Shotcrete is a combination and is manufactured by mixing about 5 to
8% per Binder of rapid seting agents on a ready-mixed concrete using
10% Portland cement (OPC). There is an advantage of initial strength
when using OPC alone, however, there is a limit to improving long-terdurabilty. Especialy, high durable concrete has esential demand of the
research and development on material technology by the importance of the
utilzation of tunels, railways, and underground spaces is becoming more
prominent.
Therefore, research and development for increase the performance of
binder for shotcrete has ben tried internationaly. Acording to the
precedent research analysis, the research on improving the binder for
shotcrete was caried out from the early 200s, and various studies on
high strength or securing long-term durabilty for shotcrete were
conducted by the neds for high performance of shotcrete. However, these
researches showed limitations, such as indor experiments on limited
conditions, or optimal mix calculations through theoretical studies. In
adition, there were limitations on practical uses, such as dificulties in
aplying the material to the site or not considering the eco-friendlines of
the material, of not considering economic feasibilty, etc. Due to above
limitations, it was thought to be dificult to practical aplication on the
actual construction site.
In this study, we have developed optimized binder for high performance
and field aplication of shotcrete that is suitable for shotcrete using a
calcium aluminate rapid seting agent. In this study, optimized binder for
shotcrete was proposed by improving Ordinary Portland Cement (OPC)
and mixing industrial by-products materials, and was verified the
performance of developed binder by concrete experiment and Mock-up
test. A summary of this study is as folows.
1) The characteristics of physical properties of binders and its hydration
reaction while controling the powder content and SO3 content of OPwere studied by microanalysis. As a result, the Blaine of OPC was found
to have no significant efect on the compresive strength of the shotcrete
using a calcium aluminate rapid seting agent, while the SO3 content has
increased penetration resistance and one-day compresive strength by
afecting the amount of etringite(AFt) generation. Thereby, in range of
this study, the optimal contents of SO3 was thought to be 2.8%
2) The optimal contents for shotcrete binder was derived by mixing
ground granulated blast-furnace slag powder(GGBS) from stel
manufacturing and fine limestone powder(LSP) from by-product of cement
manufacturing for the eco-friendlines and economic feasibilty of shotcrete
binder. As a result, contrary to the case of general mortar of concrete,
GGBS adition has not delayed a seting of shotcrete, and LSP adition
has acelerated seting of shotcrete. In adition, the adition of LSP was
found to be efective in improving the initial compresive strength, and
GGBS to long-term compresive strength. It was expected that the
optimal mix proportions is GGBS (20%) and LSP (5%) considering
physical performance (seting, compresive strength) of shotcrete that
using calcium aluminate rapid seting agent.
3) Optimized binder for shotcrete(OPC 75% + GGBS 20% + LSP 5%)
expresed workabilty and compresive strength performance higher than
that of OPC, and expected to control eflorecence phenomena that may
ocur during construction and curing period. In adition, due to the mixing
of GGBS and LSP, more dense micro structure has ben formed, as a
result, detrimental efect from the outside are supresed, in turn, securing
higher durabilty (carbonation resistance, salt resistance and frezing
melting resistance) compared to OPC.
4) As a result of Mock-up test, it has ben confirmed that the
optimized binder for shotcrete has excelent workabilty compared to OPC,
and the mechanical properties like compresive strength, flexural strength,
and flexural toughnes are more than equal to OPC. In adition, it has
ben confirmed to be a god performance on a frezing and thawing
resistance test. As a result of observation in several months, binder for
shotcrete developed in this study has ben showed no cracks of spalings
on the tested area, peling of of any aggregates, but remains healthy
states. From these results, optimized binder for shotcrete has expected to
have long-term durabilty and stabilty.
5) Based on the above research results, it was expected that the binder
for shotcrete secured basic performance (construction, mechanical
characteristics, etc.) above the equivalent level compared to the existing
OPC, and that they had high performance and practicality by securing
high durabilty, eco-friendly and economic feasibilty.
6) Future research wil be aplied to the actual site to colect opinions
from users (construction enginers, managers, etc.) about the performance
of the developed binder for shotcrete during and after construction to
continue a research on the improvements. In particular, we wil continue
to study on factors that efects on the amount of rebounds of shotcrete.
And also we have plans to study on the lining work, which is a
folow-up proces to the shotcrete, on the aplicabilty and improvement
of the shotcrete binder