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During shield tunnel construction, waste mud is a significant source of urban construction waste. However, the disposal of waste mud has always been a challenge in engineering. Addressing the challenge of harmlessly disposing of, or repurposing, mud cakes formed after pressure filtration of shield mud remains a pressing issue for many cities. To address the challenge of shield mud disposal and explore the utilization technology of this resource, this study focuses on shield mud obtained from the Shenzhen subway tunnel. Calcined shield mud powder (CSMP) was prepared by activating its potential pozzolanic properties through a calcination process. Compressive strength tests revealed that, while CSMP exhibits some pozzolanic activity, its performance is limited. When 30% of the cement is replaced, the mortar's maximum strength activity index (SAI) is only 82.6%, which makes it unsuitable as a supplementary cementitious material for concrete applications. At the same time, CSMP was also evaluated as a partial replacement for fly ash in the formulation of synchronous grouting materials, with performance metrics including fluidity, bleeding rate, hardening rate, setting time, and compressive strength systematically tested. The experimental results showed that, while CSMP reduces the fluidity of grouting, it significantly improves volumetric stability, shortens setting time, and enhances mechanical performance. Compared to the fly ash used in the study, CSMP exhibited better pozzolanic reactivity, promoting the formation of C-S-H and C-A-S-H phases, optimizing the pore structure, and increasing the density and overall performance of the grouting material. When the substitution rate is below 60%, the performance of grouting meets standard requirements, indicating the strong feasibility of utilizing CSMP to replace fly ash in synchronous grouting materials. [ABSTRACT FROM AUTHOR]

Concrete is an essential construction material, and infrastructures, such as bridges, tunnels, and power plants, consume large quantities of it. Future infrastructure demands and sustainability issues necessitate the adoption of non-conventional supplementary cementitious materials (SCMs). At the same time, global labor shortages are compelling the conservative construction sector to implement autonomous and digital fabrication methods, such as 3D printing. This paper thus investigates the feasibility of using oil shale ash (OSA) as an SCM in concrete suitable for 3D printing, and collision milling is examined as a possible ash pretreatment. OSA from four different sources was collected and analyzed for its physical, chemical, and mineralogical composition. Concrete formulations containing ash were tested for mechanical performance, and the two best-performing formulations were assessed for printability. It was found that ash extracted from flue gases by the novel integrated desulfurizer has the greatest potential as an SCM due to globular particles that contain β-calcium silicate. The 56-day compression strength of concrete containing this type of ash is ~60 MPa, the same as in the reference composition. Overall, collision milling is effective in reducing the size of particles larger than 10 μm but does not seem beneficial for ash extracted from flue gasses. However, milling bottom ash may unlock its potential as an SCM, with the optimal milling frequency being ~100 Hz. [ABSTRACT FROM AUTHOR]

Conventional cement production is a major source of carbon dioxide emissions, which creates a significant environmental challenge. This research addresses the problem of how to reduce the carbon footprint of cement paste production using agricultural and industrial waste by-products, namely wheat straw ash (WSA) and silica fume (SF). Currently, accurate models that can predict the mechanical properties of cement pastes incorporating these waste materials are lacking. To fill this gap, our study proposes a model based on response surface methodology and Box-Behnken design, designed to predict the strength of cement pastes with partial substitutions of WSA and SF. Through mechanical and characterization tests, the model demonstrated high accuracy in predicting the strength of the pastes, validated with three mixes, which showed maximum errors of less than 6% at different ages (7, 28, and 56 days). Response surface analysis revealed that replacing cement with 0–20% WSA and more than 5% SF can effectively reduce the carbon footprint by maximizing waste incorporation. This model allows for the calculation of optimal cement substitution levels based on the required strength, thus promoting sustainability in the construction industry through the use of local waste/resources. [ABSTRACT FROM AUTHOR]

