• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.245-248
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• 2006

The objective of this study is to take the first step in creating a user-friendly health monitoring system for recycled aggregate concrete structure using acoustic emission(AE). Each specimen was a cube, the edge of which was 150mm. For pull-out tests, a steel rebar, 13mm in diameter, was embedded in the center of each specimen and casting directions(i.e., vertical and horizontal) were considered in this paper. The AE parameters were analyzed for damage levels(i.e. internal cracking stage, pull-out stage) of all specimens. Results from this study show that event, duration versus amplitude of a signal, showed a clear difference for different loading stages depending upon the concrete casting directions.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.4
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• pp.3545-3554
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• 1974

The objective of this study was to investigate the characteristics of the evaporation rate, the plastic shrinkage and the compressive strength of concrete exposed to a rapid evaporation environment immediately after casting. Drying of concrete were conducted under a controlled chamber in which the temperature was mainfoimed at 30 ${\pm}$1$^{\circ}C$, the relative humidity 22 ${\pm}$1 percent, and the wind velocity 7 ${\pm}$1 m/sec. The compressive strength of concrete was tested after 28 days of standard curing. The results obtained are as follows: 1. The evaporation rate was the highest at the very beginning, was decreased as the drying progresses, and was kept almost constant after 6 hours. 2. The shrinkage of concrete was changed in three different rates for the concrete mixture having its slump vallue between 3.0cm and 7.5cm. 3. The plastic shrinkage was ended within 5 or 6 hours after casting, regardless of the water cement ratio. 4. The shrinkage was increased within the limit of slump values between 3.0cm and 7.5cm as the water-cement ratio was increased. 5. The evaporation was kept on even after the plastic shrinkage was ended. 6. Within the limit of good workability (slump value between 4.5cm and 7.5cm), the compressive strength of concrete was increased when the shrinkage rate was slow but it was decreased when the rate was rapid 7. From the result of this study it is recommended that (1) the water-cement ratio should be less as long as the workability of concrete is allowable; (2) the evaporation should be prevented at least for 4 hours after casting concrete.

• Computers and Concrete
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• v.24 no.2
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• pp.173-183
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• 2019

This study presents experimental and numerical results of prestressed concrete composite beams with different casting and stressing sequence. The beams were tested under three-point bending and it was found that prestressed concrete composite beams could not achieve monolith behavior due to interface slippage between two layers. The initial stress distribution due to different construction sequence has little effect on the maximum load of composite beams. The multi-step FE analyses could simulate different casting and stressing sequence thus correctly capturing the initial stress distribution induced by staged construction. Three contact algorithms were considered for interaction between concrete layers in the FE models namely tie constraint, cohesive contact and surface-to-surface contact. It was found that both cohesive contact and surface-to-surface contact could simulate the interface slip even though each algorithm considers different shear transfer mechanism. The use of surface-to-surface contact for beams with more than 2 layers of concrete is not recommended as it underestimates the maximum load in this study.

• Steel and Composite Structures
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• v.13 no.3
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• pp.259-275
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• 2012

Concrete filled steel tubular (CFST) member has been widely used in the construction of high-rise buildings for its high axial bearing capacity. It can also be applied on long-span structures such as spatial structures or bridges not only for its high bearing capacity but also for its construction convenience. Concrete casting effect of CFST member is considered in the study of its bearing capacity in this paper. Firstly, in order to authenticate the applicability of constitutive relationship and yield criterion of steel and concrete based on FEM, two ANSYS models are built to simulate and compared with other's test. Secondly, in order to find the huge difference in bearing capacity due to different construction processes, two full-size CFST models are studied when they are horizontally cast and axially compressed. Finally, the effects of slenderness ratio (L/D) and confining parameter (D/t) of CFST members are studied to reveal the intrinsic links between bearing capacity and slenderness ratio or confining parameter.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.304-312
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• 2001

The objective of this study is to find out effects of horizontal vibration on the compressive strength for 7days and 28 days cured concrete specimens according to the variation of fine aggregate modului, vibration velocities, and times began to vibrate. Four kinds of fine aggregate modului(40, 42, 45, 47%), three of vibration velocities(0.25, 0.5 0.1kine(cm/sec)), and four of times(0, 3, 6, 9hrs after concrete casting) were chosen as the experimental parameters in this study, the vibrations were applied for 30 minutes in each case. From this study, it could be seen that the most increase of compressive strengths were obtained in case of 47% fine aggregate modulus, and 0.25kine of vibration velocity, but the strength was decreased when vibrated after 9hrs from concrete casting.

• Magazine of the Korea Concrete Institute
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• v.7 no.4
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• pp.62-70
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• 1995

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.941-946
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• 2001

In this study, three kinds of fine aggregate (river sand, sea sand, crushed sand) were used and four different s/a (38%, 40%, 42%, 45%) were applied separately to this experimental for get the conclusion written below. Regardless of kinds of fine aggregate and casting-curing condition, maximum unit weight is seen at 40% of s/a and also to be seen in case of crushed sand. It's for that specific gravity of crushed sand is bigger comparatively than river sand and sea snad's one. Compressive strength is measured river sand, crushed sand, sea sand by order of size ; Regardless of variation of s/3, casting-curing condition and age. Compressive strength recorded maximum when s/a is 42% whatever sort of fine aggregate are. As the result, according to references, the optimum s/a of underwater antiwashout concrete is 40% but in this study, from compressive strength of view, the optimum s/a of underwater antiwashout concrete is 42%.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.533-536
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• 2003

The objective of in this study makes investigation into the characteristics of antiwashout underwater concrete as to mix proportion, casting and curing water through experimental researches. in this study, sea sand is blended with river sand, crushed sand is blended with river sand and sea sand as to investigate the quality change and characteristics of antiwashout underwater concrete with variation of blend ratio of sea sand and crushed sand(0, 20, 40, 60, 80, 100%). Higher compressive strength is measured following the order of river sand, sea sand, crushed sand regardless of age and casting condition. Except for case of using river sand, blended ratio of 40% is appeared on most compressive strength.

• Steel and Composite Structures
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• v.34 no.4
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• pp.581-597
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• 2020

Light-Weight Concrete containing Expanded Poly-Styrene Beads (EPS-LWC) is an approved structural and non-structural material characterized by a considerably lower density and higher structural efficiency, compared to concrete containing ordinary aggregates. The experimental campaign carried out in this project provides new information on the mechanical properties of structural EPS-LWC, with reference to the strength and tension (by splitting and in bending), the modulus of elasticity, the stress-strain curve in unconfined compression, the absorbed energy under compression and reinforcement-concrete bond. The properties measured at seven ages since casting, from 3 days to 91 days, in order to investigate their in-time evolution. Mathematical relationships are formulated as well, between the previous properties and time, since casting. The dependence of the compressive strength on the other mechanical properties of EPS-LWC is also described through an empirical relationship, which is shown to fit satisfactorily the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.29-32
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• 2006

Different from new or reconstruction of an apartment housing, the structural safety in the remodelling construction can be obtained through the repair and strengthening process based on the safety diagnosis and evaluation of structural performance. In this study, structural performance of existing members such as, reinforced concrete slabs, beams and columns are investigated through experimental tests. The structural members were obtained from the existing apartment housing which will be demolished. Test results showed that most specimens have a sufficient structural capacity except for some special case, for example, specimens with severe cracks or concrete loss due to improper casting. This same severe deteriorated or defective structure members originated from bad concrete casting or careless construction process should be repaired and strengthened before an remodelling construction.