New circularity indicator for decision making in the stockpile management of construction and demolition waste: Perspectives of Australian practitioners.

Despite the increasing popularity of the circular economy, there remains a lack of consensus on how to quantify circularity, a critical aspect of the practical implementation of this model. To address this gap, this article examines the industry's perspective and efforts toward implementing the circular economy in real-world scenarios. We conducted 40 interviews with engineers, project leaders, and top-level managers in the Australian construction sector. Using Saldaña's coding approach, we analysed their views on circular economy practices and efforts within their organisations. Our findings reveal while waste minimisation, reduction of greenhouse gas emissions, and cost considerations are widely regarded as essential indicators of a successful circular economy model, the significance of waste storage and long-term stockpiling while awaiting treatment has been overlooked or under-emphasised in industry practices and academic literature. Stockpiling of waste has often been seen as a staging process in waste treatment. However, based on industry insights, it accumulates to the point of mismanagement when it becomes a safety and environmental concern. Addressing this oversight, we propose a storage circularity indicator that allows incorporating waste storage and stockpiling in circular economy models. Our research contributes to various environmental and waste management aspects, supporting policies and strategies for solid waste management and excessive stockpile prevention. By emphasising the significance of storage circularity, we clarify waste prevention techniques and address socio-economic issues such as the urgent need to reduce long-term stockpiling of solid waste. This work highlights the importance of decision-support tools in waste management to facilitate the implementation of circular economy principles. Our proposed storage circularity indicator promotes industrial collaboration, aligning with the concept of industrial symbiosis to optimise resource use and minimise waste generation. By discussing these topics, we aim to contribute to the advancement of more robust waste management strategies and policies that promote sustainable production and consumption practices.

Effect of Graphene Oxide Nanomaterials on the Durability of Concrete: A Review on Mechanisms, Provisions, Challenges, and Future Prospects.

This review focuses on recent advances in concrete durability using graphene oxide (GO) as a nanomaterial additive, with a goal to fill the gap between concrete technology, chemical interactions, and concrete durability, whilst providing insights for the adaptation of GO as an additive in concrete construction. An overview of concrete durability applications, key durability failure mechanisms of concrete, transportation mechanisms, chemical reactions involved in compromising durability, and the chemical alterations within a concrete system are discussed to understand how they impact the overall durability of concrete. The existing literature on the durability and chemical resistance of GO-reinforced concrete and mortar was reviewed and summarized. The impacts of nano-additives on the durability of concrete and its mechanisms are thoroughly discussed, particularly focusing on GO as the primary nanomaterial and its impact on durability. Finally, research gaps, future recommendations, and challenges related to the durability of mass-scale GO applications are presented.

Sustainable Cement Composite Integrating Waste Cellulose Fibre: A Comprehensive Review.

This review presents the research conducted to date in the field of cement-based composites reinforced with waste paper-based cellulose fibres, focusing on their composition, mechanical properties, and durability characteristics. The literature demonstrates that the properties of raw material (depending on their own chemical composition) significantly influence the formation of the cement composite binders. When considering fresh properties, the presence of silica and magnesium compounds generally lead to favourable effects on the setting of the cement composite when combined with waste paper cellulose fibre. Reduction in density values, i.e., approximately 25%, was observed with the inclusion of waste paper fibres from 20 to 80% in cement composites. The homogeneous dispersion of fibres in the matrix is one of the crucial factors to achieve in order to develop composites with well-balanced mechanical properties incorporating waste paper cellulose fibres. Hence, dispersion of fibres can be improved by increasing water quantity corresponding to the optimal value, which was a water/cement ratio of 0.64 leading to optimum strength properties of the composite. Even though the effect of fibre dispersion in the matrix improves with the addition of water, higher porosity and voids govern the strength properties beyond an optimum water-to-cement ratio. Higher porosity leads to an increase in the water absorption and a lowering of the thermal conductivity properties with the addition of paper fibre in cement binders. Paper fibre absorbs a high amount of water leading to higher water absorption. This phenomenon is related to the hydrophilic nature of cellulosic fibres absorbing some volume of water due to their microporous structure.

A Review on Cementitious and Geopolymer Composites with Lithium Slag Incorporation.

