• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.109-113
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• 2003

Concrete and shotcrete should withstand the conditions for which they have been designed, without deterioration, over a period of years. But connote and shotcrete are being deteriorated according to aging by internal and external causes. Recently, many studies on the durability of concrete have been conducted But the durability of shotcrete is rarely studied. So, in this study, chloride ion penetration test freeze and thaw test neutralization test were conducted to examine the durability characteristics of shotcrete with several accelerator and chemical admixture types. These results indicate that shotcrete with allah free accelerator and with superplasticizer are durable. Therefore, the present study provides a fm base to make high performance shotcrete.

• Journal of the Korean Society of Safety
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• v.19 no.2
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• pp.98-103
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• 2004

Shotcrete needs the enough durability without deterioration for life time. But shotcrete is being deteriorated according to aging like concrete by internal causes whithin itself and by external causes which can be physical, chemical, or mechanical. Durable shotcrete can be made by incresing the cement content, adding chemical and mineral admixtures and so on. So, in this study, chloride ion penetration test, freeze and thaw test, neutralization test were conducted to examine the durability characteristice of shotcrete with mineral admixtures such as silica fume, blast-furnace slag and fly ash. These results indicate that shotcrete with silica fume is durable. Therefore, the present study provides a firm base to make high performance shtcrete.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.701-706
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• 2007

This study evaluated the durability of high-performance shotcrete mixed in the proper proportions using alkali-free and cement mineral accelerators as a permanent support that maintains its strength for the long term. Durability tests were performed the chloride permeability, repeated freezing and thawing, accelerated carbonation, and the effects of salt environments. Test results showed that all the shotcrete mixes included silica fume had low permeability. In addition, after 300 freeze/thaw cycles, the shotcrete mix had excellent freeze/thaw resistance more than the 85% relative dynamic modulus of elasticity. The accelerated carbonation test results were no effect of accelerator type but, the depth of carbonation was greater in the shotcrete mix containing silica fume. No damage was seen in a salt environments. Therefore, the high performance shotcrete mix proportions used in this study showed excellent durability.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.165-182
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• 2006

In this study, field test was performed to investigate the strength-improvement effect of shotcrete mixed Micro-silica fume and shotcrete quality was estimated by EFNARC standard. Deterioration test combined the Freezing-thawing and Carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of test, the compressive strength of shotcrete using Micro-silica fume was 45.2~55.8MPa and flexible strength was 5.01~6.66MPa, so a promotion ratio of strength was 37~79%, 17~61% respectively. And the strength-improvement effect of strength by silica fume addition ratio of 7.5~10% for cement mass was more superior to the others. Due to relative dynamic modulus, mass decrease rate and carbonation progress of shotcrete mixed Micro-silica fume, it was especially realized that Micro-silica fume reduced deterioration caused by steel fiber and improved a long-term durability of shotcrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.253-256
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• 2004

Recently, construction works of scale are getting larger with economic growth. Shotcreting is one of major processes in tunnels construction. Accelerator is used in tunnel and underground structures to ensure early strength of shotcrete. Silicate based accelerator and aluminate based accelerator is getting widely in the field. But these accelerators have many problems due to decesase of long-term strength and low quality of the hardened shotcrete. in order to solve these problems, recently developed powder types cement mineral accelerator. In this study, we tested chloride permeability, freezing and thawing and accelerated carbonation of shotcrete. As a result of the test, wet-mixed shotcrete with powder types cement mineral accelerator exhibited durability improvement compared to the conventional shotcrete accelerator.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1517-1521
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• 2009

A variation of pore structure of shotcrete matrix was experimented by Mercury Intrusion Porosimetry, and the relation with compressive strength was also examined. As a result of the Mercury Intrusion Porosimetry(MIP) test, RM-P1 Batch the macropore diameter of the RM-BFS2 and RM-BFS3 Batch than to have a relatively macropore can see a lot of long-term durability performance degradation. Also, K and N Batch the current is applied to the mine if the factors on shotcrete durability performance of the macropore volume of the entire appears to be a long-term durability performance in the fall.

• Tunnel and Underground Space
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• v.17 no.4
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• pp.266-284
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• 2007

Recently, many efforts have been made to construct the first unlined tunnel, without in-situ concrete lining, in Korea. However, the lack of reliability in the performance of shotcrete as permanent tunnel support prevented from its realization. Shotcrete has been regarded to have significant problems in field application and long term performance because of unsatisfactory strength level and durability compared to those of European countries. In this study, the high strength shotcrete satisfying compressive strength over 40 MPa and flexural strength over 4.5 MPa was developed from optimized mix design. The type of accelerators and the amount of silica fume were selected as the main factors in mixing process and the analyses were carried out up to the elapsed time of 2 years. In order to evaluate the short term durability of shotcrete, an array of laboratory test consisting of freeze-thaw, carbonation chloride penetration and permeability test was performed. For long-term durability tests, specimens have been put in an operated highway tunnel to expose them to the similar environment when they are actually used as an unlined tunnel support. From the strength and durability tests, it was found that only alkali-free based accelerator satisfied the target strength of this study and also, the developed shotcrete showed very high performance in its durability.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.337-340
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• 2008

As the Ready-mixed Shotcrete using Powdered Polymer Dispersion, Shotcrete Matrix as totally shotcrete gel that a part of second binder in Shotcrete materials is dense. Also, Ready-mixed Shotcrete is showed the decreasing Rebound and rising Durability. Therefore, it is possible that Ready-mixed Shotcrete for High-Strength and High-Waterproof can apply to the Powdered Polymer Dispersion.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.47-56
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• 2007

Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcrete is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcrete practice. The purpose of the study is, therefore, to explore the trobles in the current shotcreting practice, and to develop high-quality silica fume shotcrete. For the purpose of security a long-term durability of shotcrete, this study conducted combined deterioration tests. In this study, a combined deterioration test in consideration of a variety of deterioration factors were proceeded. Especially, micro-silica fume that was used frequently in overseas because of a outstanding strength-promotion effect was applied to combined deterioration test, and a long-term durability of shotcrete was investigated according to additions mixing. As a result of test, the shotcrete mixed Micro-silica fume showed a good deterioration quality compared with the other mixes. And is shows that the Micro-silica fume has an outstanding strength-promotion effect and is effective to secure a long-term durability of shotcrete by means of decreasing a deterioration caused by steel fiber mixed.