• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
• /
• pp.163-166
• /
• 2005

In this study, an unified algorithm for the degradation analysis which considers the cracks in concrete and steel corrosion is developed and implemented into finite element analysis program. Using the program, degradation analysis on reinforced concrete structures subjected to chloride attacks was carried out with time by considering the cracks and the steel corrosion and cracking due to expansion of corroded reinforcing bars. The analytical procedure proposal in this study can be used quantitative evaluation of degradation and service life prediction.

• Steel and Composite Structures
• /
• 제21권5호
• /
• pp.981-997
• /
• 2016

To avoid the cracks of cast-in-place concrete in shear pockets and seams in the traditional composite beam with precast decks, this paper proposed a new type of prefabricated steel truss-concrete composite beam (ab. PSTC beam) with pre-embedded shear studs (ab. PSS connector). To study the initial cracking load of concrete deck, the development and distribution laws of the cracks, 3 PSTC beams were tested under hogging moment. And the crack behavior of the deck was compared with traditional precast composite beam, which was assembled by shear pockets and cast-in-place joints. Results show that: (i) the initial crack appears on the deck, thus avoid the appearance of the cracks in the traditional shear pockets; (ii) the crack of the seam appears later than that of the deck, which verifies the reliability of epoxy cement mortar seam, thus solves the complex structure and easily crack behavior of the traditional cast-in-place joints; (iii) the development and the distribution laws of the cracks in PSTC beam are different from the conventional composite beam. Therefore, in the deduction of crack calculation theory, all the above factors should be considered.

• Structural Engineering and Mechanics
• /
• 제71권3호
• /
• pp.211-221
• /
• 2019

To study the eccentric compression behavior of ultra-high performance fiber reinforced concrete (UHPFRC) columns, six UHPFRC columns and one high-strength concrete (HSC) column were tested. Variation parameters include load eccentricity, volume of steel fibers and stirrup ratio. The crack pattern, failure mode, bearing capacity, and deformation of the specimens were studied. The results showed that the UHPFRC columns had different failure modes. The large eccentric compression failure mode was the longitudinal tensile reinforcements yielded and many horizontal cracks appeared in the tension zone. The small eccentric compression failure mode was the longitudinal compressive reinforcements yielded and vertical cracks appeared in the compressive zone. Because of the bridging effect of steel fibers, the number of cracks significantly increased, and the width of cracks decreased. The load-deflection curves of the UHPFRC columns showed gradually descending without sudden dropping, indicating that the specimens had better deformation. The finite element (FE) analysis was performed to stimulate the damage process of the specimens with monotonic loading. The concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC. The contribution of the UHPFRC tensile strength was considered in the bearing capacity, and the theoretical calculation formulas were derived. The theoretical calculation results were consistent with the test results. This research can provide the experimental and theoretical basis for UHPFRC columns in engineering applications.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
• /
• pp.53-54
• /
• 2015

This study is conducted to investigate the characteristics of cracks depending on the different mixture rates of calcium hydroxide and distilled water in high-strength concrete, which is substituted with a high percentage of blast-furnace slag, by using specimens produced under different heating temperatures: 600℃, 800℃, and 1000℃, respectively. According to the results of the study, the specimen heated under the temperature of 600℃ did not produce cracks; the specimen heated under 800℃ produced little cracks and showed no difference between calcium hydroxide and distilled water; whereas the specimen heated under 1000℃ produced cracks larger than 5mm on average in the case of calcium hydroxide, compared to distilled water.

• Structural Monitoring and Maintenance
• /
• 제9권4호
• /
• pp.373-388
• /
• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2023년도 봄 학술논문 발표대회
• /
• pp.187-188
• /
• 2023

In this study, the analysis of concrete cracks was conducted with a total of three variables: coating thickness, oxygen diffusion rate, and reinforced diameter of reinforced concrete structures. Cracks occurred after about 3, 4, and 6 years at the coating thickness of 30, 40, and 50mm when the coating thickness was used as a variable, and cracks occurred after about 4, 5, and 10 years at oxygen diffusivity of 2e-9, 2e-11, and 2e-12 (m²/s) when the oxygen diffusion rate was used as a variable. In the case of reinforcing bar diameters, cracks occurred after about 4, 3, and 2 years on the reinforcing bar diameters of D10, D19, and D25.

