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The strength and other properties of shotcrete are same as that for high quality
concrete. Normal shotcrete mixes are capable of strengths above 35 N/mm^2. Shotcrete is highly
durable. Shrinkage and creep for wet shotcrete is likely to be high, but for dry-mix shotcrete
shrinkage is low and creep similar to high quality concrete.The drying shrinkage usually falls
with in the range of 0.06 to 0.10 per cent.
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Shotcrete finds its applications in tunneling, repairing of old concrete and thin
sections. Though costly, shotcrete requires shuttering and formwork only on one side resulting
in economy and making it particularly suitable for thin sections. The fact that it can be conveyed
over a considerable distance in a small diameter pipe makes shotcrete suitable for sites where
access in difficult. However, it cannot be used in confined spaces as the expansion of compressed
air causes turbulences, which make accurate placing difficult. Also the variable quality of the
finished product, highly skilled personals and its cost are some of the main disadvantages
limiting its application.
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High-performance concrete (HPC) is relatively new technology. HPC originated in France in
1980, followed by Canada in 1990. In 1989, under the direction of paul Zia of North Carolina
State University, a major effort in HPC technology began in the United States with the initiation
of the Strategic Highway Research Program (SHRP). SHRP defined HPC in terms of strength,
low w/c, and freeze/thaw durability. These early efforts were in response to alarming
deterioration rates of the nation’s roads and bridges.
The concept of HPC has certainly evolved with time. What exactly is “high-performance?”
Various parameters have been attached to HPC, with high strength being a popular descriptor.
While equating HPC with high strength certainly has some merit, it doesn’t present a complete
or, in some cases, accurate picture. Other properties of the concrete must also be considered,
and may even override the strength issue. Three influences must be considered: the structure
in which the concrete will be used, including support; the environment in which the structure
will be placed; and the type and number of forces to which the structure will be subjected.
These considerations are discussed in detail, before defining HPC.
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What are we building? A plain (unreinforced) floor slab-on-grade will require vastly different
strength properties than a bridge deck; or a bridge structural member; or a slip-formed building
or cooling tower. And yet, for each respective application, these greatly different strength
ranges can certainly result in a HPC. Other concrete properties which the type of structure may
dictate include allowable heat generation during curing; volume stability; creep; crack
susceptibility/brittleness; bond to reinforcing; workability; pumpability; and the list goes on
and on. Basically, the structural and construction requirements of the structure must be met by
the concrete to be used.
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What environment conditions will the structure be exposed to? Under this factor consideration
must be given to climatic conditions, i.e., heating and cooling, wetting and drying, and freezing