This study critically reviews lithium slag (LS) as a supplementary cementitious material (SCM), thereby examining its physiochemical characteristics, mechanical properties, and durability within cementitious and geopolymer composites. The review reveals that LS's particle size distribution is comparable to fly ash (FA) and ground granulated blast furnace slag (GGBS), which suggests it can enhance densification and nucleation in concrete. The mechanical treatment of LS promotes early hydration by increasing the solubility of aluminum, lithium, and silicon. LS's compositional similarity to FA endows it with low-calcium, high-reactivity properties that are suitable for cementitious and geopolymeric applications. Increasing the LS content reduces setting times and flowability while initially enhancing mechanical properties, albeit with diminishing returns beyond a 30% threshold. LS significantly improves chloride ion resistance and impacts drying shrinkage variably. This study categorizes LS's role in concrete as a filler, pozzolan, and nucleation agent, thereby contributing to the material's overall reduced porosity and increased durability. Economically, LS's cost is substantially lower than FA's; meanwhile, its environmental footprint is comparable to GGBS, thereby making it a sustainable and cost-effective alternative. Notwithstanding, there is a necessity for further research on LS's fine-tuning through grinding, its tensile properties, its performance under environmental duress, and its pozzolanic reactivity to maximize its utility in concrete technologies. This study comprehensively discusses the current strengths and weaknesses of LS in the field of building materials, thereby offering fresh perspectives and methodologies to enhance its performance, improve its application efficiency, and broaden its scope. These efforts are driving the sustainable and green development of LS in waste utilization and advanced concrete technology.

Engineering Performance of Concrete Incorporated with Recycled High-Density Polyethylene (HDPE)-A Systematic Review.

Incorporating recycled plastic waste in concrete manufacturing is one of the most ecologically and economically sustainable solutions for the rapid trends of annual plastic disposal and natural resource depletion worldwide. This paper comprehensively reviews the literature on engineering performance of recycled high-density polyethylene (HDPE) incorporated in concrete in the forms of aggregates or fiber or cementitious material. Optimum 28-days' compressive and flexural strength of HDPE fine aggregate concrete is observed at HDPE-10 and splitting tensile strength at HDPE-5 whereas for HDPE coarse aggregate concrete, within the range of 10% to 15% of HDPE incorporation and at HDPE-15, respectively. Similarly, 28-days' flexural and splitting tensile strength of HDPE fiber reinforced concrete is increased to an optimum of 4.9 MPa at HDPE-3 and 4.4 MPa at HDPE-3.5, respectively, and higher than the standard/plain concrete matrix (HDPE-0) in all HDPE inclusion levels. Hydrophobicity, smooth surface texture and non-reactivity of HDPE has resulted in weaker bonds between concrete matrix and HDPE and thereby reducing both mechanical and durability performances of HDPE concrete with the increase of HDPE. Overall, this is the first ever review to present and analyze the current state of the mechanical and durability performance of recycled HDPE as a sustainable construction material, hence, advancing the research into better performance and successful applications of HDPE concrete.

Optimal time-dependent levels of weight-bearing for bone fracture healing under Ilizarov circular fixators.

It is known that weight-bearing exercises under Ilizarov circular fixators (ICF) could enhance bone fracture healing by mechano-regulation. However, interfragmentary movements at the fracture site induced by weight-bearing may inhibit angiogenesis and ultimately delay the healing process. To tackle this challenge, a computational model is presented in this study which considers the spatial and temporal changes in mechanical properties of fracture callus to predict optimal levels of weight-bearing during fracture healing under ICF. The study takes sheep fractures as example and shows that the developed model has the capability of predicting patient specific, time-dependent optimal levels of weight-bearing which enhances mechano-regulation mediated healing without hindering the angiogenesis process. The results demonstrate that allowable level of weight-bearing and timings depend on fracture gap size. For normal body weights (BW) and moderate fracture gap sizes (e.g. 3 mm), weight-bearing with 30% BW could start by week 4 post-operation and gradually increase to 100% BW by week 11. In contrast, for relatively large fracture gap sizes (i.e. 6 mm), weight-bearing is recommended to commence in later stages of healing (e.g. week 11 post-operation). Furthermore, increasing ICF stiffness (e.g. using half pins instead of pretension wires) can increase the level of weight-bearing significantly in the early stages up to a certain time point (e.g. week 8 post-operation) beyond which no noticeable benefits could be achieved. The findings of this study have potential applications in designing post-operative weight bearing exercises.

