To lower the carbon footprint associated with the cement industry, a detailed understanding of the available conventional raw materials and identification of new and emerging non-conventional raw materials is crucial. This review paper critically examines recent scientific literature on the origin, processing, properties, and utilization of conventional and potential alternative non-conventional raw materials available in most Nordic countries (Finland, Sweden, Norway, and Iceland) in the development of low-carbon concrete. The primary raw materials that have generated significant interest are clay minerals, limestone, and volcanic pozzolans. In addition, apart from blast furnace slag and fly ash that has been widely studied and almost fully utilized as secondary raw materials in low-carbon concrete, ongoing research is considering a much wider array of by-products and waste materials as potential alternative non-conventional raw materials. These materials are often available in high volumes and originate from different industries in the Nordics such as metallurgical (steel slags, fayalitic slags, foundry sand, bauxite, goethite, and jarosite residues etc.), mining (waste rock and mining residues), construction and demolition (mineral wools and crushed concrete), energy (fly ashes, peat ashes, biomass ashes, waste incineration ashes and slags), forest (wood ashes, green liquor dregs and other forest residues), and chemical (phosphogypsum). Depending on the by-product, they may require different pretreatment and beneficiation processes to enhance their suitability and performance as raw materials for low-carbon concrete. While most of these materials have been investigated as potential construction materials with promising results, future research and development efforts are necessary to better understand their impact on cement and concrete properties. Overall, this review provides valuable insights, highlights the latest developments, and provides recommendations for the scientific and industrial community on the uptake of a wider range of alternative raw materials in cement and concrete.

This study investigates the physical transformations and assesses the performance of blended-cement concretes exposed to temperatures ranging from ambient to 800°C. Three different grades of cement: 32.5, 42.5, and 52.5, with various contents of ground granulated blast furnace slag (GGBFS), were employed in this research. The primary focus is on understanding how variations in cement-slag ratios impact the structural characteristics of concretes exposed to elevated temperatures. Through a series of mechanical tests and matrix analysis, we examined the response of concretes incorporating supplementary cementitious materials to high temperatures. The study demonstrated that slag-cement blends exhibit superior mechanical performance compared to the conventional concrete reference sample. Notably, after exposure to 400°C, the compressive strength of the blends showed significant improvement. The results contribute to enhancing the understanding of the thermal behavior and overall performance of environmentally conscious concrete mixes in challenging conditions.

Portland cement (PC) production accounts for about 8 % of global CO2 emissions. As the demand for cement grows, sustainable alternative raw materials for cement production are essential for reducing the impacts of its production. Process residues from industrial processes like mine tailings, metallurgical slags, incinerated municipal solid wastes (MSWI), glass industry wastes, and Kraft pulp mill wastes are being studied as suitable raw materials for clinker production. These materials contain CaO, SiO2, Al2O3, and Fe2O3, which are required for the formation of tricalcium silicate (C3S, alite), dicalcium silicate (C2S, belite), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF) clinker phases. However, these raw materials may contain impurities such as alkali oxides and heavy metals, which can significantly influence the clinkering process. While alkali oxides tend to lower the eutectic temperature, heavy metals can modify phase stability and hinder the formation of essential clinker phases. This review examines whether these residues are chemically and mineralogically suitable for alternative raw materials. It examines their impact on phase transformations, reactions, environmental sustainability, hydration and performance of the resultant cement. Process residues in clinker production present challenges and opportunities, affecting hydration, workability, and setting times. However, research remains limited to the combined effects of multiple residues on clinker reaction kinetics, durability, heavy metal stabilization, and life cycle impacts.

