• 한국도로학회:학술대회논문집
• /
• 2004.10a
• /
• pp.137-142
• /
• 2004

• Journal of the Korean Ceramic Society
• /
• v.37 no.5
• /
• pp.438-443
• /
• 2000

This dissertation is focused on the study over the improvement for the early strength of belite-rich cement(BRC). For this purpose, the initial hydration behaviors according to addition of different calcium sulfate types were evaluated. From the observations by XRD, DSC and SEM, the BRC II and III with the addition of natural anhydrate and flue gas desulphurization(FGD) gypsum, respectively, formed much ettringite after 7 days more than the BRC I with the addition of chemical gypsum. The compressive strength of the BRC II and III developed outstandingly due to the formation of calcium aluminate hydrate within pores of hardened BRC paste. Especially, in the case of BRC III adding FGD with low impurities, the early as well as long term compressive strengths were shown very high, compared with other specimens.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.05a
• /
• pp.481-486
• /
• 2001

Ground granulated blast-furnace slag shows very high strength when proper alkali-activator exists. This paper deals with setting time, heat evolution rate and the strength development of alkali-activated slag cement activated by KOH, Ca(OH$)_{2}$, $Na_{2}$ $So_{4}$ , and alum(potassium aluminum sulfate). Alkali-activated slag mortar is studied by comparison with GGBF slag cement mortar. The experimental results indicate that for moisture curing at $25^{\circ}C$, the addiction of either 4% $Na_{2}$ $So_{4}$ or 4% alum increases the strength of GGBF slag cement mortar consisting of 50% GGBF slag and 50% portland cement at early age. Strength of activated GGBF slag cement mortars at 1, 3 and 7 days exceeded that of GGBF slag cement mortar. A conduction calorimeter was used to monitor early age hydration.

• International Journal of Highway Engineering
• /
• v.11 no.2
• /
• pp.185-194
• /
• 2009

The autogenous shrinkage of high-performance concrete, including very-early strength latex-modified concrete(VES-LMC), is generally bigger than that of normal strength concrete because of the low water/cement ratio, high binder contents, and usage of superplasticizer. Mix. proportion of VES-LMC has low water/cement ratio(0.38), high cement content(390kg/m$^3$), and aid of latex(15% of cement weight). Thus, these factors of VES-LMC, rapid water self-dissipation and evaporation within 3 hours of concrete placement would increase the autogenous shrinkage. The purpose of this study was to evaluate the early-age shrinkage, thermal deformation and autogenous shrinkages of VES-LMC with retarder contents(retarder solids-cement ratio, by weight) using to secure working time in field. The experimental results showed that retarder contents do not affect of the maximum hydration temperature. Early-age expansion of VES-LMC was mostly caused by thermal expansion and partly by autogenous expansion. The autogenous shrinkage is decreased by increasing the retarder contents within this study. On the other hand, the usage of retarder should be decided carefully considering the field conditions because an excessive usage of retarder can cause handful early-age expansion.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.657-660
• /
• 2006

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior of early-age concrete at the stages of design and construction. The purpose of this study was to evaluate the autogenous shrinkage of VES-LMC, having an experimental variables such as retarder and water-cement ratio. The greater the retarder content in VES-LMC, the greater the expansion at early-age. This recommend the small retarder content as possible. The effect of water-cement ratio on early-age behavior is very small, because of the wrapped specimen in order to prevent water evaporation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.171-172
• /
• 2009

A Bonded Concrete Overlay is a layer of concrete bonded to the top of an existing pavement to rehabilitate it, to restore and increase its structural and functional capabilities and forming a monolithic structure with the existing pavement. This study focuses on the field application of BCO by very early strength latex modified concrete.

• 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.

• Journal of Industrial Technology
• /
• v.21 no.B
• /
• pp.317-324
• /
• 2001

This study focused on the investigation of strength development and permeability of LMC(Latex Modified Concrete) and RSLMC(Rapid-Setting Cement Latex Modified Concrete) as the latex content, cement types and w/c ratio changed. The compressive strength of latex modified concrete decreased slightly and the flexural strength increased quitely at 15% of latex content. This may be due to the flexibility of latex filled in voids and interconnections of hydrated cement and aggregates by a film of latex particles, respectively. The permeability test results showed that the permeability of LMC was considerably lower than that of conventional concrete. Results of chloride permeability test, for RSLMC indicated very low at an early age caused by the early formation of needle-shape ettringites and latex film.

• 한국도로학회:학술대회논문집
• /
• 2005.03a
• /
• pp.121-128
• /
• 2005

• The Journal of Korean Physical Therapy
• /
• v.31 no.3
• /
• pp.141-146
• /
• 2019

Purpose: To investigate the effect of an augmented reality (AR) system on muscle strength and function level of the paretic lower limb and the balance ability in the early rehabilitation program of acute stroke patients. Methods: The participants (30 or fewer days after stroke) were randomly assigned to receive intervention with an early rehabilitation program using an AR system (n=1) or an early rehabilitation program consisting of functional electrical stimulation and tilt table use (n=1). Patients in both subjects received interventions 4-5 times a week for 3 weeks. Results: In the paretic limb muscle strength, AR subject was increased from 15 to 39.6 Nm and Control subject was increased from 5 to 30.2 Nm. The paretic limb function of AR subject motor function was increased from 8 to 28 score and Control subject motor function was increased from 6 to 14 score. But sensory function was very little difference between the two subjects (AR subject: from 4 to 10 score, Control subject: from 3 to 10 score). In the balance ability, AR subject had more difference after intervention than control subject (AR subject: 33 score, Control subject: 22 score). Conclusion: The early rehabilitation program using the AR system showed a slightly higher improvement in the motor function of the paretic lower limb and balance ability measurement than the general early rehabilitation program. The AR system, which can provide more active, task-oriented, and motivational environment, may provide a meaningful environment for the initial rehabilitation process after stroke.