•Characterization tests are mandatory when considering RA for pavement construction.•Compaction by vibration is preferable in layers with RCA to avoid generating fines.•RCA are a feasible alternative ...to NA for unbound layers with the same performance.•The use of RMA may be optimized in unbound applications if these are mixed with RCA.•Unbound applications with RAP may exhibit insufficient load bearing capacity.
The use of recycled aggregates (RA) in construction constitutes a significant step towards a more sustainable society and also creates a new market opportunity to be exploited. In recent years, several case-studies have emerged in which RA were used in Geotechnical applications, such as filling materials and in unbound pavement layers. This paper presents a review of the most important physical properties of different types of RA and their comparison with natural aggregates (NA), and how these properties affect their hydraulic and mechanical behaviour when compacted. Specifically, the effects of compaction on grading size distribution curves and density are analysed, as well as the consequences of particle crushing on the resilient modulus, CBR and permeability. The paper also contains an analysis of the influence of incorporating different RA types on the performance of unbound road pavement layers as compared with those built with NA by means of the International Roughness Index and deflection values. The results collected from the literature indicate that the performance of most RA is comparable to that of NA and can be used in unbound pavement layers or in other applications requiring compaction.
•In-situ strength of RAC was estimated using Schmidt rebound hammer and core testing.•A two-variable equation was proposed between rebound number and core testing for strength estimation of ...RAC.•Strength correlations of control concrete estimated the strength of RAC averagely about 45.5 % higher.•Strength of RAC remarkably increased at early ages, while a moderate increase occurred in most cases at older ages.
The main objective of this study was to estimate the compressive strength of recycled aggregate concrete (RAC) by means of Schmidt rebound hammer and core testing. The use of recycled aggregate in concrete has been shown to lead to a decrease in the construction cost and it can reduce the burden on the environment by saving natural aggregates. On the other hand, some non-destructive and semi-destructive techniques, such as Schmidt rebound hammer and core testing, are long-established methods for strength estimation of materials. Thus, the present study intended to obtain the compressive strength of RAC using these methods and then compare it with the results of 150 mm cube specimens. To achieve this goal, after producing concrete mixes with 70% replacement of recycled coarse aggregate, 96 cube specimens and 8 concrete slabs were cast to perform Schmidt rebound hammer, core and cube testing. In addition, the combination of the methods was used to obtain correlations between Schmidt rebound hammer and core testing. The results demonstrate that a multi-variable equation using these tests’ results can efficiently predict the compressive strength of RAC and conventional concrete and is more promising than single-variable equations based on the Schmidt rebound hammer test results.
This paper presents a literature review concerning the characteristics of MgO (magnesium oxide or magnesia) and its application in cementitious materials. It starts with the characterization of MgO ...in terms of production processes, calcination temperatures, reactivity, and physical properties. Relationships between different MgO characteristics are established. Then, the influence of MgO incorporation on the properties of cementitious materials is investigated. The mechanical strength and durability behaviour of cement pastes, mortars and concrete mixes made with MgO are discussed. The studied properties of MgO–cement mixes include compressive strength, flexural strength, tensile strength, modulus of elasticity, water absorption, porosity, carbonation, chloride ion penetration, shrinkage, expansion, and hydration degree. In addition, microscopic analyses of MgO-cement mixes are also assessed. Summarizing the results of different studies, it is concluded that MgO incorporation in cementitious materials generally decreases the mechanical strength and shrinkage, and increases the porosity, expansion, carbonation and chloride ion migration. However, it should be emphasized that the properties of the specific MgO used (mainly the calcination temperature, the reactivity and the surface area) have a significant influence on the characteristics of the cementitious materials produced.
Contrasting with previous studies that aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on their durability performance. For this, water absorption by ...capillarity and immersion, carbonation resistance, chloride penetration and shrinkage tests were performed. Mixes containing 0%, 5%, 10% and 20% of glass aggregates (GA) as replacement of natural aggregates (NA) were prepared. Also analysed is the influence of the size of the replaced aggregates (fine and coarse, separately or simultaneously), in a total of 10 concrete mixes. It was found that the particle size strongly affects the workability of concrete. Due to the lower density of the glass aggregates, the mixes made with glass had a lighter fresh density than the reference concrete. Although there is a decrease in the compressive strength as the replacement rate increases, mixes with GA are totally feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace the NA. It was found that in most cases the GA do not significantly alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of ±15%, which is well within the expectable scatter of the results from experimental research.
► Environmental impacts of different demolition practices. ► “Top-down” approach to the Life Cycle Analysis methodology. ► Results based on real buildings measurements and demolition contractor ...activities. ► Not every type of selective demolition brings about environmental benefits.
The purpose of this study is to quantify comparable environmental impacts within a Life Cycle Analysis (LCA) perspective, for buildings in which the first (Materials) and last (End of Life) life cycle stages are adjusted to several waste/material management options. Unlike most LCAs, the approach is “top-down” rather than “bottom-up”, which usually involves large amounts of data and the use of specific software applications. This approach is considered appropriate for a limited but expedient LCA designed to compare the environmental impacts of different life cycle options.
Present results, based on real buildings measurements and demolition contractor activities, show that shallow, superficial, selective demolition may not result in reduced environmental impacts. Calculations actually show an increase (generally less than 5%) in most impact categories for the Materials and End of Life stages because of extra transportation needs. However, core material separation in demolition operations and its recycling and/or reuse does bring environmental benefits. A reduction of around 77% has been estimated in the climate change impact category, 57% in acidification potential and 81% in the summer smog impact (for the life cycle stages referred).
