Metal-Packaged fibre Bragg grating strain sensors for surface mounting onto spalled concrete wind turbine foundations

In this work, we demonstrate preliminary results for a hermetically sealed, metal-packaged fibre Bragg grating strain sensor for monitoring existing concrete wind turbine foundations. As the sensor is bolted to the sub-surface of the concrete, it is suitable for mounting onto uneven, wet and degraded surfaces, which may be found in buried foundations. The sensor was able to provide reliable measurements of concrete beam strain during cyclic three- And four- point bend tests. The strain sensitivity of the prototype sensor is currently 10 % of that of commercial, epoxied fibre strain sensors

Cardiac autonomic control in the obstructive sleep apnea

Introduction: The sympathetic activation is considered to be the main mechanism involved in the development of cardiovascular diseases in obstructive sleep apnea (OSA). The heart rate variability (HRV) analysis represents a non-invasive tool allowing the study of the autonomic nervous system. The impairment of HRV parameters in OSA has been documented. However, only a few studies tackled the dynamics of the autonomic nervous system during sleep in patients having OSA.Aims: To analyze the HRVover sleep stages and across sleep periods in order to clarify the impact of OSA on cardiac autonomic modulation. The second objective is to examine the nocturnal HRV of OSA patients to find out which HRV parameter is the best to reflect the symptoms severity.Methods: The study was retrospective. We have included 30 patients undergoing overnight polysomnography. Subjects were categorized into two groups according to apneahypopnea index (AHI): mild-to-moderate OSAS group (AHI: 5-30) and severe OSAS group (AHI>30). The HRV measures for participants with low apneahypopnea indices were compared to those of patients with high rates of apneahypopnea across the sleep period and sleep stages.Results: HRV measures during sleep stages for the group with low rates of apneahypopnea have indicated a parasympathetic activation during non-rapid eye movement (NREM) sleep. However, no significant difference has been observed in the high AHI group except for the mean of RR intervals (mean RR). The parasympathetic activity tended to increase across the night but without a statistical difference. After control of age and body mass index, the most significant correlation found was for the mean RR (p =0.0001, r = -0.248).Conclusion: OSA affects sympathovagal modulation during sleep, and this impact has been correlated to the severity of the disease. The mean RR seemed to be a better index allowing the sympathovagal balance appreciation during the night in OSA.Keywords: autonomic nervous system; sleep apnea; heart rate; sleep; circadia

Molecular dynamics simulation of mechanical properties of intercalated GO/C-S-H nanocomposites

Graphene oxide (GO) cementitious composites have recently attracted considerable interest due to their improved mechanical properties and durability. However, most research is focused on the macroscale performance of these composites with very little experimental and modelling research on the characterization of their nanoscale behavior. This makes the design of these new GO-cementitious composites challenging. In this paper, we present a novel molecular dynamics (MD) model for GO-cementitious nanocomposites to understand their behavior and predict their mechanical and fracture properties. In this model, different numbers of GO nanoplatelets were inserted into the C-S-H structure and a number of nanoscale mechanical parameters and crack bridging mechanism were obtained. The MD simulation results revealed that the addition of GO sheets increased the tensile and compressive strength of C-S-H by roughly 50% and 100%. The MD simulation results also identified a double-peak phenomenon which is an indication of additional plasticity when the intercalated GO/C-S-H structures are subjected to compressive stress. The fracture simulation results showed that the failure mode of the intercalated GO/C-S-H composites was marked by high energy release. The results of fracture simulations with different notch lengths also indicated that the addition of GO could improve the fracture performance due to a good interfacial connection between the GO and the C-S-H gel

Effect of supercritical carbonation on the strength and heavy metal retention of cement-solidified fly ash

This paper presents both experimental and multi-physics studies on the carbonation and heavy metal retention properties of cement-solidified fly ashes. Cement-solidified fly ash samples with 40% and 60% fly ash ratios were tested for carbonation depth after being supercritically carbonated. Tests were also carried out for compressive strength and retention capacity of heavy metals of the samples before and after supercritical carbonation. Using CO2 absorption instead of calcium carbonate to measure carbonation degree, a multi-physics model was developed and combined with a leaching model to study the impact of carbonation on Cu and Pb leaching from the cement-solidified fly ash. The results show that supercritical carbonation has both positive and negative impacts on the strength and retention capability of heavy metals of the cement-solidified fly ashes, which suggests that both the carbonation conditions and the amount of fly ash recycled in cementitious materials should be properly controlled to maximize potential positive effect

Enhancing the self-sensing and energy storage capabilities of cementitious composites through marine sand doping

In this paper, for the first time, we investigate the inherent ionic conductivity of seawater-based cementitious composites containing marine sand aggregates, when air cured over 28 days with the objective of uncovering new functionalities. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and density functional theory (DFT) were employed to elucidate the ionic conduction mechanisms in this material system and characterize its stress self-sensing and electrochemical charge retention capabilities. The results revealed that the marine aggregates are not ionic conductive materials; however, they facilitate improved electrochemical response through enhanced formation of highly ion-exchanging calcium-silicate-hydrate (C-S-H) phases, coupled with integrated porous channels that enable sustained ion mobility despite drying. This synergistic ion transport yielded a bulk ionic resistivity around 25 kΩ⊡cm at room temperature, which lies in typical ranges seen in solid-state electrolytes for battery systems. Controlled compressive loading indicates appreciable self-sensing capacity at low-stress levels, suggesting applicability to detect the onset of mechanical damage. Negligible charge leakage upon 28 days of curing further demonstrates the electrical energy storage potential of the sea-based cement. By harnessing locally available seawater and marine sand resources to develop ionic conductive cementitious composites, this work provides the framework to optimize durable multifunctionality for sensing and electrical energy storage in reinforced concrete infrastructure. This in return improves the sustainability and energy efficiency of the built environment

