• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1199-1209
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• 2023

Where concrete structures are designed to have a service life of over 100 years, their performance must be monitored, for the prediction models available are fraught with uncertainties that need to be eliminated. The present study was conducted to meet that need by monitoring a pilot structure for low and intermediate radioactive waste storage. Long-term operation of the sensors was observed to be adequate to determine the value of the parameters that characterise structural durability, such as corrosion current density. The parameters analysed were correlated to calculate their reciprocal impact: where applied in conjunction with artificial intelligence tools, temperature, for instance, was found suitable for finding activation energy and expansion coefficients and detecting outliers. The results showed the pilot structure to perform satisfactorily.

• Journal of the Korean Society of Safety
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• v.21 no.4 s.76
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• pp.95-101
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• 2006

It is well known that the thermal load in PSC(prestressed concrete) box-girder bridge is the principal cause of detrimental crack. The longitudinal stress caused by the lateral stress from the temperature gradient in slab of PSC box-girder bridge has a considerable influence on the durability and economy of bridge structures. As the basic study for the rational consideration of thermal load and the derivation of design guide, the inverse thermal analysis program for PSC box-girder bridges using field measurement data is developed. In this paper, thermal analyses are performed using field monitoring data for the sample PSC box-girder bridge. It is proposed that the link between monitoring program and the inverse analysis program is available.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.287-297
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• 2014

Heat of hydration of mass concrete is one of the most important factors that significantly affect structural quality and construction period. Therefore, appropriate methods to control heat of hydration are essential technologies for mass concrete construction. In this study, probability of thermal cracking was checked by thermal analysis prior to the construction of a turbine foundation in a domestic power plant. Subsequently, changes of concrete mix proportion and an effective curing method were proposed to control heat of hydration of mass concrete structures. Concrete manufactured by slag cement was proposed instead of concrete produced by ordinary Portland cement, and an automated curing method was proposed to improve the curing method using typical moist curing with blanket. The automated curing method maintains the temperature difference between center and surface of concrete below a setting value by temperature monitoring. Concrete with slag cement was used for actual construction. One of two identical turbine foundations was cured by an insulated curing method, and the other was cured by the automated curing method to compare the curing methods. And then, the effects of control of heat of hydration were evaluated based on temperature/strain monitoring and crack investigations.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.1-9
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• 2015

PURPOSES : The objective of this study is to propose a quality control and quality assurance method for use during asphalt pavement construction using non-destructive methods, such as ground penetrating radar (GPR) and an infrared (IR) camera. METHODS : A 1.0 GHz air-coupled GPR system was used to measure the thickness and in situ density of asphalt concrete overlay during the placement and compaction of the asphalt layer in two test construction sections. The in situ density of the asphalt layer was estimated based on the dielectric constant of the asphalt concrete, which was measured as the ratio of the amplitude of the surface reflection of the asphalt mat to that of a metal plate. In addition, an IR camera was used to monitor the surface temperature of the asphalt mat to ensure its uniformity, for both conventional asphalt concrete and fiber-reinforced asphalt (FRA) concrete. RESULTS : From the GPR test, the measured in situ air void of the asphalt concrete overlay gradually decreased from 12.6% at placement to 8.1% after five roller passes for conventional asphalt concrete, and from 10.7% to 5.9% for the FRA concrete. The thickness of the asphalt concrete overlay was reduced from 7.0 cm to 6.0 cm for the conventional material, and from 9.2 cm to 6.4 cm for the FRA concrete. From the IR camera measurements, the temperature differences in the asphalt mat ranged from $10^{\circ}C$ to $30^{\circ}C$ in the two test sections. CONCLUSIONS : During asphalt concrete construction, GPR and IR tests can be applicable for monitoring the changes in in situ density, thickness, and temperature differences of the overlay, which are the most important factors for quality control. For easier and more reliable quality control of asphalt overlay construction, it is better to use the thickness measurement from the GPR.

