This research studies the use of a fractional coarse aggregate replacement product (PA). PA is a unique blend comprised of recycled plastics, glass, and minerals; all collected from the waste stream. The use of PA and other similar products may contribute to reducing plastic waste in the waste stream. To test the feasibility of PA as a partial, natural aggregate replacement, four different mixtures of concrete were batched and tested. The concrete mixtures were based on the standard commercial interior normal-weight concrete mixture. This is a non-air-entrained mixture, provided by a local concrete batching plant (MCM), with a design strength of 4000 psi (27.6 MPa). The four concrete mixtures tested were a control mixture with no variations to the original mixture design as well as three mixtures with 15%, 30%, and 45% coarse aggregate replacement by volume. The compression strength, tensile splitting strength, modulus of rupture, and density of the concrete are examined. The focus of the paper is the concrete compressive strength because it is the primary determining factor in concrete design. Fresh concrete properties and hardened concrete properties were examined and recorded. Slight changes to the overall fresh concrete properties of workability, density, and slump were recorded. The hardened concrete properties include compression, tensile splitting, and modulus of rupture. The results of the compression tests show a strength proportionally decreased with the percent increase in PA replacement – 15% replacement with an 18.1% decrease, 30% replacement with a 35.6% decrease, and a 45% replacement indicated a 45.3% decrease at the 28-day test. The results of the tensile splitting tests and modulus of rupture tests both indicate similar results of a decrease in strength as the replacement rate of PA increased.

Portland cement concrete has shown great potential for recycling different waste materials. Solid waste incorporated concrete (SWC) is considered to have positive environmental advantages. However, the utilization of solid wastes may negatively impact the mechanical performance and durability of concrete. Therefore, any change in the performance metrics of SWC should be accounted for in the comparative life cycle assessment (LCA). This article will review the functional equivalency with respect to the mechanical performance and durability metrics for SWC incorporating four main streams of solid wastes; recycled concrete aggregate, municipal solid waste incineration ashes, scrap tire rubber, and polyethylene terephthalate. It will be shown that while in most cases, SWC may have an inferior compressive strength and/or durability pre-treatment, sorting, and appropriate replacement rate of the solid wastes may solve the problem and make SWC functionally equal to the conventional concrete. Moreover, some types of SWC such as those incorporating scrap tire rubber and polyethylene terephthalate may be more advantageous if used in specific applications where dynamic loads are prevalent given their superior impact resistance. Finally, the article will discuss new insights into defining the functional unit based on the performance and application of SWC to conduct a reliable LCA.

Concrete has played a pivotal role in shaping the modern world’s infrastructure and the built environment. Its unparalleled versatility, durability, and structural integrity have made it indispensable in the construction industry. From skyscrapers to long-span bridges, water reservoirs, dams, and highways, the ubiquitous presence of concrete in modern society underscores its significance in global development. As we stand at the crossroads of environmental awareness and the imperative to advance our societies, the sustainability of concrete production and utilization is becoming a new engineering paradigm. The immense demand for concrete, driven by urbanization and infrastructure development, has prompted a critical examination of its environmental impact. One of the most pressing concerns is the substantial carbon footprint associated with traditional concrete production. The production of cement, a key ingredient in concrete, is a notably energy-intensive process that releases a significant amount of carbon dioxide (CO2) into the atmosphere. As concrete remains unparalleled in its ability to provide structural functionality, disaster resilience, and containment of hazardous materials, the demand for concrete production is increasing, while at the same time, the industry is facing the urgency to mitigate its ecological consequences. This special publication investigates the multi-faceted realm of concrete sustainability, exploring the interplay between its engineering properties, environmental implications, and novel solutions, striving to provide an innovative and holistic perspective. In recent years, the concrete industry has witnessed a surge of innovation and research aimed at revolutionizing its sustainability. An array of cutting-edge technologies and methodologies has emerged, each offering promise in mitigating the environmental footprint of concrete. Notably, the integration of supplementary cementitious materials, such as calcined clays and other industrial byproducts, has gained traction to reduce cement content while enhancing concrete performance. Mix design optimization, coupled with advanced admixtures, further elevates the potential for creating durable, strong, and eco-friendly concrete mixtures. Concrete practitioners will gain an advanced understanding of a wide variety of strategies that are readily implementable and oftentimes associated with economic savings and durability enhancement from reading these manuscripts. The incorporation of recycled materials, such as crushed concrete and reclaimed aggregates, not only reduces waste but also lessens the demand for virgin resources. Furthermore, the adoption of efficient production techniques, along with the exploration of carbon capture and utilization technologies, presents an optimistic path forward for the industry. This special publication aspires to contribute to the ongoing discourse on concrete sustainability, offering insights, perspectives, and actionable pathways toward a more environmentally conscious future.

This work investigates the potential of recycled carbon-based materials, obtained from industrial by-products, for the production of multifunctional cement-based composites (MCC) with self-sensing behavior, usable in structural health monitoring (SHM) systems. As recycled materials, used foundry sand (UFS) and recycled carbon fibers (RCF) have been chosen, whereas graphene nanoplatelets (GNP) and virgin carbon fibers (VCF) have been selected as reference industrial fillers and fibers, respectively. Their effects on OPC-based mortars have been tested in terms of mechanical strength (compressive, flexural), durability (water absorption), microstructure (porosity), and electrical and piezoresistive behavior (resistivity in static and under-load conditions). The results show that the combination of recycled fillers-fibers gives the best results in terms of workability, microstructure, strength, and durability. The worst compressive performances obtained with GNP are related to its hydrophobicity and the related problems in mixing. On the other hand, mixtures with UFS show a low electrical conductivity, but a high sensitivity to deformation (electrical strain-sensing). High-carbon by-products could be a functional, low-cost, and eco-friendly solution to produce high-performance and conductive concretes for self-monitoring systems.

The recycling of waste materials from the construction sector represents an opportunity for environmental protection, to save expensive landfill costs, and promote sustainability. The increased interest in the use of recycled materials is seen in several European countries with the production of concrete using granulates from demolition material. In Switzerland, the SIA 2030 standard defines recycled concrete based on a minimum percentage of 25% recycled aggregates to be added. This research focuses on the possibilities of producing high-quality recycled concrete, starting from high-quality cementitious material, i. e. concrete. The original material with known properties was demolished and used as aggregates to replace the natural aggregates. Fresh, hardened, and durable properties of concrete were evaluated on blends containing 25, 50, and 100% recycled aggregates. At early stage (2 days), the lowest value of compressive strength was already above 15 MPa for the blend with 100% recycled aggregates. Most of the recycled concrete satisfies the main mechanical and durability features, in particular with the addition of 25 respectively 50% of the recycled aggregate component.