Experimental study and multi-physics modelling of concrete under supercritical carbonation

This paper presents both experimental study and multi-physics modelling of supercritical carbonation of concrete. A novel mathematical model is proposed to simulate random distribution of coarse aggregates in concrete. Supercritical carbonation tests of concrete are carried out and the measured carbonation depth is compared with the simulation results. On the basis of previous research on random field of porosity and supercritical carbonation of cement mortar, a new supercritical carbonation model is developed to study the effect of randomly distributed coarse aggregates and porosity on the irregularities of carbonation depth of concrete. The effect of the type, volume fraction and gradation of coarse aggregates and the porosity of ITZ on the distribution of irregular carbonation depth are also studied. The results demonstrate that the proposed two-dimensional random coarse aggregates model can be used satisfactorily to generate different types, volume fraction and gradation of coarse aggregates with the designed mix proportion within a confined space. The method provides a better and more realistic predictive model for simulating carbonation depth of concrete due to random distribution of coarse aggregates and porosity

Experimental and numerical study on tensile properties of bolted GFRP joints at high and low temperatures

This paper presents both experimental and numerical studies on bolted glass fiber reinforced polymer (GFRP) joints subjected to uniaxial tension and different thermal conditions (−20 ℃, 20 ℃ and 60 ℃). Laboratory tests are conducted to obtain strength, elastic modulus and deformation of the joints. The numerical model is developed using the discrete element method (DEM) that can predict not only the above properties of the joints, but also the failure modes with detailed meso/micro damages that are in consistent with the observations from the tests. The DEM model is also used in the parametric studies to study the influence of the end distance to bolt/hole diameter ratio and the lap width to bolt/hole diameter ratio on the mechanical properties and failure models of the joints

An effective microscale approach for determining the anisotropy of polymer composites reinforced with randomly distributed short fibers

In this paper, an effective microscopic modeling scheme is presented to analyze mechanical properties of composites with random short fibers. To this end, the displacement-load tests of the standard samples, which are acquired by cutting a short fiber-reinforced composite plate of 650 mm × 650 mm × 2.5 mm, are firstly executed under the quasi-static tensile loads. To identify the geometric sizes of the short fibers and their distributions at microscopic scale, the advanced micro-computed tomography (micro-CT) is employed by testing a small sample of 1 cm × 2.5 mm × 2.5 mm. On this basis, a simplified microscopic model is reconstructed by the 3D parametric finite-volume direct averaging micromechanics (FVDAM) theory according to the statistic results of the micro-CT images. The proposed method is further validated by comparing the effective modulus obtained from tensile tests. The scanning electron microscopy (SEM) is also used to visualize the fracture morphology of the fibers. It is found that brittle fracture occurs in the short-fibers paralleled to the external loading

Failure analysis of fiber-reinforced composites subjected to coupled thermo-mechanical loading

Structures made of fiber reinforced composites have captured extensive attentions in the scientific and en-gineering communities due to their excellent performance and applicability. When these structures are in ser-vice, they are likely exposed to variations of ambient temperature that may have an impact on their strength. To study this effect, a coupled thermo-mechanical model is required. This paper develops a microscopic mechanical model to investigate failure of composite structures subjected to a coupled thermo-mechanical condition. Stiffness degradations of composite laminates are first investigated. A comparison between experimental data and theoretical results under the quasi-static loadings are presented to validate the proposed method. The method provides detailed microscopic stress distribution of the composites under the coupled thermo-me-chanical loading for failure analysis, which shows that a higher ambient temperature variation will generally cause stiffness degradation and failure strength for both uniaxially and biaxially loaded laminates

Assessing Molecular Signature for Some Potential Date (Phoenix dactylifera L.) Cultivars from Saudi Arabia, Based on Chloroplast DNA Sequences rpoB and psbA-trnH

Phoenix dactylifera L. (date palm), being economically very important, is widely cultivated in the Middle East and North Africa, having about 400 different cultivars. Assessment of date cultivars under trading and farming is a widely accepted problem owing to lack of a unique molecular signature for specific date cultivars. In the present study, eight different cultivars of dates viz., Khodry, Khalas, Ruthana, Sukkari, Sefri, Segae, Ajwa and Hilali were sequenced for rpoB and psbA-trnH genes and analyzed using bioinformatics tools to establish a cultivar-specific molecular signature. The combined aligned data matrix was of 1147 characters, of which invariable and variable sites were found to be 958 and 173, respectively. The analysis clearly reveals three major groups of these cultivars: (i) Khodary, Sefri, Ajwa, Ruthana and Hilali (58% BS); (ii) Sukkari and Khalas (64% BS); and (iii) Segae. The economically most important cultivar Ajwa showed similarity with Khodary and Sefri (67% BS).The sequences of the date cultivars generated in the present study showed bootstrap values between 38% and 70% so these sequences could be carefully used as molecular signature for potential date cultivars under trading and selection of genuine cultivars at the seedling stage for farming