Mixed Recycled Aggregates Research Articles

Development of eco-friendly geopolymers with ground mixed recycled aggregates and slag

The recycling of masonry demolition waste has attracted growing attention in recent years. In this paper, the feasibility of developing eco-friendly geopolymers using ground mixed recycled aggregates (GMRA) was investigated. Both compressive and flexural tests of GMRA based geopolymers were conducted. It was found that the compressive strength of GMRA base geopolymer could reach 70 MPa at seven days. The influences of slag replacement ratio, alkali concentration and SiO2/Na2O ratio were investigated in this paper. The relation between the compressive and flexural strength for GMRA based geopolymer was also proposed through the fitting of the test data. Besides, the environmental impact and cost-benefit analysis of GMRA based geopolymer were quantitively studied, and results showed that increasing slag replacement ratio would dramatically reduce the CO2 intensity and the cost efficiency of GMRA based geopolymer. However, slight effect of alkali concentration on the CO2 intensity and cost efficiency was observed.

Sustainability evaluation of concretes with mixed recycled aggregate based on holistic approach: Technical, economic and environmental analysis

This research combines technical, economic and environmental analysis of the use of recycled aggregates from construction and demolition wastes in concrete production. Firstly, an experimental campaign to evaluate the effect of recycled aggregate on mechanical properties was developed. The mixture designs studied were: a reference concrete (without recycled aggregate), two concretes with 20% and 100% replacement of coarse natural aggregate by recycled concrete aggregate; and three concretes with 20, 50 and 100% replacement of coarse natural aggregate by mixed recycled aggregate. To analyze their technical feasibility, these concretes were made in the laboratory and in a concrete plant. The economic viability was also studied indicating the additional costs incurred due to the utilization of recycled aggregate in different economic scenarios. Finally, the differences in environmental impacts were analyzed for each concrete. For this purpose, energy consumption, global warming, eutrophication, acidification, photochemical ozone creation, waste generation, and abiotic depletion were accounted. 20% replacement of recycled concrete aggregates does not cause practically variations in the cost or the environmental loads, only a reduction of waste generation and abiotic depletion of 8% and 10.6% respectively. In contrast, the use of 100% replacement by mixed aggregates may increase the global warming indicator an 11% when double transport distance is assumed. But in exchange, the waste generation decreases 35% and the abiotic depletion 50%. Aggregate transport distance is a key factor that will determine the cost, energy consumption, and global warming of the mixed recycled aggregate.

Leaching of Pervious Concrete Produced Using Mixed Recycled Aggregates

Abstract Waste produced by the construction sector is a problem that has grown over the last few years. Construction and demolition waste makes up about 50% by mass of the total solid waste produced in Brazil. One alternative by which to reduce this volume is recycling this material in the form of aggregates. However, it is necessary to analyze the environmental risk that the use of recycled aggregates can entail for adjacent soil and the water table. The purpose of this work was to evaluate pervious concrete samples that contained recycled aggregates and to subject them to leaching tests. The results were compared with the limits established by the Italian methodology. Aggregates with 10, 25, 50, and 100% ceramic were used, as well as a recycled concrete aggregate and a natural aggregate. With the exception of the 25% ceramic trial, all the treatments introduced chromium to the water in which they were immersed, with accumulated concentrations varying from 0.009 to 0.099 mg L-1. Cadmium was found in higher quantities, with cumulated concentrations between 0.104 and 0.417 mg L-1. Sulfate concentrations were higher after 24 h of immersion, with a maximum release of 71.7 mg L-1. The concrete made with 100% ceramic aggregate leached more chromium and sulfate than the other aggregates.

MORTEROS DE ALBAÑILERÍA ELABORADOS CON ÁRIDOS RECICLADOS MIXTOS Y ESCORIA BLANCA

The objective of this paper is to study the effect of the partial substitution of the most used natural aggregates in the western region of Cuba, specifically in Havana, by mixed recycled aggregates and the total substitution of the natural filler, lime hydrate, by ladle furnace slag, in the elaboration of recycled masonry mortars. The properties provided by recycled mortars are compared to those offered by a standard mortar, made with natural sand and natural filler, and with standard regulation these products at Cuba. The results achieved are satisfactory, since the mortars made with recycled materials meet the requirements required for masonry mortars type III (suitable laying and coating mortars for use on the ground level).

