Civil Engineering Reference
In-Depth Information
Table 8.1
MSF values
Slump range
MSF
mm Inches
<16 Unusable, too harsh
16-20 Harsh mixes, only suitable for zero slump concrete under
heavy vibration
20-22 0-50 0-2 Hard wearing floor slabs, precast products under good
external vibration
22-25 50-90 2-3.5 Good structural concrete
25-27 80-100 3-4 Good pumpable concrete, fine surface finish, heavily
reinforced sections
26-28 90-120 4-5 Pumpable lightweight concrete
27-31 >200 >8 Flowing superplasticised concrete
≥
33
Self-compacting concrete—slumpflow ≥ 550 mm,
T500 ≥ 2 seconds
Note: Add “33+ minimum flow diameter 600 mm”, “T500 time 2-7sec” self-compacting.
Remarks
Table 8.2
Modified specific surface values
Author's modified SS
values
Approximately true specific
surface (cm
2
/gm)
a
Sieve fraction
Surface modulus
>20 mm
2
1
1
20-10
4
2
2
10-4.75
8
4
4
4.75-2.36
16
8
8
2.36-1.18
27
16
16
1.18-0.600
39
35
32
0.600-0.300
58
65
64
0.300-0.150
81
128
128
<0.150
105
260
256
According to B.G. Singh (1958).
a
that, within wide limits, if the proportion of fine sand is reduced so that the
specific surface of the combined aggregates is the same as with the coarser
sand, the same water requirement and the same degree of cohesion will
result. The original SS theory did not work in practice because it was found
to overestimate the effect of very fine particles. The surface area of a sphere
approximately doubles as its diameter halves, giving rise to the second col-
umn of figures in Table 8.2 (neglecting particle shape). Day's modification
recognises that as diameter reduces, a point is reached where it takes less
water to fill the voids in the material than it does to coat its surface. On
a purely empirical basis, the first column in Table 8.2 “Modified Specific
Surface”, was originated by Day in the 1950s to implement this concept.
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