• 한국건설순환자원학회논문집
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• 제10권4호
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• pp.561-568
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• 2022

본 연구에서는 무기계 재료인 클링커 바인더, Calcium sulfoaluminate(CSA), 그리고 sodium sulfate(Na₂SO₄)가 포함된 시멘트 모르타르의 물리적 특성 및 자기치유성능을 평가하였다. 압축강도 및 휨강도 측정을 통해 시멘트 모르타르의 물리적 강도를 알아보고, 정수위 투수시험 및 기체확산시험을 통해 치유성능을 평가하였다. 또한 광학현미경과 주사전자현미경을 통해 균열부 내 침전된 치유생성물을 시각적으로 관찰하였다. 그 결과, 클링커 바인더 기반 무기계 혼합재의 혼입은 시멘트 모르타르의 초기 및 28일 재령 강도를 약 20 % 증진시켰다. 치유성능 평가방법에 따라 치유율의 편차가 존재하고 과소평과 되는 경향을 나타냈으나, 무기계 혼합재의 시멘트 모르타르 혼입 시 0.3 mm 균열 내부에서 CaCO₃가 주요 치유생성물로 침전되어 치유성능을 향상시켰다.

• Smart Structures and Systems
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• 제25권3호
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• pp.337-343
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• 2020

In this paper, we focused on the self-healing concrete using new nano-capsules. Three types of nano-capsules with respect to availability, high strength and temperature tolerance are used; type 1 is URF and polyethylene (PE) as shell and nano titanium oxide (TiO₂) as core, type 2 is URF and PE as shell and nano silica oxide (SiO₂) as core, type 3 is PE as shell and nano silica oxide (SiO₂) as core. The concrete samples mixed by nano-capsules with three percents of 0.5, 1 and 1.5. Based on experimental tests and the compressive strength of samples, the URF-PE-SiO₂ is selected for additional tests of compressive strength before and after recovery, ultrasonic test, ion chlorine and water penetration depths. After careful investigation, it is concluded that the optimum value of URF-PE-SiO₂ nano-capsules is 0.5% since leads to higher compressive strength, ultrasonic test, ion chlorine and water penetration depths.

• Smart Structures and Systems
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• 제24권2호
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• pp.157-171
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• 2019

This study investigated the effects of the geometric parameters of superelastic shape memory alloy (SE SMA) fibers on the pullout displacement recovering and self-healing capacity of reinforced cementitious composites. Three diameters of 0.5, 0.7 and 1.0 mm and two different crimped lengths of 5.0 and 10.0 mm were considered. To provide best anchoring action and high bond between fiber and cement mortar, the fibers were crimped at the end to create spear-head shape. The single fiber cement-based specimens were manufactured with the cement mortar of a compressive strength of 84 MPa with the square shape at the top and a dog-bone shape at the bottom. The embedded length of each fiber was 15 mm. The pullout test was performed with displacement control to obtain monotonic or hysteretic behaviors. The results showed that pullout displacements were recovered after fibers slipped and stuck in the specimen. The specimens with fiber of larger diameter showed better displacement recovering capacity. The flag-shaped behavior was observed for all specimens, and those with fiber of 1.0 mm diameter showed the clearest one. It was observed that the length of fiber anchorage did not have a significant effect on the displacement recovery, pullout resistance and self-healing capacity.

• Journal of Ginseng Research
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• 제14권1호
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• pp.63-66
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• 1990

The development of cracking in ginseng roots was studied to elucidate the factors affecting it in the field. The cracking of 6-year-old ginseng roots harvested in late October callld be induced in 2 days after soaking in water or in watersatllrated soil. However, it callld be slowed down by approximately 10 days when the roots were kept at a low temperature(5$^{\circ}C$). Roots excavated in late May did not develop cracking tinder the conditions tested. There was no significant difference between rice-straw shade and P.E. net shade in the rate of cracked ginseng roots. Which varied with ginseng varieties in relation to shade material. The rate of cracked roots was about 40% in 6-year plants, but it was extremely high (55.6%) in rusty roots. Healing of the wound formed by cracking was generally low but varied between harvest years.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.203-204
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• 2021

Bacteria used in self-healing concrete, which arrest the crack, helps increasing the durability is well known. However, the survival and activity of the bacteria are precisely unknown. In this research, to know the bacteria's survival curve on the surface of the cement composite, bacteria's survival curve has been measured by CFU at different curing days. The survival curve of 3 days and 7 days curing does not show the significant differences in their survival tendency. However, the slope of death phase of 7 days curing was steeper than the 3 days of curing. This research was focused on the death phase but for further research, set of interval time will be reduced and observe the lag phase and exponential phase.

• 한국구조물진단유지관리공학회 논문집
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• 제20권6호
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• pp.10-19
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• 2016

