Concrete and Circular Economy

Table of Contents

1. Valorizations of Used Materials and Industrial By-product

   1. Frontmatter

   2. Study of Leaching Behavior of Copper Slag and Its Alkaline Activation Potential

      Ingrid Farías Castillo, Diego Aponte, Marilda Barra

      Abstract

      This study investigates the mineralogical, environmental, and mechanical properties of copper slag (CS) as a precursor material (PM) for alkaline-activated binders (AABs) using sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) solutions. From an environmental perspective, the leaching behavior of 13 elements (As, Ba, Cr, Cd, Cu, Hg, Mo, Ni, Pb, Sb, Sb, V and Zn) was assessed through compliance tests, which classified CS as an inert material. However, pH-dependent leaching tests on heavy metals (Cu, Pb, Zn) and metalloids (As, Sb), revealed that under highly alkaline conditions (pH 12.9), these elements exceed the limits established for hazardous materials, despite their classification as inert waste in the compliance tests. Regarding the mechanical performance, alkaline-activated copper slag pastes achieved a compressive strength of 25 MPa at 28 days.

   3. Recycling Glass Fiber – Thermoset Composites in Cementitious Matrices

      Natalia Lora-Acevedo, Hela Bessaies-Bey, Thierry Sedran, Radhouane Masmoudi, Loic Divet, Arezki Tagnit-Hamou, Laetitia Van-Schoors

      Abstract

      Nowadays composite materials are used in a wide range of industries, including wind energy, aeronautics and transport. With the massive use of composite materials with thermosetting resins and glass fibers, a recycling problem has emerged, since their complex and cross-linked structure does not allow conventional recycling methods. Currently, the main options for their end-of-life are landfilling or incineration with energy recovery. In this study, we evaluate the valorization of glass fiber-thermoset composite waste in concrete mixtures. We study the behavior of a composite waste in an alkaline environment. Thermo-gravimetric analysis and Total Organic Carbon measurements show that the resin mass fraction in the composite waste undergoes degradation, releasing organic products in the solution. Isothermal calorimetry shows that these organic compounds delay the setting time of cement pastes. Ultimately, we find that the composite powder exhibits a pozzolanic activity comparable to other products like fly ash and glass powder.

   4. Impact of Coarse Aggregate Type on the Thermal Conductivity of Concrete

      Ahmed M. Seyam, Rita Nemes, Mohammed Abed

      Abstract

      Understanding the thermal conductivity of concrete is vital for enhancing energy efficiency and thermal comfort in buildings. This study aimed to investigate the relationship between coarse aggregate type and the concrete thermal conductivity at ambient and after subjected to elevated temperatures. Thermal conductivity was measured by analysing the temperature response to heat flow impulses. The results revealed a decreasing trend in thermal conductivity with rising temperatures, attributed to the expansion of air voids within the concrete structure, which improves insulation. Mixtures with quartz and andesite aggregates) exhibited higher thermal conductivity due to the superior heat transfer properties of these materials. Conversely, the mixture with expanded glass aggregate showed lower thermal conductivity, highlighting its insulating properties. Mixtures containing expanded clay and crushed clay bricks demonstrated intermediate thermal conductivity values. The findings underscore that the type of coarse aggregate significantly influences the thermal conductivity of concrete, with distinct differences observed across various aggregate compositions. This study contributes to a deeper understanding of how aggregate selection impacts the thermal performance of concrete, providing valuable insights for optimizing building materials for energy efficiency.

   5. Analysis of Life Cycle Environmental Impact of Artificial Aggregates

      Ilenia Farina, Areebah Abrar, Jehangeer Raza, Narinder Singh, Francesco Colangelo

      Abstract

      Artificial aggregates produced by using waste materials are a suitable alternative to natural aggregates. This work proposes a multi-criteria decision model to select artificial aggregates (AASs) through an experimental process. The integrated environmental (LCA) analysis was carried out for artificial aggregates to choose the most suitable aggregate. Three different mix design were developed by using cement (5%, 10%, 15%), fly ash (80%) (obtained from municipal waste incineration plant), ground granulated blast furnace slag (5%, 10%, 15%), and marble sludge (70%). According to the outcomes the AASs with 80% FA, 5% GGBFS and 15% OPC are the most suitable solution.

   6. The Improvement of the RCC Compactness and Strength for Pavement by the Use of the Marine Sediments of La-Goulette Harbor (Tunisia)

      Mustapha Zdiri, Mongi Ben Ouezdou, Jamel Neji, Nor-Edine Abriak

      Abstract

      The Roller Compacted Concrete (RCC) for pavement is presented as an evolutionary technology in which various types of aggregates are classically used, such as the crushed and the rolled either limestone or siliceous aggregates. The present work comported the study of the use of the marine sediments, in preparing RCC for pavement, as aggregates resulting from dredging of the La Goulette harbor (Tunisia). This approach allows a profit from their contributions to the improvement of the mechanical strengths of the RCC. This study is based on the valorization of the marine sediments, classified as waste and where their storages remain harmful for the environment. Compressive Packing Model (CPM) was used for the formulation of the RCC mixtures. This study also included a mechanical characterization of the material, demonstrating that the use of marine sediments offers significant physical and economic advantages for RCC. The higher compactness and the mechanical strengths, obtained, showed the profitability of such RCC containing sediments.

