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.

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.

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 (COV_P ) 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 (COV_GS ) 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%).

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.

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 (h_c) 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 (σ_y) and work hardening (n) for the investigated range of 0.001 < σ_y/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.

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 (W_B) of the binders. The results showed that Australian FA pastes had higher heat of hydration, adiabatic temperature rise, W_B 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 W_B 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 (σ_y/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.

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.

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.

Net incremental indirect external benefit of manufacturing recycled aggregate concrete

Concrete waste (CW) either reaches landfill with mixed waste or crushed to produce crushed concrete (CC) used as a road-base product in Australia. The coarse portion of CC, referred to as recycled concrete aggregate (RCA) has the potential to be used as an aggregate in structural concrete replacing natural aggregate (NA). The environmental performance of RAC has been studied in comparison to NAC, in terms of direct environmental implications (DEI) concerning the processes in the production chain of these products. However, when replacement at industry level is considered, the implications go beyond the DEI, and affect a series of other products/processes within a system boundary, referred to as indirect environmental implications (IEI). This paper quantifies the key IEI associated with the use of RCA in structural concrete and evaluates the external costs and benefits associated with it using economic evaluation methods. The net benefit associated with the avoidance of landfill of CW, extraction of NA, and transportation of waste and by-products are the major externalities identified and quantified in this paper. Evaluation of these suggest that there is a significant net benefit ranging from 9% to 28% of the price of natural aggregate concrete (NAC) with the production of recycled aggregate concrete (RAC), for RCA replacement rates between 30% and 100%.

Computational simulation of the early stage of bone healing under different configurations of locking compression plates

Flexible fixation or the so-called 'biological fixation' has been shown to encourage the formation of fracture callus, leading to better healing outcomes. However, the nature of the relationship between the degree of mechanical stability provided by a flexible fixation and the optimal healing outcomes has not been fully understood. In this study, we have developed a validated quantitative model to predict how cells in fracture callus might respond to change in their mechanical microenvironment due to different configurations of locking compression plate (LCP) in clinical practice, particularly in the early stage of healing. The model predicts that increasing flexibility of the LCP by changing the bone-plate distance (BPD) or the plate working length (WL) could enhance interfragmentary strain in the presence of a relatively large gap size (> 3 mm). Furthermore, conventional LCP normally results in asymmetric tissue development during early stage of callus formation, and the increase of BPD or WL is insufficient to alleviate this problem.

Measurement and analysis of electromagnetic fields from trams, trains and hybrid cars

Electricity is used substantially and sources of electric and magnetic fields are, unavoidably, everywhere. The transportation system is a source of these fields, to which a large proportion of the population is exposed. Hence, investigation of the effects of long-term exposure of the general public to low-frequency electromagnetic fields caused by the transportation system is critically important. In this study, measurements of electric and magnetic fields emitted from Australian trams, trains and hybrid cars were investigated. These measurements were carried out under different conditions, locations, and are summarised in this article. A few of the measured electric and magnetic field strengths were significantly lower than those found in prior studies. These results seem to be compatible with the evidence of the laboratory studies on the biological effects that are found in the literature, although they are far lower than international levels, such as those set up in the International Commission on Non-Ionising Radiation Protection guidelines.