• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1011-1018
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• 2005

The influence of liquid shotcrete accelerators(alkali aluminate, two types of alkali-free) was investigated. Comparing to the existing alkali aluminate accelerator, new alkali-free accelerator, AF2, shortened initial and final setting of cement system, and after curing for 1 day compressive strength was analogous with others. On the other hand, compressive strength of specimen cured for 12 hour was the highest by the addition of alkali aluminate accelerator, but final strength was the lowest by that. But compressive strengths of AF1, AF2 were similar to Plain up to 28day. Further from XRD(X-Ray Diffractometer) and DSC(Differential Scanning Calorimeter) analyses, we confirmed that setting promoted by alkali aluminate was mainly because of Ca(OH)2(calcium hydroxide), but the accelerating behavior of alkali-free was influenced by the needle-like ettringite$(6CaO{\cdot}Al_2O_3{\cdot}3SO_3{\cdot}32H_2O)$ crystal.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2C
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• pp.121-131
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• 2006

The strength standard of shotcrete in Korea is relatively lower than that in Europe where high-strength shotcrete has been developed and actively applied to the common practice, so it is hard to test a quality of high-strength shotcrete. In this study, field test was performed to find a solution improving the strength and a long-term durability on domestic shotcrete. In field test, a high-strength shotcrete was produced using high-quality additions and accelerators, and an effect of additions and accelerators was observed. In addition, quality test based on EFNARC was also performed. As a result of field test, a promotion ratio of early strength is 90~97% in case of using alkali-free accelerators, therefore, alkali-free accelerators had an effect on an increase of early strength on shotcrete. A 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. It was showed that increment effect of strength by the silica fume replacement of 7.5~10% for cement mass was remarkable. As a result of test, it was possible to apply high-strength shotcrete to the domestic practice using high-quality additions such as Micro-silica fume and accelerators such as alkali-free.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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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.