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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.

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.

Construction and demolition wastes are widely recognized as the main waste stream in the EU, and their recycling and recovery is an important issue in sustainable building industry development. The composition of construction and demolition wastes is highly heterogeneous and is influenced by several factors, including the raw materials and construction products used. The environmental performance of these materials are therefore considerably variable and, in some cases, do not comply with the regulatory limits established to ensure the protection of the natural environment. In this context, this paper presents a data analysis on the environmental behavior of construction and demolition wastes and recycled aggregates in terms of both chemical composition and the release of contaminants according to a leaching test. Subsequently, the most critical parameters for recovery were identified and statistically evaluated. The leaching results showed that SO4, Cu, and COD are critical compounds for both CDWs and RAs.

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.

Electric arc furnace dust (EAFD) presents a pollution hazard due to its heavy metal leachability. Its characterization is essential for recovery or disposal in hazardous waste landfills. The present work discusses the results of encapsulating two electric arc furnace dust samples (EAFD1 and EAFD2) by means of the stabilization/solidification (S/S) technique in cement-based mortars. The pH influence on the leaching levels of Se, Mo, Cd, and Pb was evaluated using a pH dependence test as analytical support. In addition, the compressive strength of the S/S mortars was measured to verify its behaviour as a monolithic block. The leaching procedures for granular and monolithic mortars were carried out in order to classify the EAFD samples and the S/S mortars made with EAFD according to the legal limit values imposed by the EU Council Decision 2003/33/EC. Thus, the release levels of Se, Mo, Cd, Pb and chloride in the leachate form of EAFD exceeded the legal limit values, and both EAFDs were classified as hazardous wastes. Concerning the compliance test of S/S mortars after crushing, despite lower releases being registered, none of the S/S mortars in the granular state could be classified as non-hazardous waste due to the high Pb level registered. Finally, after analysing the release levels of S/S mortars of EAFD in the monolithic state, the S/S mortars of EAFD1 were classified as non-hazardous waste. Regarding the S/S mortars of EAFD2, despite the high reduction in the Pb release level after the S/S treatment, these mortars exceeded the hazardous legal limits.

Green philosophy is gaining popularity worldwide. Recycling materials from building demolitions, reutilizing by-products from industrial facilities and exploring the potential uses of waste during a second life cycle are the objectives of this philosophy. In the present article, bottom ashes from electric power generation plants using biofuel combustion were evaluated to verify their potential use as expansive clay stabilizers. Two objectives are pursued: (1) finding a new use for waste that is typically landfilled despite its great potential arising from its technical properties and (2) improving the mechanical properties and reducing the expansive nature of the expansive clays identified during the construction of a motorway. Based on this framework, the present study demonstrated the potential of biomass bottom ashes to stabilize expansive clays. The optimum dosage to improve the properties of clays was determined based on performance parameters, such as plasticity, free swelling or soil collapse. Afterwards, the contaminating potential of ashes was evaluated, being classified as hazardous waste. However, the stabilized mixtures were classified as inert products, thus guaranteeing the environmental feasibility of their use. Finally, the technical application of the stabilized clays as filling materials for embankments and subgrade for light traffic roads was proved. Graphical abstract.

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 Cordoba, 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.

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.

This research is focused on analyzing the environmental pollution potential of biomass bottom ashes as individual materials, as mixtures manufactured with biomass bottom ashes and granular construction aggregates, and these mixtures treated with cement. For the environmental assessment of all of the samples and materials mentioned, the following leaching procedures have been performed: the compliance batch test of UNE-EN 12457-3:2003 for aggregates and bottom ashes; the column test according to NEN 7343:1994 for the mixtures prepared in the laboratory; and the tank test by EA NEN 7375:2004 for analyzing the behavior of mixtures after their solidification/stabilization with 5% cement. After the discussion of the data, the reduction of the pollution load of the most hazardous biomass bottom ashes after their combination with different aggregates can be confirmed, which implies their possible application in civil infrastructures, such as filler embankments and road construction layers, without negatively impacting the environment. In addition, the positive effect of the stabilization/solidification of the cement-treated mixtures with a reduction of the heavy metals that were released at the highest levels, namely As, Hg Cr, Ni, Cu, Se and Mo, was proven