• International Journal of Concrete Structures and Materials
• /
• 제1권1호
• /
• pp.75-81
• /
• 2007

The concrete pavement of the Seohae Highway in Korea has suffered from serious distress, only four to seven years after construction. Deterioration due to Alkali-Silica Reaction (ASR) has seldom been reported per se in Korea, because the aggregate used for the cement concrete has been considered safe against alkali-silica reaction so far. The purpose of this study is to examine the deterioration caused by an alkali-silica reaction of concrete pavement in Korea. The investigation methods included visual inspection and Automatic Road Analyzer (ARAN) analysis of surface cracks, coring for internal cracks, stereo microscopic analysis, scanning electronic microscope (SEM) analysis, and electron dispersive X-ray spectrometer (EDX) analysis. The results are presented as follows: the crack pattern of the concrete pavement in Korea was longitudinal cracking, map cracking or D-cracking. Local areas of damage were noticed four to five years after construction. The cracks started from edges or joints and spread out to slabs. The most intensive cracking was observed at the intersection of the transverse and longitudinal joints. Where cracking was the most intense, pieces of concrete and aggregate had spalled away from top surface and joint interface area. The progress of deterioration was very fast. The reaction product of alkali-silica gel was clearly identified by its generally colorless, white, or very pale yellow hue seen through a stereo optical microscopy. The typical locations of the reaction product were at the interface between aggregate and cement paste in a shape of a rim, within aggregate particles in the cracks, and in the large void in the cement paste. Most of the white products were found at interface or internal aggregates. SEM and EDX analysis confirmed that the white gel was a typical reaction product of ASR. The ASR gel in Korea mainly consisted of Silicate (Si) and Potassium (K) from the cement. The crack in the concrete pavement was caused by ASR. It seems that Korea is no longer safe from alkali-silica reaction.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
• /
• pp.525-528
• /
• 2008

건전하게 시공된 콘크리트는 충분한 내구성으로 장기수명을 갖는 것으로 알려졌다. 그러나 대다수의 콘크리트 표면에 존재하는 균열은 염소이온의 침투에 대한 빠른 침투 통로가 되어 내구성능을 저하시키는 것은 분명하다. 균열이 발생한 콘크리트의 수명을 연장하기 위한 중요한 사항은 염소이온으로 인한 부식의 위험성을 재고하는 것이다. 균열폭은 높은 철근비로 감소시킬 수 있으나, 실질적으로 균열이 발생한 콘크리트의 내구성 저하이다. 이처럼 균열폭이 작은 경우, 표면도장공법은 균열이 발생한 콘크리트의 내구성을 간단히 향상시킬 수 있는 하나의 방안으로 고려될 수 있다. 따라서, 다양한 표면도장공법이 균열이 발생한 콘크리트를 실링할 수 있는지에 대한 검토가 필요하다. 본 연구는 이와 같이 표면도포공법이 미세균열을 통한 염소이온 침투에 미치는 영향을 실험적 측면에서 고찰하고자 하였다. 실험변수로 침투재와 도포재의 단일 적용과 복합적용이 실험변수로 고려되었으며, 급속염소이온 침투 실험을 통하여 균열대비 염소이온 침투깊이를 검토하였다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
• /
• pp.251-256
• /
• 2001

Shrinkage during the curing and drying of concrete is unavoidable and results in many cracks. Shrinkage strips reduce effectively shrinkage stresses and minimize shrinkage cracks by being left open for a certain time during construction allow a significant part of the shrinkage to occur without inducing stresses. This study verifies the effectiveness of shrinkage strips and provides the guide for construction of such strips.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
• /
• pp.827-832
• /
• 2001

Shrinkage during the curing and drying of concrete is unavoidable and results in many cracks. Shrinkage strips reduce effectively shrinkage stresses and minimize shrinkage cracks by being left open for a certain time during construction to allow a significant part of the shrinkage to occur without inducing stresses. This study verifies the effectiveness of shrinkage strips and provides the guide for construction of such strips.