초속경 라텍스개질 콘크리트의 균열 억제방안

이봉학,최판길 江原大學校 産業技術硏究所 2008 産業技術硏究 Vol.28 No.A

An increase in the amount of cracking in repaired concrete bridge decks using VES-LMC(Very Early Strength - Latex Modified Concrete ; below VES-LMC) has been noticed by Yun et a1(1). Literature indicates that indeed many concrete bridge decks develop transverse cracking, most developing at early ages(3~7 days), many right after construction. The purpose of this study was to establish prevention of map, transverse and longitudinal cracking in VES-LMC and to provide a control methods for minimizing the occurrence of cracks. The proposed prevention against map and transverse cracking was verified by field ayplications. VES cement was modified, the unit cement contents was reduced into 360kg/m^(3) from 390kg/m^(3), the maximum size of coarse aggregate was increase into 19mm from 13mm, wire mesh and steel fibers were incorporated in concrete mixture. A series of variable combinations were attempted. As a results, the proposed prevention against map and transverse cracking was verified because no crack were occurred until 90 days after overlay.

AR 파라메타의 강인한 추정방법과 음성향상을 위한 적용

하판봉,이기용 國立 昌原大學校 産業技術硏究所 1992 産技硏論文集 Vol.6 No.-

기존 선형예측방법은 성도특성을 추정하는데 두가지의 주요한 문제점(음원의 특성에 의한 추정의 정확도, 가산배경잡음에 의한 추정정확도의 감소)을 가지고 있다. 이러한 문제를 다음과 같이 해결한다: 첫째, 구동잡음이 가우시안과 라프라시안의 혼합으로 본 강인한 AR모델을 사용하여 성도의 파라메타를 구한다. 이때, 잡음이 없는 환경에서 얻어진 음성신호를 이용한다. 두번째로는 위의 방법과 강인한 Kalman 필터를 사용하는 방법을 제안하고, 잡음에 오염된 음성을 향상시키기 위하여 사용하였다.

현장실험을 통한 VES-LMC 균열발생 원인분석

최판길,이봉학 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.B

Many concrete bridge decks develop transverse cracking shortly after construction. These cracks accelerate corrosion of reinforcing steel and lead to concrete deterioration, damage to components beneath the deck, unsightly appearance. These cracks shorten the service life and increase maintenance costs of bridge structures. In this study, VES-LMC overlay, which provides the same benefits as a conventional overlay, is designed to cure very quickly. Although the materials for VES overlays are more expensive, the cost is more than offset by the savings on traffic control and work zone safety measures. Otherwise, reaction of hydration occurs very rapidly in beginning step(concrete placing). As a results, thermal cracking can be occur by thermal stress in accordance with hydration-heat The purpose of this study was to estimate diagnosis of crack occurrence of VES-LMC through field tests at early-age.

실시간 Multi-Tasking Processor Scheduler에 관한 연구

하판봉 國立 昌原大學校 産業技術硏究所 1990 産技硏論文集 Vol.4 No.-

Real-time multi-tasking processor scheduler(PRCSCH)consists of four function blocks : task dispatcher (XSCAN), high-priority queue handler(XSETHI), and d-bus input queue handler(XBIQ). The last function will be supplied by inter-processor communication module and will not be described here. XSCAN schedules bus input tasks, high-priority tasks, timeout tasks, timeout tasks, normal tasks, and free-time tasks according to their status bytes. Tasks are run in the following way, XSCAN takes out top message in the d-bus input queue, translates the communication type byte(comty) contained in the message to its corresponding task index value, and runs the task when its ready bit is set. If its ready bit is reset or no message is waiting in the d-us input queue, XSCAN checks the high-priority queue. If any task is waiting in it, the task is run before any normal tasks. After bus input tasks and high-priority tasks are run. XSCAN runs normal tasks sequentially according to their status bytes. At extreme case that there are no normal tasks to be run, XSCAN runs free-time tasks(for example memory test, interface test, etc) of which free bit is set. XSETHI allows each task to upgrade the priority of the ask to high priority, thus permitting it to be run before any normal task. Multiple high-priority requests can be queued. And XTIME supplies to each task a timer that can be used to suspend its execution for a specified duration of time. These are useful for i/o timeout. If XTIME receives timeout request from a task with tick count(multiples of real-time clock period), the task will be run by XSCAN when timeout expires.

현장실험을 통한 VES-LMC 균열발생 원인 분석

최판길,이봉학 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.A

Many concrete bridge decks develop transverse cracking shortly after construction. These cracks accelerate corrosion of reinforcing steel and lead to concrete deterioration, damage to components beneath the deck, unsightly appearance. These cracks shorten the service life and increase maintenance costs of bridge structures. In this study, VES-LMC overlay, which provides the same benefits as a conventional overlay, is designed to cure very quickly. Although the materials for VES overlays are more expensive, the cost is more than offset by the savings on traffic control and work zone safety measures. Otherwise, reaction of hydration occurs very rapidly in beginning step(concrete placing). As a results, thermal cracking can be occur by thermal stress in accordance with hydration-heat The purpose of this study was to estimate diagnosis of crack occurrence of VES-LMC through field tests at early-age.

