• Polymer(Korea)
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• v.29 no.6
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• pp.605-612
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• 2005

This study investigates the isothermal crystallization behaviors of polypropylene-polyethylene-(1-butene) terpolymer and the adiabatically expanded polyolefin structured foams. For this purpose, butane gas was used as a physical blowing agent. Avrami equation has been used to interpret theoretically the experimental results obtained by either DSC or polarized optical microscope. It is believed that elongation induced crystallization occurring during the adiabatic expansion process has resulted in an increase in crystallization rate, eventually leading to a faster growth rate of spherulites and an increase in the nucleation density. An analysis of the foam by SEM images showed that the structure of foam is uniform (below diameter 30 $\mu$m closed cell) In addition, the thermal conductivity and the compressive strength of the polyolefin structured foams was measured. The thermal conductivity of foamed resin with excellent insulation characteristics is reduced compared with unfoamed resin. The compressive strength is decreased with increase in the expansion ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.229-240
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• 1987

Carbonation of concrete is one type of a chemical process. The reaction mechanism is very complex for the case when low-calcium fly ash and blast furnace slag is added. When fly ash and blast furnace slag is used as an admixture in concrete, they improve compressive strength in the long term, permeability and chemical resistance of concrete by a pozzolanic reaction and latent hydraulic property. On the other hand, the pozzolanic reaction of fly ash and latent hydraulic property of the blast furance slag leads to a reduction of the alkalinity of the concrete. It has been pointed out that this will accelerate the carbonation of the concrete and the corrosion of reinforcement steel embedded in the concrete. In order to clarify the effect of fly ash and blast furance slag on the carbonation of concrete, an accelerated carbonation testing of concrete was carried out by varying the conditions of concrete and the initial curing period in water. The test results of accelerated carbonation were compared to the carbonation test results of concrete stored for 15 years in open air, but protected from rain. As a result, the equation for the rate of carbonation based on compressive strength of concrete was proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.82-91
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• 2011

In this study, 24 prototype specimens were tested to find out the shear behavior and strength of large anchorage system exceeding 50mm(2") in anchor bolt diameter($d_0$) and 635mm(25") in effective embedment depth($h_{ef}$) not addressed by ACI349-06 Appendix B. Test variables are anchor bolt diameter($d_0$ = 63.5, 76.2, 88.9mm), effective embedment depth($h_{ef}$=635, 762mm), and edge distance($c_1$=381, 508, 762mm). Concrete compressive strength is constant($f_{ck}$=38MPa). Test results ($V_{test}$) were overestimated by $V_{aci06}$(shear strength by ACI 349-06) and $V_{ccd}$(shear strength by CCD method). In large anchorage system exceeding 50mm(2") of anchor bolt diameter($d_0$) and 635mm(25") of anchor bolt effective embedment depth($h_{ef}$), the bolt diameter variation and effective embedment depth($h_{ef}$) has no influence on the shear strenth, But, according to the analysis results of the feature ratio on edge distance($c_1$) and anchor bolt diameter, the feature ratio become smaller, which means anchor bolt diameter is bigger, predicted ratio of test results and predicted equation is larger. It was found that anchor bolt diameter is immediate cause of deterioration in the shear capacity of large anchorage system. To improve and extend the validity of current design recommendations further theoretical and numerical work is needed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.106-112
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• 2017

This paper presents a mathematical model derived from the upper-bound theorem of concrete plasticity to rationally evaluate the shear friction strength of concrete interfaces with a construction joint. The upper limit of the shear friction strength was formulated from the limit state of concrete crushing failure on the strut-and-tie action along the construction joints to avoid overestimating the shear transfer capacity of a transverse reinforcement with a high clamping force. The present model approach proposed that the cohesion and coefficient of friction of concrete can be set to be $0.27(f_{ck})^{0.65}$ and 0.95, respectively, for rough construction joints and $0.11(f_{ck})^{0.65}$ and 0.64, respectively, for smooth ones, where $f_{ck}$ is the compressive strength of concrete. From the comparisons with 155 data compiled from the available literature, the proposed model gave lower values of standard deviation and coefficient of variation of the ratios between predictions and experiments than AASHTO and fib 2010 equations, indicating that the proposed model has consistent trends with test results, unlike the significant underestimation results of such code equations in evaluating the shear friction strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.19-26
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• 2021

The lattice structure is attracting attention from industry because of its excellent strength and stiffness, ultra-lightweight, and energy absorption capability. Despite these advantages, widespread commercialization is limited by the difficult manufacturing processes for complex shapes. Additive manufacturing is attracting attention as an optimal technology for manufacturing lattice structures as a technology capable of fabricating complex geometric shapes. In this study, a unit cell was formed using a three-dimensional coordinate method. The relative density relational equation according to the boundary box size and strut radius of the unit cell was derived. Simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) with a controlled relative density were designed using modeling software. The accuracy of the equations for calculating the relative density proposed in this study secured 98.3%, 98.6%, and 96.2% reliability in SC, BCC, and FCC, respectively. A simulation of the lattice structure revealed an increase in compressive yield load with increasing relative density under the same cell arrangement condition. The compressive yield load decreased in the order of SC, BCC, and FCC under the same arrangement conditions. Finally, structural optimization for the compressive load of a 20 mm × 20 mm × 20 mm structure was possible by configuring the SC unit cells in a 3 × 3 × 3 array.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.92-103
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• 2015

