The lack of rapid screening and selection criteria limits the use of low-purity and common clays as supplementary cementitious materials (SCMs). Here the potential suitability as SCMs of 73 clays from 27 different geological formations, was investigated. Neither chemical composition nor kaolinite content were appropriate criteria to infer the calcined clays pozzolanic reactivity, which is the recommendation in existing guidelines. Clays exhibiting a total clay mineral content of >= 40 wt%, and a mica content below 60 wt% in the clay mineral fraction present moderate to high pozzolanic reactivity when calcined at 800 degrees C. Low-purity clays derived from kaolinitic Carboniferous formations, such as the Etruria and Pennine Coal Measures, consistently exhibited higher pozzolanic reactivity, compared with younger or marine-derived clays, particularly those from Jurassic, Cretaceous, and Quaternary aged-units. This new knowledge provides a novel guideline for the exploration and sourcing of promising clays for SCMs production globally.

With diminishing supplies of traditional SCMs, there is growing interest in alternatives. Two such alternatives are calcined clays and recycled concrete powder (RCP). Blending calcined clay with limestone and clinker produces limestone calcined clay cement (LC3), where portlandite from clinker hydration reacts with silicates in the clay and limestone provides an initial filler effect and subsequent material to react with aluminates in the clay. Similarly, RCP can be a source of portlandite, calcite and aluminosilicates. This study has therefore examined the partial substitution of OPC in an LC3 system with both heated and unheated recycled concrete powder (RCP) as a novel sustainable resource. The performance of these materials has been assessed by compressive strength measurements and complemented with comprehensive characterisation by thermal analysis, XRD, FTIR. While there is some loss in strength, RCP can effectively replace some OPC in LC3 systems.

Reuse of recycled concrete aggregate is often restricted to coarse aggregates, albeit with slight loss in performance. There is growing interest in valorisation techniques to improve the properties of coarse recycled concrete aggregate. One such treatment is accelerated carbonation, which is also being considered for fine recycled aggregates and recycled concrete powder, so maximising reuse potential. This study has evaluated the effect of carbonation on all size fractions arising from crushing end-of-life concrete. End-of-life concrete was crushed in a jaw crusher and then subjected to forced accelerated carbonation. Following sieve analysis, each size fraction was characterised to determine its physical properties (particle size, attached mortar, absorption, and specific gravity). Concrete mixes containing all size fractions of recycled aggregates were subsequently prepared to assess the efficacy of up to 100% recycled concrete aggregate both pre- and post-carbonation treatment. Carbonation significantly improved the characteristics of all size fractions of recycled concrete aggregate, and consequently improved the performance of the resultant concrete prepared with it. Concrete prepared with 100% recycled coarse and fine aggregate outperformed a reference mix prepared with natural aggregates.

With the need to decarbonise global cement and concrete production, much emphasis has been placed on the use of supplementary cementitious materials, such as ground granulated blast furnace slag. However, while such blends can significantly reduce the carbon footprint of cements, other options are also available to decarbonise concrete structures. For example, changing the dimensions of structural elements or concrete strengths can affect both the volume of structural concrete and its carbon footprint. This study has examined the effects of changing concrete strength, span and binder type on the carbon footprint of a hypothetical two-storey concrete structure. Furthermore, durability requirements can impose additional demands, such as higher-grade concrete or greater cover depths, affecting the structure's carbon footprint. Thus, these structures were designed to resist a non-aggressive (XC1) and a mildly aggressive (XS1) environment. Higher-strength concrete, despite allowing dematerialisation, increased the carbon footprint of the structures, as did longer beam spans. The use of a 50% GGBS CEM III/A-S cement offered significant carbon reduction potential, with greater carbon reduction in a mildly aggressive environment. GGBS is a limited resource, so while it can always reduce concrete's carbon footprint, its use should be focused where it can also offer durability benefits.

This study evaluated the mechanical and durability performance of CEM I and CEM I plus limestone blended concrete produced with calcined clays (CC) with a varying meta-kaolinite content (70, 50 or 20 wt%). Results revealed that concrete with >45 MPa can be produced with a CC with only 20 wt% meta-kaolinite. Increased compressive and flexural strengths were obtained using higher meta-kaolinite content CC. Limestone addition did not significantly change the concretes' transport or durability properties when compared to binary mixes, despite the reduced clinker factor. CC-containing concretes exhibited excellent chloride resistance, but reduced carbonation performance compared with CEM I. Using a CC with higher meta-kaolinite content enhanced the concrete's carbonation resistance, when evaluated for 650 days of natural exposure. This suggests that generalising the impact of CC addition on concrete performance can be misleading, as bespoke concrete, compliant with specific exposure class requirements, can be produced by appropriate clay selection.