본 연구의 목적은 OPC, GGBFS 그리고 FA를 사용한 삼성분계 시멘트(TBC) 페이스트의 자기치유 특성에 관한 것이다. 초음파속도(UPV)측정으로 통해 삼성분계 시멘트의 자기치유 능력에 대한 OPC-GGBFS-FA의 영향을 분석하였다. TBC 페이스트는 0.5의 일정한 물-결합재 비에 GGBFS-FA를 20%, 40% 그리고 60% 치환한 배합이다. 본 연구는 재령 28일(하중 재하 후)이후의 거동에 초점을 맞추었다. 재령 28일에 휨시험을 통해 사각형의 보 시험체에 미리 균열을 발생시켰다. 시험체들은(균열을 발생시키지 않은 것과 균열을 발생시킨) 60일까지 담수와 해수에 침지하였다. 시험결과에 따르면 TBC 페이스트의 자기치유 능력은 GGBFS의 혼합률이 증가함에 따라 증가하였다. 이는 GGBFS와 FA는 재령 28일 이후에도 계속해서 수화가 진행되는데, GGBFS와 FA의 수화반응 물질들이 미세구조의 변화와 균열을 폐합한다. 이러한 결과들로부터, 균열을 발생시킨 모든 시험체에서 자기치유가 일어났고 이는 침지 30일에서 가장 많이 발생하였다. 더구나 담수와 해수에 침지한 시험체의 치유의 대부분이 침지 30일 동안 일어났다. 해수에 침지한 시험체의 균열 치유는 담수보다 빨랐다. 해수와 담수에 침지한 시험체의 치유효과의 차이는 해수에 포함된 이온들 때문이다. 더구나 재령효과를 고려한 자기치유효과는 침지 30일까지가 가장 강력하고 그다음엔 차츰 약해졌다.

• 대한치과의사협회지
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• 제50권8호
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• pp.507-515
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• 2012

The purpose of this article is to discuss the effect of aging on the treatment of replantation and transplantation of teeth in old patients. I case of replantation and 2 cases of transplantations in old patients are reported in this article. Patients aged 65 and over are included. They had several problems such as periapical lesion, crack or foot fractures. In those cases, the replantation and transplantation were treatment of choice. White ProRoot MTA was used in apical retrograde filling and perforation repair. After replantation and transplantation of teeth, follow-up visits showed signs of healing in 3 cases. Considerations and indications for replantation and transplantation are not much affected by age. Old patients are aware that replantation and transplantation can be performed comfortably and that age is not a factor in prediction success.

• 한국건설순환자원학회논문집
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• 제2권2호
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• pp.115-127
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• 2014

Addition of fibers in cement or cement concrete may be of current interest, but this is not a new idea or concept. Fibers of any material and shape play an important role in improving the strength and deformation characteristics of the cement matrix in which they are incorporated. The new concept and technology reveal that the engineering advantages of adding fibers in concrete may improve the fracture toughness, fatigue resistance, impact resistance, flexural strength, compressive strength, thermal crack resistance, rebound loss, and so on. The magnitude of the improvement depends upon both the amount and the type of fibers used. In this paper, locally available waste fibers such as coir fibers, sisal fibers and polypropylene fibers have incorporated in concrete with varying percentages and l/d ratio and their effect on compressive, split, flexural, bond and impact resistance have been reported.

• Journal of Microbiology and Biotechnology
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• 제29권12호
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• pp.1982-1992
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• 2019

The alkaliphilic, calcium carbonate precipitating Bacillus sp. strain AK13 can be utilized in concrete for self-repairing. A statistical experimental design was used to develop an economical medium for its mass cultivation and sporulation. Two types of screening experiment were first conducted to identify substrates that promote the growth of the AK13 strain: the first followed a one-factor-at-a-time factorial design and the second a two-level full factorial design. Based on these screening experiments, barley malt powder and mixed grain powder were identified as the substrates that most effectively promoted the growth of the AK13 strain from a range of 21 agricultural products and by-products. A quadratic statistical model was then constructed using a central composite design and the concentration of the two substrates was optimized. The estimated growth and sporulation of Bacillus sp. strain AK13 in the proposed medium were 3.08 ± 0.38 × 10⁸ and 1.25 ± 0.12 × 10⁸ CFU/ml, respectively, which meant that the proposed low-cost medium was approximately 45 times more effective than the commercial medium in terms of the number of cultivatable bacteria per unit price. The spores were then powdered via a spray-drying process to produce a spore powder with a spore count of 2.0 ± 0.7 × 10⁹ CFU/g. The AK13 spore powder was mixed with cement paste, yeast extract, calcium lactate, and water. The yeast extract and calcium lactate generated the highest CFU/ml for AK13 at a 0.4:0.4 ratio compared to 0.4:0.25 (the original ratio of the B4 medium) and 0.4:0.8. Twenty-eight days after the spores were mixed into the mortar, the number of vegetative cells and spores of the AK13 strain had reached 10⁶ CFU/g within the mortar. Cracks in the mortar under 0.29 mm were healed in 14 days. Calcium carbonate precipitation was observed on the crack surface. The mortar containing the spore powder was thus concluded to be effective in terms of healing micro-cracks.

• Journal of Microbiology and Biotechnology
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• 제30권3호
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• pp.404-416
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• 2020

Bacteria that are resistant to high temperatures and alkaline environments are essential for the biological repair of damaged concrete. Alkaliphilic and halotolerant Bacillus sp. AK13 was isolated from the rhizosphere of Miscanthus sacchariflorus. Unlike other tested Bacillus species, the AK13 strain grows at pH 13 and withstands 11% (w/v) NaCl. Growth of the AK13 strain at elevated pH without urea promoted calcium carbonate (CaCO₃) formation. Irregular vaterite-like CaCO₃ minerals that were tightly attached to cells were observed using field-emission scanning electron microscopy. Energy-dispersive X-ray spectrometry, confocal laser scanning microscopy, and X-ray diffraction analyses confirmed the presence of CaCO₃ around the cell. Isotope ration mass spectrometry analysis confirmed that the majority of CO₃^2- ions in the CaCO₃ were produced by cellular respiration rather than being derived from atmospheric carbon dioxide. The minerals produced from calcium acetate-added growth medium formed smaller crystals than those formed in calcium lactate-added medium. Strain AK13 appears to heal cracks on mortar specimens when applied as a pelletized spore powder. Alkaliphilic Bacillus sp. AK13 is a promising candidate for self-healing agents in concrete.