Search Results (27)

Supplementary cementitious materials (SCMs) provide a practical solution for reducing greenhouse gas emissions associated with Portland cement production while enhancing the economy, performance, and service life of concrete and mortar. Currently, there is a significant disparity in the availability, supply, and utilisation levels of SCMs worldwide, particularly in South Africa. This paper presents an in-depth analysis of the characteristics and performance of various SCMs, including local availability, factors driving demand, production, and utilisation. The findings indicate that fly ash and limestone calcined clay are the most widely available SCM resources in South Africa, with deposits exceeding 1 billion tonnes each. Fly ash stockpiles continuously increase due to the reliance on coal-fired power plants for 85% of generated electricity and a low fly ash utilisation rate of 7%, significantly below international utilisation levels of 10–98%. Conversely, slag resources are depleting due to the steady decline of local steel production caused by energy and input costs, alongside the growing importation of steel products. Combined, the estimated production of slag and silica fume is about 1.4 million tonnes per annum, leading to their limited availability and utilisation in niche applications such as high-performance concrete and marine environments. Furthermore, 216,450 tonnes of SCM could potentially be processed annually from agricultural waste. In addition to quality, logistics, costs, and other challenges, this quantity can only replace 1.5% of clinker in South Africa, raising concerns about the viability of SCMs from agricultural waste. Based on its findings, this study recommends future research areas to enhance the performance, future availability, and sustainability of SCMs. Full article

Cement production significantly contributes to global CO₂ emissions. Limestone Calcined Clay Cement (LC³)—a mixture of limestone, calcined clay, cement clinker, and gypsum—offers a promising alternative by significantly reducing clinker contents without compromising mechanical performance. This study assesses the environmental and social hotspots of various LC³ mortars produced in Germany, a context not yet explored in previous research. While prior studies have mostly focused on LC³ in concrete applications and in low- to middle-income countries, this is the first to evaluate LC³-based mortar in a high-income, highly industrialized context using both Life Cycle Assessment (LCA) and Social Risk Assessment (SRA) to determine the main environmental and social drivers of this material. The LCA revealed that LC³ mixtures achieve substantial reductions in key impact categories compared to conventional Ordinary Portland Cement (OPC) mixes, including Climate Change (up to 42.6% reduction) and Particulate Matter (up to 15.8% reduction). The SRA highlights significant social risks related to corruption, fair competition, and workers’ rights, including fair wages, discrimination, and safe working conditions. This study underscores LC³ as a promising sustainable solution in cement applications while emphasizing the importance of region-specific assessments to address unique environmental and social considerations. Full article

The environmental impact of cement production is strongly associated with the high clinker content and its corresponding CO₂ emissions. This study examines the performance of low-emission cement mortars incorporating supplementary cementitious materials (SCMs), such as ground granulated blast-furnace slag (GGBFS) and fly ash, which partially replace clinker and contribute to CO₂ reduction. Six cement types (CEM I, CEM II/B-V, CEM II/B-S, CEM III/A, CEM V/A (S-V), and CEM V/B (S-V)) were assessed in 104 mortar formulations using a polycarboxylate-based superplasticizer, under varied curing temperatures (10 °C, 20 °C, 29 °C, and 33 °C). The present study is an experimental analysis of the impact of different plasticising and superplasticising admixtures on the demand for admixtures to achieve high flowability and low air content in cement-standardised mortar for admixture testing. PN-EN 480-1. The results indicate that mortars containing CEM III/A and CEM V/B (S-V) exhibited compressive strengths comparable to or superior to CEM I at 28 days, with strength gains exceeding 60 MPa at 20 °C. Workability retention at elevated temperatures was most effective in slag-rich cements. The plasticizing efficiency of the admixture decreased at temperatures above 29 °C, especially in fly ash-rich systems. The incorporation of SCMs resulted in an estimated reduction of up to 60% in clinker, with a corresponding potential decrease in CO₂ emissions of 35–45%. These findings demonstrate the technical feasibility of using low-clinker, superplasticized mortars in varying thermal environments, supporting the advancement of sustainable cementitious systems. Full article