Water transport mechanisms in concretes bearing mixed recycled aggregates

Aggressive agents present in the environment that penetrate concrete through its pore structure induce deterioration, compromising the service life of concrete members. Determining the viability of using recycled materials in structural concrete calls for a prior understanding of their effect on water transport, the primary vehicle for external agent ingress. This article describes durability indicators such as electrical resistivity, water permeability (pressure testing), total water absorption, effective porosity and sorptivity that directly or indirectly measure water penetration and consequently performance across the service life of concrete bearing 20% to 100% mixed recycled aggregate (MRA). The 28 d concretes studied here with up to 75% MRA exhibited <7% weight gain due to water absorption, <15 vol% porosity and <30 mm maximum depth of water penetration under pressure, all indicative of high quality concrete. In 90 d materials, the values of the aforementioned parameters were 40% lower. Even in concrete with up to 100% MRA (with 28 d readings of 50 Ω m to 100 Ω m), electrical resistivity remained unaffected, The present findings reveal that high quality high durability structural concrete can be viably manufactured with up to 75% MRA.

Real-scale study of a heavy traffic road built with in situ recycled demolition waste

This real-scale study carries out a research of the behaviour of building demolition wastes in a road with high intensity traffic. A mobile recycling plant treated in situ the demolition wastes from 105 single-family homes. Recycled aggregates were made from two different sources: one aggregate came from concrete taken out of slabs and foundations (recycled concrete aggregate) and the second aggregate came from the remaining reinforced concrete structures, walls and roofs (recycled mixed aggregate). Both recycled materials and a crushed stone formed the granular base and subbase of the experimental paved section. A leaching test analysed the potential pollutant emissions of the recycled aggregates. Different tests were performed during construction of the experimental section, such as densities, loading plates and falling weight deflectometry. This research evaluated deflections and surface roughness for a period of seven years to study the behaviour of these recycled materials long term. The recycled aggregates used did not satisfy all the stipulations of the Spanish standards for granular material as road subbases/bases, such as size distribution, Los Angeles test limit, soluble salt and organic matter content in subbases. Despite this lack of compliance, the results of on-site tests over time compared the mixed recycled aggregate as subbase and the recycled concrete aggregate as the base with natural aggregates; the recycled aggregates presented a better structural behaviour and less surface deterioration than natural aggregates under a mean daily heavy vehicle flow of 371 vehicles per lane and an average daily traffic of 4469 vehicles per lane on average. The article includes the calculation of moduli through forward and back calculations for the recycled aggregates, which is a key aspect in pavement design The bearing capacity of recycled materials increased with time in the structural layer, which is unlike the trend in bearing capacity of the natural aggregates.

Rendering mortars with incorporation of very fine aggregates from construction and demolition waste

The intense rate of construction and demolition waste generation (CDW) over the years should boost recycling. The use of CDW as constituents of cementitious composites has been considered a feasible alternative to dumping. This paper presents a study of the behaviour of cementitious renderings incorporating very fine recycled aggregates from two types of CDW. Only particles of recycled aggregates below 0.149 mm were used as filler, hereinafter referred as recycled concrete aggregate (RCA) and mixed recycled aggregate (MRA). The incorporation’ percentages used were 0%, 10%, 15% and 20% of natural aggregates’ volume. Several tests have been carried out, in order to evaluate the mortars in terms of mechanical strength, workability, water absorption, dimensional instability and water vapour permeability. The experimental programme consisted in three consecutive phases, in which the mortars that presented the best performances were selected for a deeper analysis of their features. The test results showed that modified mortars had a better behaviour in most of tests compared with the reference mortar (with no CDW). Mortars with incorporation of 20% of RCA and 15% of MRA presented the best performance.

Estudio del comportamiento de los morteros reciclados frente al ruido de impacto

En la actualidad existe una amplia gama de sistemas y materiales que se emplean como atenuadores del ruido de impacto, ofreciendo buenas prestaciones a la hora de evitar la transmisión de vibraciones a través de los forjados. En este trabajo, se han elaborado placas de mortero de cuatro centímetros de espesor con cuatro tipos de árido diferentes combinados con distintas tipologías de aislamiento. Aprovechando la menor densidad de los morteros elaborados con árido reciclado, se ha llevado a cabo una investigación en la que se propone sustituir el 100% del árido natural por árido reciclado para la fabricación de morteros empleados en el sistema de losa flotante, ya que ofrecen una solución más eficiente desde el punto de vista acústico. Los morteros elaborados con áridos reciclados de cerámica y mixto los que presentan la solución óptima para atenuar impactos producidos sobre la superficie, reduciendo hasta en un 20% la velocidad de transmisión de impactos frente a sus homólogos elaborados con árido natural.

