Long-term behaviour of particulate-filled epoxy-based polymers

Epoxy-based polymers are now widely used in civil engineering applications including bonding of structural elements, filling for structural repair, and coating for railway sleepers. Recently, different particulate fillers were introduced to reduce the cost of epoxy-based polymers. While the optimum amount of fillers was found to enhance the short-term properties of epoxy-based polymers, their effect on the long-term properties is still unknown. Understanding the long-term behavior of epoxy-based polymers is important as this material is subject to different environmental conditions, which can limit their application range. This study systematically investigated the long-term durability through deep understanding of the mechanistic response of particulate-filled epoxy-based polymer coating containing fire retardant (FR) and fly ash (FA) fillers. It focused on the weathering effects of high moisture, elevated in-service temperature, and solar ultraviolet (UV) radiation, and the synergistic effects of these severe environmental conditions on the mechanical, physico-chemical and microstructure behavior of particulate-filled epoxy-based polymer. New empirical models were also developed to predict the changes in the mechanical characteristics of epoxy-based polymers when exposed to harsh environmental conditions. The effect of in-service elevated temperature (from room temperature to 80°C) was evaluated as the first study. FR and FA filler materials were increased from 0% to 60% (with an increment of 20%) in the epoxy based matrix. The physical, mechanical and microstructure of particulate-filled epoxy polymers epoxy-based polymer matrix was examined. The results showed that sensitivity of epoxy resin against in-service temperatures can be significantly improved by the inclusion of fillers by up to 60% by volume. A simplified prediction equation based on power function showed a strong correlation to the experimental strength properties of particulate-filled epoxy based resin at different levels of in-service elevated temperature. The effect of the combined moisture and temperature (hygrothermal conditioning) on the durability of particulate-filled epoxy resin was investigated as the second study. The epoxy resin was conditioned for up to 3000 h at temperatures up to 60ºC and a relative humidity of 98%. Inclusion of fillers was found to decrease the moisture absorption, increase the glass transition temperature and slightly reduce the mechanical properties after hygrothermal conditioning. Based on the Arrhenius model, the filled epoxy polymers can retain more than 70% of their mechanical properties at 100 years of service in the Australian environment. The behaviour of the particulate filled epoxy polymer coating when exposed to UV was investigated as the third study. Epoxy-based resin system filled with FR and FA was exposed to UV for up to 2000 h. It was found that adding up to 60% by volume of FR and FA reduced the UV degradation to 0.5 mm, which is 5 times less than that of the neat epoxy resin. The developed prediction equation showed that providing a polymer coating of 11 mm will result in up to 100 years UV resistant materials. Finally, the synergistic effect of temperature, moisture and UV on the long-term performance of the particulate filled epoxy polymer coating was evaluated. The polymer coating was conditioned at a relative humidity of 98% and temperature of 60ºC for 2000 h (HG). These specimens were then exposed to UV for 2000 h. It was found that not all environmental conditions were detrimental to the properties of particulate filled epoxy, indicating its suitability as a protective coating material. An in-depth understanding of the long-term behaviour of particulate filled epoxy polymer coating was the significant outcome of this study. The results from this work provided a good representation and comparison of the long-term properties and durability performance of particulate filled epoxy polymer coating in different harsh environments. The experimental data, theoretical models and predictions equations derived from this study are critical for a safe mix design and use of epoxy-based polymers as coating for civil infrastructure

The Legibility Efficacy of Historical Neighborhoods in Creating a Cognitive Map for Citizens

Nowadays, historical neighborhoods in Iran are in a state of decay due to the lack of spatial legibility with respect to their organic spatial layout. Hence, the level of interaction among people and their perception of the environment has gradually diminished. Historical neighborhoods no longer possess their former prosperity and function, and citizens prefer to inhabit neighborhoods with newer configurations to meet their demands. The aim of this study was to investigate the role of the spatial legibility of historical neighborhoods in creating a suitable cognitive map for citizens. Quantitative and qualitative methods were applied using a questionnaire and simulation test instruments. In addition, in order to analyze the spatial configuration of the target areas, the Space Syntax method was implemented using Depthmap 10. The findings indicated that landmarks and navigation signs were identified as the most important factors affecting legibility from the viewpoint of users. Furthermore, the correlation between integration and connectivity illustrated that the studied areas possessed poor spatial legibility due to the organic texture of their spatial configurations. Accordingly, solutions such as enhancing the interaction between highly integrated streets and identified landmarks were emphasized to ameliorate the legibility of these spaces. The present study contributes to sustainable urban design with respect to the rejuvenation of historical districts by proposing a set of pragmatic alterations of urban spatial configurations. This research may be fruitful for urban designers, planners and managers seeking to revitalize historical neighborhoods

