• Explosives and Blasting
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• v.21 no.4
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• pp.11-21
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• 2003

An experimental study was carried out in order to reduce the period and cost of construction of Missiryung tunnel, which is a relatively long one 3.6 km long. An allowable vibration level for curing concrete was established based on the extensive case studies done over the world. and assessment was performed on the possibility of constructing concrete structures like lining during tunnel blasting. Attenuation relationships were obtained by processing more than 130 measurement data from a series of tunnel blasting in the site. A Guideline for safe construction work was suggested. To verification, low small concrete blocks with a constant standoff distance were installed in the floor of the tunnel After the blocks were exposed to blast vibrations for 28 days, compressive strength tests were performed on 20 specimens taken from the blocks. It was shown that the suggested guideline was appropriate for the safe construction work at the site.

• Resources Recycling
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• v.27 no.6
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• pp.59-67
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• 2018

Efflorescence is a white deposit of powders in the surface of cement concrete which can also occur in geopolymers. Efflorescence occurs when sodium ions in alkali activator react with atmospheric carbon dioxide to form sodium carbonate components. In this study, we investigated whether the secondary efflorescence can be reduced by controlling the Na/Al mole ratio or by changing the curing temperature and heat curing time in fly ash-based geopolymers. The 28 days compressive strength in geopolymers having Na/Al ratio of 1.0 was higher than geopolymers having Na/Al ratio of 0.8. The strength increased with the increasing curing temperature and longer heat curing time. On the other hand, efflorescence was lower when the curing temperature was high and the heat curing time was longer in the geopolymers having Na/Al ratio of 1.0. The geopolymers having Na/Al ratio of 0.8 showed accelerated efflorescence occurrence than the geopolymers having Na/Al ratio of 1.0. In order to reduce the occurrence of the secondary efflorescence of fly ash-based geopolymers, it will be advantageous to maintain the Na/Al ratio at 1.0, increase the curing temperature, and lengthen the heating curing time.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.191-194
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• 1999

Recently in Korea, may workers have reported the effects of the granulated blast furnace slag[BFS] of high fineness on the strength development of slag cement. We have studied the effect of slag fineness on the strength development of mortar with curing conditions, in order to get the basic data of high strength concrete using BFS. In this paper, we discussed the effects of slag fineness and porosity of mortar and the reaction of slag in hardened slag cement.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.6
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• pp.82-89
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• 1999

This paper present the strength estimation of precast concrete products by chloride ion penetration method. The relation between the strength of precast concrete product and the ion passing charge is linear and a numerical model of FCK =515.96-0.201Q is prposed. The results showe good agreement at about 9.0% error ration with the estimated model results for real precast concrete product.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.04a
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• pp.13-18
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• 1992

Moisture movement which is controlled by water potential and permeability of concrete is a very important phenomenon which affects the shrinkage of concrete. Thermocouple psychrometer were used to measure the moisture potentials in concrete. Based on the measured moisture potentials, three method have been proposed to calculate hycraulic conductivity and diffusivity. And also the hystresis of sorption isotherm due to drying and wetting cycle has been crawn.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2002.05a
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• pp.109-114
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• 2002

건설공사의 공종 중 거푸집공사는 전체공사기간의 대략 25％를 차지하고 있으며 공사비 비율은 일반적으로 전체공사비의 10～15％, 철근콘크리트공사비의 20～30％를 차지하고 있어 구조물의 안전성, 경제성 및 작업성과 품질관리에 중요한 역할을 한다. 또한 거푸집은 콘크리트가 양생되면 곧 해체되는 가설구조물로써 작업상에서 많은 위험요소를 포함하고 있으며 특히, 아파트공사의 경우 전체 재해발생의 17％로 가장 높은 비율을 차지하고 있다. 이와 같이 거푸집공사는 가장 우선적으로 관리하여야 할 위험공종이며 전체공기를 좌우하는 주공정으로서 이를 재해발생의 측면에서 제어하는 것이 안전관리에 있어서 가장 효율적이며 큰 효과를 나타낼 수 있는 것으로 생각된다.(중략)

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.777-783
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• 2004

In this study, for improving of concrete properties, those are used ground granulated blast slag(GGBS) and fly ash(FA). There are some advantage to add the GGBS and FA in plain concrete. The objective of this study is to find the characteristics of fresh and hardened antiwashout underwater concrete which is followed by blended ratio of GGBS and FA. Experimental parameters were chosen that W/C was 50%, S/a was 40% and as the blended ratio of GGBS was set at 0, 10, 20, 30, 40, 50, 60% and FA was set at 0, 10, 15, 20, 25, 30, 35% in order to prove the properties of antiwashout underwater concrete can be changed by blended ratio of GGBS md FA. It was measured pH, suspension and slump flow of fresh antiwashout underwater concrete and compressive strength of hardened antiwashout underwater concrete in age of 7 days, 28 days and 56 days. The experimental results of fresh concrete show that pH, suspension and slump flow were all satisfied with KSCE (Korea Society of Civil Engineering) standard value and mix design standard value. To synthetically consider, the optimum blended ratio is about 30% of GGBS and FA.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.11-20
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• 2009

By using the artificial lightweight aggregate for the natural aggregate depletes and destruction of environment and the application of lightweight concrete in structure, the lightweight concrete is manufactured. The fundamental characteristics by the waterbinder ratio was evaluated. It is suggested the method to control of pre-absorbed water of the lightweight aggregate. Lightweight concrete with pre-absorbed aggregate has similar characteristics compared to normal weight concrete regardless of water-binder ratio. According to the water-binder ratio, the drying condition, and the rebar, the unit mass of the lightweight concrete showed the reduction of 14.6${\sim}$21.0% as the range of 1,668${\sim}$1,998 $kg/m^3$ in comparison to the normal weight concrete. The lightweight aggregate pre-absorbed water showed the deferent evaporation quantity according to the water-binder ratio. As the water-binder ratio is lower, the oven dry vapour water is larger, therefore the internal curing water is increasing. In the same water-binder, comparing the normal concrete the lightweight concrete shows lower compressive strength which is due to the different strength of an aggregate. In the air dry curing, the normal weight concrete has a lower strength improvement effect in w/c 0.3 than the ratio 0.4 and 0.5. However, the strength improvement effect has increasing as the water-binder ratio was low in the light concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.445-446
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• 2010

Water existed inside of bubble sheet applied at the job site sometimes results in undesirable heat insulation capability of bubble sheet. Therefore, the objective of this paper is to examine experimentally the effect of water presence in bubble sheet on heat insulation capability and strength of the concrete cured with double bubble sheet.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.04a
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• pp.89-93
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• 2011

본 연구는 고강도콘크리트의 폭렬성상과 공극구조와의 관계를 실험적으로 규명하는 것을 목적으로 하였다. 실험변수는 양생방법, 압축강도, 공극구조로 설정하였으며, ISO834 화재온도이력곡선을 15분 적용하여 콘크리트의 초기 폭렬특성을 실험적으로 검토하였다. 그 결과 50 MPa급 이상의 고강도 콘크리트 시험체의 경우, 가열 이후에도 $0.05{\mu}m$ 이하의 공극이 많이 존재하고 있는 것을 알 수 있었으며, 가열을 받은 고강도 콘크리트는 고강도화될수록 공극이 세공화 되어 탈수 현상이 지연되는 것을 도출 할 수 있었다.