A probabilistic approach for modelling bone fracture healing under Ilizarov circular fixator.

Bone fracture treatments using Ilizarov circular fixator (ICF) involve dealing with uncertainties about a range of critical factors that control the mechanical microenvironment of the fracture site such as ICF configuration, fracture gap size, physiological loading etc. To date, the effects of the uncertainties about these critical factors on the mechanical microenvironment of the fracture site have not been fully understood. The purpose of this study is to tackle this challenge by using computational modelling in conjunction with engineering reliability analysis. Particularly, the effects of uncertainties in fracture gap size (GS), level of weight-bearing (P), ICF wire pretension (T) and wire diameter (WD) on the fracture site mechanical microenvironment at the beginning of the reparative phase of healing was investigated in this study. The results show that the mechanical microenvironment of fracture site stabilised with ICF is very sensitive to the uncertainties in P and GS. For example, an increase in the coefficient of variation of P (COVP ) from 0.1 to 0.9 (i.e., an increase in the uncertainty in P) could reduce the probability of achieving a favourable mechanical microenvironment within the fracture site (i.e., Probability of Success, PoS) by more than 50%, while an increase in the coefficient of variation of GS (COVGS ) from 0.1 to 0.9 could decrease PoS by around 30%. In contrast, an increase in the uncertainties in T and WD (COV increase from 0.1 to 0.9) has little influence on the fracture site mechanical microenvironment (PoS changes <5%).

Optimising the computational domain size in CFD simulations of tall buildings.

Recently, there has been a growing interest in utilizing computational fluid dynamics (CFD) for wind resistant design of tall buildings. A key factor that influences the accuracy and computational expense of CFD simulations is the size of the computational domain. In this paper, the effect of the computational domain on CFD predictions of wind loads on tall buildings is investigated with a series of sensitivity studies. Four distinct sources of domain error are identified which include wind-blocking effects caused by short upstream length, flow recirculation due to insufficient downstream length, global venturi effects due to large blockage ratios, and local venturi effects caused by insufficient clearance between the building and top and lateral domain boundaries. Domains based on computational wind engineering guidelines are found to be overly conservative when applied to tall buildings, resulting in uneconomic grids with a large cell count. A framework for optimizing the computational domain is proposed which is based on monitoring sensitivity of key output metrics to variations in domain dimensions. The findings of this paper help inform modellers of potential issues when optimizing the computational domain size for tall building simulations.

The Potential Use of Hypochlorous Acid and a Smart Prefabricated Sanitising Chamber to Reduce Occupation-Related COVID-19 Exposure.

This work is part of a project on the development of a smart prefabricated sanitising chamber (SPSC) to provide extra measures against the transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Stabilised hypochlorous acid (HOCl) is an approved disinfectant against SARS-CoV-2 by the Environmental Protection Association US in its liquid form on non-porous surfaces. This review is extended to cover its viricidal/bactericidal efficacy in aerosolised or sprayed form which showed an effective dose of as low as 20 ppm and the exposure duration of at least 60 s. The aerosolised application was also recommended with particle size of less than 200 µm to increase the contact with pathogens. The review also includes the safety and toxicity of HOCl with different concentrations. The review calls for more investigations into the effect of HOCl in mist and fog form on the respiratory system when transitioning through the proposed SPSC.

Impact of atmospheric boundary layer inhomogeneity in CFD simulations of tall buildings.

Recently, there has been a growing interest in utilizing computational fluid dynamics (CFD) for wind analysis of tall buildings. A key factor that influences the accuracy of CFD simulations in urban environments is the homogeneity of the atmospheric boundary layer (ABL). This paper aims to investigate solution inaccuracies in CFD simulations of tall buildings that are due to ABL inhomogeneity. The investigation involves two steps. In the first step, homogenous and inhomogeneous ABL conditions are generated in an empty computational domain by employing two different modelling approaches. In the second step, the homogenous and inhomogeneous conditions are each applied to an isolated tall building, and simulation results are compared to investigate impact of ABL inhomogeneity on wind load predictions. The study finds that ABL inhomogeneity can be a significant source of error and may compromise reliability of wind load predictions. The largest magnitude of inhomogeneity error occurred for pressure predictions on the windward building surface. Shortening the upstream domain length reduced inhomogeneity errors but increased errors due to wind-blocking effects. The study proposes a practical approach for detecting ABL inhomogeneity that is based on monitoring sensitivity of key output metrics to variations in upstream domain length.