The impact of COVID-19 on visitors’ wayfinding within healthcare centers

The novel COVID-19 pandemic has caused substantial calamities in developing countries such as Iran, which initially suffered from inadequate infrastructure essential for the pandemic control. Due to the ongoing development of this malady, healthcare centers are recognized as one of the most significant hotspots within public settings so they are directly pertinent to the physical and mental health of visitors. The main objective for conducting the present study is to investigate the impact of the COVID-19 pandemic on the visitors' wayfinding procedure within Qa'em hospital, located in Rasht, northern Iran. The adopted methodology in the present study is based on a comparison between the collected data regarding the wayfinding behavior of visitors before and after the outbreak of the COVID-19 pandemic using mixed methods, namely Space Syntax, gate counting, people following, and semi-structured interviews. The obtained empirical results displayed that visitors were significantly confused and hesitant throughout their wayfinding process after the outbreak of the pandemic. Indeed, spatial accessibility and legibility were not found to be adequate for facilitating the wayfinding of the visitors. Moreover, the requirements for the reconfiguration of furniture layout in the waiting areas, according to the underlying notions of social distancing, became conspicuous as the pragmatic implications for the post-pandemic healthcare centers

Effect of nano-CuO on engineering and microstructure properties of fibre-reinforced mortars incorporating metakaolin: experimental and numerical studies

In this study, the effects of nano-CuO (NC) on engineering properties of fibre-reinforced mortars incorporating metakaolin (MK) were investigated. The effects of polypropylene fibre (PP) were also examined. A total of twenty-six mixtures were prepared. The experimental results were compared with numerical results obtained by adaptive neuro-fuzzy inference system (ANFIS) and Primal Estimated sub-GrAdient Solver for SVM (Pegasos) algorithm. Scanning Electron Microscope (SEM) was also employed to investigate the microstructure of the cement matrix. The mechanical test results showed that both compressive and flexural strengths of cement mortars decreased with the increase of MK content, however the strength values increased significantly with increasing NC content in the mixture. The water absorption of samples decreased remarkably with increasing NC particles in the mixture. When PP fibres were added, the strengths of cement mortars were further enhanced accompanied with lower water absorption values. The addition of 2 wt % and 3 wt % nanoparticles in cement mortar led to a positive contribution to strength and resistance to water absorption. Mixture of PP-MK10NC3 indicated the best results for both compressive and flexural strengths at 28 and 90 days. SEM images illustrated that the morphology of cement matrix became more porous with increasing MK content, but the porosity reduced with the inclusion of NC. In addition, it is evident from the SEM images that more cement hydration products adhered onto the surface of fibres, which would improve the fibre–matrix interface. The numerical results obtained by ANFIS and Pegasos were close to the experimental results. The value of R2 obtained for each data set (validate, test and train) was higher than 0.90 and the values of mean absolute percentage error (MAPE) and the relative root mean squared error (PRMSE) were near zero. The ANFIS and Pegasos models can be used to predict the mechanical properties and water absorptions of fibre-reinforced mortars with MK and NC

A three-dimensional numerical comparison of bearing capacity and settlement of tapered and under-reamed piles

Tapered piles by top cross sections larger than the toe cross sections and under-reamed piles by having one or more bulbs, have the potential for substantial major sides over conventional straight-sided piles. Most of the studies on tapered and under-reamed piles have been conducted on the experimental side, while, theoretical studies, such as finite element method, have been mainly confined to conventional straight-sided piles. On the other hand, although several field, laboratory and experimental studies have been conducted to study the behaviour of tapered and under-reamed piles, few numerical studies have been carried out to simulate the behaviour of the piles. In addition, there is no research to compare and evaluate behaviour of these two piles due to different geotechnical and geometrical properties. Therefore, the aim of this study was to numerically investigate bearing capacity and settlement of tapered and underreamed piles by changing the soil type, cohesion, angle of internal friction, the length and diameter of piles, tapering degree and the number of bulbs using finite element method. Based on the FEM results, it was found that by increasing the values of geotechnical and geometrical properties, bearing capacity of the tapered pile was more than that of the under-reamed one (i.e. settlement of tapered pile was less than that of the under-reamed one). The reason for this trend could be attributed to increasing contact surface area, friction resistance and more adhesion between soil and the tapered pile. In addition, bulb number of under-reamed piles and tapering degree of tapered piles had significant effects on settlement and bearing capacity of the piles