Construction and demolition waste (CDW) puts significant pressure on landfills and natural resources worldwide. Although partial substitutions of Portland cement (PC) with various recycled materials have been reported, a complete (100 %) replacement using recycled concrete remains problematic. In the present study, a novel binder was produced entirely from recycled concrete fines (RCF), while recycled aggregates were incorporated to replace virgin aggregates. High-energy grinding in a planetary ball mill was applied to the RCF fraction below 150 µm. Particle size reduction occurred after grinding, resulting in a decrease in d50 from 139 μm to 3.18 μm. The intensity of the X-ray diffraction (XRD) peaks corresponding to muscovite, microcline, and portlandite decreased significantly. On the other hand, quartz was only slightly affected. Activated RCF was used as a 100 % PC replacement in paste and concrete mixes. Compressive strengths of approximately 20 MPa were obtained after 28 days in laboratory tests for concrete with w/c equal to 0.6. A preliminary life cycle assessment (LCA) was performed to evaluate the environmental impacts, focusing on carbon emissions and resource depletion. The LCA results suggested over 90 % reduction in CO2 emissions compared to traditional cement-based mixes. Even at the laboratory-scale milling with high energy consumption per 1 kg of RCF, the impacts correspond to 50 % of traditional concrete (TC). Benefits remain significant over short transporting distances of the processed recycled ingredients; however, resource depletion exceeds TC after about 200 kilometers, and carbon emissions go beyond TC after approximately 800 kilometers.

In recent years, substantial progress has been achieved in the development of multifunctional cement-based composites, targeting improved energy efficiency and environmental sustainability while minimizing material depletion. Leveraging the high thermal capacity of these materials facilitates controlled heat storage and release, providing versatile applications in renewable energy management and heat regulation, influencing structural integrity and long-term resistance. Recent research has integrated phase change materials (PCMs) into these composites to harness their superior thermal energy density. This comprehensive review examines the latest experimental research findings on these hybrid materials, emphasizing their thermo-physical behaviour and influence on structural properties and durability. Furthermore, it provides an overview of PCM characteristics and their integration into cement-based matrices. It critically analyses the interaction between PCMs and the cement matrix, explaining effects on structural performance, hydration processes, and freeze–thaw mechanisms. Furthermore, the paper explores recent experimental techniques and protocols for measuring and assessing the structural and thermo-physical properties of these composites. By identifying key trends, the review aims to provide valuable insights into the design and optimization of cement-based composites with PCMs, ultimately enhancing energy efficiency and resource conservation.

The EU Bioeconomy Strategy underscores the importance of fostering a shared understanding of the shift to a bioeconomy and raising awareness of the diverse biomass demand. Since concrete is a globally prevalent material with a substantial environmental impact, it presents an enticing opportunity to integrate biomass products. Particularly, in the context of the burgeoning interest in digital concrete manufacturing, the use of bio-based cementitious “ink” could offer a promising resolution to the environmental challenges faced by the construction sector. This paper examines the current trends in substituting traditional concrete components with bio-based materials, such as bio-binders and bio-admixtures, for use in 3D printing technologies. Natural Language Processing (NLP) methods are employed to extract features from a substantial number of published documents automatically. This process aids in identifying the most frequently occurring bio-based ingredients and their biomass sources. Latent Dirichlet Allocation (LDA) is utilized to perform topic modeling and unveil underlying patterns within the corpus. A comprehensive discussion of both current and potential future developments is conducted. 

Frost durability, a critical parameter for concrete, especially in harsh exposure regions, has been extensively researched, with almost four thousand papers published since the 1970s. However, a systematic mapping of this research is yet to be explored. This paper presents a novel approach based on Natural Language Processing (NLP) and machine learning to semi-automatically analyze the existing literature on frost durability of cementitious materials. The aim is to identify research gaps and provide insights for future work, offering a comprehensive understanding of the freeze and thaw (FT) research area. Data sets containing academic abstracts on FT tests have been created, and the identified articles are topically structured using a latent Dirichlet allocation (LDA) topic modeling approach. The publication volume associated with each topic over time has been quantified, providing an overview of the research landscape. The results show that NLP and t-SNE effectively review large volumes of technical text data, identifying 12 dominant themes in FT research, such as mechanical properties and material composition. Over recent decades, there has been a shift from focusing on structural performance to emerging topics like cracking and Supplementary Cementitious Materials (SCMs). Additionally, t-SNE and K-means clustering revealed four main clusters, suggesting future research should focus on the FT durability of eco-friendly materials, accelerated testing, and enhanced FT durability materials. These findings not only facilitate the identification of gaps and opportunities for future work but also have practical implications for developing more durable and sustainable concrete.