Circular economy (CE) quantification features intrinsic complexity, mandating the application of systems thinking and associated methodologies to navigate multifaceted and dynamic intricacies; posing challenges for science-policy interfacing. Well-established approaches such as System Dynamics (SD) and emergent Agent-Based Modeling and Simulation (ABMS) are adept at interrogating such complexities within intricate systems. While SD employs a macroscopic, top-down lens, ABMS delves into a microscopic, bottom-up perspective. However, to date there are no comprehensive reviews quantifying circularity through systems thinking and its associated complexity modelling. Here, we analyse this topic through a systematic scoping review using PRISMA-ScR. Our analysis has identified core limitations in existing approaches, regarding the extent to which CE complexity has been captured holistically. Although both SD and ABMS can address circularity’s dynamic interactions and feedback loops, they are predominantly applied in isolation due to the absence of standardised platforms that can integrate both approaches, and to reduce computational costs. Exploration of the potential synergies from combining these two approaches and coupling them with traditional decision-support tools such as life-cycle and multi-criteria ones are minimal. Such a fragmented approach limits their ability to model internal dynamics; in turn restricting their utility to inform system-wide decision-support. The review also accentuates the lack of standardised metrics and the need for a more holistic evaluation framework for CE incorporating economic, environmental, social, and technical value metrics. A more unified approach to support sustainable, informed decisions in the pursuit of circularity is imperative for improving evidence-based policymaking and empowering industrial adoption of circularity.

Huge quantities of construction and demolition waste are produced each year, and about a third of this is concrete. With growing interest in circular economy, there is a need to examine how this can be applied to end-of-life concrete. While there is a potential market for recycled coarse aggregate, the reuse of fine aggregate and recycled concrete powder is more limited. However, recycled concrete powder constitutes up to 10% of the mass of crushed end-of-life concrete, and comprises almost 80% hardened cement paste. This calcium- and silicon-rich paste is ripe for reactivation. This study has examined the latent hydraulic behaviour of recycled concrete powder and investigated how various treatment methods can produce an effective supplementary cementitious material. Heat treatment and carbonation, either in isolation or combined has been used to produce materials with activity indices approaching unity at 20% replacement. The performance of these materials has been understood via detailed characterization by thermal analysis, XRD and FTIR. It has proven possible to produce effective supplementary cementitious materials from waste recycled concrete powder, thus finding a use for this end-of-life material and potentially reducing cement’s carbon footprint.

The global construction sector consumes 40 billion tonnes of raw materials and is responsible for considerable CO2 emissions. With growing awareness of its environmental impact, the construction sector is looking to transition from a linear economy “take-make-waste” scenario towards more circular economy principles. Lightweight exterior infill walls are built between floors of primary structural frames to provide building façades. The design of these components is usually based on the current linear economic model. While lightweight exterior infill walls are becoming increasingly common in building construction in the UK, no studies have investigated the potential environmental benefits of designing them with circularity in mind. This means there's a lack of research on both the carbon footprint of these walls and the potential environmental benefits of reusing them. Thus, this article assesses the significance of the carbon emissions from lightweight exterior infill walls and examines whether there is any carbon reduction when lightweight exterior infill walls are demounted from the building frames and reused. This paper first examines the construction process of lightweight exterior infill walls and explores the opportunity to demount and reuse them. Then, the environmental impacts of the lightweight exterior infill walls are analysed using a lifecycle assessment framework. Sensitivity and uncertainty analyses are also conducted. The results demonstrate that (i) the embodied carbon of the lightweight exterior infill walls over their lifecycle represents approximately 22% of the embodied carbon of the entire building, and (ii) the disassembly and reuse of infill walls can reduce a building's embodied carbon over its typical lifetime by about 6% compared to the linear scenario where the walls were not reused.

