• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.731-736
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• 2003

Alkali silicate system has wide application to accelerating admixture for shotcrete, but it has several problems that decrease long-term strength and delay setting time. So alkali-free system was gradually focused on accelerating admixtures for shotcrete due to its environmental property. The aim of this study is to investigate effect of alkali-free accelerating admixtures on aluminum sulfate system containing diethanolamine or acrylic acid etc. The alkali-free accelerating admixture has better properties than silicate system accelerating admixtures on compressive strength and low pH as shotcrete. Especially, the compressive strength of alkali-free accelerating admixture containing diethanolamine was increased about 10% compared with the value of ordinary portland cement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.715-718
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• 2005

The purpose of this paper is to investigate on hydration, setting time and compressive strength properties of cement paste mixed alkali-free accelerator using aluminum sulfate for shotcrete. The experimental focus is to variouse added element with alkali-free accelerator for shotcrete using aluminum sulfate. When diethanolamine was used as a component of alkali-free accelerator, alkali-free accelerator contributed to increasing early hydration, setting time and compressive strength properties of cement paste and mortar.

• 한국농공학회논문집
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• 제46권3호
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• pp.65-72
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• 2004

Modern underground and tunnel works that the wet type shotcrete is getting widely designed and applied in a large scale project. Further to its applications, the needs of improving the performance of the shotcrete, such as new and developed additives and accelerators fur increasing the performance of shotcrete, become the most important issue in the field. The main objective of this study evaluated to performance of steel fiber reinforced shotcrete using alkali free based accelerator for the durability and high quality of shotcrete. The major test variables are accelerator type and its dosage. One type silicate based accelerator and one type aluminate based accelerator and one type alkali free based accelerator were used. The dosage of accelerators is determined by the manufactures and laboratory test condition. Compressive strength test results showed that the dosage of silicate and aluminate based accelerators caused reduction of mechanical properties of shotcrete. Compressive strength of alkali free based accelerator is more stable than of silicate and aluminate based accelerators. Also, according to the compressive strength and flexural test results, it was found that steel fiber reinforced shotcrete used alkali free based accelerator could attain significant improvement in the mechanical and flexural performance.

• Journal of the Korean Wood Science and Technology
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• 제21권2호
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• pp.49-56
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• 1993

This study was performed to investigate the pollution-free Korean traditional papermaking characteristics from paper mulberry by sulfomethylation pulping. Bast fibers were pulped by sulfomethylated cooking liquor, and by alkali and alkali-peroxide processes for the comparison. Sulfomethylated pulping resulted in the superior pulp with high yield and better quality compared to those of alkali and alkali-peroxide pulps. Since the pulp was so bright, there was almost no need additional bleaching. Pollutant loads of sulfomethylated pulping effluent were very low in terms of pH, turbidity and color compared to those of alkali. Pollution-free effluents was accomplished by simple filtering treatment with pine bark, charred rice hull and sawdust compost. Pine bark was the most effective in reduction rate of pollutants.

• 콘크리트학회논문집
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• 제17권6호
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• pp.1011-1018
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• 2005

액상 숏크리트 급결제(알칼리 알루미네이트, 2종의 알카리프리)가 시멘트 계의 수화 특성에 미치는 영향을 조사했다. 새로운 알카리프리계 숏크리트용 급결제(AF2)를 적용할 경우 기존의 알칼리 알루미네이트 급결제에 비해 초결, 종결 시간은 단축되었고, 1일 압축 강도는 유사했다. 12시간 경과된 모르타르 시편의 압축 강도는 알칼리 급결제가 첨가된 시편이 가장 높았으나, 이후 최종 강도는 알칼리 급결제를 첨가한 시편이 가장 낮았다. 그러나 알카리프리가 첨가된 AF1, AE2 시편의 압축 강도는 28일까지 plain과 유사했다. XRD와 DSC 분석을 통해 알칼리계 급결제는 주로 수산화칼슘, 알카리프리계 급결제는 에트링자이트 결정 성장으로 응결이 촉진된 것을 확인했다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.277-280
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• 2006