   7. Thermo-Physical Properties of Concrete Containing PET and Artificial Aggregates Prepared from Industrial By-Products

      Jehangeer Raza, Areebah Abrar, Ilenia Farina, Francesco Colangelo, Narinder Singh

      Abstract

      In this work lightweight concrete was prepared from industrial by-products like municipal solid waste incineration fly ash (MSWI-FA), ground granulated blast furnace slag (GGBFS), marble sludge (MS) and recycled polyethylene terephthalate (PET). The MSWI-FA were pre-washed to reduce the content of hazardous components and then along with GGBFS and cement were used to prepare single-bonded lightweight artificial aggregates via cold bonding. After 28 days curing double-bonded aggregates were prepared by applying another layer of MS, GGBFS and cement. The lightweight concrete prepared from produced lightweight artificial aggregates (LAAs) and small amount of PET in sand form. The small content of PET was used to ensure good mechanical properties and improved thermal performance of concrete. The results confirm that LAAs based concrete samples have shown better thermal performance (up to 25%) but the compressive strength was compromised (up to 30%). Furthermore, the addition of 10% PET further enhances the thermal insulation properties of concrete. Such concrete will bring circularity and sustainability by utilizing various industrial wastes, particularly fly ashes which help to lower use of cement and lead towards lesser greenhouse gas emissions.

   8. The Contribution of Tire Recycled Materials in the Circular Economy of Cement-Based Composites

      Alessandro P. Fantilli, Isabella Bianco, Gian Andrea Blengini, Bernardino Chiaia

      Abstract

      Materials coming from end-of-life tires (so-called Tire Recycled Materials—TRM) can provide a valuable contribution to enhance the circularity of mortars and concretes. Within a cementitious mixture, secondary rubber from end-of-life tires can partially substitute stone aggregates, which is scarce in some areas of the Earth. However, this substitution is not always effective. As the content of rubber increases, both the reduction of strength and the increment of the potential impact on climate change can be observed in cement-based composites. Accordingly, a new assessment procedure, based on the eco-mechanical analysis, is herein proposed for mortars containing TRM. The aim is to increase mechanical performance and the use of secondary materials, as well as to reduce the environmental impacts. As a result, through a suitable combination of both rubber and steel fibers from end-of-life tires, new mortars showing better structural and environmental performances can be introduced.

   9. Valorization of Plastic Bottle Wastes as Pavement Blocks

      Azer Maazoun, Oussema Atoui, Ahmed Siala

      Abstract

      This study investigates the use of polyethylene terephthalate (PET) from plastic bottles as a binder in the production of pavement blocks, aiming to replace conventional cement with melted PET.

      Four formulations were examined. Plastic bottle waste was cut into small pieces and melted at controlled temperatures ranging from 180 °C to 200 °C. The molten PET was then combined with crushed sand (0–5 mm) and clay in varying proportions to create paver block samples. The PET content was fixed at 30%, while the crushed sand proportion was adjusted to 70%, 65%, 63%, and 60% based on the clay addition of 0%, 5%, 7%, and 10%, respectively.

      The produced pavement blocks underwent a series of mechanical and physical tests to assess their performance, including tensile splitting strength, abrasion resistance, and water absorption. For each test, three specimens per formulation were analyzed to determine the optimal composition offering the best mechanical properties. The results demonstrate that pavement blocks incorporating plastic waste and aggregates exhibit promising mechanical performance, comparable to conventional concrete pavers in terms of tensile strength and wear resistance, while significantly reducing water absorption.

      The formulation containing 5% clay achieved a remarkable 93% reduction in water absorption compared to traditional concrete pavers. Microscopic analysis revealed that clay plays a crucial role in filling voids between aggregates, thereby enhancing both cohesion and structural integrity. However, an excessive clay content above 5% adversely affects overall performance.

   10. Recycling of Waste Fresh Concrete as Aggregate Granules

       Katalin Kopecskó, Valentina Sütő-Kreisz, Olivér Czoboly, György L. Balázs

       Abstract

       A significant part of the fresh concrete is returned to the production plants. In our study, we investigated the influence of recycled waste fresh concrete as aggregate granules on the fresh properties, strength of concrete, and transport properties. In this method, the fresh concrete is recycled with its cement paste or mortar fraction. The recyclable aggregate granules were produced using fresh concrete according to the product instructions. This new recycled aggregate must be distinguished from aggregates produced by backwashing fresh concrete or crushing demolished concrete. The recycled aggregate granules were used in increasing doses (5%, 30%, and 50%) according to the reference concrete recipe, and compared with the properties of the reference concrete. The particle size distribution of the original aggregate and the recycled aggregate granules was determined. The sieve analysis resulted in a coarser aggregate for recycled aggregate granules as for the original natural aggregate. Consistency, workability, density, and air content were measured on fresh concrete mixtures. The compressive strength was tested at the ages of 2, 7, and 28 days, and the chloride ion migration test was performed at the age of 28 days. The apparent porosity, water absorption coefficient, and capillary water absorption were also studied. After evaluating the tests, the following conclusions could be drawn: a 5% dosage of recycled aggregate granule does not significantly affect the properties of the concrete. According to the MSZ 4798:2016 standard and its amendments, 5% by weight of recycled aggregates can be used in concrete without any further requirements. The dosages of 30 or 50% also met our expectations, however, future research is needed to study the long-term behavior of concretes made with these recyclable aggregate granules. The innovative material and method allow the returned fresh concrete to be fully recycled, thus reducing the amount of waste concrete. With these achievements, the concrete industry can also move towards a circular economy.

2. Backmatter