Low-purity calcined clays are becoming increasingly popular as supplementary cementitious materials (SCMs) due to their wide availability, and potential ability to reduce the carbon footprint associated with concrete production. To ensure the longevity of concrete structures, it is crucial to understand the mechanisms governing long-term durability when using new SCM-containing cement formulations. Understanding of the carbonation resistance of cements containing calcined clay is limited, and this remains a concern. This research is part of the collaborative USA-UK project “Response to CO2 exposure of concrete with natural supplementary cementitious materials” (RENACEM), aiming to understand the connections among the properties of natural clays, activation treatments to enhance their chemical reactivity, and the response to CO2 exposure of cements, mortars and concretes produced with them. The current study presents the carbonation resistance results of binary and ternary materials containing calcined clays upon exposure to natural CO2 concentrations under controlled relative humidity (57

By replacing a large portion of Portland cement with calcined clay, carbon emissions associated with concrete production can be significantly reduced, facilitatingnet-zero targets in construction projects. Vast amounts of soil waste generated from major infrastructure projects could serve as a valuable resource for producing cement replacements or supplementary cementitious materials (SCMs); however, it is largely unknown whether low-purity, low-kaolinite content clays are suitable for producing resilient concrete. This study investigated the use of low-purity calcined clay, derived from excavation operations in the greater London area, as an SCM in the production of concrete. Specifically, the effects of replacing CEM I with calcined excavated London Clay (30 wt.

The World Bank study predicts that 4 degrees C warming will bring high temperatures, sea-level rise, and saltwater intrusion to coastal areas, damaging coastal concrete structures. Increased CO2 from industrialization exacerbates this, necessitating durable, low-carbon concrete. Combined use of fly ash (FA) and ground granulated blast furnace slag (GGBFS) as high-volume OPC replacements boosts performance while reducing concrete's carbon footprint. In this perspective current study examines the durability of concrete against aggressive agents (H2SO4, MgSO4, NaCl, and CO2) causing premature deterioration of concrete structures. Initially, three cost-effective sustainable concrete mix designs were developed, incorporating 50% replacement of OPC with locally available supplementary cementitious materials, specifically FA and GGBFS. These mixes were then evaluated for their mechanical and durability performances. The impact of aggressive ions (SO42-, Cl-, and CO32-) was studied by examining the changes in mechanical performance and phase assemblages. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques were used to estimate the phase compositions. Ternary blended concrete having 50% OPC+ 30% GGBFS + 20% FA exhibited optimal synergistic performance, enhancing pozzolanic and hydraulic reactions for better resistance to harmful ions. The sorptivity test confirmed that as the GGBFS content increased, the sorption rate decreased, indicating the higher reactive nature of GGBFS to that of FA. Deleterious compounds formed due to the action of SO42-, Cl-, and CO32- were identified to be ettringite (Ca6Al2(SO4)3(OH)12.32H2O, AFt) and gypsum (CaSO4.2H2O, Gy), Friedel's salt (Ca4Al2(OH)12Cl2.4H2O, Fs) and polymorphs of calcium carbonate (CaCO3), respectively through TG mass loss curve. These results were corroborated by FTIR analysis, which showed predominant characteristic bands at 662 cm-1 for SO42-, 459 cm-1 for Mg-O stretching, 790 cm-1 for Al-OH bending, and 1431-1443 cm-1 for C-O, confirming the presence of the deleterious compounds.

Supersulfated cement (SSC) is a traditional low-carbon cement, but its slow hydration and strength development has limited its practical applications. Nano silica (NS) was used to activate the hydration of SSC by taking advantage of its ability to regulate silicate and aluminate reactions. The mechanical performance of various mixes was determined, as a function of sulfation degree and NS addition, as pore structure, phase assemblage, hydration degree, and microstructure. Results showed that NS improves the hydration degree of slag, densifies the microstructure, and significantly increases both early- and late-age compressive strength. The enhancement was attributed to its effects on the hydration of slag in SSC: delaying ettringite formation, but promoting C-(A)-S-H precipitation, reducing microporosity. This study reveals the critical role of the regulation of hydration kinetics of silicate and aluminate in controlling the performance of SSC as NS does.

