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The search for sustainable alternatives for waste disposition other than disposal and evaluation of the feasibility of a second life cycle for waste should be a priority in the research and characterisation of alternative materials. In civil engineering infrastructure applications (e.g. railway, pipe bending, or road construction), large volumes of aggregate are required, which necessitates the consumption of natural resources and significantly impacts soils and the environment in the surrounding area. Occasionally, when the in situ soil does not possess the appropriate mechanical properties or has low load bearing capacity for traffic or other loads, chemical stabilising agents are used to improve the soil characteristics. However, the development and implementation of sustainable alternatives must become a priority in economic, social, scientific, and technical strategies to address current environmental challenges. This study analyses the environmental viability of using eco-friendly agents instead of the chemical additives traditionally used in soil stabilisation. Based on the findings, it is affirmed that the bottom ashes from the combustion of an olive and grape waste biomass in cogeneration plants possess adequate properties as an eco-stabiliser, are not harmful to the environment, and are feasible as an eco-agent for expansive soils in civil engineering works.

For many decades, researchers have been working on finding innovative and sustainable solutions to address the enormous quantities of plastic waste that are produced every year which, after being collected, are transformed into energy, recycled, or sent to landfills. Giving a second life to plastic waste as a material to be incorporated, in the form of macro-fibres, into concrete, could be one such solution. The purpose of this study was to analyse the mechanical and physical behaviour of the hardened concrete reinforced with macro plastic fibres (RPFs) obtained from food packaging waste (FPW) discarded during the packaging phase. By varying the quantity of macro-fibres used, physical and mechanical properties such as compressive strength, modulus of elasticity, flexural strength, and toughness were evaluated. It was observed that, although the presence of macro plastic fibres reduced the mechanical resistance capacity compared to that of traditional concrete, their contribution proved to be of some importance in terms of toughness, bringing an improvement in the post-crack resistance of the composite material. This innovative mixture provides a further impulse to the circular economy.

Construction and demolition recycling is regarded as an essential subject in the EU, as the target established by its policies to 2020 ratio is far from being achieved. The use of materials recycled from such waste has been widely deemed a contribution to the sustainability of the construction sector. Gypsum is one the limiting components of recycled aggregates used as a base layer in road construction. The aim of this research was to analyse the effect on mechanical properties, leaching behaviour and dimensional changes at long term in recycled aggregates with different gypsum contents. Load bearing capacity was conducted by California bearing ratio on prepared samples. Moreover, the compressive strength was conducted on samples prepared with a 3% cement addition. Both tests were studied long term. Dimensional changes were studied through swelling in California bearing ratio test mould under the modified Proctor conditions for 1 year and using an oedometer device for 5 months. Furthermore, environmental risk assessment was performed, classifying the material with gypsum addition as non-hazardous, given that sulphate anion was above the inert limit. Good mechanical behaviour in the long term and no significant dimensional changes were found regardless of gypsum content.

The circular economy is an economic model of production and consumption that involves reusing, repairing, refurbishing, and recycling materials after their service life. The use of waste as secondary raw materials is one of the actions to establish this model. Construction and demolition waste (CDW) constitute one of the most important waste streams in Europe due to its high production rate per capita. Aggregates from these recycling operations are usually used in products with low mechanical requirements in the construction sector. In addition, the incorporation of photocatalytic materials in construction has emerged as a promising technology to develop products with special properties such as air decontamination. This research aims to study the decontaminating behavior of mortars manufactured with the maximum amount of mixed recycled sand without affecting their mechanical properties or durability. For this, two families of mortars were produced, one consisting of traditional Portland cement and the other of photocatalytic cement, each with four replacement rates of natural sand by mixed recycled sand from CDW. Mechanical and durability properties, as well as decontaminating capacity, were evaluated for these mortars. The results show adequate mechanical behavior, despite the incorporation of mixed recycled sand, and improved decontaminating capacity by means of NOx reduction capacity.