The construction industry is responsible for 39% of global CO₂ emissions related to energy use, with cement responsible for 5–8% of it. Limestone calcined clay cement (LC³), a ternary blended binder system, offers a low-carbon alternative by partially substituting clinker with calcined clay and limestone. This study investigated the use of waste clay brick powder (WBP), a waste material, as a source of calcined clay in LC³ formulations, addressing both environmental concerns and SCM scarcity. Two LC³ mixtures containing 15% limestone, 5% gypsum, and either 15% or 30% WBP, corresponding to clinker contents of 65% (LC³-65) or 50% (LC³-50), were evaluated against general purpose (GP) cement mortar. Tests included setting time, flowability, soundness, compressive and flexural strengths, drying shrinkage, isothermal calorimetry, and scanning electron microscopy (SEM). Isothermal calorimetry showed peak heat flow reductions of 26% and 49% for LC³-65 and LC³-50, respectively, indicating a slower reactivity of LC³. The initial and final setting times of the LC³ mixtures were 10–30 min and 30–60 min longer, respectively, due to the slower hydration kinetics caused by the reduced clinker content. Flowability increased in LC³-50, which is attributed to the lower clinker content and higher water availability. At 7 days, LC³-65 retained 98% of the control’s compressive strength, while LC³-50 showed a 47% reduction. At 28 days, the compressive strengths of mixtures LC³-65 and LC³-50 were 7% and 46% lower than the control, with flexural strength reductions being 8% and 40%, respectively. The porosity calculated from the SEM images was found to be 7%, 11%, and 15% in the control, LC³-65, and LC³-50, respectively. Thus, the reduction in strength is attributed to the slower reaction rate and increased porosity associated with the reduced clinker content in LC³ mixtures. However, the results indicate that the performance of LC³-65 was close to that of the control mix, supporting the viability of WBP as a low-carbon partial replacement of clinker in LC³. Full article

Concrete and mortar production consumes significant natural resources, leading to environmental concerns and sustainability challenges. Sustainable alternatives, such as industrial byproducts, have been explored to replace clinkers and aggregates. Basalt rock powder (BRP) is a promising option due to its physical and chemical properties, including its better particle size distribution and compatibility with cementitious composites, and studies have highlighted its pozzolanic activity and its potential to improve mechanical properties (compressive strength, flexural strength, and durability). Reusing rock dust as a raw material could transform it into a mineral byproduct, benefiting the new material and reducing waste volumes. This article presents a systematic literature review on the use of BRP in construction materials, conducted using the Scopus, ScienceDirect, PubMed, and Web of Science databases and following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) procedures. The search resulted in 787 articles (up to December 2024) and, after the screening process, 17 met the inclusion criteria. From the selected articles, information regarding the utilization of this waste product; its influence on mechanical properties, pozzolanic activity, and durability; and the sustainability associated with its use was compiled. The risk of bias was low as the search was comprehensive, all the papers were peer-reviewed, and all authors reviewed the papers independently. In conclusion, the studies demonstrate the potential of using BRP as a component of cementitious materials, indicating it as a possible innovative solution to the current challenges in the construction industry. Full article

The production of hydraulic binders, representing the essential constituent part of concrete and mortar, can be associated with high energy consumption and huge CO₂ emissions (at least 2.4 billion tons in 2022). Without appropriate measures, the situation will only worsen. The global annual output of cement stood at 4.4 billion tons of cement, whereas the annual production has been increasing at a rate of ca 5%. In order to significantly reduce CO₂ emissions, the following solutions are most widely used in the world: clinker additives; unconventional fuels; decreased energy-related expenses; and technological innovations. However, these are not sufficient to cut down on greenhouse gas emissions and bring them close to zero. Therefore, the utilization and development of alternative binders denoted by a reduced CO₂ footprint in comparison to that of conventional cement are among the main objectives of building materials manufacturers as well as researchers. This paper reviews obstacles, solutions and alternatives for the fabrication of hydraulic cementitious materials, along with the general principles of the carbonization of binders, such as natural processes and intensified processes, the impact of various parameters on the chemical and physical transformations, as well as the mechanism of interaction of OPC, belite, and blended cement with CO₂. The production of low-lime binders, along with time-optimized carbonation, can significantly improve carbon footprint values. However, due to the huge variety of blended cements, their hardening process by mineral carbonation needs to be investigated extensively and systematically, as it is emphatically dependent on many numerical values and criteria. Environmentally and economically acceptable production can only be achieved on the grounds of the optimized parameters of the entire process. Full article