Effective utilization and recycling of mixed recycled aggregates for a greener environment

Abstract Both global warming issue and ozone layer depletion have triggered the awareness of the utilization of recycled materials in construction industry for a greener environment. The utilization and recycling of mixed recycled aggregates (MRA) comprising recycled fine aggregates (RFA) and recycled coarse aggregates (RCA) were explored for construction applications using the coupled Taguchi-RSM optimization approach. Under stringent durability requirements, 35% RCA combined with 6% RFA can be utilized while 70% RCA combined with 30% RFA under non-stringent conditions for non-structural applications. Our study also revealed large potential applications of pretreated mixed recycled aggregates in above-ground structural construction applications. Furthermore, review of literatures revealed presence of behavioral, technical, legal and market barriers which can be overcome through proposed measures. Our study also revealed a payback period of 3 years for recycling investments and revenue generation of HK$ 12 billion within the first ten years of operation and prevention of 20.9–50.1 × 106 KgCO2 equivalent emission annually. In order to achieve these benefits, a pragmatic, recycling-based closed-loop construction and demolition management approach is recommended to achieve a greener environment. Government should take active leading role towards CDW recycling through high-impact policy making and implementation.

The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars

Abstract In recent years, the number of studies on the incorporation of recycled aggregate (RA) into mortars has grown considerably. However, mixed recycled aggregate (MRA) is investigated on a much smaller scale due mainly to its high-water absorption capacity and higher powder content (

Concreto com cinza de casca de arroz (CCA) e resíduos de construção e demolição (RCD)

A construção civil é um setor que contribui com enormes quantidades de resíduos depositados no meio ambiente e retira grande parte da sua matéria prima da natureza, sendo que o processamento de algumas dessas matérias primas é altamente poluente. A busca por minimizar os impactos dessa atividade é incentivo para se estudar materiais que possam integrar o concreto de forma a suprir as necessidades do setor. O presente estudo visa analisar a utilização da cinza de casca de arroz (CCA) em substituição ao cimento, e do agregado reciclado, em substituição parcial ao agregado graúdo. Foram avaliados através de ensaios físicos e mecânicos dois tipos de concreto, o primeiro utilizando apenas cimento e agregados naturais, e o segundo utilizando 10% de CCA e 25% agregado reciclado misto. Os resultados indicam que há diferenças significativas entre os agregados naturais e reciclados, principalmente no quesito absorção e porosidade. Essas diferenças refletiram em menores resistências e menor módulo de elasticidade, entretanto atesta-se a viabilidade de utilização destes materiais na fabricação de concretos estruturais.

Measuring system of capillary rising damp in cement mortars

One of the most frequent pathologies in the building is an appearance of damp that impacts negatively the comfort and the health of users, undermining the state of the building. The study of the behaviour of materials in relation to water absorption can help to prevent and to diagnose the appearance of capillary damp in the building. This research proposes a measurement method that complements one proposed by the standard UNE-EN 1015-18, using a sensor able to measure the distribution of moisture in mortar samples. For that, two types of cement mortar were used: traditional mortar fabricated with natural aggregate and recycled mortar fabricated with 100% of mixed recycled aggregate. The new measuring equipment is able to detect variations of moisture due to the water absorption by capillarity in masonry mortars. According to the results, recycled mortars show higher water absorption by capillarity due to the larger capillary system formed in this type of mortar as a result of high absorption of recycled aggregates.

Feasible use of recycled alumina combined with recycled aggregates in road construction

Several studies have applied recycled aggregates (RA) in road layers and demonstrated appropriate results. In general, RA can be one of two types: recycled concrete aggregates (RCA) or mixed recycled aggregates (MRA), each of which has lower density, higher water absorption, and lower mechanical strength than natural aggregates (NA). Alumina waste (AW), obtained from the process of aluminum refinement, could be mixed with RA in order to improve its properties, such as compaction and bearing capacity, for application in road construction. Few studies have investigated the use of AW with RA in civil constructions. This paper presents the results of a laboratory study of different materials based on the addition of AW to RCA and MRA. In the experiment, the mechanical behaviors and microstructural properties of RCA, MRA, and mixes of RCA or MRA with AW were compared. Different specimens of unbound recycled mixtures demonstrated increased resistance properties, and the formation of new cement hydrated particles was observed in these novel mixtures. The properties of the mixtures of RCA and MRA with AW suggest that these recycled materials can be used in unbound road layers to improve the long-term mechanical behavior.

