현장 : 성결가족이셨군요 ; 한국국제경제학회 회장 김신행 장로 - 성진교회 -

최판길 기독교대한성결교회 활천사 1997 활천 Vol.525 No.-

화상분석 실험을 이용한 열화된 줄눈콘크리트 포장의 내구성 지수 평가

최판길,김용곤,윤경구,권수안 한국방재학회 2009 한국방재학회논문집 Vol.9 No.5

The primary objective of this study was to estimate the deterioration degree of jointed concrete pavement which was major concrete pavement type in Korea. First of all, visual survey of concrete pavement was performed to observe deterioration types. In the result of visual survey, the majority of concrete pavement deterioration was investigated in joint area. It is appeared that most of the distresses are durability cracking and joint distress. Second, concrete core specimens were taken from eight locations including good section (4 locations) and bad section (4 locations) based on visual survey. The deterioration reasons of concrete pavement were analyzed with ultrasonic pulse velocity test, splitting tensile strength test, and image analysis for concrete core specimens. Among the image analysis test result for 21 concrete core specimens, only two specimens satisfied the Kansas DOT criteria of spacing factor, 250㎛, and the remains of 19 specimens were estimated to be above 250㎛. The durability factor of concrete was estimated very low. As a result, it was analyzed that the main deterioration reason of the deteriorated jointed concrete pavement was to be freezing and thawing damages 본 연구의 목적은 콘크리트 포장의 한 종류인 줄눈콘크리트 포장의 열화정도를 평가하는 것이다. 첫째로, 열화종류를 관찰하기 위하여 콘크리트 포장 육안조사를 실시하였다. 육안조사 결과 콘크리트 포장 파손의 형태는 대부분 줄눈 부위에서 조사되었고, 내구성 균열과 줄눈 파손이 주를 이루는 것으로 나타났다. 둘째로, 육안조사 결과에 기초하여 콘크리트 포장을 양호한 단면(4개소)과 불량한 단면(4개소)으로 구분하여 총 8개소에서 콘크리트 코어시편을 채취하였고, 콘크리트 열화 원인을 콘크리트 코어시편의 초음파 강도추정, 쪼갬인장강도 실험 및 화상분석 실험을 이용하여 분석하였다. 화상분석 실험결과, 총 21개의 시험편에서 Kansas DOT 기준(간격계수 250㎛이하)을 만족하는 시험편은 단지 2개에 불과했고, 나머지 19개의 시험편의 간격계수는 250㎛ 이상으로 평가되어 내구성 지수가 매우 낮은 것으로 나타났다. 따라서 조사된 콘크리트 포장의 주 열화 원인은 동결융해작용인 것으로 분석되었다.

연속철근콘크리트 포장의 횡방향 철근 설계방법 및 시공관련 이슈 검토

최판길,원문철 한국도로학회 2014 한국도로학회논문집 Vol.16 No.4

PURPOSES: The objective of this study is to evaluate construction issues and design for transverse steel in continuously reinforced concretepavement(CRCP). METHODS : The first continuously reinforced concrete pavement(CRCP) design procedure appeared in the 1972 edition of the“ AASHTOInterim Guide for Design of Pavement Structures,”which was published in 1981 with Chapter 3 “Guide for the Design of Rigid Pavement”revised. A theory that was accepted at that time for the analysis of steel stress in concrete pavement, called subgrade drag theory(SGDT), wasutilized for the design of reinforcement of CRCP - tie bar design and transverse steel design - in the aforementioned AASHTO Interim Guide. However SGDT has severe limitations due to simple assumptions made in the development of the theory. As a result, any design proceduresfor reinforcement utilizing SGDT may have intrinsic flaws and limitations. In this paper, CRCP design procedure for transverse steel wasintroduced and the limitations of assumptions for SGDT were evaluated based on various field testing. RESULTS: Various field tests were conducted to evaluate whether the assumptions of SGDT are reasonable or not. Test results show that1) temperature variations exist along the concrete slab depth, 2) very little stress in transverse steel, and 3) warping and curling in concreteslab from the field test results. As a result, it is clearly revealed out that the assumptions of SGDT are not valid, and transverse steel and tiebar designs should be based on more reasonable theories. CONCLUSIONS : Since longitudinal joint is provided at 4.1-m spacing in Korea, as long as joint saw-cut is made in accordance withspecification requirements, the probability of full-depth longitudinal cracking is extremely small. Hence, for transverse steel, the design shouldbe based on the premise that its function is to keep the longitudinal steel at the correct locations. If longitudinal steel can be placed at the correctlocations within tolerance limits, transverse steel is no longer needed.