An experimental investigation into the effects of Cr2O3 and ZnO2 nanoparticles on the mechanical properties and durability of self-compacting mortar

In this paper, the effects of using Cr2O3 and ZnO2 nanoparticles on the mechanical properties and durability of self-compacting mortars are investigated. A fraction of Portland cement was replaced with 1, 2, 3, 4 or 5 wt.% of either Cr2O3 or ZnO2 nanoparticles, and 25 wt.% fly ash. The rheological properties of these mortars were determined through the mini-slump flow diameter and V-funnel flow time tests. The mechanical and durability characteristics were evaluated by compressive and flexural strength, water absorption, electrical resistivity and rapid chloride permeability tests. The microstructure of the mortars was assessed through the use of scanning electron microscopy. The inclusion of 2 wt.% Cr2O3 or 4 wt.% ZnO2 nanoparticles had the best result in compressive and flexural strength tests. Also, mixtures containing either 3 wt.% of Cr2O3 or 5 wt.% of ZnO2 nanoparticles obtained the best result in terms of durability. It can be deduced that the properties of these mixtures are significantly improved by the addition of Cr2O3 and ZnO2 nanoparticles

Investigating the role of spatial configuration on visitors’ spatial cognition in health-care spaces: case studies in Gilan, Iran

Purpose: This study aims to explore the impact of spatial configuration on behavioral patterns of visitors in the ground floor of health-care spaces. Design/methodology/approach: In this study, the Space Syntax analysis was used to combine visibility graph analysis and axial line analysis with empirical observation of visitors' activities. Two types of observation methods on visitors were conducted to discover the behavioral patterns of individuals, respectively, named 'gate counts' and 'people following.' Findings The outcomes of this research revealed that the spatial arrangements of pathways, public areas, vertical circulations, entrance space, lobby, emergency department, reception desk and pharmacy have a significant influence on the way that visitors perceive the health-care environment. Research limitations/implications The current research is limited to two aspects of effective wayfinding (configuration of health care and geometry). Future work can investigate the other potential factors coupled with the current factor as an integrated research for enhancing wayfinding and sustaining accessibility. Another limitation is that the observation results for this study had been conducted before the COVID-19 pandemic and future studies can compare these results with the current COVID-19 situation within health care environments. Originality/value: A large amount of research has focused on the needs of populations in developed countries. This topic has not been investigated thoroughly by professionals in developing countries such as Iran. Accordingly, this study benefits environmental psychologists and architects by revealing the effective characteristics of legible spaces in health-care environments

Effects of ultraviolet solar radiation on the properties of particulate-filled epoxy based polymer coating

Exposure to solar ultraviolet (UV) radiation causes photochemical damage near the exposed surface, which results in the degradation of composite reinforcing elements. To minimise the UV degradation, epoxy polymers are being applied as protective coatings to composite materials to retain properties during their design service life. In this study, the effects of UV exposure on the physical, mechanical, and thermo-mechanical properties, including the microstructure particulate-filled epoxy-based polymer coating, were investigated. The polymer coating contains up to 60% by volume of hydrated alumina powder fire retardant (FR) and fillers such as an industrial waste like fly ash (FA) and is exposed to simulated UV conditions either 1000 h or 2000 h. Physical observations showed yellowing at the surface of neat epoxy coating after UV exposure but the presence of particulate FR and FA fillers minimised fading and weight loss. Similarly, no reduction in the flexural strength was observed for polymer coating containing at least 40% fillers, indicating that the FR and FA retained the structural performance of the coating. SEM observation revealed formation of microcracks in the surface of the neat epoxy resin but a dense microstructure in particulate filled epoxy resin after exposure to UV radiation. FTIR analyses indicated that photo-degradation due to UV radiation was limited only on the thin surface of the coating. From the results of this study, a coating thickness of at least 11 mm is required for epoxy based polymer coating with 60% by volume fillers, which is 5 times thinner than neat epoxy resin, to provide 100 years of UV resistance