With the increasing demand for lithium resources and the enhancement of global environmental awareness, how to efficiently and environmentally develop clay-type lithium resources is of great strategic significance for future development. Clay-type lithium slag (LS) is a byproduct resulting from the extraction of lithium from clay-type lithium ores. Its primary chemical constituents include SiO₂ and Al₂O₃, and it exhibits potential pozzolanic properties. Clay-type lithium ore is of low grade, so a large amount of clay-type LS is produced during its production. In this study, calcined clay-type LS, limestone powder (LP), and cement clinker were used as the main raw materials to prepare low-carbon LC³ cementitious materials. The study focused on the effect of clay-type LS and LP on the new mixing properties, mechanical properties, hydration kinetics, and microstructure formation and transformation of the cementitious materials. The findings revealed that incorporating clay-type LS and LP significantly raised the standard consistency water demand of cement and reduced the setting time of the binding material. While clay-type LS and LP initially weakened the mechanical performance of the cement mortar, it enhanced these properties in the later stages. The compressive strength of LC-10 and LC-20 at 180 days exceeded that of the reference by 3.7% and 1.1%, respectively. In addition, the number of micropores between 3 and 20 nm in LC³ cement increased significantly. It showed that the addition of clay-type LS and LP could optimize the pore structure to some extent. According to research, the optimal content of clay-type LS and LP should not exceed 30%. This method not only consumes the solid waste of clay-type LS, but also facilitates the green and low-carbon transformation of the cement industry. Full article

The literature on belitic cement reveals adequate properties for use in mortars: increased workability, greater strength, durability, and a significant reduction in the temperature of clinker synthesis. Therefore, this material has great potential for minimizing the negative environmental impact caused by the cement industry. The scarcity of natural resources has been a major problem, and the valorization of industrial waste could be an alternative in the production of belitic cement. The characterization of by-products has been investigated to improve cement and mortar performance. The presented systematic mapping of the literature aims to identify innovative studies and methods for using industrial waste incorporated into the production of belitic cement. Initially, 150 articles were identified and, after filtering by the inclusion and exclusion criteria, 65 articles were selected. Six different types of belitic cement were identified and diverse waste and formulations were used. The results indicated that 10.7% (7/65) of the studies analyzed the performance of belitic cement, 83% (54/65) used industrial waste in cement formulation, 15.3% (10/65) used belitic cement based on industrial waste in mortar composition, and 33.8% (22/65) reported that the sinthetization temperature of the clinkers was less than 1350 °C, revealing low energy production and low CO₂ emissions during the sinthetization of clinkers. Full article

Autogenously calcined clays from tailings dumps, which are formed by the ignition of the contained residual coal, represent a huge resource of potentially pozzolanic material worldwide. This work presents preliminary studies of samples from the Western coal regions in Germany and investigations on the first industrially produced cement with autogenously calcined tailings concerning its suitability as supplementary cementitious material (SCM). Samples of the tailings materials and blended cements were thoroughly characterized physically, chemically and mineralogically. The reactivity was studied using the R³ test and mortar compressive strength testing. The influence on cement hydration was studied using X-ray diffractometry (XRD) and isothermal calorimetry. The preliminary investigations showed that the material is basically suitable as SCM, as it consists mainly of SiO₂ and Al₂O₃, which partially occurs in X-ray amorphous form and has a low content of impurities, which can impair cement properties such as carbon or sulfur. The R³ reactivity and the relative compressive strength differed significantly depending on the sample. For the industrial cement production trial, low-processed material was used which still contained inert fractions. The average sample showed a relatively low R³ reactivity but still significantly higher than mostly inert materials such as limestone or quartz powder. Calorimetry and XRD investigations on cement pastes showed that the clinker reactions remain basically unaffected by the tailings. Mortar tests showed that the material contributes to strength development at a late age. It can be concluded that the tailings are basically suitable as SCM and, in appropriate blends, the clinker factor and, thus, the CO₂ footprint of cement can be reduced. Full article

In this study, the impact of binder granulometry as well as chemical additives on the early strength and early age stiffness development of eco-efficient mortars with low clinker content and ternary blended cements with high contents of slag and limestone powder was investigated. With regard to granulometry, the particle size distribution of the slag was varied in two steps. In addition, admixtures based on nano-granular C-S-H seeds were used for the acceleration of the hydration reaction. Both the compressive strength at 1d and the in-situ ultrasound pulse velocity for the first 36 h were determined. The granulometric optimization of the slag leads to an improvement in compressive strength of up to 162% in the early phase of the first 24 h. In addition, C-S-H seeding enhanced the hydration reaction mortars as early as 6 h after water addition (at 20 °C). An increase in the dosage level of the C-S-H seeding admixture further resulted in a corresponding increase in early strength, particularly when the clinker content exceeds 30 wt% up to 103%. The proposed combined granulometric and admixture-based approach significantly improves the reaction of the binder in the early phase, so that the clinker factor can be significantly reduced while maintaining a comparable binder intensity. Full article

