Testing - Concrete Mix Design, Quality Control and Specification - page 161

Slump Comparison (Using pressure @ 1.5 rpm)
(IBB Probe System vs. Manual Slump Te st)

300 300

250 250

200 200

150 150

100 100

Israel producer
UAE producer

50 50

0 0

300

0 50 150

Manual Slump Te st (mm)

100 200 250

Figure 7.9 Comparison of measured and estimate slump from IBB probe.

slump in specifications on the assumption that it defines workability on an
absolute scale. It may be acceptable for special purposes to specify slump
limits in addition to precisely specifying the type of concrete required (such
as special wear resisting floors) but generally workability (slump or other-
wise) is the business of the concreter, not the specifier. The concreter should
be permitted to strike his own balance between the higher cost of more
workable concrete and the reduced cost of placing, always providing that
such aspects as shrinkage, segregation, bleeding settlement, and so on are
given adequate consideration.
Even the above half-hearted endorsement of the slump test does have
its limits. Obviously it cannot be used for no-slump (or almost no-slump)
concrete. Such concrete is likely to be used in precasting factories or roller
compacted concrete (RCC) applications and alike. In such locations a V-B
consistometer (AS1012.3, 1983) (in which essentially a workability test
is performed in a cylindrical container and the time taken to re-form the
slump cone into the cylindrical shape under standard vibration is measured)
is likely to be convenient.
At the opposite end of the scale, flowing superplasticised/SCC/super
workable concrete is becoming more popular. A flow table (DIN 1048)
used to be the choice for accurate measurement of its workability. In this
test it is the diameter of spread under a slight jolting motion that is mea-
sured. However with the higher fluidity now available, a simpler variant,
the slump flow test (ASTM C1611) has taken over. The test also allows a
subjective assessment of stability and a good indication of plastic viscosity
with the T500 mm (20″) time.