• International Journal of Highway Engineering
• /
• v.6 no.2 s.20
• /
• pp.61-70
• /
• 2004

Cement treated Soil has superior characteristics as pavement-base including strength, curability, hardness, freezing resistance. However drying shrinkage of Cement treated base has been indicated as disadvantage, since reflection crack of surface layer is induced from drying shrinkage of cement treated base. This study propriety about low-shrinkage cement treated base that can control shrinkage of cement and control reflection crack at asphalt overlay & concrete slab.

• Journal of the Korea Concrete Institute
• /
• v.27 no.5
• /
• pp.569-577
• /
• 2015

The aim of this study is to qualitatively evaluate the cracking control effects of expansive concrete used in reinforced concrete building. The result of experiments in laboratory shows that autogenous shrinkage and drying shrinkage are suppressed by using expansive additive. The tensile stress-strength ratio is lower in expansive concrete than normal concrete under fully restrained condition. Compression stress could be effectively generated in early age in the walls in buildings by the use of expansive additive, and tensile stress due to drying shrinkage at later age eventually decreased. Additionally, visual observation at long-term ages shows that the cracking area of expansive concrete was approximately 35% of normal concrete, which confirms that the use of expansive additive reduces concrete cracking in reinforced concrete buildings.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.12 no.2
• /
• pp.201-214
• /
• 1999

이 연구는 2경간 연속 PSC-Beam 교량의 경간 내측 지지점의 바닥판에서 발생할 수 있는 균열의 제어에 관한 내용을 다루고 있다. PSC-Beam 교량은 주형인 PSC-Beam을 거치시킨후 바닥판을 현장타설 콘크리트로 시공된다. 이로 인하여 주형 콘크리트와 바닥판 콘크리트의 시간의존적 거동차이, 주형의 연속화에 따른 거동 등에 의하여 부모멘트가 가장 크게 걸리는 지점부에서 균열이 쉽게 발생된다. 따라서 이 논문에서는 2경간 연속 PSC-Beam 교량의 연속화에 따른 거동을 수치적 방법으로 해석하여 지점부 바닥판의 균열거동이 예측되었다. 이를 위하여 해석모델에는 콘크리트의 시간의존적 현상인 크리프와 건조수축이 고려되었으며, 2경간 연속 PSC-Beam 교량의 거동에 영향을 나타내는 여러 가지 인자가 고려되어 해석되었다. 끝으로 콘크리트의 모델식을 이용하여 지점부 균열을 억제하기 위한 현장에서 관리가능한 방안이 수치적으로 제안되었다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.4D
• /
• pp.609-615
• /
• 2006

Crack and seat method has been used in United States to prevent reflection cracks of overlay that may be caused by excessive movement at discontinuity of old concrete pavement. This method provide optium space of discontinuity by generating additional discontinuity in old concrete pavement. In this study the effect of various factors on the performance such as IRI and distress at after applying crack and seat method were investigated by using LTPP data.

• Journal of the Korea Concrete Institute
• /
• v.18 no.1 s.91
• /
• pp.57-64
• /
• 2006

The crack presented in concrete structures causes a structural defect, the durability decrease, and external damages etc. Therefore, it is necessary to improve durability through the effort to control the crack. Fluosilicic acid($H_2SiF_6$) is recovered as aqueous solution which absorbs $SiF_4$ produced from the manufacturing of industrial-graded $H_3PO_4$ or HF. Generally, fluosilicates prepared by the reaction between $H_2SiF_6$ and metal salts. Addition of fluosilicates to cement endows odd properties through unique chemical reaction with the fresh and hardened cement. Mix proportions for experiment were modulated at 0.45 of water to cement ratio and $0.0{\sim}2.0%$ of adding ratio of fluosilicate salt based inorganic compound. To evaluate correlation of concrete strength and adding ratio of fluosilicate salt based inorganic compound, the tests were performed about design strength(21, 24, 27 MPa) with 0.5% of adding ratio of fluosilicate salt based inorganic compound. Applications of fluosilicate salt based inorganic compound to reduce cracks resulted from plastic and drying shrinkage, to improve durability are presented in this paper. Durability was evaluated as neutralization, chloride ion penetration depth, freezing thawing resistant tests and weight loss according reinforcement corrosion. It is ascertained that the concrete added fluosilicate salt based inorganic compound showed m ability to reduce the total area and maximum crack width significantly as compared non-added concrete. In addition, the durability of concrete improved because of resistance to crack and watertightness by packing role of fluosilicate salt based inorganic compound obtained and pozzolanic reaction of soluble $SiO_2$ than non-added concrete.

