Testing - Concrete Mix Design, Quality Control and Specification - page 172

7.6.2 Sorptivity
One popular sorptivity test is the initial surface absorption test or ISAT as
prescribed in BS:1881:Part 5:1984, which has been withdrawn. Although
the procedure and performance criteria were developed on oven dried
specimens, the standard procedure allows testing after only 48 hours ambi-
ent drying. The limited drying of 150 mm cube specimens means that
compliance testing based on ISAT results in very low values. In the Middle
East, ISAT is used as one of four so-called durability compliance tests. The
commonly used performance criterion is 0.15 ml/m²/s at 10 minutes (60%
of the value recommended in Concrete Society TR31). On one project, over
150 separate ISAT compliance results taken from three different grades of
concrete never exceeded 0.03 ml/m²/s or 20% of the performance criterion.
Any test procedure with such limited discrimination is of no benefit in
performance specification, as it will not highlight changes in performance.
For the New South Wales (NSW) road transport (RJA, now Roads
Maintenance Service, RMS) authority, the sorptivity test procedure involves
drying of 100 mm × 100 mm × 350 mm concrete beams at 23°C and 50%
RH for 35 days if the concrete will be exposed to the tidal/splash zone. In
2011, the sorptivity test was effectively downgraded to only a curing effec-
tiveness test. The performance criterion was 8 mm water penetration after 24
hours in contact with water. The Cement, Concrete & Aggregates Australia
publication on “Chloride Resistance of Concrete” dated June 2009 states that
“RTA sorptivity of 1 mm is equivalent to 0.026 mm/min ½ , and RTA (RMS)
sorptivity of 3.8 mm is equivalent to 0.1 mm/min ½ ”. However, the test mea-
sures the depth of water penetration not the volume as other typical sorptivity
tests such as ASTM C1585, Capillary Index, and the TE Sorption procedures.
When converting from the RTA sorptivity one needs to consider the porosity
of the concrete to convert from penetration depth to penetration volume.
The measured sorptivity is strongly influenced by the degree of drying
of the test specimen prior to contact with water. The RTA (RMS) T362
procedure dries at 50% RH for 35 days. The ASTM C1585 procedure
involves drying specimens for 3 days at 50°C and 80% RH and then sealing
for 15 days. The 30 minute absorption, Capillary Index, and TE Sorption
tests oven dry at 105°C. Each test procedure will give different relative sorp-
tivity values with lower sorptivity for less intense drying. The justification
for longer drying conditioning is that it is more representative of ambient
conditions. However, increasing the time and complexity of a compliance
test profoundly reduces both the number of test results obtained as well as
the ability to respond to variation and noncompliance.
The time taken to complete the procedure due to the prolonged drying
coupled with the approved concrete mix register has meant that RTA (RMS)
sorptivity test was not used as an ongoing compliance test. Therefore sta-
tistical assessment of the variability of the test is difficult. As reported in