Spalling Related to Coefficient of Thermal Expansion (CoTE) of Continuously Reinforced Concrete Pavement in Texas

최판길 대한토목학회 2015 KSCE Journal of Civil Engineering Vol.19 No.6

Concrete volume changes due to temperature and moisture variations (environmental loading) are severely restrained in Continuously Reinforced Concrete Pavement (CRCP) by longitudinal reinforcement and base friction, resulting in numerous transverse cracks, which are held tight by primarily longitudinal steel. Tight transverse cracks provide good load transfer at transverse cracks, ensuring good performance of CRCP. In general, an adequate amount of longitudinal steel and base friction used in CRCP will restrain concrete volume changes to an adequate level, keeping transverse cracks tight and providing good CRCP performance. In Texas, the performance of CRCP is excellent; however, severe spalling problems have been observed in CRCP sections where a certain type of coarse aggregate was used, resulting in costly repairs and traffic delays. This study investigated the causes of severe spalling problems in CRCP in Texas. Fourteen CRCP sections with severe spalling and 10 sections with no spalling distress were identified. A minimum of two cores were taken from each section and concrete material properties, including Coefficient of Thermal Expansion (CoTE) and modulus of elasticity, were evaluated. Test results indicate a strong correlation between spalling and concrete CoTE. Concrete with a CoTE larger than 9.9 × 10−6/oC (5.5 × 10−6/F) is quite prone to severe spalling. On the other hand, CRCP sections with a concrete CoTE smaller than 9.9 × 10−6/oC showed almost no spalling problems.

포스트텐션 콘크리트 포장 적용을 위한 실리카흄과 플라이 애시를 사용한 삼성분계 콘크리트의 특성

최판길,심도식,이봉학 한국방재학회 2009 한국방재학회지 Vol.9 No.3

포스트텐션 콘크리트 포장(post-tensioned concrete pavement ; PTCP)은 초장스팬 콘크리트 포장(l=120 m)을 구현하고 장기 공용성(40년 이상)을 확보하기 위해 개발되었다. 본 논문에서는 PTCP공법의 장점을 효율적으로 활용하기 위하여 고내구성 콘크리트 재료개발에 대한 연구를 수행하였다. 첫째로, 알칼리 골재반응을 억제할 수 있도록 플라이 애시를 20% 치환(단위바인더량 대비)하고, 둘째로, 조기강도확보 및 투수저항성을 개선하기 위하여 실리카흄을 적용하였다. 삼성분계 콘크리트의 역학적 특성, 투수저항성 및 표면박리저항성을 평가한 결과, 실리카흄 첨가에 따라 조기강도가 현저히 개선되고, 투수저항성이 "Low"에서 "Very Low" 등급으로 개선되는(ASTM C 1202 기준) 것으로 나타났다. 그러나 실리카흄 첨가량이 증가함에 따라 표면박리저항성이 저하되므로, 내구성을 고려한 현장 적용성을 확보하기 위해서는 단위바인더량 대비 5%이하로 첨가되는 것이 바람직한 것으로 나타났다. 공극구조 분석결과, 개선배합에서 간격계수(spacing factor)가 250±15μm로 평가되어 내구성 지수가 향상된 것으로 나타났다. Post-tensioned concrete pavement(PTCP) was developed to built long-span concrete pavement(120 m span) and to maintain long-term service life(over 40 years) of concrete pavement. In the present study, research for high-durable concrete was conducted to utilize the advantage of PTCP construction method efficiently. First of all, 20% of fly ash(by binder weight) was replaced to control alkali silica reaction. Second, silica fume was applied to improve the water-permeability and early-age strength. Results of tests for mechanical properties, water-permeability resistance, and surface-scaling resistance of ternary blended cement concrete showed that the early-age strength was improved significantly with addition of silica fume. The water-permeability resistance was improved from "Low" to "Very Low"(ASTM C 1202). However, surface-scaling resistance was decreased with an increase of silica fume, therefore, content of silica fume should be kept in less than 5%(by binder weight) to assure field application considering durability. The results of air-void analysis showed that durability factors were improved since spacing factors were estimated as 250±15 micron in adjusted mixtures.