• Journal of the Microelectronics and Packaging Society
• /
• v.21 no.4
• /
• pp.57-62
• /
• 2014

Using flexible bismaleimide-triazine co-polymer as a substrate, inkjet-printed Cu films were also investigated for low-cost and process feasibility of flexible electronics. After annealing at $200^{\circ}C$ for 1 h under various reducing ambient, surface color was changed to red and electrical resistivity was decreased to the level of conductor under formic acid ambient. However, its resistivity was much higher than conventional copper films due to surface crack. In order to reduce the residual film stress after annealing, additional isothermal treatment was inserted before anneal hiring the stress relaxation applied in processes of amorphous materials. As a result, no surface crack was observed and electrical resistivity of $3.4{\mu}{\Omega}cm$ was measured after annealing at $230^{\circ}C$ with stress relaxation while electrical resistivity of $7.4{\mu}{\Omega}cm$ was observed after normal annealing without relaxation. The effect of stress relaxation was also confirmed by observing surface crack after decreasing the relaxation time to 0 min.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.1
• /
• pp.7-13
• /
• 2003

A hot press method was use for the optimal manufacturing condition for a shape memory alloy(SMA) composite. The bonding between the matrix and the reinforcement within the SMA composite by the hot press method was strengthened by cold rolling. In this study, the objective was to develop an on-line monitoring system for the prevention of the crack initiation and propagation by shape memory effort of SMA composite. Shape memory effect was used to prevent the SMA composite from cracking. For the system to be developed, an optimal hE parameter should be determined based on the degree of damage and crack initiation. When the SHA composite was heated by the plate heater attached at the composite, the propagating cracks appeared to be controlled by the compressive force of SMA.

• Geotechnical Engineering
• /
• v.10 no.3
• /
• pp.119-134
• /
• 1994

In order to assess the possibility of using steel fibers in the fissured ciays, uniaxial compression tests were performed on both unreinforced and reinforced clay samples containing a pre-existing crack. Test results showed that the steel fiber reinforcement increased resistance to cracks initiation and their propagation, and therefore increased both stress at crack growth initiation and peak stress at failure. The increase in resistance to cracks initiation and their propagation was related to the arresting or deflecting the crack propagation in clay samples by steel fibers. A theoretical interpretation of experimental results was made using fracture mechanics theory and pull-out mechanisms in fiber reinforced materials. It was revealed that the steel fibers had bridging effect through their pull-out action that caused an increased resistance to the propagation of the cracks in the samples. The predicted pull-out force based on theoretical analyses agreed reasonably well with the measured values obtained from pull-out tests.

• International Journal of Highway Engineering
• /
• v.11 no.2
• /
• pp.229-238
• /
• 2009

This paper describes the methods to propose the optimal material properties and construction steps that prevent cracks due to the thermal stresses induced by the hydration heat under the construction of the concrete underpass structures. To achieve the goal of this study, the heat transfer theories were employed and the three-dimensional finite element model of the underpass structure was developed and used for the structural analyses. If the volume of the concrete member that is placed at one time is significantly large, the member is assumed to be the mass concrete and is easy to induce cracks. In order to minimize the cracks during the construction, two different methods can be utilized: one is to arrange the construction steps optimally and the other is to change the materials to reduce the probability of the crack occurrence. In this study, the analyses were performed by considering the changes in material properties with time, the characteristics of the hydration heat generation for cements and admixtures, the volume of the concrete placement at one time, and the environmental conditions.

• 한국도로학회지:도로
• /
• v.5 no.1 s.15
• /
• pp.22-27
• /
• 2003