Development, Characterization, Application and Recycling of Novel Construction Materials

1. Introduction

The construction industry ranks among the most polluting sectors globally. Efforts are underway, guided by international forums and conference resolutions, to reduce CO₂ emissions. Since the onset of the industrial revolution, the growing impact of human activity has become increasingly pronounced, exacerbated by one key indicator: carbon footprint. This footprint is considered a major factor in climate change and is a phenomenon that continues to intensify. According to the Intergovernmental Panel on Climate Change (IPCC), post-2030 temperature increases are projected to range between +1.1 °C and +6.4 °C. In its latest 2023 report, the IPCC proposed mitigation measures such as emission reduction or resource consumption proportioning to limit global warming to +1.5 °C by 2050 [1,2,3]. Thus, at the beginning of the 21st century, humanity faces an unprecedented challenge: How can we ensure sustainability by protecting nature and biodiversity for future generations while simultaneously meeting the current growing demands for energy, materials, and resources? More recently, between 2020 and 2022, the EU launched its new climate action plan, unveiling ambitious initiatives throughout the entire lifecycle of products. This plan includes product design, promotes circular economy processes, and encourages sustainable consumption. Known as the “climate package”, this approach aims to minimize waste proliferation and conserve resources for as long as possible [4]. Resource efficiency and environmental protection have become major concerns in addressing climate issues. Global economic growth and the rapid development of cities, which are responsible for approximately 80% of global CO₂ emissions [5], significantly increase the demand for materials, natural resources, and energy. The need for resources such as water, land, energy, and minerals has never been higher. There is an urgent need to enhance resource efficiency and increasingly reuse building materials [6,7,8] by adopting a circular economy approach. The UN sustainable cities program, aligned with the Paris Agreement (COP 21, 2015), proposes an action plan that emphasizes integrating environmental concerns into urban planning and management: “Mainstreaming environmental concerns in urban planning and management” [1,9,10]. Finding solutions for wastes, i.e., secondary materials generated from industries, infrastructure, and construction activities, has become imperative.

Concrete, predominantly made from ordinary Portland cement (OPC), is the most widely used building material. Each constituent in OPC production impacts the environment, leading to sustainability concerns. The manufacture and use of cement and concrete significantly affect the environment, driven by infrastructure development, building operations, and CO₂ emissions, which constitute 7–8% of global emissions [11]. Consequently, the construction industry faces pressure to develop eco-friendly alternatives. As the environmental issues associated with OPC have become evident, numerous studies are seeking new binding materials that can match the cost and performance of currently used construction materials. Also, currently, alternative binders based on sustainable materials, e.g., geopolymers, seem to be preferred to conventional cementitious materials. Scientific studies have highlighted several key reasons why geopolymers are considered promising alternatives to traditional construction materials [12]. The concrete production process is notably energy-intensive, with studies by Muhamad et al. [13] and Shirkani et al. [14] highlighting the cement sector’s significant contribution to global carbon dioxide emissions and climate change.

Hence, the utilization of binders made from byproducts and alternative materials, like metakaolin, fly ash, sludge ash, blast furnace slag, silica fume, fiber glass, and waste rubber, is strongly encouraged, as their effectiveness is well documented [15,16,17,18]. This approach addresses the previously mentioned environmental concerns and enhances the durability of structures exposed to harsh conditions [16]. For this purpose, several solutions have been envisaged in the construction sector involving the use of greener and more innovative materials, for example, using alternative fuels for material combustion in cement kilns and enhancing decarbonization through replacing some raw materials (such as calcium carbonate) with other products that are already decarbonated and confer the same chemical properties.

2. An Overview of Published Articles

Recent advancements in the field of cementitious materials have focused on enhancing mechanical properties, sustainability, and durability through innovative approaches, such as incorporating waste materials, innovative additives, and recycled aggregates. One notable approach involves using waste rubber in cement-bound aggregates (CBAs) to reduce their traditionally high stiffness. By developing prediction models for compressive strength and the modulus of elasticity based on non-destructive ultrasonic pulse velocity (UPV) tests, it was found that incorporating rubber not only reduces stiffness but also simplifies the prediction of mechanical properties, especially compressive strength, which does not significantly depend on the curing period [19].

Additionally, the incorporation of solid–solid phase change materials (SS-PCMs) into cementitious composites was studied due to their heat storage capabilities. While increasing porosity and reducing mechanical strength, SS-PCMs enhanced thermal insulation and shrinkage resistance, demonstrating superior stability over multiple thermal cycles despite their fast carbonation kinetics due to their high porosity. Research on concrete with crystalline hydrophilic additives (CAs) has focused on enhancing resistance to freeze–thaw cycles. Standard air-entraining agents have been found to be effective, but CAs, especially at a 1% dosage, can improve internal damage resistance.

Another innovative study investigated the role of moisture in CO₂ diffusion and particle cementation in carbonated steel slag. Optimal moisture content was crucial for balancing CO₂ diffusion and particle cementation, enhancing the compressive strength and carbon sequestration capacity of the slag, and thus contributing to the development of effective carbon sequestration materials. These researchers also analyzed the mechanical performance of eco-concrete using recycled concrete aggregates. They found minimal strength decreases and increased permeability with higher concentrations of recycled content, demonstrating the viability of incorporating recycled aggregates into eco-concretes. In examining low-carbon cementitious materials, the effects of external sulfate attack (ESA) were assessed. It was found that a mix of CEM I, slag, and metakaolin exhibited the highest resistance to sulfate attack, while a 100% CEM I mix deteriorated significantly. This highlights the importance of using supplementary cementitious materials to increase durability in sulfate-rich environments [20].

The use of flaxseed mucilage (FM) as a bio-admixture in ordinary Portland cement was explored. FM delayed the time taken for the cement to set but did not hinder its hydration properties. It increased the cement’s porosity and carbonation while reducing its bulk density and thermal conductivity. FM’s hygroscopic properties and controlled water release improved the mechanical properties of the cement over time, suggesting that it may confer potential self-healing capabilities. In another study, vegetal fabric-reinforced cementitious matrix (FRCM) sandwich panels were investigated for their sustainable advantages. When using vegetal fabrics like hemp and sisal in combination with extruded polystyrene cores, these panels showed competitive strength compared to synthetic fibers, with steel connectors providing enhanced stiffness and shear strength [21].

The recycling of 3D-printed concrete waste as aggregate in new concrete mixtures was also explored. It was found that replacing conventional aggregates with recycled ones from 3D-printed waste at a ratio of up to 67% did not significantly reduce the compressive strength of the concrete and sometimes even improved it, particularly in higher-strength classes like C40/50.

These studies collectively highlight significant advancements in the field of cementitious materials, with the goal of enhancing mechanical properties, sustainability, and durability.

3. Conclusions

By exploring the incorporation of waste materials, innovative additives, and recycled aggregates into construction materials, these research efforts contribute to the development of more resilient and environmentally friendly construction materials. The sustainable alternatives considered include waste rubber, vegetal fabrics, and recycled aggregates, which could all be used to enhance materials. Innovations like solid–solid phase change materials, crystalline hydrophilic additives, and low-carbon cementitious materials improve the durability and performance of construction materials. Overall, these advancements aim to facilitate the creation of eco-friendly construction materials.