Ho-Seop Jung

Diffusion of Chloride Ions in Limestone Powder Concrete

In this study, the diffusion of chloride ions in cement concrete made with and without the limestone powder was investigated. In order to study the effect of the limestone powder, all mixtures were prepared at a fixed water-cementitious ratio (0.45). From the experimental results, the setting time of limestone powder concrete is faster than that of control concrete, and compressive strength of all specimens decreased with increasing replacement ratio of limestone powders. The diffusion properties of limestone powder concretes indicated a trend increasing with curing period. LSA10 and LSA20 concretes, the diffusion coefficient was smaller than that of control concrete. The addition of limestone powder reduces the diffusion coefficient of chloride ions, irrespective of fineness levels of limestone powder.

Properties on the Freeze-Thaw of Concrete Subjected to Seawater Attack

공용중인 콘크리트 구조물의 내구성 연구는 한 가지 원인에 대한 단독열화 연구를 주로 연구하였지만 실제 구조물의 공용시기에는 두 가지 이상의 환경에 노출되어 있어 이러한 복합열화에 대한 관심이 최근 증가하고 있는 실정이다. 복합열화에 대해 일반적으로 염해와 동결융해에 대해서는 일부 연구가 진행되어 있지만 ...In this study, deterioration degrees of concrete were investigated at laboratory under seawater attack and cycling freeze-thaw, which are major durability performance deterioration factors of concrete. Deteriorations of mixed concrete using Portland & blended cement were examined by instrumental analysis of changes in relative dynamic modulus of elasticity and compressive strength. After 520 cycles of freeze-thaw, relative dynamic modulus of elasticity and compressive strength of concrete mixed with normal Portland and LHC over 75% showed relatively low resistance of approximately 44% of those values of SRC. Concrete replaced with 50% fine powder of blast furnace slag showed the most excellent freeze-thaw resistance among the tested blended cement concrete.

Influence of Binder Type on the Chloride Threshold Level for Steel Corrosion in Concrete

The present study concerns the influence of binder type on the chloride-induced corrosion being accompanied by the chloride threshold level (CTL), chloride transport and as their results the corrosion-free lift. Two levels of cement content, PFA and GGBS concrete were employed. It was found that the most dominant factor to the CTL is the entrapped air void content at the steel-concrete interface, irrespective of the chloride binding capacity, binder type and acid neutralisation capacity of cement matrix. The CTL for lower interfacial air void contents was significantly increased up to by weight of cement, whereas a same mix produced for a higher level of voids. Because of a remarkable reduction in the diffusion fur GGBS concrete, its time to corrosion ranges from 255 to 1,250 days, while the corrosion-free life for control varies from 20 to 199 days sand for PFA concrete from 200 to 331 days.

Occurrence of Thaumasite in Lining Concrete of Old-Tunnel Structure

The sampling examination on the lining concrete of a 70-year-old tunnel structure was carried out. The compressive strength and RCPT test on the core samples were also performed. In order to identify product formed in the lining concrete, microstructural observations were conducted on the samples obtained from the lining concrete using x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. From the results of the examination, it was confirmed the presence of thaumasite formation as well as ettringite formation induced by sulfate attack. Especially, thaumasite solid solution led to a low compressive strength showing cracks and delamination on the surface part of the core samples.

Sulfate Resistance of Cement Matrix Containing Limestone Powder

In order to improve the performance of concrete, generally, modern cements often incorporate several mineral admixtures. In this study, the experimental included the flow value, air content of mortar containing limestone powder and length change and compressive strength of mortar specimen immersed in sulfate solutions. From the experimental results, the limestone powder cement matrices improved the physical properties and sulfate resistance of cement matrices at replacement ratio of limestone powder. The replacement ratio of limestone powder was significantly deteriorated in sodium sulfate solution. Irrespective of fineness levels of limestone powder, length change and SDF of mortar specimens with only replacement was much superior to the other replacements.