Stabilization/Solidification (S/S) using Portland cement is a common soil remediation technique for heavy metal-contaminated sites. However, due to the hindrance of cement hydration by heavy metals (HMs) and the high CO2 emissions from cement production, efforts have been made to reduce cement consumption. Supplementary cementitious materials (SCMs) present an efficient alternative for this purpose. This study investigates the impact of hydrochar and modified hydrochar as SCMs for remediating soils contaminated with Zn, Pb, and Cd. Forty treated soil samples were evaluated using unconfined compressive strength (UCS), pH, Toxicity characteristic leaching procedure (TCLP), and sequential extraction procedure (SEP) tests, and statistical analysis was conducted to assess the effects of binder content, hydrochar dosage, and hydrochar type. Results show that substituting cement with hydrochar or modified hydrochar reduces UCS by 10–40%, with hydrochar having a greater negative impact than modified hydrochar. pH values ranged from 6.98 to 12.64, facilitating HMs precipitation. In heavily contaminated samples, hydrochar or modified hydrochars significantly decreased the Zn, Pb, and Cd TCLP values by 55%, 63%, and 50%, respectively. In moderately contaminated samples, the reduction was slight for Zn and Pb, with no significant change for Cd. SEP test results indicated that hydrochar or modified hydrochar in cement improves the transformation of the acid-soluble fraction to the residual fraction of Zn and Pb, but not for Cd-contaminated soil samples. Overall, these findings suggest that incorporating hydrochar or modified hydrochar as SCMs in cement contributes to reducing cement usage and CO2 emissions while enhancing the stabilization efficiency of certain heavy metals in contaminated soils. [ABSTRACT FROM AUTHOR]

Test results were obtained for normal concrete, concrete with partial replacement of cement by Metakaolin, concrete with partial replacement of cement by Metakaolin and Steel Slag, accelerated curing results of concrete with partial replacement of cement by Metakaolin. For Compressive Strength cubes of size 100 mm x 100 mm x 100 mm were cast and tested at 7, 21, and 28 days of curing period. The addition of 15% of Metakaolin as replacement to cement shows optimum enhancement in properties of concrete, with increase in Strength parameters as high as 48% in comparison to control mix. Hence Metakaolin up to 15% replacement can be utilized as a partial replacement to cement in binary blend as well as ternary blend with Steel Slag for high Strength, accelerated Strength and high durability concrete. [ABSTRACT FROM AUTHOR]

This study explored the potential of natural red clay as a supplementary cementitious material (SCM) to reduce greenhouse gas emissions and costs associated with the cement industry. Given that cement production is one of the largest contributors to global greenhouse gas emissions, developing sustainable alternatives is of paramount importance. Recognizing the environmental impact of cement production, this research investigates the substitution of conventional cement with raw red clay, aiming to balance mechanical performance with enhanced thermal properties and a lower environmental footprint. Through chemical characterization using X-ray Fluorescence (XRF), along with comprehensive mechanical and thermal performance testing, this study identifies the dual role of raw clay in mortar. It was found that incorporating up to 5% by weight of raw clay slightly impacted compressive strength while significantly improving thermal conductivity and diffusivity, cost-efficiency, and environmental sustainability, making it an appealing option for structural applications requiring high mechanical resistance. Conversely, a higher proportion of clay (beyond 5%) compromises compressive strength, but further enhances thermal properties and environmental benefits, suggesting its suitability for applications where low mechanical resistance is acceptable. This investigation highlights the viability of raw clay as a promising SCM, offering a pathway to more sustainable construction materials without the need for energy-intensive processing, thereby contributing to the reduction in the construction sector's carbon footprint and energy demand. [ABSTRACT FROM AUTHOR]

