Testing - Concrete Mix Design, Quality Control and Specification - page 173

Concrete Society Technical Report 31, a study on the variability 110 separate
30-minute absorption tests on a single grade of concrete found an average
of 2.2% with a standard deviation of 0.35% equivalent to a coefficient of
variation of 15.9%. This was far lower than for the other penetrability tests.
Summers (2004) used the Capillary Index test for compliance testing of
a major project in Bahrain. The average value for the 557 results was 4.4 ×
10 -4 vol/vol/s ½ and variability is shown in Figure 7.10.
CSIRO (1998) found that the Road Traffic Authority (NSW) sorptivity
was a reasonably good indicator of chloride diffusion coefficient after one-
year exposure (Khatri et al., 1998). However, in the recently released ver-
sion of B80, the sorptivity test is used to assess curing only, not durability.
Chloride diffusion or migration coefficients are the current performance
criteria. This change was not due to any durability problems associated
with concrete conforming with the sorptivity requirement but due to the
belief that chloride diffusion was the primary transport property of interest.
Another popular “sorptivity” test is the 30-minute absorption test (BS
1881:Part 122:1983). Measuring water absorption into concrete after a short
period of immersion is effectively a sorptivity test, as it gives an indication of
the rate of absorption before full saturation can occur. The test procedure
is simple and relatively quick to perform (as the specimens are oven dried
at 105°C) requiring no specialised equipment. One of the authors promoted
this test for performance specification some 30 years ago and advocated
testing at an earlier age to enable quicker response to variation. The test is
used as one of the four so-called durability compliance tests in the Middle
East. Unlike ISAT, the 30-minute absorption test does provide useful results.
Malier and Regourd (1995) established an accelerated wetting and
drying test for chloride penetration. The procedure involves drying at 40°C

Within-Sample CV: Grouped
n = 557

350
300
250
200
150
100
50
0

0-5 5-10 10-15 15-20 20-25

Intervals, CV, %

25-30 30-35 35-40 40-45

Figure 7.10 Variability of the capillary index test. (From Summers, C. R., Concrete Tech.
Today , 3, 1, 22-29, 2004.)