Experimental Study on Using the Ground Calcium Carbonate As a Concrete Admixture

ABSTRACT Recently, the research results have been announced for the purpose of making high quality, according to the trend of a high performance of concrete structure. In this respect, we began to research the use of Ground Calcium slurry Carbonate (GCC) to a concrete admixtures which crushed the limestone until about 1.5 μm. We examined about the quality of GCC to fine out whether or not it would be feasible to use as the concrete admixture. The mechanical properties of concrete blended with GCC and silica fume were investigated. This study showed that air contents of concretes were constant regardless of replacement of GCC and the slump value of fresh concrete was decreased with replacement of it. Especially, concrete replacement with 10% of GCC, had a good trend with respect to compressive strength. In case of simultaneous use of GCC and silica fume, the workability and compressive strength of the concretes seemed to be favorable in mechanical properties. This study indicated that the most reasonable replacement amount of GCC was 10% of cement weight as concrete admixture.

Characterization of Deterioration on the Shotcrete Lining Immersed in Various Sulfate Solutions

This study is to evaluate the characterization of shotcrete exposed to sulfate solution on long-term. Surface examination, compressive strength test, adhesive strength test and micro-structural analysis were performed to analyze the deterioration of shotcrete specimens, which were cored at cast-in-place shotcrete lining. The shotcrete specimens were immersed in 1, 2, and 5% of sodium sulfate solutions upto 35-weeks. From the test results, the compressive strength and adhesive strength of shotcrete specimen increased up to 56 days of immersion period. The reason was that the cement matrix was densified in filling the pore of shotcrete with cement hydrate products in the early age of immersion period. After 56 days of immersion period, the compressive strength and adhesive strength decreased with increasing immersion period of shotcrete specimens in sodium sulfate solutions. The deterioration of shotcrete was caused by the gypsum, ettringite, and thaumasite formation in the shotcrete specimens. These results were confirmed by XRD, SEM and EDS analyses.

LONG-TERM CHARACTERISTICS OF SHOTCRETE LINING IN TEST TUNNEL

This study is to evaluate long-term characteristics of shotcrete lining in test tunnel built in 1996 in Korea. Visual examination, carbonation depth, water analysis, compressive strength, X-ray diffraction (XRD) analysis, and Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses were performed to evaluate the properties of shotcrete on long term. 6 shotcrete specimens were cored in the test tunnel, and ground water were collected at 2 positions in tunnel. From the visual examination, crack and efflorescence were widely existed on shotcrete surface. From the test results, pH values of groundwater and carbonation depth of shotcrete specimens were 7.42–7.50 and 3.1–22.8mm, respectively. The compressive strengths of shotcrete specimens by Schmidt hammer and uniaxial were 12.98–24.52MPa and 8.0–19.0MPa. The formation of gypsum and ettringite, which decrease the durability of shotcrete, was detected in the shotcrete specimens from the XRD, SEM, and EDS analyses. It is showed that the shotcrete have been deteriorated by chemical components in the groundwater.

An Experimental Study of Permeable Concrete Pavement for Practical Use in the Field

In rainy weather, permeable concrete pavement has advantages such as good drainage, increased skid resistance, reduced splash and spray behind vehicles for improving the safety of driving vehicles as well as reduction of the traffic noise. It also contributes to improvement of traffic environment. In this study, the fundamental properties of permeable concrete in accordance with maximum size of aggregate, sand percentage and unit cement content were investigated for practical use of permeable concrete pavement. Although the permeability standard for typical permeable asphalt-concrete pavement is , the researchers determined that the coefficient of permeability of the permeable concrete should be set higher at . Then, the researchers measured the coefficient of permeability, strength, void ratio, and continuous void ratio of the permeable concrete while varying maximum size of the aggregate, sand percentage, unit cement content for detailed analysis. It was found that the void ratio, continuous void ratio, and flexural strength were about 15%, 12%, and 5.0MPa, respectively, when the permeability of the concrete was set at . Given that the maximum size of aggregate was , we reached the conclusion that the best mix design for permeable concrete was of sand percentage and of unit cement content.