Agricultural waste availability implies the possibility of recovering energy as biomass. The collateral effect is the production of ashes that, in some cases, have the potential to be reused in the manufacture of cement, mortar, and concrete. This article presents the study of the auto-combustion (unlike all previous studies) of corn (maize) straw (stems and leaves). The auto-combustion temperature was monitored, and the obtained corn straw ash (CSA) was characterized by means of X-ray fluorescence, X-ray diffraction, thermogravimetry, and scanning electron microscopy. Finally, the behavior of ground CSA was analyzed in both the fresh state by measurement of workability on the spreading table and the hardened state by compressive strength measurement on mortars in which 10% of ordinary Portland cement (OPC) was replaced with CSA. These values were compared to both a control mortar (OPC) and a mortar in which OPC was partially replaced with 10% limestone filler. Ashes showed adequate pozzolanic reactivity because, at 90 curing days, the compressive strength of the mortars with 10% replacement of OPC with CSA was practically equal (98% of the strength) to the control mortar without pozzolan replacement. The auto-combustion of biomass is a process that can be easily available, and the results on pozzolanic reactivity of CSA are satisfactory. The auto-combustion could be used by low-income communities to reduce Portland cement clinker use and to recover waste. Full article

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios. Full article

Low-grade limestone (LGL) is not used to produce cement clinker, but this leftover material in cement quarries increases the water demand when used as a filler in concrete production. In this study, the effect of six commercial superplasticizers on the performance of cement mixes containing 35% LGL and 2% gypsum was investigated. The optimal doses of these superplasticizers were found in a range of different water/binder (w/b) ratios by conducting several Marsh cone and mini-slump tests. The addition of a superplasticizer with a higher active solid content produced a maximum cement flow, regardless of the w/b ratios. The LGL-based mortar samples admixed with this superplasticizer obtained a maximum compressive strength of about 36 MPa at the end of 28 days. SEM and XRD results showed the formation of a new calcium-rich mineral in their microstructure. These findings highlight the impact of the type and properties of superplasticizers on the performance of concrete mixes containing LGL as a supplementary cementitious material. Full article

Industrial solid waste is characterized by complex mineral phases and various components. Low-carbon cementitious materials can be prepared through precise regulation based on the material composition and properties of various industrial solid wastes. In this study, electrolytic manganese residue (EMR), carbide slag (CS), and granulated blast-furnace slag (GBFS) were used as alternatives to cement to prepare multicomponent solid waste cementitious materials. The effects of the proportions of EMR and CS on the cementitious activity of GBFS and the activation mechanism of alkali and sulfur were studied. The results showed that with increasing EMR content, the strength first increased and then decreased. At a GBFS content of 20%, CS content of 2%, and EMR content of 8%, the compressive strength was highest, reaching 45.5 MPa after 28 days of curing, mainly because the OH⁻ in CS and SO₄²⁻ in EMR synergistically stimulated the active components in GBFS. Hydrated products such as ettringite and hydrated calcium silicate (C–S–H gel) were generated and interlaced with each other to improve the densification of the mortar. Overall, the proposed system provides an avenue to reduce or replace the production of cement clinker and achieve the high-value-added utilization of industrial solid waste. Full article

The high kaolinite content of metakaolin makes it valuable to other industries, thereby affecting its availability and affordability for the production of limestone calcined clay cement (LC³). This work presents a study on the potential utilization of low-grade clay in place of pure metakaolin in the preparation of LC³ for mortar formulations. CEM I was partially substituted with calcined clay and limestone by 20, 30, 40, and 50 wt.%. The weight ratio of calcined clay and limestone was maintained at 2:1 for all mixes and the water-to-binder ratio was 0.48. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and isothermal conduction calorimetry were used to study the hydration process and products after 28 days. Mechanical and durability assessments of the LC³ mortar specimens were conducted. LC³ specimens (marked LC20%, LC30%, LC40%, and LC50%) trailed the control sample by 1.2%, 4%, 9.8%, and 18%, respectively, at 28 days and 1.6%, 2.3%, 3.6%, and 5.5%, respectively, at 91 days. The optimum replacement of OPC clinker, calcined clay, and limestone was 20% (LC20%). Full article