The cement industry significantly contributes to global CO2 emissions, posing several challenges for a future low-carbon economy. In order to achieve the target established by the European Sustainable Development Goals of reaching carbon neutrality by 2050, the European Cement Association (Cembureau) has devised a comprehensive roadmap based on five key approaches, referred to as the 5C strategies. Portland clinker is one of the crucial concerns, since its production emits over 60% of the cement manufacturing emissions. Therefore, supplementary cementitious materials (SCMs) to partially replace clinker content in cement have gained significant attention in providing alternatives to traditional clinker in cement production. This paper evaluates the potential of Portuguese calcined clays (CCs) as viable substitutes for clinker to enhance sustainability in cement manufacturing. More than 50 clays were characterised through chemical and mineralogical analyses to assess their reactivity and suitability for calcination using the strength activity index (SAI), along with XRD, XRF, and TGA techniques. This study investigated the calcination conditions that provide the best clay reactivity, which were subsequently used for calcination. This investigation is part of a project to evaluate the behaviour of calcined clays through mechanical, hydration, and durability properties. The findings indicate that Portuguese calcined clays exhibit promising pozzolanic activity. Furthermore, these clays could significantly reduce CO2 emissions and raw material consumption in cement production. This research underscores the potential of local calcined clays as a sustainable clinker substitute, promoting eco-friendly practices in the construction industry. [ABSTRACT FROM AUTHOR]

Abstract The concept of sustainability has become a crucial concern for safeguarding the planet. The current research has focused on developing affordable and eco-friendly mortar by using industrial wastes. This study explores the use of fly ash (FA) and ground granulated blast furnace slag (GGBFS), byproducts of steelmaking and coal burning, in mortar production. It examines their impacts on the compressive strength and setting times, when utilizing varying proportions of the materials. The study also evaluates water requirements for the workability, thus demonstrating the sustainability of these waste products in construction. The cementitious materials were employed in finely ground form and were replaced with further tertiary mixes including both supplements at 10%, 30%, and 50% of each. The mixtures were allowed to cure for 7, 14, and 28 days by immersion in water. The results showed improvements in the compressive strength of mortar samples incorporating FA and GGBFS at various curing ages. However, the water requirement and workability of mortar samples were altered as a result of utilizing these supplementary cementitious materials (SCMs). These findings will serve as a standard for environmentally responsible mortar using GGBFS and/or FA as SCMs.

This study focuses on investigating the chemical degradation characteristics of cementitious barriers used in low- and intermediate-level radioactive waste repository by reactive transport modeling. The impact of the blending with supplementary cementitious materials (SCMs) in the barriers on the chemical degradation was evaluated to find the optimum barrier design. A number of different barrier designs were examined by replacing ordinary Portland cement (OPC) by SCMs (i.e., fly ash, silica fume, and blast-furnace slag). The simulation results showed that silica fume blended barrier has better durability against chemical degradation by rainwater compared to fly ash or blast-furnace slag blended barriers. In addition, the chemical durability of silica fume-based barrier increased with increasing replacement level up to about 20 %. It seems that the amount of formed calcium silicate hydrate (CSH) in the initial cement-based barrier highly affects the overall chemical durability. The newly developed reactive transport model demonstrated its capability for understanding the barrier performance and investigating the optimal design of the barrier system.

Global industry relies on a linear approach for economic growth. One step towards transformation is the implementation of a circular economy and the reclamation of anthropogenic deposits. This study examines two filter dusts, one German and one Argentinian, from the production of calcined clays, representing such deposits. Investigations and comparisons of untreated and calcined filter dust and the industrial base product pave the way for using waste product filter dust as supplementary cementitious material (SCM). In the future, some twenty thousand tons of contemporary waste could potentially be used annually as SCM. The results confirm the suitability of one material as a full-fledged SCM without further treatment and a measured pozzolanic reactivity on par with fly ash. Sample materials were classified into two groups: one was found to be a reactive pozzolanic material; the other was characterized as filler material with minor pozzolanic reactivity. Additionally, important insights into the physical properties of oven dust and heat-treated oven dust were obtained. For both material groups, an inversely proportional relationship with rising calcination temperatures was found for the specific surface area and water demand. The impact of the calcination temperature on both the particle size distribution and the potential to optimize the reactivity performance is presented. [ABSTRACT FROM AUTHOR]

