Civil Engineering Reference
In-Depth Information
30
Specic surface
40
28
45
50
26
55
60
24
1.20
1.15
22
1.10
1.05
Relative water demand
1.00
20
36
38
40
42
Percent Voids
44
46
48
50
Figure 3.6
Correlation of water demand and specific surface with flow test properties.
surface we can assess the dependence of water demand on either voids or
flow time. For example, for SS = 50 (a middle-of-the range value), RWDs
of 1.05 and 1.20 (i.e., 15% increase) correspond to 40.2% and 45.0%
voids respectively, a difference of just under 5%, very close to the estimate
from the ACI parameter. The chart also shows that water demand is not
linked uniquely to voids or flow time separately, but to combinations of
the two properties.
The test offers a quicker and simpler means than sieve analysis of
detecting changes in grading during production use of a sand. In addi-
tion it simultaneously checks for any deterioration in particle shape or
surface texture. The latter may be considered fairly unlikely to change
for a natural sand from a particular location but would be well worth
monitoring for crusher fines and would be very difficult to check by any
other means.
A further use for the sand flow cone is in blending two sands. It is a
simple procedure to carry out a set of flow and voids tests with varying pro-
portions of two sands, and a plot of the resulting properties from the flow
test is very revealing as to the range of compatible proportions. An example
is shown in Figure 3.7, in which the coarse sand is a low cost material,
which is too coarse for use by itself in typical concrete mixes, but in blends
with the more expensive fine sand gives a suitable and cost-effective fine
aggregate for concrete.
In conclusion it must be emphasised that the flow test does not measure
either the specific surface of a fine aggregate or its effect on water demand.
Percent voids and flow time are properties that respond to characteristics
of the shape and surface texture of the particles, and the grading, to which
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