Two waste streams result from biomass combustion for power generation: biomass fly ash (BFA), which is used as fertilizer in agriculture, and biomass bottom ash (BBA) currently with no practical applications and generally deposited in landfills. This study provides significant information about the mechanical behaviour of mortars made with BBA, and the influence of several variables on such behaviour, namely type of cement, cement content, BBA incorporation ratio, and material type replaced with BBA. Two mortar families were produced according to the type of cement applied (CEM-I and CEM-II). In each family, three volumetric replacement ratios of natural sand (NS) with BBA (0%, 10% and 20%) and three cement contents (515 g/L, 485 g/L and 450 g/L) were used. Mortars with replacement of cement with BBA (10% and 20% in cement volume) were also produced. Four mechanical properties were analysed: porosity, density, flexural strength and compressive strength. Strength was analysed at different ages to assess its evolution over time. There was a declining trend with the application of BBA for all properties analysed. Different behaviours were observed depending on the type of cement used or the material type replaced with BBA. Furthermore, there is an influence of porosity and density on strength due to the high absorption of BBA, allowing establishing meaningful relationships between the properties analysed. This paper proves the viability of bedding mortars with BBA depending on the cement type and content and the BBA incorporation ratio.

Construction and Demolition Waste come from debris generated during construction, renovation and demolition of buildings, roads, and bridges. Recycling and reuse are essential in terms of sustainability, mainly from an environmental point of view. Although the recommendation of the use of these recycled aggregates is currently included in some technical specifications, its use is still not widespread due mainly to the lack of knowledge on their technical application. This work is a compilation of the recommendations proposed in the “Catalogue of road pavements with recycled aggregates”, supported by the construction of experimental stretches. It proposes different structural sections for road pavements by using recycled aggregates.

The construction and demolition waste is one of the heaviest and most voluminous waste streams generated in the European Union. It comprises approximately one third of the waste generated. Recycling this stream waste will provide ecological and sustainable benefits. The recycled aggregates from the construction and demolition waste are beginning to be used in civil construction, as substitutes for natural aggregates. The possible applications of recycled aggregates in the infrastructure construction projects will mainly depend on the quality of the recycled aggregates. This will be determined by the nature and the origin of the construction and demolition waste, and the treatment system used. It requires a comprehensive response by part of the processing agents, mainly construction and demolition companies, and above all public administrations. This work proposes recommendations for the handling of the construction and demolition waste, both in the demolition and in the treatment plants. A quality control system is suggested too.

Recently, both nationally and internationally, cement-treated granular materials (CTGMs) have been widely used as road base layer. However, all the researches on CTGM with recycled aggregates (RA) are limited to the coarse fraction, with a size range of 0–40 mm. In Spain, one of the recycled materials most commonly produced in construction and demolition waste (CDW) treatment plants is a mixture with around 75% of fine recycled aggregates (hereby called FRA), with 5–8 mm nominal maximum size. This material is commonly used in pipe bedding, an application that provides little or no added-value. The intent of this paper is to study the feasibility of using CTGM made with FRA as road base layer. For this purpose, six mixtures have been produced, comprising 0–8 mm FRA and 0–40 mm coarse aggregates, made of mixed recycled aggregates and recycled concrete aggregate. The main mechanical (unconfined compressive strength and modulus of elasticity) and durability (dimensional changes) properties were studied and th...

Recycled materials of various types have been used as substitutes for coarse recycled aggregates and natural sand in the manufacture of concrete. Generally, the values of mechanical and durability properties decreases when applying different replacements of natural aggregates with recycled aggregates in both fine and coarse granulometries. However, new waste from the combustion of biomass as bottom ash has not been applied as a substitute for fine aggregate in the manufacture of concrete. In this research, concrete consisting of recycled aggregate substitutions was manufactured by applying different replacement rates of natural sand with biomass bottom ash. An efficient dosage method can be applied to obtain an optimal ratio of recycled concretes made with biomass additions. Mechanical properties and durability were evaluated in order to know the possibilities of application of these recycled materials in real concretes. The results showed a worse behaviour in these properties, however these reductions were inferior than it can be expected, due to the appropriate manufacture of the concrete applied.

This research evaluates the short- and long-term properties of masonry mortar manufactured with different replacement ratios of natural sand by fine recycled concrete aggregates. The recycled materials were collected from a recycling plant and after passage through a 4 mm sieve, were directly used to make the mixtures, maintaining their original particle size distribution. A pozzolanic CEM-IV/A (V) 32.5 N, with 29% fly ash in its compositions, was used at a 1:7 volumetric cement-to-aggregate ratio. Five mortars with different replacement ratios by volume were tested: 0%, 5%, 10%, 20% and 40%. The data were analysed using one-way analysis of variance to determine whether the “replacement ratio” had a statistically significant effect on the different fresh and hardened properties. DRX and electron microscope techniques were used to examine the morphologies and evolution of the main mineral phases over time during a curing period of 180 days. The results proved that a replacement ratio of up to 40% is a viable alternative for producing environmentally friendly masonry mortar.