Box-Wilson experimental design method, known as central composite design, is the design of any information-gathering exercises where variation is present. This method was devised to gather as much data as possible in spite of the low design cost. This method was employed to model the effect of mixing factors on several performances of 60 MPa high strength self compacting concrete and to numerically calculate the optimal mix proportion. The nonlinear relations between factors and responses of HSSCC were approximated in the form of second order polynomial equation. In order to characterize five performances like compressive strength, passing ability, segregation resistance, manufacturing cost and density depending on five factors like water-binder ratio, cement content, fine aggregate percentage, fly ash content and superplasticizer content, the experiments were made at the total 52 experimental points composed of 32 factorial points, 10 axial points and 10 center points. The study results showed that Box-Wilson experimental design was really effective in designing the experiments and analyzing the relation between factor and response.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.102-109
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• 2003

The grouted splice steeve has been applied widely due to its superior construction efficiency, such as the unnecessity of post concrete and the large allowable limit to the arrangement of reinforcing bars. However, studies on grout-filled splice steeve still have not been sufficiently peformed. The purpose of this study is to investigate the confining effect of mortar grouted splice sleeve on reinforcing bar, known to strengthen the bond capacity between grout mortar and reinforcing bar. To accomplish this objective, totally 6 full-sized specimens were made and tested under monotonic loading. Each specimens were equipped with strain gauges at the 12 location of sleeve and reinforcing bar. The experimental variables adopted in this study are embedment length and size of reinforcing bars. Following conclusions are obtained; 1) Under ultimate strength condition, the confining pressure of grouted splice sleeve calculated from measured tangential and axial strain of the sleeve is over $200{\sim}300kgf/{cm}^2$ at any location of sleeve and improved with reduction in embedment length of reinforcing bar. 2) Untrauer and Henry's equation which describe bond strength of mortar as a function of its compressive strength and confining pressure, predicted the measured bond capacity of this test within the 5% limits.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.661-671
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• 2018

Domestic studies on steel plate concrete structures have focused on nuclear structures with high strength. In this study, the SC structure was applied to the general structure, and the SC structure that is advantageous in terms of safety and construction was limited to a special structure. As a basic study for applying SC, this paper proposes basic design information of a SC structure applying cement concrete to plan the structure, which is suitable for eco - friendliness by replacing concrete cement, an important factor in a SC structure, with blast furnace slag. This study examined the compression characteristics and the effective length factor under central compression load. To calculate the effective length factor, the Euler column theory was applied without applying plate theory. The effective length factor was calculated from the yield strength of the steel plate, buckling of the steel plate, and the point at which the concrete was broken. In addition, this study examined whether the maximum compressive strength meets the national and international reference equations with the slenderness ratio (B/t) as a parameter. By analyzing the buckling of the specimen by applying the column theory and selecting the strain of the measured steel plate, the effective length factor was analyzed and compared with the value presented in the reference equation.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.155-165
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• 1999

In completely weathered granite gneiss,8 of 40cm cast-in-situ concrete piles are constructed, and static pile load tests are executed on the piles to study the bearing behavior of rock-socketed piles. Subsurface explorations are carried out on the test site in three phases, in which 14 borehole investigations as well as the seismic investigation are performed. Rock socketd depths of the piles in the weathered rocks are varied as 3m, 6m and 9m to separate the shaft resistance from the end bearing resistance, and for a couple of piles, styrofoam of 10cm thickness is installed under the pile point to eliminate the effect of the end resistance. Strain gages are instrumented on re-bars to pick-up the transferred loads along the pile length. From the results of the pile load tests, the allowable shaft resistance and the allowable end bearing values of weathered rocks are proposed as $8.6t/m^2\;and\; 84t/m^2$, respectively. The empirical equation relating the elastic modulus of rock mass with the uniaxial compressive strength of the rock specimen is also proposed for the weathered rocks.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.18-24
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• 2013

Recently, the interest is increasing about the eco-friendly concrete. Accordingly, the blast furnace slag(BFS), a by-product of industry is known for improving the durability through compaction in concrete and is expanding the use. The research about BFS in concrete be accomplished frequently. In this study, we should know the hydration characteristic of BFS concrete the through the adiabatic temperature rise test due to the replacement of a variety of BFS. In addition, we produced the regression analysis factors through the test result and analyzied the effect for the replacement of BFS. According to test results, the compressive strength showed a slight degradation or equal and the the adiabatic temperature rise figure and rising factors are went down for rising replacment of BFS. In the future, the study about the adiabatic temperature rise equation for the various replacement of BFS and binder is considered necessary.