Transversely isotropic elastic-plastic properties in thermal arc sprayed Al-Zn coating: a microporomechanics approach.

The transversely isotropic behaviour of thermal sprayed aluminium and zinc coating has been investigated based on a combination of nanoindentation experimental data and microporomechanics theory. A recently developed strength homogenisation approach comprises of the solid and porous medium is adopted to investigate the morphology properties of thermal sprayed aluminum and zinc coating. The finding of this paper demonstrates that the individual aluminum and zinc phases in the coating have a characteristic packing density close to the theoretical highest spherical packing ratio for face-centred cubic and hexagonal close packed. Also, the plasticity properties of solid particles in both aluminum and zinc are found to have a significant transversely isotropic condition, while the elasticity properties are close to isotropic. These findings led to the conclusion that the anisotropic condition of the coating is dominantly affected by the plasticity properties, in terms of cohesion and friction coefficient.

Cohesive-strength homogenisation model of porous and non-porous materials using linear comparison composites and application.

An estimation of the strength of composite materials with different strength behaviours of the matrix and inclusion is of great interest in science and engineering disciplines. Linear comparison composite (LCC) is an approach introduced for estimating the macroscopic strength of matrix-inclusion composites. The LCC approach has however not been expanded to model non-porous composites. Therefore, this paper is to fill this gap by developing a cohesive-strength method for modelling frictional composite materials, which can be porous and non-porous, using the LCC approach. The developed cohesive-strength homogenisation model represents the matrix and inclusion as a two-phase composite containing solids and pores. The model is then implemented in a multiscaling model in which porous cohesive-frictional solids intermix with each other at different scale levels classified as micro, meso and macro. The developed model satisfies an upscaling scheme and is suitable for investigating the effects of the microstructure, the composition, and the interface condition of the materials at micro scales on the macroscopic strength of the composites. To further demonstrate the application of the developed cohesive-strength homogenisation model, the cohesive-strength properties of very high strength concrete are determined using instrumented indentation, nonlinear limit analysis and second-order cone programming to obtain material properties at different scale levels.

Relationship of Stiffness-Based Indentation Properties Using Continuous-Stiffness-Measurement Method.

The determination of elastic modulus (E) and hardness (H) relies on the accuracy of the contact area under the indenter tip, but this parameter cannot be explicitly measured during the nanoindentation process. This work presents a new approach that can derive the elastic modulus (E) and contact depth (hc) based on measured experiment stiffness using the continuous-stiffness-measurement (CSM) method. To achieve this, an inverse algorithm is proposed by incorporating a set of stiffness-based relationship functions that are derived from combining the dimensional analysis approach and computational simulation. This proposed solution considers both the sink-in and pile-up contact profiles; therefore, it provides a more accurate solution when compared to a conventional method that only considers the sink-in contact profile. While the proposed solution is sensitive to Poisson's ratio (ν) and the equivalent indentation conical angle (θ), it is not affected by material plasticity, including yield strength (σy) and work hardening (n) for the investigated range of 0.001 < σy/E < 0.5. The proposed stiffness-based approach can be used to consistently derive elastic modulus and hardness by using stiffness and the load-and-unload curve measured by the continuous-stiffness-measurement (CSM) method.

Study of Strain-Hardening Behaviour of Fibre-Reinforced Alkali-Activated Fly Ash Cement.