The present work discusses the results of an experimental study investigating the performance of cement-treated granular materials, which were prepared from natural aggregates, recycled concrete aggregates, crushed clay bricks and gypsum. Recycled aggregates can potentially contain large amounts of acid-soluble sulphates. High sulphate contents can lead to the formation of ettringite, which causes dimensional instability in cement-treated materials. The tested samples were manufactured with different types of cement (CEM II and Sulphate-Resistant Portland Cement) and different compositions of the recycled materials to observe the effects of the sulphate content on the mechanical behaviour and the dimensional stability. As a result, the influence of the amount of sulphates on the deformation was determined, which is an aspect that must be considered in applications of this recycled product in road layers.

Recycled aggregates from construction and demolition waste have previously been used to manufacture recycled concrete. Generally, these aggregates weaken the physical properties of concrete, such as the density, durability, compressive strength, flexural strength, water penetration, and chloride penetration. This is predominately attributed to the porosity of particles with adhered mortar or to ceramic particles. In other studies, cements with additions (fly ash, slag, silica fume …) were used to compensate for the effect of incorporation of recycled aggregates. In another, plasticizers were used to improve workability or mechanical properties of recycled concrete. However, the innovation of this research is the use of different amounts of cement according to replacement ratios of natural aggregates for recycled concrete aggregates to achieved structural concretes. Also, two different water/cement ratios were used to analyse if these reached compressive strength similar to control concrete manufactured with natural aggregates. The results revealed that a small increase in the volume of cement (12%) maintained the mechanical properties and reduced the loss of concrete durability. Therefore, increasing the amount of cement in recycled concretes is a feasible technique in works with low exposure to aggressive agents.

The production of energy from renewable resources, such as biomass, is increasing rapidly. Therefore, environmentally friendly and economic solutions to recycle the resulting by-products are essential. The present study was performed to search for possible applications of the biomass bottom ashes that result from biomass combustion at three biomass combustion plants located in the Andalusia region of southern Spain. The analysis of chemical parameters indicated the applicability of biomass bottom ashes as an alternative material in civil construction. Thus, the limiting chemical parameters were analysed according to Spanish regulations. According to the results, biomass bottom ashes could be used as filler in road embankments, cement-treated materials or non-structural concrete, depending on the replacement percentage. This study determined that a review of the chemical parameters specified by the limiting regulations is recommended to promote the use of biomass bottom ashes as a building material in applications that do not require high structural strength.

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.

Social awareness aims to increase practical skills, such as sustainable development, which seeks to increase the use of different types of waste in construction activities. Although insufficient attention is sometimes given to these actions, it is essential to spread information regarding new studies in the field of waste recycling, which encourages and promotes waste use. Reusing and recycling construction waste in the creation of buildings and infrastructure are fundamental strategies to achieving sustainability in the construction and engineering sectors. In this context, the concept of waste would no longer exist, as waste would become a material resource. Therefore, this study analyses the behaviours of two unbound mixed recycled aggregates (MRA) in the structural layers of an unpaved rural road with low traffic (category T43). The sections were built on inappropriate soil (A-7-6) with a high degree of free swelling. The experimental road consisted of three sections: the first was made with natural aggregates (NA) that were used as a control, the second was composed of MRA in the subbase and NA in the base, and the third section was completely composed of MRA. The materials were characterised in the laboratory. The behaviours of the structural layers in the experimental road were determined by controlling compaction (“in situ” density and moisture) and measuring the deflections and load capacity (deflectometer) during the 18 months after construction. The results show that the sections made with recycled aggregates meet the technical specifications required by General Technical Specifications for Road and Bridge Works (PG-3). Therefore, the water-soluble sulphate content and Los Angeles abrasion coefficient limits can be increased for recycled aggregates without compromising the quality of this type of road with low traffic. To the best of our knowledge, this is the first study regarding the use of unbound MRA made from construction and demolition waste (CDW) in the construction of an unpaved rural road with low traffic on an expansive clay subgrade.

