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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.
- 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.
- 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.
- 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.
- Thermal performance of concrete with reactive magnesium oxide as an alternative binderPublication . Forero Valencia, Javier Andres; Bravo, Miguel; Pacheco, João; Brito, Jorge de; Evangelista, LuisThis study evaluates the thermal conductivity of concrete produced with reactive magnesium oxide (MgO) as a partial replacement for cement. MgO is a viable option for the concrete industry, mainly due to its benefits in sustainability and reducing CO2 emissions compared to cement emissions. Four different MgO's produced in Australia, Canada, and Spain were used in concrete mixes as a partial replacement of cement at 5%, 10%, and 20% by mass. The experimental results showed that the thermal conductivity is higher when MgO increases in mixes after 28 days of curing. With the incorporation of MgO, the thermal conductivity increased between 3.2% and 10.2%, and the mechanical properties declined: compressive strength between 12.7% to 26.2%, splitting tensile strength between 9.7% to 34.0%, and modulus of elasticity between -4.1% to 7.8%. Finally, it is important to highlight that the addition of different contents of MgO in the concrete mixes modified the microstructure of the cement matrix. As a result, there was an increase in porosity, which negatively influenced the mechanical properties and thermal conductivity. Therefore, the relationships between these properties were also analyzed.
- 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.
- The influence of curing conditions on the mechanical performance of concrete made with recycled concrete wastePublication . Fonseca, N.; De Brito, Jorge; Evangelista, LuisResearch 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. (C) 2011 Elsevier Ltd. All rights reserved.
- Durability performance of concrete made with fine recycled concrete aggregatesPublication . Evangelista, Luis; De Brito, JorgeFine 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.