This paper presents a study of parameters affecting the fibre pull out capacity and strain-hardening behaviour of fibre-reinforced alkali-activated cement composite (AAC). Fly ash is a common aluminosilicate source in AAC and was used in this study to create fly ash based AAC. Based on a numerical study using Taguchi's design of experiment (DOE) approach, the effect of parameters on the fibre pull out capacity was identified. The fibre pull out force between the AAC matrix and the fibre depends greatly on the fibre diameter and embedded length. The fibre pull out test was conducted on alkali-activated cement with a capacity in a range of 0.8 to 1.0 MPa. The strain-hardening behaviour of alkali-activated cement was determined based on its compressive and flexural strengths. While achieving the strain-hardening behaviour of the AAC composite, the compressive strength decreases, and fine materials in the composite contribute to decreasing in the flexural strength and strain capacity. The composite critical energy release rate in AAC matrix was determined to be approximately 0.01 kJ/m 2 based on a nanoindentation approach. The results of the flexural performance indicate that the critical energy release rate of alkali-activated cement matrix should be less than 0.01 kJ/m 2 to achieve the strain-hardening behaviour.

Strength Development and Thermogravimetric Investigation of High-Volume Fly Ash Binders.

To address sustainability issues by facilitating the use of high-volume fly ash (HVFA) concrete in industry, this paper investigates the early age hydration properties of HVFA binders in concrete and the correlation between hydration properties and compressive strengths of the cement pastes. A new method of calculating the chemically bound water of HVFA binders was used and validated. Fly ash (FA) types used in this study were sourced from Indonesia and Australia for comparison. The water to binder (w/b) ratio was 0.4 and FA replacement levels were 40%, 50% and 60% by weight. Isothermal calorimetry tests were conducted to study the heat of hydration which was further converted to the adiabatic temperature rise. Thermo-gravimetric analysis (TGA) was employed to explore the chemically bound water (WB) of the binders. The results showed that Australian FA pastes had higher heat of hydration, adiabatic temperature rise, WB and compressive strength compared to Indonesian FA pastes. The new method of calculating chemically bound water can be successfully applied to HVFA binders. Linear correlation could be found between the WB and compressive strength.

An Investigation of Nanomechanical Properties of Materials using Nanoindentation and Artificial Neural Network.

Mechanical properties of materials can be derived from the force-displacement relationship through instrumented indentation tests. Complications arise when establishing the full elastic-plastic stress-strain relationship as the accuracy depends on how the material's and indenter's parameters are incorporated. For instance, the effect of the material work-hardening phenomenon such as the pile-up and sink-in effect cannot be accounted for with simplified analytical indentation solutions. Due to this limitation, this paper proposes a new inverse analysis approach based on dimensional functions analysis and artificial neural networks (ANNs). A database of the dimensional functions relating stress and strain parameters of materials has been developed. The database covers a wide range of engineering materials that have the yield strength-to-modulus ratio (σy/E) between 0.001 to 0.5, the work-hardening power (n) between 0-0.5, Poisson's ratio (v) between 0.15-0.45, and the indentation angle (θ) between 65-80 degrees. The proposed algorithm enables determining the nanomechanical stress-strain parameters using the indentation force-displacement relationship, and is applicable to any materials that the properties are within the database range. The obtained results are validated with the conventional test results of steel and aluminum samples. To further demonstrate the application of the proposed algorithm, the nanomechanical stress-strain parameters of ordinary Portland cement phases were determined.

The Effects of Dynamic Loading on Bone Fracture Healing Under Ilizarov Circular Fixators.

Early weight bearing appears to enhance bone fracture healing under Ilizarov circular fixators (ICFs). However, the role of early weight bearing in the healing process remains unclear. This study aims to provide insights into the effects of early weight bearing on healing of bone fractures stabilized with ICFs, with the aid of mathematical modeling. A computational model of fracture site was developed using poro-elastic formulation to simulate the transport of mesenchymal stem cells (MSCs), fibroblasts, chondrocytes, osteoblasts, osteogenic growth factor (OGF), and chondrogenic growth factor (CGF) and MSC differentiation during the early stage of healing, under various combinations of fracture gap sizes (GS), ICF wire pretension forces, and axial loads. 1 h of physiologically relevant cyclic axial loading followed by 23 h of rest in the post-inflammation phase (i.e., callus with granulation tissue) was simulated. The results show that physiologically relevant dynamic loading could significantly enhance cell and growth factor concentrations in the fracture site in a time and spatially dependent manner. 1 h cyclic loading (axial load with amplitude, PA, of 200 N at 1 Hz) increased the content of chondrocytes up to 37% (in all zones of callus), CGF up to 28% (in endosteal and periosteal callus) and OGF up to 50% (in endosteal and cortical callus) by the end of the 24 h period simulated. This suggests that the synergistic effect of dynamic loading-induced advective transport and mechanical stimuli due to early weight bearing is likely to enhance secondary healing. Furthermore, the study suggests that relatively higher PA values or lower ICF wire pretension forces or smaller GS could result in increased chondrocyte and GF content within the callus.

