62 research outputs found
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Fibre Bragg Grating-based Cascaded Acoustic Sensors for Potential Marine Structural Condition Monitoring
This paper explores the potential of using multiple Fibre Bragg grating (FBG)-based sensors for acoustic emission (AE) detection, thus offering an effective alternative to conventional piezoelectric (PZT) sensors, especially where they have shown limitations in use, such as in the marine sector. A cascaded fibre optic acoustic sensor system, using optical filter signal demodulation has been developed and its performance extensively evaluated. To undertake this under standardized conditions, the optical sensor system was evaluated using a glass plate to detect the acoustic signal, followed by an evaluation using a metal plate to identify the location of acoustic sources, when subjected to sonotrode excitation, mimicking acoustic detection in cavitation detection. Under these circumstances, a very good agreement has been reached between the outputs of the optical acoustic sensors and of the co-located PZT acoustic sensors. This work confirms the utility of these sensors – they can detect not only weak AE signals, but also enable multipoint simultaneous measurement, showing their potential for condition monitoring applications, especially in the marine sector
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Optimization of the accelerated curing process of concrete using a fibre Bragg grating-based control system and microwave technology
In this paper, an investigation into the suitability of using fibre Bragg gratings (FBGs) for monitoring the accelerated curing process of concrete in a microwave heating environment is presented. In this approach, the temperature data provided by the FBGs are used to regulate automatically the microwave power so that a pre-defined temperature profile is maintained to optimize the curing process, achieving early strength values comparable to those of conventional heat-curing techniques but with significantly reduced energy consumption. The immunity of the FBGs to interference from the microwave radiation used ensures stable readings in the targeted environment, unlike conventional electronic sensor probes
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Application of fibre Bragg gratings for the optimization of microwave-cured concrete
In this paper, the suitability of using ‘intelligent’ fibre Bragg gratings (FBGs) as sensors for the temperature feedback control of concrete cured in a microwave environment has been presented and experimentally demonstrated. In this novel approach, the temperature data provided by the embedded FBGs are processed on the fly (using a feedback control algorithm) in order to regulate the microwave power so that an internal curing temperature of 70°C is maintained. The immunity of the FBGs to microwave radiation ensures that the embedded sensors remain stable, unlike conventional metallic/electrical probes
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Potential of Microwave Curing for Precast Concrete Manufacture
In this paper, an ongoing research sponsored by Innovate UK on developing an intelligent microwave system for manufacturing concrete products is introduced. The key features of this microwave system include using optical fibre Bragg grating (FBG) sensors to control the temperature and the humidity inside concrete and microwave oven cavity, respectively. Using this tailor-made microwave system, research is ongoing in the Advanced and Innovative Materials (AIM) Group at University College London to explore the potential of curing two types of low-carbon cementitious systems, namely high-volume fly ash (HVFA) and alkali-activated fly ash (AAFA). In both systems, thermal curing is essential for the strength development, in particular, early strength development. Their results indicate that, by using the microwave curing technique, the low-carbon performance can be achieved from both systems whilst the early strength was not affected. The current results also demonstrate a good potential of microwave curing for manufacturing low-carbon precast concrete elements in the future
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Novel Sensor Design Using Photonic Crystal Fibres for Monitoring the Onset of Corrosion in Reinforced Concrete Structures
In this paper, a novel sensing technique has been designed and investigated for the direct, in-situ detection of steel corrosion distributed in reinforced concrete structures. At present, structural health monitoring (SHM) in reinforced concrete structures is generally focused on monitoring the corrosion risk of the reinforcing steel. It is of significant importance, however, to inform industry of both the onset of corrosion and the corrosion rate as these are key contributors to structural degradation and thus evaluating the service life of the structures. This paper aims to address the above challenges by describing a novel corrosion sensor design using birefringent photonic crystal fibres (PCFs). The technique exploits fully both the birefringence of the fibres for force/pressure measurement and their very low temperature sensitivity to detect the onset of corrosion. This new type of sensor not only determines the onset of corrosion but also allows for better monitoring along the length of a reinforcement bar
Styrene-Associated Health Outcomes at a Windblade Manufacturing Plant
Background: Health risks of using styrene to manufacture windblades for the green energy sector are unknown.
Methods: Using data collected from 355 (73%) current windblade workers and regression analysis, we investigated associations between health outcomes and styrene exposure estimates derived from urinary styrene metabolites.
Results: The median current styrene exposure was 53.6 mg/g creatinine (interquartile range: 19.5–94.4). Color blindness in men and women (standardized morbidity ratios 2.3 and 16.6, respectively) was not associated with exposure estimates, but was the type previously reported with styrene. Visual contrast sensitivity decreased and chest tightness increased (odds ratio 2.9) with increasing current exposure. Decreases in spirometric parameters and FeNO, and increases in the odds of wheeze and asthma-like symptoms (odds ratios 1.3 and 1.2, respectively) occurred with increasing cumulative exposure.
Conclusions: Despite styrene exposures below the recommended 400 mg/g creatinine, visual and respiratory effects indicate the need for additional preventative measures in this industry
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Densification of Fresh Concrete by Microwave
Concrete mixes with different fly ash replacement levels, namely 0%, 35% and 55% at a fixed water to binder ratio (W/B) of 0.6 were heated by a tailor-made microwave oven up to 50oC immediately after casting until initial setting in order to remove excessive free water. The compressive strengths of microwave densified samples after 7 days were 3.2%, 7.7% and 29.6% higher than those of oven heated batches. It demonstrated that higher density, lower water absorption and better microstructure were achieved after microwave heating, indicating microwave heating can be a promising technique for densifying fresh concrete
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