• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.698-707
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• 2002

A review is presented of experimental studies on the strength performance of concrete exposed at short-term and rapid heating as in a fire and after cooling. Emphasis is placed on concretes with high original compressive strengths, that is, high-strength concrete(HSC). The compressive strength-temperature relationships from the reviewed test programs are distinguished by the test methods used in obtaining the data(unstressed, unstressed residual strength, and stressed tests) and by the aggregate types(normal or lightweight), The compressive strength properties of HSC vary differently with temperature than those of NSC. HSC have higher rates of strength loss than lower strength concrete in the temperature range of between 20$^{\circ}C$ to about 400$^{\circ}C$. These difference become less significant at temperatures above 400$^{\circ}C$ compressive strengths of HSC at 800$^{\circ}C$ decrease to about 30 ％ of the original room temperature strength. A comparison of lest results with current code provisions on the effects of elevated temperatures on concrete compressive strength and elastic modulus shows that the CEN Eurocodes and the CEB provisions are unconservative.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.269-275
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• 2016

In this study, the mechanical properties and the neutron shielding rate of concrete with the borosilicate glass and the amorphous boron steel fiber were investigated. The measures of this investigation includes air contents, slump loss, compressive strength, static modulus of elasticity, compressive toughness, flexural strength, flexure toughness and neutron shielding rate. As a result, the neutron shielding rate of the concrete with borosilicate glasses increased even though the compressive strength and flexural strength decreased in comparison with that of plain concrete. Also, the mechanical toughness and the neutron shielding rate of the concrete with amorphous boron steel fiber increased in comparison with that of plain concrete.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.819-830
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• 2021

To evaluate the performance of concrete load bearing walls in a structure under horizontal loads after being exposed to real fire, two steps were followed. In the first step, an experimental study was performed on the thermo-mechanical properties of concrete after heating to temperatures of 200-1000℃ with the purpose of determining the residual mechanical properties after cooling. The temperature was increased in line with natural fire curve in an electric furnace. The peak temperature was maintained for a period of 1.5 hour and then allowed to cool gradually in air at room temperature. All specimens were made from calcareous aggregate to be used for determining the residual properties: compressive strength, static and dynamic elasticity modulus by means of UPV test, including the mass loss. The concrete residual compressive strength and elastic modulus values were compared with those calculated from Eurocode and other analytical models from other studies, and were found to be satisfactory. In the second step, experimental analysis results were then implemented into structural numerical analysis to predict the post-fire load-bearing capacity response of the walls under vertical and horizontal loads. The parameters considered in this analysis were the effective height, the thickness of the wall, various support conditions and the residual strength of concrete. The results indicate that fire damage does not significantly affect the lateral capacity and stiffness of reinforced walls for temperature fires up to 400℃.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1069-1080
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• 1994

For complying with the demand of developing high strength concrete, the high strength concrete with higher cement contents and lower water-cement ratio using high range water reducing admixture has been manufactured. In this study, for the purpose of improving the strength of concrete, concrete with silica fume and gypsum was produced so that it was acquired to high compressive strength of $1,058kg/cm^2$, $1,170kg/cm^2$ at age 28 and 91 days, respectively. But neither tensile strength nor modulus of elasticity were highly improved although the compressive strength of the concrete increased. And it was concluded that a higher slump loss of fresh high strength concrete and interior temperature increment of concrete in according to elapsed time than convential concrete should be solved.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.99-104
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• 1998

A study is carried out to investigate the characteristics of concrete various level(0~60%) of fly ash. These results indicate that compressive strength of fly ash concrete seems to be slightly higher than that of ordinary concrete between 7 and 28 days, thereafter the strength of fly ash concrete is significantly higher. In fresh properties of the fly ash concrete, the loss of slump and air content with time up to 120 minutes is lower, but the setting time is increased with increasing fly ash content.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.30-35
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• 1995

This paper presents fundamental experiment for the properties of high performance concrete in its fresh and hardened state made with ground granulated blast-furnace (GGBF) slag. The result is that the effect of decreasing xoncrete temperature is to the mixing ratio of GGBF slag, but it presents disadvantage in the slump loss phase. In addition to, we know that the splitting tensile strength, compressive strength and elastic modulus of concrete mixed with high fineness GGBF slag are increased at age 28days.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.89-92
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• 2000