The assessment of ceramic and mixed recycled aggregates for high strength and low shrinkage concretes

Very few studies on recycled aggregate concretes (RC) have been extended to the use of recycled ceramic and mixed aggregates in relation with high strength concretes. In the main they concentrate only on the analysis of the physical and mechanical properties. This study deals with the investigation of the influence that different percentages (up to 30% substitution for natural aggregates) of high porous ceramic and mixed recycled aggregates have over the plastic, autogenous and drying shrinkage of the concretes. The physical and mechanical properties as well as the chloride resistance were also determine in order to assess the viability of the use of ceramic and mixed recycled aggregates in high strength concretes. The results revealed that the employment of highly porous recycled aggregates reduced the plastic and autogenous shrinkage values of the concrete with respect to those obtained by conventional concrete (CC). Although the total drying shrinkage of the recycled concrete proved to be 25% higher than that of the CC concrete, the CC concrete had in fact a higher shrinkage value than that of the RC from 7 to 150 days of drying. It can be concluded that the RC concrete produced employing up to 30% of fine ceramic aggregates (FCA, with 12% of absorption capacity) achieved the lowest shrinkage values and higher mechanical and chloride ion resistance. In addition, the concrete produced with low percentage (10–15%) of recycled mixed aggregates also had similar properties to conventional concrete.

Statistically significant effects of mixed recycled aggregate on the physical-mechanical properties of structural concretes

The mixed recycled aggregate obtained from processed construction and demolition waste accounts for the largest share of recycled aggregate produced worldwide. Efficient and appropriate use of these new resources will help reduce and confront the major environmental problems facing today’s economic growth model. The research discussed in this paper assessed the performance of structural concretes containing 20%, 25%, 50%, 75% or 100% mixed recycled coarse aggregate, analysing fresh concrete workability, density and air content and hardened concrete compressive, flexural and splitting tensile strength. An analysis of variance (ANOVA) run on the findings to determine the effect of the factors on the variables showed that curing age and percentage of recycled aggregate had a statistically significant impact on concrete performance. The decline in strength relative to conventional concrete was smaller at longer curing ages. Concretes bearing up to 50% recycled aggregate exhibited declines in performance of 10% or under in most of the properties studied, even at late ages. In light of the present findings, the mixed recycled aggregates used in this research may be deemed apt for use in structural concrete with a characteristic strength of up to 30 MPa.

Feasibility study of roller compacted concrete with recycled aggregates as base layer for light-traffic roads

This research aims to produce roller compacted concrete (RCC) using recycled aggregates (RAs) from construction and demolition waste (CDW) with low cement content. Previous research has confirmed that RA performs favourably when applied to a road base layer as a granular material or as a cement-treated granular material. In addition, previous studies have made progress in analysing the feasibility of using RCC with different types of RA, such as recycled concrete aggregate (RCA) and recycled pavement aggregate (RPA). Under this framework, the technical feasibility of using RCC with a 100% coarse RA incorporation ratio and low cement content in the base layer of light-traffic roads was determined. For that purpose, two series of RCC mixtures were produced with different cement contents: 150 and 250 kg/m3. Each series consisted of RCC mixtures with one natural aggregate (NG) and three different types of RA, specifically, one RCA and two mixed recycled aggregates (MRA), as coarse fraction. The percentage of ceramic particles in the RA ranged from 2.5% to 23.4%. The mechanical properties (e.g. the compressive strength, splitting tensile strength and elastic modulus) and drying shrinkage were studied in the RCC specimens produced. Mechanical properties were diminished as percentage of ceramic increased. These reductions in mechanical properties were near 30% for the RCC with RA with the greatest ceramic elements, respect to RCC with NG. The results support the feasibility of using RCC with a 100% coarse RA incorporation ratio and low cement content to form light-traffic-road base layers, such as residential streets, sidewalks and bike lanes.

