• Journal of the Korea Concrete Institute
• /
• v.12 no.5
• /
• pp.131-139
• /
• 2000

Porous Concrete usually contains large amount of voids(about 10∼20%) after compaction so that it has relatively high permeability. It has been introduced in domestic since early 1980's but it has problems such as lack of optimized mixture, low strength and durability, and other defects, etc. The purpose of this study is to manufacture high-performance porous concrete using polymer to enhance the mechanical properties. The results of this study are as follows; the compressive strength range 12 92∼207kgf/㎠, the tensile strength range is 14∼28kgf/㎠, the bending stength range is 42∼73kgf/㎠, and the coefficient permeability range is 5.77×10-2∼6.79×10-1cm/sec. To develope high-performance porous concrete. further studies are needed on optimum mixture of fineness modulus and admixture.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.10a
• /
• pp.27-32
• /
• 2002

In this research influences of type and concentration of alkali activator and curing condition on the hydration, and properties of alkali activated blast furnace slag(AAS) concrete were investigated. Sodium carbonate and sulfate were used as alkali activators and their concentration were 4~10 weight percent with Na$_2$O equivalent to binder. The curing conditions were standard curing using 23$^{\circ}C$ water and activated curing chamber at $65^{\circ}C$. Results show that in case of sodium carbonate addition high early strengths were gained by activation of early hydration, but later strength gained was slight. On the other side sodium sulfate strengths were continuously increased with adding amount and ages. Steam curing activated early hydration so that early strengths were improved but later strengths were similar to standard curing. The strength reduction of AAS mortar with sodium sulfate was less than OPC mortar in 5% sulfuric acid solution so that AAS concrete can be useful for acid-resistance concrete.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.2 no.1
• /
• pp.46-51
• /
• 2014

In this study, strength development properties of high volume fly ash concrete was evaluated through compressive strength of concrete with reduction of unit water content. And concrete specimens were prepared according to target strength 3 level and variation of unit water content. As a result, the improved fluidity were obtained as a result of the ball bearing action of the spherical, the electrostatic repulsion and the particle size distribution of fly ash particles in case of using more than 50% fly ash. Through this, the mixture of fly ash has been shown to reduce the amount of water required in concrete. Also, the early strength of high volume fly ash concrete with reduction of unit water content was improved more about 66% than general concrete mixture.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.1135-1140
• /
• 2001

The purpose of this study is to investigate the shrinkage properties of high strength concrete according to the S/A ratio at early age. The main parameters are as follows : S/A ratio is 30, 35, 38, 41, 45%, W/B ratio 24.9%, SF/B ratio 8%. FA/B 15%. The size of specimen is l0$\times$10$\times$40cm and the shrinkage is measured by the embedded gage at each end of the specimens. From the test, it was found that the slump-flow of concrete was high, and also autogenous shrinkage increased and drying shrinkage decreased as S/A ratio increased.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2008.05a
• /
• pp.117-121
• /
• 2008

This study investigates practical application of high early strength type concrete using fine particle classifying cement, and the results are summarized as following. The replacement use of FC 30% did not great influence on concrete mix, therefore mixing without additional SP and AE was available using equal mix with OPC. The ratio of increasing temperature by heat of hydration was similar with OPC, and the compressive strength was over then 5MPa at -28℃ outside temperature on 2nd day. Therefore, it is considering that the first purpose, the effect of shortening terms of work by early demolding, will be available. The rebound rate of type "P" schumidt hammer was relative with compressive strength, and the rebound rate for verifying 5MPa of compressive strength was estimated about 55 considering rate of safety. Therefore, assuming demolding date is available efficiently.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.10a
• /
• pp.239-242
• /
• 2002

This study is intended to investigate the relationship between rebound value of P type schmidt hammer and the compressive strength with various aggregates, and a series of experiments about early strength quality control by P type schmidt hammer was performed. According to the results, the compressive strength of concrete using basalt and limestone aggregate is higher by 3% and lower by 4% than that of concrete using granite aggregate respectively. Concrete using basalt and lime stone aggregate show high rebound value in vertical strike. Estimation of the compressive strength does not show differences in horizontal strike, but the compressive strength is estimated high in order of granite, basalt and limestone aggregate in vertical strike. A good correlation between the rebound value of schmidt hammer and the compressive strength is confirmed regardless of aggregate types, so it could be possible to control the quality of concrete by P type schmidt hammer test when basalt and limestone aggregates are used at the same time.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2012.11a
• /
• pp.221-222
• /
• 2012

This study is to high early concrete development which reveals 14 MPa within 12 hours in order to reduce the mold time of dismantlement and not do the steam curing of the precast concrete product. About (40~50) min could shorten the final setting time if the coagulation test result cement amount 100 kg/m3 was increased. In the case of the compressive strength, it was exposed to be satisfied the target value with the cement amount 500 kg/m3 combination according to the hardening accelerator addition.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.571-574
• /
• 2000

When fresh concrete is exposed to low temperature, the concrete may suffer from the frost damage at early ages and the strength development may be delayed. To solve such problems of cold weather concreting admixtures called agent for enduring cold climate are developed to prevent the fresh concrete from being frozen at early ages. In this study, the experiments are carried out on several kinds of agent for enduring cold climate to present their performance. According to experimental results, most kinds of agent for enduring cold climate show the strength development in the range $-5^{\circ}C$ of curing temperature, it tends to be delayed at long term maturity without agents for enduring cold climate. while it gains high strength maturity when agents for enduring cold climate is applied.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2005.05a
• /
• pp.25-28
• /
• 2005

This study shows the early quality improvement of concrete with calcium sulfa aluminate(CSA). For the properties of slump, plain concrete incorporating BS $35\%$ and UP $15\%$ resulted in high fluidity compared with OPC without any admixture. As displacement ratio of CSA increased. the fluidity decreased. The fluidity also declined with setting time. Increase of incorporation ratio of CSA declined bleeding and accelerated setting time. Importantly, using more CSA helped to improve early compressive strength and decrease drying shrinkage. In term of water curing, drying shrinkage hardly ever occurred.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.6
• /
• pp.124-133
• /
• 2012

Compressive strength in concrete increases with time. Regression analysis with time is conventionally performed for strength evaluation and prediction. In this study, hydrate amount is assumed as a function of hydration rate and porosity, and modeling on compressive strength is carried out considering decreasing porosity with time, which does not need the regression analysis with time. For twenty one mix proportions of HPC (High Performance Concrete), DUCOM (FE program) which can simulate the behavior in early aged concrete is utilized, and porosity from each mix proportions is obtained with time. For HPC with OPC (Ordinary Portland Cement) concrete, modeling on compressive strength is performed considering hydration rate, unit content of cement, and porosity with time. For HPC with mineral admixtures, a long-term parameter which can handle long-term strength development is additionally considered. From the comparison with the previous test results, the applicability of the proposed model is verified.