• 한국방재학회:학술대회논문집
• /
• 2009.02b
• /
• pp.68.1-68.1
• /
• 2009

• Magazine of the Korea Concrete Institute
• /
• v.6 no.6
• /
• pp.151-158
• /
• 1994

In this work, in order to inrprove the flexural strength of hardened portlarid cerncrit paste, mix ing water was reduced to water ccrnent ratio of 0.1 aid water soluble polymer such as hydroxy propyl methyl cellulose was adclelri to the paste to obtain a better dispersion. The paste was kneaded by the twin roll mill for cornpact and homogeneous mixing. The high strength mechanism of the hardened cement paste may be due to the removal of macropores larger than 100${\mu}m$, the reduction of capillary pores acting as the passage of crack propagation, the increase of Young's moculus with iticrease of unhytlratcci cenxxnt ard the incicasc of fracture toughnevs with the crack toughening mechanism (grain bridging, polymer fibril bridging and fritional inter-locking).

• Advances in concrete construction
• /
• v.12 no.6
• /
• pp.507-515
• /
• 2021

To evaluate the influence of slag on the alkalinity of pore solution and microstructure of concrete, this paper performs a leaching experiment on hardened cement-slag pastes (HCSP) slice specimens with different slag content in purified water. The pH value of pore solution, average porosity, morphology, phase composition and Ca/Si of HCSP specimens in the leaching process are measured by solid-liquid extraction, saturated-dried weighing, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD). Results shows that the addition of slag can mitigate an increase in porosity and a decrease in Ca/Si of HCSP in the leaching process. Besides, an appropriate slag content can improve the microstructure so as to obtain the optimum leaching resistance of HCSP, which can guarantee the suitable alkalinity of pore solution to prevent a premature corrosion of reinforced bar. The optimum slag content is 40% in HCSP with a water-binder ratio of 0.45, and an excessive slag causes a significant decrease in the alkalinity of pore solution, resulting in a loss of protection on reinforced bar in HCSP.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.5
• /
• pp.67-76
• /
• 2013

In this study, the inhibitive effect of electrochemical treatment subjected to fresh and hardened concrete and literature reviews in terms of the treatment were performed. In hardened concrete, chloride ions are mixed during casting to destroy the passivity of steel, and then the current was provided for 2 weeks with 250, 500 and $750mA/m^2$. After completion of electrochemical treatment, the extraction of chloride ions was quantified and repassivation of steel was observed. Simultaneously, the equated levels of current density for 2 weeks were applied to fresh concrete. Steel-concrete interface in concrete was observed by BSE image analysis and the concrete properties in terms of the diffusivity of chloride ions and the resistance of steel corrosion was measured. As the result, electrochemical treatment is very effectiveness to rehabilitate the passive film on the steel surface and 63-73% of chloride ions in concrete were extracted by the treatment. As the treatment was applied to fresh concrete, the resistance of steel corrosion was improved due to the densification of $Ca(OH)_2$ layers in the vicinity of steel. However, an increase in the current density resulted in an increase in surface chloride content of concrete.

• Computers and Concrete
• /
• v.13 no.6
• /
• pp.709-737
• /
• 2014

Fibre-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fibre addition. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the conventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened properties of the concrete. Therefore, it is vital to investigate whether all the assumed hypotheses about CC are also valid for SCC structures. In the present paper, the experimental results of short-term flexural load tests on eight reinforced SCC and FRSCC specimens slabs are presented. For this purpose, four SCC mixes - two plain SCC, two steel, two polypropylene, and two hybrid FRSCC slab specimens - are considered in the test program. The tests are conducted to study the development of SCC and FRSCC flexural cracking under increasing short-term loads from first cracking through to flexural failure. The achieved experimental results give the SCC and FRSCC slabs bond shear stresses for short-term crack width calculation. Therefore, the adopted bond shear stress for each mix slab is presented in this study. Crack width, crack patterns, deflections at mid-span, steel strains and concrete surface strains at the steel levels were recorded at each load increment in the post-cracking range.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10a
• /
• pp.392-397
• /
• 1998

In this paper, the properties of cement mortar used recycled aggregate are analyzed and compared with river and crushed sand mortar. Recycled aggregates are made by crushing wasted concrete had various compressive strength, and test items are the properties of fresh mortar, hardened mortar and durability. According to the experimental results, flow, unitweight, strength and durability of cement mortar used recycled aggregates decrease compared with those of river and crushed sand mortar.