In some recycled aggregates applications, such as component of new concrete or roads, the total content of soluble sulphates should be measured and controlled. Restrictions are usually motivated by the resistance or stability of the new structure, and in most cases, structural concerns can be remedied by the use of techniques such as sulphur-resistant cements. However, environmental risk assessment from recycling and reuse construction products is often forgotten. The purpose of this study is to analyse the content of soluble sulphate on eleven recycled aggregates and six samples prepared in laboratory by the addition of different gypsum percentages. As points of reference, two natural aggregates were tested. An analysis of the content of the leachable amount of heavy metals regulated by European regulation was included. As a result, the correlation between solubility and leachability data allow suggest a limiting gypsum amount of 4.4% on recycled aggregates. This limit satisfies EU Landfill Directive criteria, which is currently used as reference by public Spanish Government for recycled aggregates in construction works.

One of the main applications of recycled aggregates is the construction of sub-bases for roads as unbound materials, substituting for natural aggregates. For this application, recycled aggregates obtained from crushed concrete are mostly used. Nevertheless, in the Mediterranean area, a large amount of mixed (concrete plus masonry) recycled aggregates is produced, making it advantageous to investigate the possible applications of this type of material, which has a highly variable composition. This work is focused on studying the possible relationship between different constituents of recycled aggregates and their mechanical behaviour for possible application in roads. To meet this goal, 31 types of aggregates have been studied (four natural and 27 recycled from 11 different treatment plants). Characterisation trials were carried out on all of them, together with mechanical behaviour tests (Los Angeles coefficient, Modified Proctor and C.B.R.). The obtained results were analysed using the standard statistical tests ANOVA and simple and multiple linear correlation analysis.

In Spain, the use of recycled aggregates (RA) in the construction of road sub-bases and embankments is growing. Some authors have studied the possibility of using RA in applications with a higher added value, such as the construction of untreated granular sub-bases. However, there is little research on the properties and behaviour of mixed RA treated with cement when used in actual projects as a base for paving roads. This paper includes an investigation of the source of the construction and demolition waste used in RA, the processing plant for the production of RA that manufactures the material treated with cement, and the actual use of RA in a construction project as the sub-base of a motorway access ramp. The results show that the use of some of these aggregates in roads is entirely feasible and that the benefits associated with these aggregates extend beyond the environmental aspects of their use. Some authors have studied the possibility of using these recycled materials in the laboratory, but there are few studies based on real uses of RA from construction and demolition waste (CDW) in roads.

This paper presents an overview of different national and international regulations and recommendations about pavement design in cycle lanes and analyzes the specifications for surface roughness and slip/skid resistance that each offers. After a comparative study, it highlights the lack of specific design criteria and the need to unify the standard test methods and limit values of acceptance and / or rejection to ensure the safety and comfort of the new constructed sections, thus promoting cycling mobility in cities., Este trabajo presenta una revisión de diferentes normativas y recomendaciones nacionales e internacionales de diseño de pavimentos de vías ciclistas y analiza las especificaciones en cuanto a regularidad superficial y resistencia al deslizamiento/ derrape contempladas en las mismas. Tras un estudio comparativo, se pone de manifiesto la carencia de criterios específicos de diseño y la necesidad de unificar métodos de ensayo normalizados y valores límites de aceptación y/o rechazo que garanticen la seguridad y comodidad de los nuevos tramos construidos, favoreciendo así la movilidad ciclista en las ciudades.

Each year, millions of tonnes of waste are generated worldwide, partially through the construction and demolition of buildings. Recycling the resulting waste could reduce the amount of materials that need to be manufactured. Accordingly, the present work has analysed the potential reuse of construction waste in concrete manufacturing by replacing the natural aggregate with recycled concrete coarse aggregate. However, incorporating alternative materials in concrete manufacturing may increase the pollutant potential of the product, presenting an environmental risk via ground water contamination. The present work has tested two types of concrete batches that were manufactured with different replacement percentages. The experimental procedure analyses not only the effect of the portion of recycled aggregate on the physical properties of concrete but also on the leaching behaviour as indicative of the contamination degree. Thus, parameters such as slump, density, porosity and absorption of hardened concrete, were studied. Leaching behaviour was evaluated based on the availability test performed to three aggregates (raw materials of the concrete batches) and on the diffusion test performed to all concrete. From an environmental point of view, the question of whether the cumulative amount of heavy metals that are released by diffusion reaches the availability threshold was answered. The analysis of concentration levels allowed the establishment of different groups of metals according to the observed behaviour, the analysis of the role of pH and the identification of the main release mechanisms. Finally, through a statistical analysis, physical parameters and diffusion data were interrelated. It allowed estimating the relevance of porosity, density and absorption of hardened concrete on diffusion release of the metals in study.