The 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.
•Structural concrete with fine and coarse recycled concrete aggregates (RCA) was studied.•RCA of different origins were used: from real waste and produced in laboratory.•The mechanical, durability ...and long-term performance of concrete with RCA was analysed.•Similar performances using different RCA can be achieved.•Total incorporation of RCA in the production of structural concrete is deemed possible.
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.
Fine 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.
In the light of the ever-increasing need of circular economy in the construction industry and of the recent advances in research and development on the use of recycled aggregates, produced from ...construction and demolition waste, in new construction materials, this paper presents a compilation of representative case studies of several applications, namely recycled aggregates in unbound, hydraulically-bound and bitumen-bound applications, as well as in (non-)structural concrete in road and building construction. Experience has shown that, in spite of the positive outcomes and comprehensive know-how gained over the course of several years in those exploratory studies, there is a considerable underuse of recycled aggregates mostly due to lack of confidence in the material amongst contractors and designers. This paper, using a range of case studies undertaken in several countries worldwide, highlights the technical viability and appropriateness of using recycled aggregates in a broad range of construction applications.
•Case studies on recycled aggregates in building and road pavement construction.•Extensive positive experience exists on applications with high replacement levels.•High economic viability of sourcing locally available recycled aggregates.•Some countries routinely use recycled aggregate concrete in structural elements.
This paper's aim is to characterize the freeze–thaw resistance of normal strength and high-strength concrete with partial or total replacement of fine natural aggregate (FNA) by fine recycled ...concrete aggregate (FRCA). The surface scaling, mass loss, length change, residual ultrasound pulse velocity and residual compressive strength were monitored for different FRCA replacement ratios (0%, 20%, 50% and 100%) subjected to 300 freeze–thaw cycles according to ASTM C666 – Proc. A. In general, the mechanical strength decreases with the incorporation of FRCA, especially in high-strength concrete. Contrary to high-strength concrete, normal strength concrete was not frost resistant, regardless the type of aggregate used. The w/c ratio had a greater influence on the freeze–thaw resistance than the type of aggregate. The air entraining had a slightly beneficial effect on high-strength concrete. Generally, it is concluded that the incorporation of FRCA is not detrimental to the freeze–thaw resistance of concrete. Only the total replacement of FNA by FRCA led to lower residual mechanical strengths after freeze–thaw action than those obtained in reference mixes. However, surface scaling tends to be more severe in concrete with FRCA if it can be saturated near the concrete surface.
•Concrete with different fine recycled concrete aggregates (FRCA) replacement ratios.•Freeze–thaw resistance of normal strength and high-strength concrete with FRCA.•Freeze–thaw resistance was more affected by the w/c than by the type of aggregate.•FRCA was non-detrimental to freeze–thaw internal cracking resistance of concrete.•Surface scaling was more severe in concrete with FRCA.
•State of the art systematic review on the study of recycled aggregates for concrete production.•Statistical analysis of the main properties of recycled aggregates and comparison with those of ...conventional aggregates.•Proposal of a performance-based classification system for recycled aggregates meant for concrete production.
Arising from a systematic, as opposed to narrative, literature review of 236 publications published over a period of 38years from 1977 to 2014, the paper examines the factors affecting the physical, chemical, mechanical, permeation and compositional properties of recycled aggregates sourced from construction and demolition waste, intended for concrete production. Classifications based on their composition and contaminants have been studied. The data were collectively subjected to statistical analysis and a performance-based classification, mainly for use in concrete construction, is proposed. The results allowed producing a practical means of measuring the quality of recycled aggregates, which can be used to produce concrete with predictable performance.
•Statistics on the mechanical properties of concrete with and without recycled aggregates.•Full recycled aggregate incorporation has little effect on the variability of the properties tested.•Normal ...distributions suited all properties of the 12 mixes tested.•Intermediate incorporation ratios increased the concrete’s variability.•Other’s statistics on the properties of natural aggregate concrete agree with our results.
Research 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.
•Source of recycled concrete aggregates (RCA) highly influences concrete properties.•RCA from medium/high strength concrete have little influences on concrete properties.•Lab-sourced RCA are ...equivalent to equal strength precast elements-sourced RCA.•This proves the reliability of previous researches made with lab-sourced RCA.
This paper intends to evaluate the capacity of producing concrete with a pre-established performance (in terms of mechanical strength) incorporating recycled concrete aggregates (RCA) from different sources. To this purpose, rejected products from the precasting industry and concrete produced in laboratory were used. The appraisal of the self-replication capacity was made for three strength ranges: 15–25MPa, 35–45MPa and 65–75MPa. The mixes produced tried to replicate the strength of the source concrete (SC) of the RA. Only total (100%) replacement of coarse natural aggregates (CNA) by coarse recycled concrete aggregates (CRCA) was tested. The results show that, both in mechanical and durability terms, there were no significant differences between aggregates from controlled sources and those from precast rejects for the highest levels of the target strength. Furthermore, the performance losses resulting from the RA’s incorporation are substantially reduced when used medium or high strength SC’s.
•Literature review on the fresh properties of recycled aggregate concrete (RAC).•Workability, stability, heat of hydration, air content and density were analysed.•Control over the recycled ...aggregates’ manufacture is key to obtain high quality RAC.•Predictable properties are achieved by adding adequate amount of compensating water.
This paper presents a literature review concerning the fresh properties of concrete containing recycled aggregates from beneficiated construction and demolition wastes. It starts with the identification of the main variables affecting the workability of concrete, such as the quality and moisture state of the recycled aggregates. The effectiveness of water-reducing admixtures and of mineral additions on the fresh properties of recycled aggregate concrete is also analysed. A brief insight is given on the influence of using recycled aggregates on the main characterizing parameters of the material’s rheological behaviour. Other properties of recycled aggregate concrete in its fresh state are also discussed, including stability (i.e., bleeding and segregation), temperature of hydration, air content, and fresh density.
•Leachability of applications containing municipal incinerator bottom ashes (MIBA).•Uses of MIBA include binder constituent, aggregate replacement, and ceramics.•Applications with MIBA in its unbound ...form show risk of heavy metal accumulation.•Properly treated, MIBA can be considered a substitute material for natural resources.
This paper presents a literature review concerning the performance from an environmental viewpoint of construction related products made with municipal solid waste incinerator bottom ash. It starts with an initial assessment of the bottom ash, and how it performs when used as aggregate substitute in cement-based products, as cement constituent and as raw feed in cement production. Evaluation of the material’s environmental performance when used as aggregate replacement in unbound and cement-bound base and subbase layers for road pavement construction, as well as in asphalt concrete layers, is also undertaken. This paper also appraises the behaviour of ceramic-based products, including glass, glass-ceramics, and general ceramics. As a result of the high quantities of potentially leachable contaminants inherent to the bottom ash, the environmental assessment carried out throughout this paper is mostly based on the materials’ leaching behaviour, but also based on life cycle assessments and gas emission analyses. The results of several leaching trials, conducted according to various specifications, were reviewed and paralleled with corresponding regulations, with the objective of establishing the products’ viability from an environmental point of view.
PDF
