• Advances in materials Research
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• v.5 no.1
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• pp.21-34
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• 2016

Fire is one of the most destructive powers to which a building structure can be subjected, often exposing concrete elements to elevated temperatures. The relative properties of concrete after such an exposure are of significant importance in terms of the serviceability of buildings. Unraveling the heating history of concrete and different cooling regimes is important for forensic research or to determine whether a fire-exposed concrete structure and its components are still structurally sound or not. Assessment of fire-damaged concrete structures usually starts with visual observation of colour change, cracking and spalling. Thus, it is important to know the effect of elevated temperatures on strength retention properties of concrete. This study reports the effect of elevated temperature on the mechanical properties of the concrete specimen with polypropylene fibres and cooled differently under various regimes. In the heating cycle, the specimen were subjected to elevated temperatures ranging from $200^{\circ}C$ to $800^{\circ}C$, in steps of $200^{\circ}C$ with a retention period of 1 hour. Then they were cooled to room temperature differently. The cooling regimes studied include, furnace cooling, air cooling and sudden cooling. After exposure to elevated temperatures and cooled differently, the weight loss, residual compressive and split tensile strengths retention characteristics were studied. Test results indicated that weight and both compressive and tensile strengths significantly reduce, with an increase in temperature and are strongly dependent on cooling regimes adopted.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.638-644
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• 2002

The stress-strain relationship of polymer concrete flexural member was evaluated using C-shaped polyester concrete specimen, the compressive strength of which is 1400 kgf/$\textrm{cm}^2$. Eccentric compression test was performed to estimate the parameters, ${\alpha}$, ${\beta}$1, ${\gamma}$ for equivalent rectangular stress block. The ultimate moment strength ware obtained from the bending test on reinforced polymer concrete beams which were prepared with S different tensile steel ratios with a shear span ratio of 4.0. These values were compared with theoretical ultimate moment strengths, which were obtained using the parameters ${\alpha}$=0.61 and ${\beta}$1=0.73 from stress-stain curves of C-shaped specimens. The results showed that, when tensile steel ratio was over 0.50 $\rho$b, the experimentally obtained moment strengths were well matched with theoretically calculated values. In order to develop accurate criteria for polymer concrete flexural members, however, many other expermental studies for parameter determination are necessary using C-shaped specimens which have various compressive strengths and different sizes.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.99-116
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• 2014

The American Concrete Institute (ACI) 318-11 permits the use of the moment magnifier method for computing the design ultimate strength of slender reinforced concrete columns that are part of braced frames. This computed strength is influenced by the column effective length factor K, the equivalent uniform bending moment diagram factor $C_m$ and the effective flexural stiffness EI among other factors. For this study, 2,960 simple braced frames subjected to short-term loads were simulated to investigate the effect of using different methods of calculating the effective length factor K when computing the strength of columns in these frames. The theoretically computed column ultimate strengths were compared to the ultimate strengths of the same columns computed from the ACI moment magnifier method using different combinations of equations for K and EI. This study shows that for computing the column ultimate strength, the current practice of using the Jackson-Moreland Alignment Chart is the most accurate method for determining the effective length factor. The study also shows that for computing the column ultimate strength, the accuracy of the moment magnifier method can be further improved by replacing the current ACI equation for EI with a nonlinear equation for EI that includes variables affecting the column stiffness and proposed in an earlier investigation.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.318-321
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• 2000

Most compressive strengths commonly used in the construction field are in a range of 240 to 300 kgf/$\textrm{cm}^2$ at 28 days. To get this rage of strengths, however, high-flowing concrete requires cementitious binders more than 400 to 450 kg/$\textrm{cm}^2$ for preventing segregation and sedimentation of aggregates. This amount of cementitious binder generates a large emission of excessive hydration heat, which may consequently induce harmful cracks in concrete structure. In order to reduce excessive hydration heat, thus, this paper aims at fabricating a high-flowing concrete under the condition that cement content is kept as low as 350kg/$\textrm{cm}^3$ by using viscose agents. In a parametric study, effects of cement types such as a ternary blended cement and Type V on he physical characteristics of high-flowing concrete were evaluated. In addition, the influence of viscosity was also investigated by applying two different viscose agents, one in a range of 6,000 to 10,000 cps and the others of 10,000 to 14,000 cps. In terms of chemical admixtures used in concrete mixture, the superplasticizer was Sulfonated Melamine-Formaldehyde Condensate with about 30,000 of molecular weight, and main component of viscose agent was HPMC (Hydroxy Propyl Methyl Cellulose). Slump flow was fixed at 50cm with different dosages of superplasticizer in weight.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.241-246
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• 2000

In the strut-tie model design of structural concrete, the importance of the effective strength of concrete strut has been overlooked by many practitioners. The authors believe that the effective strength of concrete strut is an important factor not only in determining steel tie forces but also in verifying the nodal zone strength and geometric compatibility condition of a selected strut-tie model. This study evaluate the effect of the effective strength of concrete strut on structural concrete design by applying the different effective strut strengths to the strut-tie model design of a post-tensioned anchorage zone and a continuous concrete deep beam.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.3
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• pp.3472-3476
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• 1974