• Magazine of the Korea Concrete Institute
• /
• v.14 no.4
• /
• pp.56-58
• /
• 2002

$\ulcorner$콘크리트표준시방서$\lrcorner$ 에서는 "서중 콘크리트로서 시공해야 할 시기를 일률적으로 정하기는 곤란하나, 하루평균 기온이 $25^{\circ}C$ 또는 최고온도가 3$0^{\circ}C$를 초과하는 시기에 시공할 경우에는 일반적으로 서중 콘크리트로서 시공할 수 있도록 준비해 두어야 한다."고 규정하고 있고, $\ulcorner$ACI 305R$\lrcorner$ 에서는 "서중(hot weather)은 수분 손실률과 시멘트 수화율의 가속에 의하여 굳지 않은 콘크리트(fresh concrete)와 굳은 콘크리트(hardened concrete)의 품질을 저하시키는 다음 조건들이 공존하는 상태이다."고 규정하고 있으며 그 조건들은 a. 높은 대기 온도 b. 높은 콘크리트 온도 c. 낮은 상대습도 d. 바람의 세기(풍속) 이다.(중략)

• Proceedings of the Korea Concrete Institute Conference
• /
• 1996.10a
• /
• pp.373-378
• /
• 1996

This paper presents the characteristics of various strengths of underwater non-segregation concrete. Three types of cements including low-heat cements has been used to make the test specimens for compressive strength, modulus of rupture and bond strength. The test specimens have been made both in ambient and underwater conditions to take into account the variation according to the environmental condition.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.04a
• /
• pp.142-147
• /
• 1995

In this study, styrene-maleic anhydride copolymer (SMA) was synthesized from styrene and maleic anhydride and further reacted with sulfuric acid to obtain water-soluble SMA and the flow and strength tests of cement mortar mixed with copolymers were carried out to evaluate the capability of copolymers as high range water reducer for the concrete. It was found from flow experiment that the fluidity of cement mortar mixed with sulfonated SMA (SSMA) was larger than that miced with aminophenol-substituted SSMA (SmSMA). The decreasing rate of the flow of cement mortar mixed with SSMA and SmSMA was decreasing rate of the flow of cement mortar mixed with SSMA and SmSMA was significantly lower than that mixed with naphthalene condensate (NSC). The compressive strength of the hardened cement mortars containing 0.5% copolymers after 28 days curing was examined. The compressive strength of hardened cement mortar containing SSMA and SmSMA was increased up to 32% and 13%, respectively, when compared to the plain. As the results, the copolymers (SSMA and SmSMA) used in this study are greatly expected as a good high range water reducers for the concrete.

• Journal of Korean Society of Steel Construction
• /
• v.14 no.2
• /
• pp.375-383
• /
• 2002

To evaluate the applicability of the construction method involving infilling CFT columns by pumping-up, a trial construction was done using 6 actual size test samples. The 12.8m-high test samples were similar to a four-story building scale. The pumping-up level was controlled at 12m. The test used two types of high performance concrete with $450kgf/cm^2$ standard design strength, and a concrete pump which is used domestically. The pressure changes in pipes or pump as well as the changes in concrete characteristics were measured during construction. in order to evaluate applicability. After the concrete hardened, the column was dismantled. The filled state of the concrete, concrete strength distribution according to column height, etc., were checked to evaluate the quality of the concrete, From the results, some basic data which characterize the pumping-up pressure were suggested. Also, the strength of hardened concrete as well as the filled state were proven to be acceptable ranges.