The concept of sustainability has become a crucial concern for safeguarding the planet. The current research has focused on developing affordable and eco-friendly mortar by using industrial wastes. This study explores the use of fly ash (FA) and ground granulated blast furnace slag (GGBFS), byproducts of steelmaking and coal burning, in mortar production. It examines their impacts on the compressive strength and setting times, when utilizing varying proportions of the materials. The study also evaluates water requirements for the workability, thus demonstrating the sustainability of these waste products in construction. The cementitious materials were employed in finely ground form and were replaced with further tertiary mixes including both supplements at 10%, 30%, and 50% of each. The mixtures were allowed to cure for 7, 14, and 28 days by immersion in water. The results showed improvements in the compressive strength of mortar samples incorporating FA and GGBFS at various curing ages. However, the water requirement and workability of mortar samples were altered as a result of utilizing these supplementary cementitious materials (SCMs). These findings will serve as a standard for environmentally responsible mortar using GGBFS and/or FA as SCMs. [ABSTRACT FROM AUTHOR]

The utilization of recycled concrete and glass aggregates in concrete production has emerged as a highly promising method to significantly increase the recycling rate of waste materials. However, the interaction between alkaline environment and silica present in concrete detrimentally impacts mechanical properties and durability of the concrete due to the significant silica content of the aggregates. This study aims to develop a high‐performance and sustainable concrete to resist alkali–silica reaction (ASR). The study focuses on the use of a blend of ground granulated blast furnace slag (GGBS) and fly ash (FA) as binder materials to mitigate negative effects of the ASR on the mechanical properties and and durability of concrete made with crushed glass sand and coarse recycled concrete aggregate (RCA). Various tests, including ASR expansion, flow, slump, density, compression, three‐point bending, water absorption, and chloride attack, were conducted. Furthermore, microanalysis using scanning electron microscopy and energy‐dispersive x‐ray spectroscopy was performed. Based on the results, it is found that the GGBS is less effective than the FA in reducing the ASR expansion of the concrete, with only 3%, 9%, and 12% decreased expansion as a result of the addition of 20%, 40%, and 70% GGBS to the concrete containing 30% FA, respectively. It is also shown that combining 20% GGBS with 30% FA in the RCA concrete containing glass sand develops similar compressive and flexural strengths and water absorption compared to that containing natural sand. This can be related to the pozzolanic reaction of the FA and GGBS, which helps to retain the alkalis for reducing the crack development and propagation in the concrete. However, further GGBS content leads to a decrease in the strengths and an increase in the water absorption of the concrete. The results of this study point to the significant potential of combining FA and GGBS at an optimum ratio to mitigate the ASR effect on RCA concretes containing crushed glass sand. This approach helps in minimizing the emission of greenhouse gases and other pollutants generated during cement production, thereby mitigating environmental pollution. Additionally, it helps the preservation of natural resources by reducing the depletion of natural sand and coarse aggregate. [ABSTRACT FROM AUTHOR]

The valorisation of sludges from aggregate production into construction materials is required for full circularity in mining waste management. This study explores valorisation pathways, relevant regulatory frameworks, and End-of-Waste (EoW) criteria for specific settings in Spain and Norway. The explored valorisation routes involved the production of filler, supplementary cementitious materials (SCMs), and lightweight aggregates (LWAs) for the production of cement-based products, and precursors for 3D printed construction material. The sludge from Norway revealed a non-polluted stream and a stream contaminated with organic phases and clays. Sludge-based filler proved suitable in concrete production with contents of up to 40% of total binder, providing adequate consistency and cohesion. However, clays in the sludge increased the demand for water and superplasticizer. Clay contents were still insufficient for the applications as SCMs, as the calcined sludge demonstrated limited reactivity. The application to produce LWAs was promising, but further microstructure optimization is still required. The clay content was also relevant for the sludge from the site in Spain, as it provided 3D printing mixes with good plasticity. The dosage optimization still required the addition of enzymes, limestone, and natural fibres to improve cohesion, workability, and resistance to the cracking of the 3D printing mix. [ABSTRACT FROM AUTHOR]

This paper gives an overview of various factors that influences the performance of Limestone Calcined Clay Cement (LC3) concrete. Among the various research related to ternary cements, this paper discusses the influential factors, based on the strength and durability aspects. The factors such as the type and purity of kaolinite, limestone, gradation of the limestone, concentration of gypsum, calcined clay, limestone ratio, clinker content, water-to-binder ratio, method and effect of calcination, grinding criteria, optimum temperature of calcination, calcined clay content, method of curing and other factors are interpreted. Even low-grade materials with minimum purity have also been found to achieve the desired properties. Therefore depending upon the knowledge of the importance of every parameter, the best quality concrete could be developed with the available source and facilities. With the available quality and quantity of material, sustainable ternary cement could be obtained. By optimizing the various factors that influence the behavior of LC3 concretes, more economical and durable concrete can be produced. [ABSTRACT FROM AUTHOR]