VES-LMC의 열 특성을 고려한 자기수축

최판길,이봉학 강원대학교 산업기술연구소 2005 産業技術硏究 Vol.25 No.B

Durability of concrete structures is seriously compromised by cracking at early-age concrete, particularly in high-strength or high-performance concrete structures. Since early-age cracking is influenced by various factors that affect the hydration process, early-age shrinkage and stress/strain development, the behavior at early-age is highly complex and no rational methodologies for its control have yet been established. Concrete structures often present volumetrical changes particularly due to thermal and moisture related shrinkages. Volumetric instability is detrimental to the performance and durability of concrete structures because structural elements are usually restrained. These restrained shrinkages develop tensile stresses which often results in cracking in combination with the low fracture resistance of concrete. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior of early-age concrete at the stages of design and construction. The purpose of this study was to propose a shrinkage models of VES-LMC (very-early strength latex-modified concrete) at early-age considering thermal deformation and autogenous shrinkage.

초속경 라텍스개질 콘크리트의 균열발생 특징분석

이봉학,최판길 강원대학교 산업기술연구소 2007 産業技術硏究 Vol.27 No.A

Concrete is a material that will crack during its service life by its very nature. For bridge decks this is especially significant as these cracks allow accelerated ingress of chlorides and the subsequent corrosion of the reinforcing steel and deck deterioration. Very-early strength latex-modified concrete (below ; VES-LMC) was developed in order to realize early-opening-to-traffic bridge deck concrete. Although there has been little research to document the degree of cracking in VES-LMC overlay, there has been a general perception among highway agencies that overlay cracking of VES-LMC, particularly early-age cracking, is a one of problems which should be solved. The purpose of this study was to analyze the cause of map, transverse and longitudinal cracking in VES-LMC and to provide a control methods for minimizing the occurrence of cracks. The proposed prevention against map and transverse cracking was verified by field applications. VES cement was modified, the unit cement contents was reduced into 360kg/㎥ from 390kg/㎥, the maximum size of coarse aggregate was increase into 19mm from 13mm, wire mesh and steel fibers were incorporated in concrete mixture.

고강도 철근과 콘크리트 강도수준에 따른 최적조합에 관한 연구

최판길,이봉학 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.B

The reinforced concrete structure is one of the most popular structures in real construction, Concrete has been strengtened rapidly due to the development of new material and construction technology. But as the concrete has been getting stronger, the brittleness of material has increased and the better ductility has been required. So, the study for strengthening stiffener has been urgently needed. As we said above, it is expected that the use of high strength steel and concrete will be increased. However, The experimental data is not enough for solving problems of the use of high strengthened steel and concrete. In this research, we analyzed 45 combinations of the strength levels of concrete, the thickness of material and the steel strength with regard to simple Reinforced Concrete SLAB Beam bridge. The program MIDAS CIVIL was used to find the optimal combination. As a result, it was found that strength ratio per unit section is in inverse proportion to the strength of material and that the strengths of steel are respectively 400 MPa for low strengthened concrete and 300 MPa for high strengthened concrete. For economic aspect and usability, the effect of high strength steel is not as high as we expected it would be.

Robust Thresholding을 이용한 Wavelet 기반의 영상잡음 제거연구

하판봉 國立 昌原大學校 産業技術硏究所 2002 産技硏論文集 Vol.16 No.-

Approaches to wavelet-based denoising (or signal enhancement) have so far relied on the assumption of normally distributed perturbations. To relax this assumption, which is often violated in practice, we derive a robust wavelet thresholding technique based on the minimax description length principle. We first determine the least favorable distribution in the ε-cintaminated normal family as the member that maximizes the entropy. We show that this distribution and the best estimate, constitute a saddle point. This results in a threshold that is more resistant to heavy-tailed noise, but for which the estimation error is still potentially unbounded. We address the practical case where the underlying signal is known to be bounded, and derive a two-sided thresholding technique that is resistant to outliers and has bounded errors. We provide illustrative examples.

초속경 라텍스개질 콘크리트의 초기수축 및 구속건조수축

최판길,김용곤,심도식,이봉학 江原大學校 産業技術硏究所 2005 産業技術硏究 Vol.25 No.A

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. VES-LMC provides the advantage of very-early-strength, as well as high flexural strength, bond strength, durability, resistance to corrosion, reduced water permeability and resistance to damage from freeze-thaw cycles. The compressive and flexural strength of VES-LMC are 21 MPa and 4.5 MPa at 3 hours after concrete placing, respectively. However, VES-LMC would have a relatively large shrinkage at early-age because of reduced water-cement ratio, big water self-dissipation, and rapid hydration reaction. Therefore, the purpose of this study was to evaluate the early-age and restrained shrinkage of VES-LMC, having an experimental variables such as latex contents and cement types. The latex contents included 0%, 5%, 10%, 15% and 20%, and the cement types included ordinary portland cement and very-early strength cement.