In this paper, setting and mechanical properties of cement mortar using retarding agents are investigated. According to the experimental results, as dosage of retarding agents increases, flow and ar content of mortar are shown to be higher. Flow loss of mortar using retarding type water reducing agents is larger than that using gluconic acid by 3 times. As for setting time it is found that mortar using gluconic acid takes much longer setting time than that using retarding type water reducing agent. In case of compressive strength, when retarding agent is applied, cement mortar gains high strength compared with that of plain mortar. However, we can not measure compressive strength of cement mortar contaning more than 0.6% of gluconic acid.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.137-138
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• 2023

This study proposed the optimal mixing time for pre-mixed cement and post mixed cement using the statistical analysis method of box plots. Pre-mixed cement can prevent material seegregation, strength loss, and quality variation if mixed for at least 60 seconds, and the data median is shown to be within the box range. Post-mixed cement should be mixed for at least 180 seconds to prevent material segregation, strength loss, and quality variation, and compressive strength tends to increase with longer vibrating times. Therefore, it is suggested that using pre-mixed cement can shorten the vibrating time and increase the productivity of the concrete.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4575-4591
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• 1978

In order to investigate the effects of grain size distribution, cement content, and molding pressure on the strength and durability of soil-cement mixtures, a laboratory test of soil cement mixtures was performed at four levels of cement content, five levels of molding pressure, and four levels of normal curing periods. The results are summarized as follows: 1. Optimum moisture contents in loam soil and maximum dry density in sand soil increased with the increase of cement content, but in others, both optimum moisture contents and maximum dry density were changed ununiformly. 2. When the specimens were molded with molding pressure, 50kg/$\textrm{cm}^2$, strength of soil cement mixture with cement content, 2 and 4 per cent, was lower than the strength of soil cement mixture without cement content by more than 40 to 50 per cent. 3. The strength of soil-cement molded with molding pressure, 100kg/$\textrm{cm}^2$, was higher than the strength of soil-cement molded with M.D.D. obtained from standard compaction test more than 40 per cent in sand loam cement and 50 per cent in loamy cement. 4. There was highly significant positive correlation among molding pressure, cement content and unconfined compressive strentgh and so the following multiple regression equations were obtained. Loam: fc=1.9693C+0.197P-0.84 Sandy loam: fc=2.9065C+0.235P-0.77 5. When the specimens were molded with molding pressure, 20 to 100kg/$\textrm{cm}^2$, the regression equation between the 28-day and 7-day strenght was obtained as follows. Loam : q28=1.1050q7+7.59(r=0.9147) Sandy loam : q28=1.3905q7+3.17 (r=0.9801) 6. At the cement contents of above 50 per cent, the weight losses by freeeze-thaw test were negligible. At the cement content of below 8 per cent the weight losses were singnificantly high under low molding pressure and remarkably decreased with the increase of molding pressure up to 80kg/$\textrm{cm}^2$. 7. Resistance to damage from water and to absorption of water were not improved by molding pressure alone, but when the soil was mixtured with cement above 6 per cent, damage seldoms occurred and absorbed less than 5 per cent of water. 8. There was highly significant inverse-corelationship between the compressive strength of soil cement mixtures and their freeze-thaw loss as well as water absorption. By the regression equation methods, the relationships between them were expessed as followed fc=-7.3206Wa+115.6(r=0.9871) log fc=-0.0174L+1.59(r=0.7709) where fc=unconfined compressive stregth after 28-days curing. kg/$\textrm{cm}^2$ Wa=water absorption, % L : freeze-thaw loss rate, %

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.3
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• pp.3533-3538
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• 1974

This study was attempted in order to search for physical properties of sail cement. In this study, soil samples were specified according to soil particle analysis and used for compaction, strength, abrasion, absorption tests respectively according to different cement contents. Cement content sused in each treatment were 6%, 8%, 10% and 12% of total weight of soil-consent mixture. In the test, compressise strengths of the specimens were measured at the following ages; 3 days, 7-days, 14-days, 21-days and 28-days. Abrasion and absorption tests of the specimens were carried out at the 7-days age only. The results obtained from the tests are summarized as follows; 1. As the cement contents were in creased, the compressive strengths of soil-cement were almost proportionally increased. 2. The Compressive strength of soil-cement was not always proporportional to ages. The gradient of compressive strength of the soil-cement was steeper as the cement content was rucreased. 3. As the cement content was increased, the amount of the weight loss of the samples due to the abrasion was decreased remarkably, giving no abrasion for about 8% of the cement content. 4. As the cement content was increased, the absorption ratio of the specimens was not changed remarkably.