► The main environmental impacts prevented derive from virgin material replacement. ► They can be up to 10 times those generated from the CDW recycling operation. ► This figure relates to industrial ...processes and includes transportation needs. ► Another issue is CO2eq. emission savings in operating a CDW recycling plant. ► They can be up to 10 times those from a MSW processing network.
This work is a part of a wider study involving the economic and environmental implications of managing construction and demolition waste (CDW), focused on the operation of a large scale CDW recycling plant. This plant, to be operated in the Lisbon Metropolitan Area (including the Setúbal peninsula), is analysed for a 60year period, using primary energy consumption and CO2eq emission impact factors as environmental impact performance indicators.
Simplified estimation methods are used to calculate industrial equipment incorporated, and the operation and transport related impacts. Material recycling – sorted materials sent to other industries, to act as input – is taken into account by discounting the impacts related to industrial processes no longer needed.
This first part focuses on calculating the selected impact factors for a base case scenario (with a 350tonnes/h installed capacity), while a sensitivity analysis is provided in part two. Overall, a 60year global primary energy consumption of 71.4thousand toe (tonne of oil equivalent) and a total CO2eq emission of 135.4thousand tonnes are expected. Under this operating regime, around 563thousand toe and 1465thousand tonnes CO2eq could be prevented by replacing raw materials in several construction materials industries (e.g.: ferrous and non-ferrous metals, plastics, paper and cardboard).
The use of recycled aggregates from construction and demolition waste in concrete is not new. One of the main problems found in this application is the aggregates' high water absorption and, ...therefore, low workability. Incorporating water-reducing admixtures (plasticizers) can reduce the amount of water required, improving the compactness of concrete. This research aims at determining the suitability of using two types of water-reducing admixtures to improve the characteristics of concrete made with recycled aggregates. Three series of concrete with various replacement ratios (0%, 20%, 50% and 100%) of natural aggregate by coarse recycled concrete aggregate were manufactured for this study and used without admixtures, with a traditional plasticizer and a high-performance plasticizer. The basic properties of the aggregates were considered, and the workability and density of fresh concrete and key mechanical properties of hardened concrete, such as compressive strength, tensile strength, elastic modulus and abrasion resistance, were studied. The results obtained were encouraging to use plasticizers in concrete with recycled aggregates.
The quarrying of marble, a well-known ornamental stone, has a substantial positive impact on Portugal's economy, but it also generates large environmental impacts. The amount of waste produced during ...quarrying can be as much as 80% of all stone/soil extracted. That waste is then dumped near the quarry, where it accumulates indiscriminately because a viable alternative for its disposal has not yet been found. In this context, solutions must be found that can transform this waste into a by-product and restore some of its economic value.
The main goal of this study was to evaluate the influence of the replacement of primary aggregates (PA) with marble aggregates. No additions or admixtures were used, as those could change the fresh or hardened properties of the resulting concrete and disguise the influence of the replacement under study. This evaluation required the production of three concrete families. The conventional primary aggregates (PA; basalt, granite and limestone) were replaced in the three families by coarse marble aggregates (CMA) at ratios of 20%, 50% and 100% of the total volume of aggregates. These mixes were tested in the concrete's fresh state for workability and density and in its hardened state for compressive strength, water absorption by capillarity and immersion, carbonation and chloride penetration. The results indicate that there are no significant differences between a concrete produced using CMA and one made with PA in terms of durability, making the use of this waste as concrete aggregate perfectly feasible.
The mechanical properties of the concrete made with CMA were assessed in the scope of concurrent work also performed at the Instituto Superior Técnico (Lisbon, Portugal).
This research assessed the performance of mortars in which recycled concrete aggregates (RCA) was a component. It replaced natural sand but kept the same particle size distribution. Three mortars ...were produced with replacement ratios of 20%, 50% and 100% as well as a reference mortar containing no recycled aggregate. The compressive and flexural strength, water absorption by capillarity, drying capacity and susceptibility to cracking of these mortars were analyzed first. Then, based on these results, the most satisfactory replacement ratio was chosen and the following properties were analyzed: water retentivity, shrinkage, adhesive strength, modulus of elasticity, and water vapor permeability. Somewhat surprisingly the best results in the first stage occurred for 20% and 100% replacement ratios, leading to a cautious choice of the 20% ratio for the second stage. Generally the mortar with 20% replacement ratio performed better than the reference mortar, except for adhesive strength and dimensional stability.
The effective management of construction and demolition waste (CDW) is a major challenge for the construction sector. To address such needs, this research work focuses on a specific type of CDW – ...annealed plate glass – to be incorporated into cementitious renderings.
Studies on glass waste are very recent, scarce, and usually limited to the alkali-silica reaction (ASR), but they tend to involve other types of glass. This work characterizes the physical–mechanical and performance of these modified mortars, something that has not yet been done. A main reason for this lack of knowledge is the serious concern that there is an ASR potential. However, a recent study 1 concluded that the approach set out in ASTM C 1260 (accelerated mortar bar test) 2 may be overly conservative for renderings because it significantly increases the cement content. That study concluded that the use of mortars containing waste glass is technically viable in terms of ASR-related durability as long as the cement type and content are controlled, as well as the size of the aggregates, which proved to be the most decisive parameter 1.
In our study, mortars with a cement-to-sand volumetric ratio of 1:4 were produced with a fraction of the sand replaced by fine glass aggregates (0%, 20%, 50% and 100% by volume), while the aggregate’s size distribution in the replacement remained constant so that the material itself was the single factor under analysis.
The study reveals significantly improved results, especially at the level of the mechanical performance and physical compatibility with the substrate, when these mortars are compared with similar ones containing other waste types and a conventional mortar (with only natural sand as aggregate).
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