포스트텐션 콘크리트 포장 적용을 위한 실리카흄과 플라이 애시를 사용한 삼성분계 콘크리트의 특성

최판길,이봉학,심도식 한국방재학회 2009 한국방재학회논문집 Vol.9 No.3

Post-tensioned concrete pavement(PTCP) was developed to built long-span concrete pavement(span=120m) and to maintain long-term service life(over 40 years) of concrete pavement. In the present study, research for high-durable concrete was conducted to utilize the advantage of PTCP construction method efficiently. First of all, 20% of fly ash(by binder weight) was replaced to control alkali silica reaction. Second, silica fume was applied to improve the water-permeability and early-age strength. Results of tests for mechanical properties, water-permeability resistance, and surface-scaling resistance of ternary blended cement concrete showed that the early-age strength was improved significantly with addition of silica fume. The water-permeability resistance was improved from "Low" to "Very Low"(ASTM C 1202). However, surface-scaling resistance was decreased with an increase of silica fume, therefore, content of silica fume should be kept in less than 5%(by binder weight) to assure field application considering durability. The results of air-void analysis showed that durability factors were improved since spacing factors were estimated as 250±15 micron in adjusted mixtures. 포스트텐션 콘크리트 포장(post-tensioned concrete pavement ; PTCP)은 초장스팬 콘크리트 포장(l=120m)을 구현하고 장기공용성(40년 이상)을 확보하기 위해 개발되었다. 본 논문에서는 PTCP공법의 장점을 효율적으로 활용 하기위하여 고내구성 콘크리트 재료개발에 대한 연구를 수행하였다. 첫째로, 알칼리 골재반응을 억제할 수 있도록 플라이 애시를 20% 치환(단위바인더량 대비)하고, 둘째로, 조기강도확보 및 투수저항성을 개선하기 위하여 실리카흄을 적용하였다. 삼성분계 콘크리트의 역학적 특성, 투수저항성 및 표면박리저항성을 평가한 결과, 실리카흄 첨가에 따라 조기강도가 현저히 개선되고, 투수저항성이 “Low"에서 ”Very Low" 등급으로 개선되는(ASTM C 1202 기준) 것으로 나타났다. 그러나 실리카흄 첨가량이 증가함에 따라 표면박리저항성이 저하되므로, 내구성을 고려한 현장 적용성을 확보하기 위해서는 단위바인더량 대비 5%이하로 첨가되는 것이 바람직한 것으로 나타났다. 공극구조 분석결과, 개선배합에서 간격계수(spacing factor)가 250±15μm로 평가되어 내구성 지수가 향상된 것으로 나타났다.

울트라 파인 플라이 애시를 사용한 초속경 LMC의 공극구조 특성

최판길,박원일,윤경구,이봉학 한국방재학회 2010 한국방재학회논문집 Vol.10 No.2

초속경 LMC(Very-Early Strength Latex-Modified Concrete ; VES-LMC)는 작업성, 강도발현 및 장기 내구성 측면에서 콘크리트 타설 후 3시간 이내에 교통개방을 가능하게 할 목적으로 개발되었고, 교량바닥판 긴급보수 공사에 유용하게 사용되고 있다. 그러나 초속경 LMC에서 라텍스의 사용이 콘크리트의 내구성은 향상시키지만 다량의 갇힌 공기를 양산한다는 단점이 있다. 따라서 취약한 공극구조를 개선하기 위해서는 특별한 방법이 필요하며, 본 논문에서는 울트라파인 플라이 애시가 사용되었다. UFFA VES-LMC의 공기량은 재령 1일에 포졸란 반응의 대부분이 발생하여 재령 1일 공기량이 경화전 공기량보다 저하되었다. 또한 재령 28일 공기량은 재령 1일 공기량의 공극구조와 동일하게 나타나, 포졸란 반응에 의해 콘크리트의 전체 공기량이 감소함을 확인하였다. 수산화칼슘의 첨가는 200이하 크기의 연행공기를 현저하게 증가시키고, UFFA를 15%이상 사용하면 간격계수를 200 이하까지 확보할 수 있어 VES-LMC의 공극구조 개선에 매우 효과적인 것으로 나타났다. Very-early strength latex-modified concrete (VES-LMC) was developed with a focus on workability, strength development and long-term durability that would allow for opening a bridge to traffic only 3 hours after concrete placement, which would be useful when repairing concrete bridge deck overlays. However, even though usage of latex in VES-LMC improves the durability, it has a disadvantage that it produces lots of entrained air. Therefore, specific plan is necessary since it is weak for freezing and thawing in air-void structure. In the present study ultra-fine fly ash (UFFA) was used. Test results are follows ;Air content of VES-LMC UFFA (VES-LMC using UFFA) concrete was decreased since major pozzolan reaction was happened in one day. It was also found that total air content of concrete was decreased with pozzolan reaction since air content in 28 days was the same with one day air content. The addition of calcium hydroxide increased entrained air which is smaller than size of 200. It was effective to improve the air-void structure of VES-LMC since spacing factor can be confirmed as smaller than size of 200 using more than 15% of UFFA.

설계사무소 구성원들의 지각 및 이용에 대한 작업공간의 환경행태적 연구

최판길,이광영,김정재 대한건축학회 2001 대한건축학회논문집 Vol.17 No.2

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.

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.