Testing - Concrete Mix Design, Quality Control and Specification - page 166

the presence of dense reinforcement, whilst maintaining homogeneity and
without the need for any additional compaction”. Whereas most tests focus
on the flowability or passability of SCC, the key consideration and distin-
guishing feature of SCC must be its segregation resistance and maintaining
homogeneity. The most commonly used procedure is the visual stability
index on the concrete perimeter after the slump flow test (ASTM C1611).
The qualitative nature of the assessment makes it dependent on the experi-
ence of the tester. Another problem is that any effect can be masked by the
presence of liquid water on the surface of the baseplate. The column segre-
gation test (ASTM C 1610) is not suitable as a compliance or field test and
therefore only appropriate for research.
The 5-minute V-funnel test is a useful method where a more than 3-second
increase in flow time suggests the SCC does not have sufficient segregation
resistance. The V-funnel test is described in Annex B2 of the EFNARC guide-
lines on SCC. The GTM screen stability test weighs the amount of mor-
tar passing through a 5 mm sieve. This quick test is suitable for field use.
ASTM C1712 “Rapid Assessment of Static Segregation Resistance of Self-
Consolidating Concrete Using Penetration Test” is a practical field procedure
with a suitable guideline for interpretation. Another important thing to
remember is that segregation resistance can change over time when the effect
of viscosity modifying admixtures wears off. Testing segregation resistance
over time should be conducted to confirm that this is not a problem.
7.5.4 Compacting factor
The compacting factor test achieved a degree of success in the United
Kingdom at replacing the slump test but is virtually unused commercially
elsewhere and must now be regarded as historical. It is a device using two
hoppers mounted above each other in a frame, with the lower hopper
discharging into a standard cylinder mold. The concept is that the first
hopper fills the second in a standard manner and the drop from the second
hopper into the cylinder mold subjects the concrete to a standardised com-
pactive effort. The result is expressed as a proportion of full compaction
achieved by dividing the weight of concrete in the mold by the weight of a
fully compacted cylinder.
The test is a little more accurately repeatable and is a more absolute
basis of comparison between the relative workabilities of different concrete
mixes than the slump test. However, the test is not greatly superior to the
slump test in quantifying variations in water content of successive deliveries
of the same mix, and since it is less widely used and involves more cumber-
some and expensive equipment, it does not seem likely to survive. It may be
reasonable to assume that if anything more elaborate than a slump test is
desired, a portable rheometer is the way to go.