The study investigates the influence of multi-walled carbon nanotubes (MWCNTs) on the macro- and microstructure of cement paste (CP) subjected to thermal shock conditions. CPs with 0–0.3 % MWCNTs content, exposed to a sudden temperature load in a range 50–600 °C, were analyzed in terms of mechanical properties, chemical and phase composition, air pore structure, and microstructure of cement hydration products (Si/Ca, Al/Ca, portlandite, unhydrated part of cement). The research found the optimum MWCNT range to be 0.05–0.1 %, enhancing CP's thermal performance by strengthening cement hydration products and their cohesion, by more the nucleation effect than bridging effect. With the application of MWCNTs, the density of the solid cement phase increased, and the amount of the unhydrated part of cement decreased by up to 21.5 %, at 0.1 % MWCNTs content. Unfortunately, the increase in the MWCNTs content resulted in an increase in the pore volume in the worst case, up to 12.7 %, but it did not negatively affect the strength parameters. The MWCNTs effect caused an increase in tensile strength (fcf) by up to 41.0 % at temperatures above 400 °C, where in the most favorable case improvement in compressive strength reached 16.7 %. The study showed that MWCNTs as an admixture to cement composites is suitable for environments where there is a high variability in terms of thermal loads.

Concrete's ability to auto-repair the cracks reduces the need for maintenance and repair. Autogenous self-healing is an intrinsic property of concrete highly dependent on the binder composition. The urgent necessity to decrease CO2 emissions of concrete by replacing cement with “greener” materials provides challenges and opportunities for self-healing cementitious materials. This research aims to verify the self-healing behavior of environmentally friendly multi-component binders. An experimental study is conducted to test the effect of binder composition-related parameters (e.g., phase composition, porosity) and crack geometry on the self-healing efficiency of the “green” mortars. Cementitious materials with 50 wt.%cement replacement with limestone powder blended with fly ash, blast furnace slag, and silica fume are investigated. Sorptivity change, compressive strength regains, and crack closure after self-healing are used to quantify the self-healing efficiency. Quantitative analysis and correlations between chemical composition/microstructural features, geometrical crack characteristics, and self-healing measures are investigated. The results indicate that “green” binder composition affects the self-healing mechanism leading to different levels of performance recovery. Some SCMs-limestone binder formulations enable a better self-healing efficiency than pure OPC or OPC/limestone cementitious materials, presumably due to a synergistic effect between the limestone and the mineral additions. Correlation analysis indicated that geometrical complexity characterized by fractal dimension and tortuosity of the crack does not affect the external crack closure, whereas the fractal dimension and maximum crack width are correlated with the internal crack healing.

Autogenous self-healing of post-fire damaged concrete enables structure performance auto-recovery leading to reduced repair costs, less generated waste, and lower CO2 emissions. In this paper, to improve the efficiency of this process and understand the underlying mechanism, the self-healing of 0.1 wt% MWCNT-modified and pure cement paste subjected to novel environmental stimulators was tested. High-temperature damage was induced at 200 °C and 400 °C, followed by a self-healing cyclic treatment with water, a mixture of water with phosphate-based retarding admixture, and limewater. The self-healing efficiency of the proposed solutions were compared based on crack closure, strength regains, porosity, and chemical composition changes. The surface crack closure after 200 °C varied between 33% and 60%, whereas for 400 °C, only retarding admixture exposure obtained over 50% crack closure and the most considerable decrease in average crack width of 33% for MWCNT-modified paste. The highest values of compressive strength recovery, equal to 18% and 14%, exceeding the intact specimen's compressive strength, were observed for the MWCNT-modified paste healed in water and limewater. Water exposure with an extended wetting phase enhanced the compressive strength recovery of the MWCNT-modified materials. Strong (r = 0.87) and moderate (r = 0.52) positive correlations were observed between temperature loading and compressive and flexural strength recovery parameters, respectively. Higher porosity and interconnected crack network, caused by high temperature, facilitated the self-healing process. Porosity changes before and after healing were pronounced in contrast to the amount of unhydrated cement, which did not exhibit noticeable changes. The healing mechanism included three processes: calcite formation, further hydration inside the cracks, and rehydration of the bulk cement paste.Previous article in issue