This paper presents the findings on the sulfate resistance of mortar specimens with or without alkali-free accelerator exposed to sodium sulfate solution for 270 days. Test results confirms a negative effect of alkali-free accelerator on the sulfate deterioration. Additionally, the influences of exposure concentration and temperature of sulfate solution on expansion were investigated. Especially, at a high concentration of solution a significant expansion of mortar specimens with alkali-free accelerator was observed. Further, low temperature also promoted the deterioration of the cement system due to sulfate attack.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.953-956
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• 2006

Sulfate resistance of mortar specimens with or without alkali-free accelerator exposed to sulfate solutions for 360 days was investigated. Test results confirms a negative effect of alkali-free accelerator on the sulfate deterioration, irrespective of attacking sources. Based on the ASTM C1012 expansion test, the experimental findings demonstrated that higher $C_3A$ content in cement led to the higher expansion, especially in the mortar specimens with alkali-free accelerator.

• 한국세라믹학회지
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• 제22권3호
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• pp.60-66
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• 1985

The formation mechanism of unstable alkali and its existing states in the clinker were studied. The relation of unstable alkali content vs. other water-soluble components porosity and the distributionof potassium were investigated. The results are as follows :1) Two states of unstable alkali seem to exist in clinker ie compounds of $K_2O-Al_2O_3$ system and free $K_2O$ 2) The content of water-soluble $Al_2O_3$ tends to increase with increase of unstable alkali content, 3) Most of alkalies in clinker are concentrated in liquid phase at high temperature. Therefore it is possible to make various $K_2O-Al_2O_3$ system compounds according to the content of $K_2O$ in the liquid phase of clinker. In this experiment we found out a $K_2O-Al_2O_3$ compound of high $Al_2O_3$ content (34%) and high $K_2O$ content (33%) in clinker with 1.09% unstable alkali. 4) The porosity of clinker tends to increase with increase of unstable alkali content. 5) The amount of trapped alkali vapor may increase in closed pore in the clinker with high alkali and low $SO_3$ condecent. Therefore free $K_2O$ is the condensed alkali on the wall of closed pore in the clinker.

• 한국터널지하공간학회 논문집
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• 제5권1호
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• pp.23-31
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• 2003

최근 NATM 터널 현장타설 콘크리트 라이닝의 시공성 향상과 균열에 따른 유지관리비 절감을 위해 양질 암반의 배수형 터널 시공에 있어서는 숏크리트만으로 라이닝을 대체하려는 영구지보 개념의 터널시공 (Single-Shell Tunnel, NMT 등)이 세계적으로 증가하고 있는 추세이다. 이러한 영구지보 개념의 터널 시공을 위해서는 고성능 숏크리트의 개발이 선결되어야 하며, 이러한 목적에서 본 논문에서는 조강시멘트와 최근 주목받고 있는 환경친화적인 alkali-free 급결제의 조합을 통해 고성능 숏크리트의 개발 가능성을 확인하였다. 그 결과, 보통시멘트(OPC)를 사용한 숏크리트보다 약 25%의 높은 초기강도를 확보하였으며, 용수부에서도 뛰어난 부착특성을 확인할 수 있었다.

• 한국세라믹학회지
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• 제22권1호
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• pp.25-34
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• 1985

The states of alkali occuring in Portland cement clinker were studied. Potassium was added to raw mixture by there kinds ; $K_2SO_4$, $K_2CO_3$ and KOH. In case of $K_2CO_3$ and KOH addition the new state of unstable alkali was found when alkakli content is high and $SO_3$ content is low in the clinker. Unstable state of highly basic free 4K_2O$ causes lowering burnability much more than alkali sulfate especially at the early stage of burning. Lowered burnability by 4K_2O$ became more serious with higher LSF. Unstable free-4K_2O$ which is readily soluble with water reacts with gypsum to form $Ca(OH)_2$ and syngenite as soon as water is added. As a results the liberation rate of heat of hydration at the early hydration process(1st peak) was increased.