Effects of dynamic loading on fracture healing under different locking compression plate configurations: A finite element study.

The design of patient specific weight-bearing exercises after the surgical implementation of internal fixations is of critical importance for bone fracture healing. The purpose of this study is to theoretically investigate the effects of physiologically relevant dynamic loading on early stage of fracture healing under different locking compression plate (LCP) configurations. The finite element results show that dynamic loading enhanced transport of bone cells and growth factors in the fracture callus is much dependent on the flexibility of LCP. In comparison to free diffusion, a relatively flexible LCP together with dynamic loading could significantly enhance solute transport in callus. For example, a flexible LCP achieved by increasing WL (Working Length) and BPD (Bone Plate Distance) (e.g. WL=100 mm and BPD=2 mm) together with a 5-h 150 N@1 Hz dynamic loading could increase the uptake of chondrocytes by around 280% compared to free diffusion, osteoblasts by around 180%, osteogenic growth factors by around 120% and chondrogenic growth factors by around 220%. In addition, dynamic loading enhanced transport of cells and growth factors under LCP is spatially dependent with a relatively higher enhancement in far cortex zone than that in near cortex zone. The outcomes from present study could potentially assist orthopaedic surgeons to determine optimal loading regimes with consideration of patient specific LCP configurations.

Bone fracture healing under Ilizarov fixator: Influence of fixator configuration, fracture geometry, and loading.

This study aims to enhance the understanding of the relationship between Ilizarov fixator configuration and its effects on bone fracture healing. Using Taylor spatial frame (TSF) as an example, the roles of critical parameters (ie, TSF ring diameter, wire pre-tension, fracture gap size, and axial load) that govern fracture healing during the early stages were investigated by using computational modelling in conjunction with mechanical testing involving an advanced 3D optical measurement system. The computational model was first validated using the mechanical test results and then used to simulate mesenchymal stem cell (MSC) differentiations within different regions of the fracture site under various combinations of TSF ring diameter, wire pre-tension, fracture gap size, and axial load values. Predicted spatially dependent MSC differentiation patterns and the influence of each parameter on differentiations were compared with in vivo results, and good agreement was seen between the two. Gap size was identified as the most influential parameter in MSC differentiation, and the influence of axial loading and TSF configuration (ie, ring diameter and wire pre-tension) on cell differentiation was seen to be gap size dependent. Most changes in cell differentiation were predicted in the external callus (periosteal), which is the crucial region of the callus in the early stages. However, for small gap sizes (eg, 1 mm), significant changes were predicted in the endosteal callus as well. The study exhibits the potential of computational models in assessing the performance of Ilizarov fixators as well as assisting surgeons in patient-specific clinical treatment planning.

Role of Dynamic Loading on Early Stage of Bone Fracture Healing.

After fracture, mesenchymal stem cells (MSCs) and growth factors migrate into the fracture callus to exert their biological actions. Previous studies have indicated that dynamic loading induced tissue deformation and interstitial fluid flow could produce a biomechanical environment which significantly affects the healing outcomes. However, the fundamental relationship between the various loading regimes and different healing outcomes has not still been fully understood. In this study, we present an integrated computational model to investigate the effect of dynamic loading on early stage of bone fracture healing. The model takes into account cell and growth factor transport under dynamic loading, and mechanical stimuli mediated MSC differentiation and tissue production. The developed model was firstly validated by the available experimental data, and then implemented to identify the loading regimes that produce the optimal healing outcomes. Our results demonstrated that dynamic loading enhances MSC and growth factor transport in a spatially dependent manner. For example, compared to free diffusion, dynamic loading could significantly increase MSCs concentration in endosteal zone; and chondrogenic growth factors in both cortical and periosteal zones in callus. Furthermore, there could be an optimal dynamic loading regime (e.g. 10% strain at 1 Hz) which could potentially significant enhance endochondral ossification.