• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.668-671
• /
• 2004

Recently, the concern for mechanical properties at early age concrete are increasing because of the importance of the thermal stress and the determination of removal time of form work and prestressing work. In this study, an estimation for the development of compressive strength and elastic modulus with age in concretes isothermally cured $(10^{\circ}C,\;20^{\circ}C)$ and having W/C ratio of 30, 40, and $50\%$ were investigated. According to experiment results, the development of compressive strength and elastic modulus shows higher values at early ages as the W/C ratio decreases and curing temperature increases. When the maturity concept, for estimation of the strength, is adopted, a modification for W/C ratio is required at early ages.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.573-576
• /
• 2003

We have developed and applied the super high early strength concrete overlay pavements for repairing asphalts pavements within 24hours. This pavements repairing method by the super high early strength concrete have already applied in U.S.A, japan, England, etc. The super high early strength concrete developed by Ssangyong cement co. for repairing pavements speedily have replaced at No. 2, 17 pavements in managing by Sunchoen national pavements management office. In the results, all of works have finished within 16~24hours after intercepting traffics and all of traffics was opened to be hamonious. In present, this pavements is sound and strong

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.443-444
• /
• 2010

In this study, It is confirmed the validity for determination of the form removal time, utilizing prediction expression for early-stage strength which depended on the variation of curing history for early strength concrete which be passible to construction work period reduction, in apartment.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10b
• /
• pp.1215-1220
• /
• 2000

Blast-Furnace Slag, a by-product of the iron or steel industry, has potential sa a cementitious material. The addition of a Blast-Furnace Slag generally reduces the heat of hydration and can confer significant improvements in resistance to sulfate attack and alkali-aggregate reaction, as well as increases in ultimate strength. But it also reduces early-age strength. In this study, for the purpose of improvement of early-age quality of Blast-Furnace Slag concrete, we choose blaine fineness of $6, 000~8, 000cm^2/g$ of Blast-Furnace Slag, and investigate the various properties of concrete. As a result, workability and early-age strength of Blast-Furnace Slag concrete were improved according to the increase of blaine fineness of Blast-Furnace Slag.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.11a
• /
• pp.305-308
• /
• 2004

Cold weather concrete is the concrete which is used during construction under low-temperature' environment, and this kind of concrete has to be taken care not to be frozen in early ages of setting-hardening, It is specified in the Concrete Standard Specification(2003) as 'the cold weather concrete must be used on the weather condition under the average daily outdoor temperature below $4^{\circ}C$.' In this research, the mechanical characteristics and hydration heat on the cold weather concrete using high early strength portland cement were studied. As a result, the excellent quality was obtained and high early strength portland cement is expected to be used widely as the cold weather concrete.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2020.06a
• /
• pp.98-99
• /
• 2020

The objective of the study is to investigate the compressive strength of damaged part by early frost damage and sound part of the concrete placed when exposed to a low temperature of -20℃ for 24 hours in normal concrete. Test results indicated that the compressive strength of damaged part was 14.5 MPa lower than that of sounf part due to early frost damage.

• Journal of Korean Society of Environmental Engineers
• /
• v.37 no.7
• /
• pp.412-417
• /
• 2015

This study investigated to recycle geobond and ash produced in thesewage sludge incinerator using reduction/stabilization. Nonsintering process was performed by binding cement (High Early Strength Portland cement, Micro cement), geobond and sand mixed with sewage sludge ash (SSA). Chemical ingradients of the sewage sludge ash was mainly composed of $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO and others, which were similar to those of the each binders consisting High Early Strength Portland cement, Micro cement and geobond. Results showed that unconfined the long term compressive strength could be obtained components of sewage sludge ash. It exceeded more than double score 64.6 MPa of the Korean standard ($22.54MPa=229.7kg/cm^2$). Microstructure of solidified block for the different admixture was related to the compressive strength according to SEM analysis. Optimum mixing range of the sewage sludge ash to each binders were found to be 10~40% which can widly safely regulate the confined a long term compressive strength. The best binder of long term compressive strengh was revealed Geobond more than High Early Strength Portland cement and Micro cement. This study revealed the sewage sludge ash can be partial replacement of the inorganic binder & application block for recycling.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.601-604
• /
• 2008

This study as using admixture (G), high early strength agent, calcium hydroxide {a(OH)2} and fine particle cement, etc which have been newly developed for the purpose of quality improvements like the improvement of early strength of concrete that the FA was substituted by 20%, etc, reviewed the possibility of the utilization in the great quantity and the results are summarized as the followings. Slump loss by the kind of mixing material of high early strength agent and Ca(OH)$_2$ showed the smaller width of decrease than that of plain to appear the improved results and fine particle cement and G admixture showed the large slump loss. Air contents were appeared to satisfy the target air contents at all mixing materials. Regarding the compressive strength of the concrete by the kind of mixing material, G admixture was appeared to be highest all on aging 3 days, 7days and 28days at the initial strength. And fine particle cement and high early strength agent showed higher strength increase rate on aging 3days than plain but showed that the increase of strength becomes gradually dulled as aging is increased. And Ca(OH)$_2$ had almost no effect.

• Tunnel and Underground Space
• /
• v.16 no.5 s.64
• /
• pp.405-412
• /
• 2006

It is well known that shotcrete is the most important support member for the construction of large underground spaces. Generally, the strength of the field shotcrete is heavily dependent on the field mixing and spraying conditions so that it is different from the strength of the shotcrete mixed in laboratories. As a support member, the early strength of shotcrete unlike concrete is very important to the initial stabilization of the underground spaces. Therefore, the field methods to efficiently test the early strength of shotcrete have been highly required. This paper aimed to verify the pneumatic pin penetration test and the point load test for measuring the early strength of the field shotcrete. As a result of the experiments through a series of uniaxial compression, pin penetration, and point load tests for the range of the early shotcrete strength, two equations to estimate reliably the uniaxial compressive strength by the pin penetration and the point load tests were acquired.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.04a
• /
• pp.118-123
• /
• 1997

The strength development of Flyash concrete containing various amount of Flyash (0, 10, 30, 50%) using as a cement replacement material was investigated two types of curing conditions, namely water curing at $21^{\cire}C$ and steam curing at $25^{\cire}C$ were adopted for this work, in water curing the strength development of Flyash concrete was always inferior to that of OPC (Ordinary Portland Cement) concrete at early ages, although the differences were dependant up percentage of Flyash. The strength of Flyash concrete based on equivalent strength development at 28 days was also tested and the results exhibited that the strength was improved at early days, specially, the concrete containing 30% of Flyash, in steam curing for the same mix(270kg/$\textrm{cm}^2$) the strength of Flyash concrete similar to that of OPC concrete, in other words. Flyash was strongly influenced by curing temperature in the strength development.