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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.

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.

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 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.

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.