Carbon emission reduction and steel slag (SS) treatment are challenges in the steel industry. The accelerated carbonation of SS and carbonated steel slag (CSS) as a supplementary cementitious material (SCM) in cement can achieve both large-scale utilization of SS and CO2 emission reduction, which is conducive to low-carbon sustainable development. This paper presents the utilization status of CSS. The accelerated carbonation route and its effects on the properties of CSS are described. The carbonation reaction of SS leads to a decrease in the average density, an increase in the specific surface area, a refinement of the pore structure, and the precipitation of different forms of calcium carbonate on the CSS surface. Carbonation can increase the specific surface area of CSS by about 24–80%. The literature review revealed that the CO2 uptake of CSS is 2–27 g/100 g SS. The effects of using CSS as an SCM in cement on the mechanical properties, workability, volume stability, durability, environmental performance, hydration kinetics, and microstructure of the materials are also analyzed and evaluated. Under certain conditions, CSS has a positive effect on cement hydration, which can improve the mechanical properties, workability, bulk stability, and sulfate resistance of SS cement mortar. Meanwhile, SS carbonation inhibits the leaching of heavy metal ions from the solid matrix. The application of CSS mainly focuses on material strength, with less attention being given to durability and environmental performance. The challenges and prospects for the large-scale utilization of CSS in the cement and concrete industry are described. [ABSTRACT FROM AUTHOR]

The decarbonisation of the steel and cement industry is of utmost importance in tackling climate change. Hence, steel production in modern integrated steel mills will be shifted towards electric arc furnaces in the future, in turn causing dwindling supplies of blast furnace slag, which is used as a supplementary cementitious material inter alia to reduce the CO2 emissions of cement production. Achieving a sustainable circular steel and building material economy requires the valorisation of currently landfilled steel slags and investigating utilisation options for electric arc furnace slag, which is increasingly being generated. For this purpose, different metallurgical residues and by-products were treated by carbothermal reduction in an inductively heated graphite crucible and then rapidly cooled by wet granulation, yielding a slag fraction similar to granulated blast furnace slag and a metal fraction valuable as a secondary raw material. A spreadsheet-based model was developed to calculate residue combinations to accomplish target compositions of the slag and metal fractions to fulfil previously identified requirements of the targeted cementitious and ferrous products. The results demonstrate the high accuracy of the model in predicting the properties (e.g. main oxide composition) of the generated slag and metal fraction, which fulfil the needed requirements for their use as (i) a supplementary cementitious material and (ii) a secondary raw material in steel production. [ABSTRACT FROM AUTHOR]

Mineral wool is commonly used in construction as thermal insulation material. After the product's lifetime, it is classified as hazardous waste if no trademark of the European Certification Board for Mineral Wool Products (EUCEB) or the German Institute for Quality Assurance and Labelling (RAL) exists. Mineral Wool Waste (MWW) is typically landfilled in Europe, which is challenging due to its low bulk density and dimensional stability. This circumstance highlights the need for alternative recycling methods that increase the recycling rate of construction and demolition (C&D) waste. This article outlines the recycling opportunities of MWW and focuses on the use of thermochemical treatment of different mixtures of input materials to produce a supplementary cementitious material (SCM). The material characterisation results and investigations on the binder suitability demonstrate that the slag fractions after the thermochemical treatment are well-qualified to be used as reactive binder components. Additionally, a material flow analysis was conducted to estimate the substitution potential of MWW as SCM in the Austrian cement industry. [ABSTRACT FROM AUTHOR]