• International Journal of Highway Engineering
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• v.17 no.5
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• pp.33-38
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• 2015

PURPOSES : The purpose of this paper is to investigate the application of thermoelectric technology to concrete structures for harvesting solar energy that would otherwise be wasted. In various fields of research, thermoelectric technology using a thermoelectric module is being investigated for utilizing solar energy. METHODS: In our experiment, a halogen lamp was used to produce heat energy instead of the solar heat. A data logger was used to record the generated voltage over time from the thermoelectric module mounted on a concrete specimen. In order to increase the efficiency of energy harvesting, various factors such as color, architecture, and the ability to prevent heat absorption by the concrete surface were investigated for the placement of the thermoelectric module. RESULTS : The thermoelectric module produced a voltage using the temperature difference between the lower and upper sides of the module. When the concrete specimen was coated with an aluminum foil, a high electric power was measured. In addition, for the power generated at low temperatures, it was confirmed that the voltage was generated steadily. CONCLUSIONS: Thermoelectric technology for energy harvesting can be applied to concrete structures for generating electric power. The generated electricity can be used to power sensors used in structure monitoring in the future.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1551-1552
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• 2013

• Smart Structures and Systems
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• v.7 no.1
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• pp.27-40
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• 2011

Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength and strength gain rate, retainage of structural properties in elevated temperature environments, chemical stability in highly acidic conditions and environmental benefits. Combining the above mentioned characteristics with induced electrical conductivity, could enable geopolymer cement to serve as a smart and sustainable cementitious material suitable for health monitoring of civil structures. Carbon fibers were added to fresh geopolymer and OPC (ordinary Portland cement) mixes to enhance their electrical conductivities. AC-impedance spectroscopy analysis was performed on the specimens with fiber fraction ranging from 0.008 to 0.8 with respect to the weight of cementitious binder, to measure their electrical resistivity values and to determine the maximum beneficial fiber content required to attain electrical percolation. Experimental observations suggest that CFR-geopolymer cement exhibits superior performance to CFR-OPC in terms of conducting electrical current.

• Computers and Concrete
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• v.20 no.5
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• pp.605-616
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• 2017

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.3
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• pp.194-204
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• 1998

This study was performed to suggest the proper maintenance method for the deteriorated gerber type PC box girder bridge by using the long term displacement monitoring data. For this study, the monitoring system which can measure the long term displacement and the concrete surface temperature was designed and operated. From the measurement and structural analysis results, the cause of the permanent deformation which the bridge has already was estimated, and based on this result, the allowable permanent displacement value at the hinge was suggested. From this study, it was known that the long term monitoring system can be applied to the active maintenance of the deteriorated bridge and the suggested allowable permanent displacement could be used for the maintenance of the bridge.

• Smart Structures and Systems
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• v.1 no.4
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• pp.355-368
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• 2005

Large and complex structures are being built now-a-days and, they are required to be functional even under extreme loading and environmental conditions. In order to meet the safety and maintenance demands, there is a need to build sensors integrated structural system, which can sense and provide necessary information about the structural response to complex loading and environment. Sophisticated tools have been developed for the design and construction of civil engineering structures. However, very little has been accomplished in the area of monitoring and rehabilitation. The employment of appropriate sensor is therefore crucial, and efforts must be directed towards non-destructive testing techniques that remain functional throughout the life of the structure. Fiber optic sensors are emerging as a superior non-destructive tool for evaluating the health of civil engineering structures. Flexibility, small in size and corrosion resistance of optical fibers allow them to be directly embedded in concrete structures. The inherent advantages of fiber optic sensors over conventional sensors include high resolution, ability to work in difficult environment, immunity from electromagnetic interference, large band width of signal, low noise and high sensitivity. This paper brings out the potential and current status of technology of fiber optic sensors for civil engineering applications. The importance of employing fiber optic sensors for health monitoring of civil engineering structures has been highlighted. Details of laboratory studies carried out on fiber optic strain sensors to assess their suitability for civil engineering applications are also covered.