• International Journal of Concrete Structures and Materials
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• v.6 no.1
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• pp.31-40
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• 2012

Self-consolidating concrete (SCC) is a recently developed innovative construction material. SCC fills in a formwork without any vibrating consolidation, which allows us to eventually achieve robust casting. However, high formwork lateral pressure exerted by SCC is a critical issue regarding its application as cast-in-place concrete. In order to control the risk caused by high formwork pressure, a comprehensive prediction model for the pressure was previously proposed, investigated, and validated with various SCC mixtures. The model was originally designed to simulate the intrinsic pressure response of SCC mixtures while excluding other extrinsic influencing factors such as friction and flexibility of the formwork. The model was then extended to consider extrinsic factors such as friction between SCC mixtures and formwork. In addition, other interesting topics for peak formwork pressure and mineral admixture effects were summarized in the paper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.395-405
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• 2009

The purpose of this study was to investigate the performance of precast segmental PSC bridge columns with precast concrete footings. The proposed system can reduce work at a construction site and makes construction periods shorter. The precast concrete footings is intended to support precast segmental PSC bridge columns and provides an alternative to current cast-inplace systems, particularly for areas where reduced construction time is desired. Shortened construction time, in turn, leads to important safety and economic advantages when traffic disruption or rerouting is necessary. A model of precast segmental PSC bridge columns was tested under a constant axial load and a cyclically reversed horizontal load. In the companion paper, the experimental and analytical study for the performance assessment of precast segmental PSC bridge columns with precast concrete footings is performed.

• Structural Engineering and Mechanics
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• v.37 no.5
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• pp.459-473
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• 2011

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.101-107
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• 1996

In this study, the wedge splitting test (WST) specimens with various strength levels were tested to investigate the fatigue crack growth behavior of concrete. Selected test variables were concrete compressive strength with 2 levels (28 MPa, 60 MPa, 100 MPa) and maximum fatigue loading with 2 levels (75%, 85%). Fatigue testing was preceded by fracture energy test and the crack growth was measured by means of the compliance calibration method, 60 WST specimens were cast for the fatigue test, and 6 companion cylinders ($\phi$100${\times}$ 200 mm) for each batch. In fatigue test, the frequency of loading cycle was 1 Hz, and the minimum fatigue loading level was 5~10 % of ultimate monotonic loading. On the basis of the experimental results, a fracture mechanics-based empirical relationships for fatigue crack growth rate (da/dN-$\Delta$KI relationships) were presented. In addition, the effect of initial notch depth on the fracture energy and the validity of compliance calibration technique for the WST were shown.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.451-459
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• 1997

Current domestic building market is in the face of a tise in construction cost as a result of labor cost and materials problems, so improvements for productivity are doing their best for finding a way out of the difficulties. But the most of technical of from work is just considered the basic role and shape. As for environment protection, the utilization of waste concrete is important. But many of studies were interesting on the resource recycling for structural concrete. The purpose of this study is the development of thin precast form using recycled aggregate and the assembling systems for permanent form by cast-in-place.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.119-122
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• 2009

As architectures have recently become high-risers and mega-structured, stable high strength products have been ensured. Accordingly, use of precast concrete accouplement has been increased in order to facilitate air compression and rationalize construction. Since not only external heating but a1so internal temperature rise caused by the accumulation of cement hydration heat in manufacturing process, precast concrete members with large cross-section used for high-rise mega-structure's columns and beams may exhibit different temperature history compared to the precast concrete members for wall and sub-floor with relatively small cross-sections. Therefore, this study aims to elucidate the characteristics of temperature history of mass concrete members cast with high-strength concrete fur precast concrete application. In this study, large cross-sectional precast concrete mock-up, unit cement quantity, and temperature histories in manufacturing precast concrete member under different curing condition were inclusively investigated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.38-39
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• 2015

For the purpose of reducing defects (cracking) in topping concretes cast as artificial greening layer base, synthetic macro fibers were mixed. The flexural strength of synthetic macro fiber mixed topping concretes was tested via comparing its performance with current topping concrete. According to the results of the testing, topping concrete with adjusted mixing ratio after mixing with 1kg of synthetic macro fiber showed approximately 15% higher flexural strength compared to the current topping concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.135-138
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• 1999

The objective of this study is to investigate the compressive strength property of antiwashout underwater concrete with curing water through experimental researches. Type of casting and curing water(fresh water, sea water) are used as main experimental parameter, additionally a few variables affecting compressive strength property are used ; water-cement ratio (45%, 48%, 50%, 52%, 55%), and unit weight of admixtures (antiwashout underwater agent ; 0.6%, 0.8%, 1.0%, 1.2%, 1.4% of unit weight of water, superplasticizer ; 0.5%, 1.0%, 1.5%, 2.0%, 2.5% of unit weight of cement)) Compressive strength level of antiwashout underwater concrete which was cast and cured in fresh water is higher than other one. Consequently, incremental modulus has to increase when the antiwashout underwater concrete is made use of underwater work from ocean.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.769-774
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• 2000

The first thing in developing precast post-tensioned concrete frame system verify the shear resistance capacity of the beam-column connection at which the transfer of member forces become discontinuous. Complying with the necessity of such experimental research, shear tests have been performed for six test specimens which were cast and cured at Dong-Ah Concrete Manufacturing Company and post-tensioning at Concrete Laboratory of Inha University. Shear key and magnitude of post-tensioned force are taken test variables. From the test results, it has been observed that the shear resistance of the specimens attained to higher values than those of theoritical calculations based on the shear friction with shear friction coefficient being 0.6.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.351-354
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• 2005

Quality of concrete required to achieve the desired levels of strength and durability depend on the effectiveness of the curing method. During cold weather, the concrete at the time of placement should be taken to prevent damage to concrete due to freezing. Since the cement-water reaction is exothermic by nature, the temperature within mass concrete can be quite high. The temperature control for massive sections should be taken more careful than for shallow sections. However, in the constructing hydraulic structures, the curing temperature control for concrete had been very difficult to be taken in a proper way because the conditions constructing them are poor and contractors are small enterprises. For several. reasons including above, Rural Research Institute has developed a device and program for recording curing temperature history in cold weather concrete and mass. As there are two major advantages of the device, namely cheapness and availability, this program and device has been recommended to the use of curing temperature control in cold weather concrete and mass.