Corrosion of steel reinforcement due to chloride attack remains a major reinforced concrete durability concern. The problem is prevalent for concrete structures located within marine environments or frost-prone locations where chlorides containing de-icing salts are used. This paper is a state-of-the-art review into chloride binding in Portland cement concrete, with consideration of the differences induced by the presence of sulphates, such as found in seawater. The review also considers the use of supplementary cementitious materials (SCMs), the use of which has increased because of their potential to enhance durability and reduce the carbon footprint of concrete production. Such materials impact on phase assemblage and microstructure, affecting chloride binding and transport properties. Therefore, field and laboratory studies are critically reviewed to understand how these could help in the design of more durable concretes. The contributions of chloride binding, hydrate compositions and microstructures of the binding materials affecting chloride transport in concretes are also evaluated to suggest a more robust approach for controlling the problem of chloride attack.

Most supplementary cementitious materials (SCMs) are predominantly poorly-crystalline or amorphous. Their reactivity is routinely evaluated through SEM image analysis (SEM/IA), which is a laborious and resource intensive technique. Quantitative X-ray diffraction (QXRD) provides an alternative, facilitating simultaneous evaluation of reaction kinetics and phase assemblages. However, QXRD requires relevant model structures, which are lacking for amorphous phases. In this study, we use the Phases of No Known Crystal Structures (PONKCS) method to model and calibrate ground granulated blast furnace slag (GGBS) and assess robustness in quantifying the GGBS content in synthetic and hydrated ternary blended CEM I-GGBS-limestone cements. Implications of sample preparation, in particular hydration stopping methods on the quantification was measured via the external standard method. Subsequently, the results are compared with SEM/IA calculations, based on backscattered images and magnesium maps. Robustness of the calibrated PONKCS phase is demonstrate with and without hydration stopping. However, X-ray absorption by the cements must be accounted in the attenuation co-efficient calculation. Freeze-drying destroyed water-rich phase assemblages and led to overestimation of the calibrated GGBS phase contents.

The valorisation of waste or by-products in Portland clinker production is a promising alternative for developing sustainable cements. The complexity of the chemical reactions during clinkering demands an adequate dosing method that considers the effect of feedstock impurities to maximise the potential substitution of natural resources by waste or by-products, while guaranteeing the clinker reactivity requirements. This study proposes a raw meal proportioning methodology for optimising co-processing of natural feedstocks with alternative raw materials in clinker production, intending to reduce the content of natural raw materials needed, while promoting an optimal clinker reactivity. A thermodynamic modelling sequence was developed considering the variability of raw materials composition and heating temperatures. The model was then validated by comparing simulation outcomes with results reported in previous studies. An experimental case study was conducted for validation of the proposed method using a spent fluid catalytic cracking catalyst (SFCC), a by-product from the oil industry as an alternative alumina source during clinkering. The modelling simulations indicated that substitution of natural feedstocks by 15 wt% SFCC promotes the formation of reactive clinkers with more than 54% tricalcium silicate (C3S). Mixes with the potential to form the highest C3S were then produced, and heating microscopy fusibility testing was applied for evaluating the clinkers’ stability. The main factors governing the reactivity and stability of the clinker phases were the melt phase content, alumina modulus, and formation of C3S and dicalcium silicate (C2S). The self-pulverisation of clinker during cooling was observed in selected mixes, and it is potentially associated with high viscosity and low Fe content in the melt phase. The proposed framework enables optimisation of the dosing of raw meals containing alternative alumina-rich feedstocks for clinker production and allows a deeper interpretation of limited sets of empirical data.

Ground granulated blast furnace slag (GGBS) is an important supplementary cementitious material (SCM) for producing low carbon and durable concrete. There are however questions around the early age reactivity of GGBS and the factors that influence this. To elucidate the fundamental mechanisms controlling the early age reactivity and particularly the influence of anionic species, simplified systems comprising GGBS and calcium hydroxide were examined in the presence of limestone, anhydrite, or both at 4:1 SCM-to-activator ratio. Limestone and GGBS were considered as SCMs, but calcium hydroxide and anhydrite were considered as activators. Multiple techniques, including isothermal calorimetry, thermogravimetry, X-ray diffraction, electron microscopy, mass balance calculation and mercury intrusion porosimetry were used to study hydration and microstructure. The results show that GGBS hydration commences immediately in the alkaline media provided by calcium hydroxide. Sulphates and limestone influence hydration through reactions with aluminates to form ettringite and carboaluminates, but prevalence of macro-capillary pores in sulphate containing binders sustains diffusion-controlled hydration. Consequently, optimization of the alumina to sulphate and carbonate ratios is essential for exploiting the pore solution and space filling effects in composite cements.