Amorphous silica (a-SiO2), found in rice husk ash, is a valuable material due to its high silica content, large surface area, excellent pozzolanic properties, and strong binding ability with cement. These characteristics make it ideal for use as a supplementary cementitious material and a sustainable alternative for the partial replacement of ordinary Portland cement. This study aims to optimize the recovery process of amorphous silica from rice husks cultivated under various soil conditions (normal, drought, saline, and acidic soils), which are experiencing significant fluctuations due to climate change in many rice-producing countries. Experiments were conducted on rice husks under different pyrolysis conditions at temperatures of 700 ℃, 800 ℃, and 900 ℃, with varying calcination durations. Through comprehensive analysis using Scanning electron microscopy (SEM) and X-ray diffraction (XRD), along with the evaluation of amorphous silica recovery efficiency, we identified the optimal conditions for producing amorphous silica from rice husks. The analysis revealed that the highest recovery efficiency was achieved at a pyrolysis temperature of 700 ℃ for 1 hour. Under these conditions, the recovery efficiencies were 87.9% for normal soil RHA, 96.5% for saline soil RHA, 94.8% for drought soil RHA, and 95.6% for acidic soil RHA. The phase structure, surface morphology, and particle size of the RHA-derived amorphous silica, ground to micrometer sizes, were found to be similar to commercial products such as ordinary Portland cement and silica fume. This study provides a foundation for scaling up the production of amorphous silica from rice husk ash on an industrial scale, considering the relationship between optimal recovery efficiency and the origin of the rice husk ash, thus contributing to the development of environmentally friendly construction materials. [ABSTRACT FROM AUTHOR]

A detailed examination was carried out by substituting waste ceramic powder (WCP) for specific ratios of cement in concrete. To achieve this, five different WCP percentages (10%, 20%, 30%, 40%, and 50%) were used in manufacturing of concrete. First, the workability and slump values in the fresh state of concrete were determined by performing a slump test. Subsequently, several tests, including compressive strength (CS), splitting tensile strength (STS), and flexural strength (FS), were conducted on the specimens to assess the effectiveness of concrete fabricated using WCP. Variations in the strength were determined in terms of the various amounts of WCP. The findings demonstrated that by including WCP at levels of 10%, 20%, 30%, 40%, and 50%, there were corresponding reductions in CS of 5.8%, 21.8%, 47.1%, 63.2%, and 73.6%, respectively. The decreases in STS were 6.3%, 13.8%, 35.2%, 49.7%, and 65.4%, respectively, when a concrete STS value of 1.59 MPa was considered. Similarly, when the WCP content increased, FS was reduced by 15.3%, 21.4%, 31.6%, 44.9%, and 54.1%, respectively. This is very significant because it represents one of the key issues in calculating the optimal quantity of WCP in relation to both the strength and the amount of WCP utilized. Furthermore, taking into account our experimental research and previous studies on concrete produced utilizing WCP, straightforward equations were provided for practical use to predict CS, STS, and FS. In addition, scanning electron microscopy was done to validate the findings obtained from the experimental part of the study. The artificial neural network modeling technique was adopted to estimate the concrete properties with average coefficients of determination (R2) as 0.945 (CS), 0.901 (STS), and 0.856 (FS) with K-fold cross-validation.

New sources of reactive supplementary cementitious materials (SCMs) are essential to help the cement industry to further lower CO2 emissions. A co-calcination process in which bauxite residue (BR) is mixed with kaolinitic clay before calcination can deliver such SCM. The main novelty of the work discussed here is that acceptable reactivity as a SCM can be reached when co-calcining the BR with clays having only 40 wt% of kaolinite. The use of such low-grade kaolinitic clay greater increases the process economics and therefore likely increases overall feasibility. A high inherent reactivity of the desilication products present in the BR is the cause of this ability of using low-grade kaolinitic clays. Cement mortars were made with 30 wt% replacement of CEM I, which showed adequate strength at 28 days and increased strength in comparison with calcined clays or other SCMs in the literature at early age (2–7 days). A wide process temperature window with relatively constant reactivity was observed, but a range of 700–750 °C is recommended for process stability. In addition, a life-cycle assessment underlines that at these conditions a sufficiently low embodied CO2 relative to Portland clinker production is obtained.