therefore their composition, has on the characteristics of the concrete mixes produced. Both coarse and fine RA were used to determine the influence of their size on concrete’s performance. The analysis of the durability performance allowed concluding that the use of RA is highly detrimental. This is mostly true when fine RA are used. The carbonation resistance is the property most affected by the use of RA, leading to increases in the carbonation depth between 22.2% and 182.4% for the various RA types. However, the most influencing factor is by far the RA’s composition.
- Microstructure of concrete with agg regates from construction and demolition waste recycling plantsPublication . Bravo, Miguel; Silva, António Santos; De Brito, Jorge; Evangelista, LuisThis paper intends to analyze the microstructure of concrete with recycled aggregates (RA) from construction and demolition waste from various Portuguese recycling plants. To that effect, several scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed. Various concrete mixes were evaluated in order to analyze the influence of the RA’s collection point and consequently of their composition on the mixes’ characteristics. Afterward all the mixes were subjected to the capillary water absorption test in order to quantitatively evaluate their porosity. Results from the SEM/EDS analysis were compared with those from capillary water absorption test. The SEM/EDS analysis showed that the bond capacity of aggregates to the new cement paste is greatly influenced by the RA’s nature. On the other hand, there was na increase in porosity with the incorporation of RA.