Self-consolidating concrete

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Self-consolidating concrete or self-compacting concrete (SCC)

yield stress, high deformability, good segregation resistance (prevents separation of particles in the mix), and moderate viscosity
(necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets).

In everyday terms, when poured, SCC is an extremely fluid mix with the following distinctive practical features – it flows very easily within and around the

additives
that ensure particles disperse and do not settle in the fluid mix) and viscosity-enhancing admixtures (VEA).

Ordinarily, concrete is a dense, viscous material when mixed, and when used in construction, requires the use of vibration or other techniques (known as compaction) to remove air bubbles (

aerated concrete
) is not desired and weakens the concrete if left. However it is laborious and takes time to remove by vibration, and improper or inadequate vibration can lead to undetected problems later. Additionally some complex forms cannot easily be vibrated. Self-consolidating concrete is designed to avoid this problem, and not require compaction, therefore reducing labor, time, and a possible source of technical and quality control issues.

SCC was conceptualized in 1986 by Prof. Okamura at Kochi University, Japan, at a time when skilled labor was in limited supply, causing difficulties in concrete-related industries. The first generation of SCC used in

admixtures
, usually superplasticizer to enhance flowability and stability. Such high-performance concrete had been used mostly in repair applications and for casting concrete in restricted areas. The first generation of SCC was therefore characterized and specified for specialized applications.

SCC can be used for casting heavily

water-cement ratio
, and the high-range water reducer (HRWR) demand. The reduction in free water can reduce the concentration of viscosity-enhancing admixture (VEA) necessary to ensure proper stability during casting and thereafter until the onset of hardening. It has been demonstrated that a total fine aggregate content ("fines", usually sand) of about 50% of total aggregate is appropriate in an SCC mix.

Overview

  • SCC is measured using the flow table test (slump-flow test) rather than the usual concrete slump test, as it is too fluid to keep its shape when the cone is removed. A typical SCC mix will have slump-flow of around 500 – 700 mm.
  • SCC is weakened, not strengthened, by vibration. As vibration is not needed for compacting the mix, all that it achieves is to separate and segregate it.

See also

References

  1. ^ selfconsolidatingconcrete.org: National Ready Mixed Concrete Association

External links

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