‘Project code-named Humpty’ is a performative art piece involving the creation, fragmentation, and reconstruction of a 2.7 m high classically inspired sculpture. It was conceived to complement an archaeological science research project setting out to explore the use of digital scanning technologies in artefact reconstruction. The statue’s form was free sculpted in clay over a period of four years. It was cast in a self-supporting cementitious material specifically for the purpose of ceremonial fragmentation and subsequent reconstruction by archaeologists. In this chapter, we explore the project’s human/machine intentions, interactions, development processes and their wider implications leading to fragmentation. We explore how 3D terrestrial laser scanning with photogrammetry was used to chart the creation of the sculptural form and how scans informed finite element analysis, essential for safe casting and fragmentation. We show how structured light scanning was essential to create a digital backup of the mould and how drone imagery documented fragmentation tests and 360° imaging recorded studio and quarry activity.

This paper presents the results of an experimental study that investigated changes in the mechanical properties of two types of concrete under normal and extreme loading conditions pre- and post-carbonation. Specimens of CEM I and CEM II concrete (concrete prepared with 20% replacement cement with pulverised-fuel ash) were cured for 28 days before accelerated carbonation under 4% carbon dioxide (CO2) for 28 days at 20°C and 57% relative humidity. Static compressive mechanical tests at ambient temperature were carried out for both concrete types. For CEM I concrete, static compressive mechanical tests were performed at elevated temperatures of 300, 500 and 650°C, and high-strain-rate tests were performed at ambient temperature and elevated temperature of 500°C. The results show that the mechanical performance of CEM I concrete was improved after carbonation – that is, static compressive strength increased at ambient and elevated temperatures, and the dynamic strength was higher than that of fresh concrete at the same strain rate at both ambient and elevated temperatures. However, CEM II concrete suffered reductions in compressive strength after carbonation.

Existing methods to quantify the degree of hydration of cementitious materials, such as selective dissolution and image analysis of scanning electron micrographs, are either laborious or unreliable. Meanwhile, quantitative X-ray powder diffraction (QXRD), routinely used to study kinetics and phase evolution of hydrating cements, presents opportunities to determine quantities of crystalline and poorly crystalline phases simultaneously. The profile fitting technique, however, requires structure files, which are nonexistent for poorly crystalline materials, including most supplementary cementitious materials (SCMs). This contribution is focused upon developing a pseudo-structure file for ground granulated blast furnace slag (GGBS), a Phase of No Known Crystal Structure (PONKCS) for implementation in the Rietveld refinement. Factors affecting the developed model and its stability are assessed. Following, the model is used to quantify the residual GGBS content in hydrated composite cement. The effect of hydration stoppage technique on accuracy of the PONKCS phase is assessed on a binary slag cement. The results show that the PONKCS phase was stable in synthetic and hydrated cements. Hydration stopping methods that modified the background through decomposition of phase assemblages, e.g., freeze-drying, also caused overestimation of the PONKCS phase. The QXRD/PONKCS technique is less laborious, has good consistency with the quantified crystalline phase, and enables the degree of hydration of SCMs to be measured alongside hydrated phase assemblages.

Despite the relatively benign characteristics of construction and demolition waste, its mismanagement can result in considerable harm to human health for 200 million workers and those who live and work in proximity to construction and demolition activities. The high number of workers classified as informal, results in a large unregulated and vulnerable workforce at a high risk of exposure to hazards. We focused a systematic scoping review (PRISMA-ScR) on evidence associating construction and demolition waste with hazards and risks in low- and middle-income countries. We reviewed more than 3,000 publications, narrowed to 49 key sources. Hazard-pathway-receptor scenarios/combinations were formulated, enabling indicative ranking and comparison of the relative harm caused to different groups. Though the evidential basis is sparse, there is a strong indication that the combustible fraction of construction and demolition waste is disposed of by open burning in many low- and middle-income countries, including increasing quantities of high chloride-content PVC; risking exposure to dioxins and related compounds. A long-standing and well-known hazard, asbestos, continues to represent a health threat throughout the world, claiming 250,000 lives per annum despite being banned in most countries. In the coming decades, it is anticipated that more than half of all deaths from asbestos will take place in India, where it is still sold. Comparatively, the highest risks from construction and demolition waste exist in low- and middle-income countries where attention to risk mitigation and control is needed.