Investigation of mechanical properties of mortar with mixed recycled aggregates

In this study two phases were considered. In the first phase, demolition of building materials such as concrete, brick, ceramic and tile, and stone were crushed and 30–40% stone, 10–20% ceramic, 5–15% brick, and 50–60% concrete waste were used to produce recycled sand. The initial properties of aggregates such as chemical properties, water absorption, moisture content, density, and abrasion were investigated. In the second phase, the mechanical properties of mortar with substitute of natural aggregates with recycled aggregates from 0 to 100% were examined. In addition, the sand to cement ratio was varied from 2, 2.5, and 3. The results showed that the compressive strength in sand to cement ratio of 3 is higher than other ratios. Water absorption test showed that the use of recycled sand increases the water absorption in all ratios of sand to cement. The flexural strength test showed that the use of 0–40% recycled sand in sand to cement ratio of 2.5 is higher than other specimens, but by increasing the waste to between 50 and 70%, specimens with sand to cement ratio of 3 have higher result. Increasing the recycled sand to 100%, produced higher results for sand to cement of 2. Additionally, backpropagation neural network was used to estimate the mechanical properties of mortar. With regression of up to 70% and mean standard error lower than 0.3, this network has good precision to predict the mortar properties.

Risk assessment by percolation leaching tests of extensive green roofs with fine fraction of mixed recycled aggregates from construction and demolition waste.

Extensive green roofs are urban construction systems that provide thermal regulation and sound proofing for the buildings involved, in addition to providing an urban heat island mitigation or water retention. On the other hand, policies towards reduction of energy consumption, a circular economy and sustainability are core in the European Union. Motivated by this, an experimental study was carried out to evaluate the environmental risk assessment according to release levels of polluting elements on leachates of different green roof substrate mixtures based on recycled aggregates from construction and demolition waste through (i) the performance in laboratory of two procedures: compliance and percolation tests and (ii) an upscaled experimental leaching test for long-term on-site prediction. Four plots were built on a building roof and covered with autochthonous Mediterranean plants in Córdoba, South of Spain. As growing substrate, four mixtures were used of a commercial growing substrate with different proportions of a fine mixed recycled aggregate ranging from 0 to 75% by volume. The results show that these mixtures were classified as non-hazardous materials according to legal limits of the Landfill Directive 2003/33/CE. The release levels registered in extensive green roofs were lower compared to the laboratory test data. This shows how laboratory conditions can overestimate the potential pollutant effect of these materials compared to actual conditions.

Life cycle assessment of non-hazardous Construction and Demolition Waste (CDW) management in Lombardy Region (Italy)

Abstract Construction and Demolition Waste (CDW) has been identified as a priority waste stream by the European Union due to its significant generation level and its high recycling potential. The purpose of the present study, which was supported by the local government of Lombardy Region (Italy), is to apply the Life Cycle Assessment (LCA) methodology to evaluate the environmental performance of the current regional management of CDW and to identify critical aspects and possible improving actions. The focus has been placed on the waste fraction mostly present in CDW that is the mixed non-hazardous waste (identified by the European Waste Code 170904). In the recycling plants, this is usually blended with cement, tiles and ceramics, and, to a lesser extent, with bituminous mixture and gypsum-based waste to obtain mixed recycled aggregates. These are mostly used in road construction works and in environmental fillings/restoration. The LCA of the current CDW management system showed that the induced environmental impacts are in general higher than the benefits arising from recycling activities. At the same time the current system performs better than a scenario where all the CDW is sent to landfill. On the basis of several sensitivity and scenario analyses, a best-case scenario has been defined by optimizing all the main system parameters. Finally, recommendations were formulated to improve the environmental performances of the system.

Functional and structural parameters of a paved road section constructed with mixed recycled aggregates from non-selected construction and demolition waste with excavation soil

This paper evaluates the lab and in situ mechanical properties of non-selected mixed recycled aggregates from construction and demolition waste (CDW) used as base and subbase unbound materials. Excavation materials are mixed with CDW to produce recycled mixed aggregates with soil, as well as a finer material referred to as mixed recycled soil. The research was divided into two different stages: a laboratory study characterizing the properties of recycling aggregates and a road test track evaluating the long-term performance of these materials under real traffic and weather conditions. During construction, several density, plate load, and falling weight deflectometer tests were performed to determine the bearing capacity of all layers. A laser profiler was also used to obtained the international roughness index. After the road was opened to traffic, a follow up of deflections and surface roughness was performed during the following seven years.Two different moduli calculation methods were used: back calculation and forward calculation. Both methods shown acceptable values for these recycled materials. Low quality recycled mixed aggregates can be used as substitutes for natural aggregates as unbound layers. The mechanical performance and surface roughness values obtained from the experimental road shown an acceptable behaviour.