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- Experimental investigation on the variability of the main mechanical properties of concrete produced with coarse recycled concrete aggregatesPublication . Pacheco, João; De Brito, Jorge; Chastre, Carlos; Evangelista, LuisResearch on the variability of the properties of recycled aggregate concrete is lacking and is necessary for the development of reliability analyses and code calibration procedures. This paper presents an experimental programme on the within-batch variability of the compressive strength, Young's modulus, and splitting tensile strength of several recycled and natural aggregate concrete mixes. The influence of the recycled concrete aggregates on the mechanical properties and variability of concrete is analysed and discussed and benchmarks with standard predictions for the variability of natural aggregate concrete are made. It was found that full recycled aggregate concrete incorporation did not increase the variability of any of the properties tested, but intermediate ratios of recycled aggregate incorporation did. The properties of high-strength concrete mixes were more variable than that of all other mixes, irrespective of recycled aggregate incorporation. All properties of all compositions were suitably modelled by normal distributions. The coarse recycled aggregates were sourced from concrete waste.
- 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.
- A New Method to Determine the Density and Water Absorption of Fine Recycled AggregatesPublication . Rodrigues, Fernando; Evangelista, Luis; De Brito, JorgeThe 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.
- 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.
- 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.
- 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.
- Statistical analysis of Portuguese ready-mixed concrete productionPublication . Pacheco, João; De Brito, Jorge; Chastre, Carlos; Evangelista, LuisThis paper evaluates and compares the statistics of compressive strength data from three Portuguese ready-mixed concrete plants. A hierarchical model showed that different groups of concrete strength records are not statistically equivalent, even if they were produced in the same plant and using the same concrete composition. This finding is related to autocorrelation. For the same specified strength class, compositions produced less often result in higher average compressive strength and variability. The statistics of one of the plants were quite different from those of the others, even though the concrete of this plant also complied with the specifications. It was found that the average compressive strength of a mix may be quite dependent on the plant that produced it, even if the compressive strength complies with quality control specifications. Conformity with the target slump and strength class was checked following the conformity criteria of EN 206-1 for continuous production. Nonconformity with slump is more frequent than failure to comply with the strength class. A bias factor for reliability analyses was proposed.
- 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.
- 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.
- 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.