• Smart Structures and Systems
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• v.8 no.5
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• pp.471-486
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• 2011

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

• Advances in concrete construction
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• v.5 no.2
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• pp.145-154
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• 2017

In the present day scenario, concrete construction is rapidly becoming uneconomical and non sustainable practice, due to the scarcity of raw materials and environmental pollution caused by the manufacturing of cement. In this study an attempt has been made to propose recycled aggregates from demolition wastes as coarse aggregate in geopolymer concrete (GPC). Experimental investigations have been conducted to find optimum percentage of recycled aggregates (RA) in GPC by replacing 20%, 30%, 40%, 50% and 60% of coarse aggregates by RA to produce recycled aggregate geopolymer concrete (RGPC). From the study it has been found that the optimum replacement percentage of recycled aggregates was 40% based on mechanical properties and workability. In order to study and compare the flexural behaviour of RGPC and GPC four beams of size $175mm{\times}150mm{\times}1200mm$ were prepared and tested under two point loading. Test results were evaluated with respect to first crack load, ultimate load, load-deflection characteristics, ductility and energy absorption characteristics. Form the experimental study it can be concluded that the addition of recycled aggregate in GPC causes slight reduction in its strength and ductility. Since the percentage reduction in strength and behaviour of RGPC is meager compared to GPC it can be recommended as a sustainable and environment friendly construction material.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.55-62
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• 2004

In this study, the effects of Ca content and processing variables on hot rolling properties of gravity cast AZ31-xCa alloys were evaluated systematically. The number and length of side crack were decreased with increasing preheating temperature and decreasing reduction ratio per pass and Ca content. The UTS and YS were not strongly dependent on the Ca content but the elongation decreased with increasing Ca content. The decrease of elongation in Ca containing alloys was least when the sheets were fabricated under preheating temperature of $400^{\circ}C$ and reduction ratio per pass of $15\%$. The sheets had the sound external features with little side cracks by homogenization of gravity cast AZ31-xCa alloys before hot rolling. In the cases of AZ31-xCa alloys containing under $1wt.\%$ Ca, the annealed sheets after homogenization and hot rolling had the similar tensile properties to those of AZ31 sheet.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.95-98
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• 2003

This paper presents the results of field experiment to apply the difference of setting tine method using super retarding agent for reducing hydration heat of mass concrete of foundation. According to the results, as the properties of fresh concrete, base concrete satisfies aimed slump and air content, and there is no difference of slump and air content with mixture of super retarding agent. The mixing ratio of super retarding agent is determined for setting time to be retarded by 12 hours in comparison with base concrete, but because the temperature of the air and concrete is low, the difference of setting time is retarded to 24 hours. In man concrete of foundation to which the difference of setting time method is applied, crack by hydration heat is not seen because the lower concrete of super retarding agent generates heat after generation of hydration heat of the upper concrete.

• Computers and Concrete
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• v.15 no.1
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• pp.37-54
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• 2015

In general, cracks significantly deteriorate the in-situ performance of concrete members and structures, especially in urban metro tunnels that have been embedded in saturated soft soils. The microcapsule self-healing method is a newly developed healing method for repairing cracked concrete. To investigate the optimal microcapsule parameters that will have the best healing effect in concrete, a 3D analytical probability healing model is proposed; it is based on the microcapsule self-healing method's healing mechanism, and its purpose is to predict the healing efficiency and healing probability of given cracks. The proposed model comprehensively considers the radius and the volume fraction of microcapsules, the expected healing efficiency, the parameters of cracks, the broken ratio and the healing probability. Furthermore, a simplified probability healing model is proposed to facilitate the calculation. Then, a Monte Carlo test is conducted to verify the proposed 3D analytical probability healing model. Finally, the influences of microcapsules' parameters on the healing efficiency and the healing probability of the microcapsule self-healing method are examined in light of the proposed probability model.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.371-379
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• 2013

This paper investigates the cracking and tension-stiffening behavior of 100 MPa shrinkage-compensated strain-hardening cement composite (SHCC) and conventional concrete tie elements in monotonic and cyclic tension. Strain and surface crack formation of tension ties were monitored with two strain displacement transducers and a photo microscope with a lens of magnification 50 times. Three different cement composites such as conventional concrete, shrinkage-compensated SHCC, and normal SHCC were used in the tie specimens to investigate the influence of the cement composite type on the tension stiffening and cracking behavior. Test results indicated that initial shrinkage of the ultra high-strength cement composites is greatly reduced as the 10% replacement of cement by the shrinkage-compensating admixture based on calcium sulfo-aluminate (CSA). The test results on the SHCC tension ties showed that the first cracking load decreases proportionally to the initial shrinkage strain. Reinforced ultra high-strength SHCC ties with the initial shrinkage compensation exhibited improved tension stiffening and smaller crack spacings, i.e. the reduction in crack width. Cyclic loading did not have a significant effect on tension stiffening and cracking behavior of tension ties with normal concrete and SHCC materials.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.263-271
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• 2005

HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1992-1996
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• 2007

This study focuses on the hydrogen embrittlement of iron tube for fuel line of PEMFC (Proton Exchange Membrane Fuel Cell). PEMFC is operated by feed of hydrogen as a reactant and steam for proton conductivity of membrane. However, the environment with hydrogen and steam occur the hydrogen-induced degradation in BOP system. When iron tube was exposed to hydrogen and steam condition for 24 hours, the oxide layer on the surface was decreased by reduction. When the ambient temperature was 90$^{\circ}C$ micro cracks were found on the surface than any other temperature. The mechanical strength of iron tube was 3% lower than that of non-experiment tube. Maximum tensile stress was decreased 8%.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.11-14
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• 2004

In this paper, field application of mass concrete using setting time difference of super retarding agent is reported to reduce hydration heat of concrete placed at newly constructed apartment house in Busan. Horizontal placing lift is applied. According to test results. slump and air content meets the requirement of target values. For compressive strength, it exceeds the nominal strength ordered by the costumer. Compressive strength of concrete cured in place is achieved more than the values of nominal strength at l4days. For temperature history, maximum temperature of center at top section shows 58.5$^{\circ}C$, and at bottom section, 62.6$^{\circ}C$. According to naked eye's investigation, no hydration heat crack is observed at the surface of concrete.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.2
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• pp.80-87
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• 2009

Effects of retained austenite contents on ductility of medium carbon spring steels according to steel alloy compositions and heat treatment conditions were studied. Contents of retained austenite varied with steel compositions and heat treatment conditions, and some retained austenite were found to transform to martensite on stress. Reduction of area (RA) increased with contents of retained austenite, then saturated through its maximum, and subsequently decreased. Increase in RA with retained austenite contents could be due to crack blunting effect by retained austenite on stress, however, more contents of martensite transformed from retained austenite in its higher contents could cause decrease in RA.