This test was attempted to investigate the effects of some mix designs of concreteon the compressive strengths and corrosive rates when exposed to sea water of the West Sea. In this test, concrete mixes consisted of an ordinary concrete, a pozzolan concrete and concretes with different admixtures such as fly ash, pozzolith and vinsol resin. Compressive strengths of the concrete were measured at ages of 1-year and 2-years when exposed to both sea water and fresh water. Corrosive rate was tested at ages of 1-year and 2-years when exposed to sea water only. The results obtained from the test may be summarized as follows: (1) When all of concretes were exposed to fresh water, compressive strength of an ordinary concrete was the lowest at all mixes of concretes, and all of them showed higher strength as the exposing age is longer. It was evidance that the uses of pozsolan cement, fly ash, pozzolith and vinsol resin in mix design of concrete had an effect on increasing compressive strength and that fresh water also had an effect on curing concretes even though at a long-time age. (2) When concretes were exposed sea water, a concrete with fly ash was the highest in compressive strength and its strength was increasing as the exposing age is longer, but the other concretes were decreased at 2-year exposure. It was found that a concrete with fly ash was the most effective on compressive strength of all concrete, but the other concretes were attacked by action of the sea water. (3) The use of vinsol resin admixture was the most resistant to corrosion by sea water, while the use of pozzolith was the most serious at corrosion and the others were corroded to almost same extent. (4) The relationship between corrosions and compressive strengths of concretes was not clearly correlated yet. It was known that the corrosive rate of concretes could not affect to compressive strengths by 2-year exposure of the sea water. (5) Pozzolan concrete was the most effective in compressive strength when exposed to fresh water only, However, the use of a fly ash admixture was available for compressive strength when exposing to both fresh water and sea water. It was also noticed that the use of vinsol resin was not available for strengths of concrete but for resistance to corrosion when exposed to sea water. (6) It was found that the use of pozzolith was so defective in compressive strengths and corrosiive resistance when exposing to sea water that it was only available for fresh water.

• Magazine of the Korean Society of Agricultural Engineers
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• v.25 no.2
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• pp.67-75
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• 1983

The objectives of this paper were to measure the bond strengths of reinforced concrete in which the steel rods were coated with five different kinds of anticorrosion paints, and to compare their prevention effects in salt water. The paints used in the study were epoxy resin I . II . III, Z.R. P., and silicone resin, which were applied at rates recommended by the manufacturers. The bond strengths were measured on the 7-, 14-, and 28-th days after molding. Corrosion conditions of coated steel plate under fresh water, seawater, 10 % salt water, and 20% salt water, were inspected every month during four months test peoriods, respectively. The results obtained from tests are summarized as follows: 1. Paint-coating may reduce the bond strengths of reinforced concrete. Silicone resin paint showed some 20% reduction in the strength compared to those without the paint. However, the other paints seemed not to significantly affect the strength. 2. Picture analyses showed that epoxy resin I and II significantly prevented corrosion steel plates in seawater. Epoxy resin I and silicone resin coating did not do a good job in corrosion prevention. Z.R. P. paint was found to be moderate as preventive coating paint. 3. Varying soluble salt contents had little effects on the corrosion prevention of tested paints. 4. Epoxy resin I and II were found to be appropriate as a coating material to prevent the corrosion of steel rods in seawater. Z.R.P. may also be used for the purpose.

• Advances in concrete construction
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• v.9 no.1
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• pp.9-22
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• 2020

The present work looks at the possibilities of recycling more than once demolished concrete as coarse aggregates, to produce new concrete. Different concrete mixes were made with substitutions of 50%, 75% and 100% of recycled concrete aggregates respectively as coarse aggregates. The physico-mechanical characterization tests carried out on the recycled concrete aggregates revealed that they are suitable for use in obtaining a structural concrete. The resulting concrete materials had rheological parameters, compressive strengths and tensile strengths very slightly lower than those of the original concrete even when 100% of two cycles recycled concrete aggregates were used. The durability of the recycled aggregates concrete was assessed through water permeability, water absorption and chemical attacks. The obtained concretes were thought fit for use as structural materials. A linear regression was developed between the strength of the material and the number of cycles of concrete recycling to anticipate the strength of the recycled aggregates concrete. From the results, it appear clear that recycling demolished concrete represents a valuable resource for aggregates supply to the concrete industry and a the same time plays a key role in meeting the challenge for a sustainable development.

• Journal of the Korean Society of Safety
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• v.16 no.2
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• pp.91-96
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• 2001

Theoretical definitions of mixed behavior of PE panel and connote should have preceded to cause a mixed behavior of connote and polyethylene which have different elastic module, one-line expansion coefficients, poison ratios, compressive strengths and tensile strengths. Consequently, changes are analyzed through experiment process to identify the effects on interpretation of mixed behavior on the basis of temperature change of structures, temperature rise of concrete other than PE panel due to hydration heat temperature rise of concrete other than PE panel due to drying and contraction, working of hydrostatic pressure by storage and temperature gradient From the results of interpretation of the analysis, it is concluded that PE panel have slight influences on the change of guess of structures and maintains structural stability compared with concrete structures without PE panel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.205-215
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• 2005

The main objective of this study is to investigate the behavior of NSC and HSC beams with stirrups. Main variables were the concrete compressive strength and amount of vertical stirrups. A total of 24 beams was tested; 4 beams without web reinforcement and 20 beams with web reinforcement in the form of vertical stirrups. Main variables were 2 different compressive strengths of concrete of 26.9MPa and 63.5MPa, 5 different spacing of stirrups of 200, 150, 120, 100 and 90mm. Therefore, the results were compared with the strengths predicted by the equations of ACI code 318-99 and other researchers. The shear reinforcement ratio, where the test beams were failed simultaneously under flexure and shear, were $0.63{\rho}_{vmax}$ for NSC beams and $0.53{\rho}_{vmax}$ for HSC beams, respectively. The ACI code equation was found to be very conservative for shear design.