Testing - Concrete Mix Design, Quality Control and Specification - page 175

accumulation in a partially immersed condition. A 30-minute absorption
limit of approximately 1.2% was found to provide good long-term perfor-
mance, over 40 years.
7.6.3 Volume permeable voids (vpv) or porosity
Porosity tests achieve virtually full saturation of pores and microcracks by
the completion of the test. Such porosity tests would include AS 1012.21,
ASTM C642, RILEM CPC No. 11.1, and CPC No. 11.3.
The Australian and American standards achieve virtual saturation by
using relatively small specimens that are placed in boiling water for consid-
erable periods. RILEM CPC No. 11.1 involves soaking the specimen until
constant weight gain. In RILEM CPC No. 11.3, the oven-dried specimen is
placed in a vacuum followed by immersion in water.
Vicroads in Australia requires maximum VPV values for all grades of
concrete. The range of maximum values for rodded cylinders varies from 12%
for 55 MPa concrete with a maximum w/cm of 0.36 to 15% for 32 MPa con-
crete with a maximum w/cm of 0.5. The test method has been used for per-
formance specification in Victoria for 20 years (Andrews-Phaedonos, 2012).
Although advocates of this procedure point to the low coefficient of variation
associated with the test (2.4% according to Whiting, 1988), one reason for
the low variability is the very limited discrimination within the test procedure.
Comparing the data from the repeatability figures in Andrews-Phaedonos
(2012), the variation in average 7 day VPV for Mix 4 (VR400/40) is 13.7%
to 12.6% or a difference of 1.1%. The difference in average VPV for the same
mix from 7 days to 28 days and 90 days water curing is 0.9% and 1.2%.
According to the data presented, the potential difference between two mixes
with the same proportions under laboratory conditions after 7 days curing is
of the same order as the difference due to an additional 83 days water curing.
The mix design and chloride diffusion coefficients at various ages are not pre-
sented. If the mix contained up to 25% fly ash or 40% GGBS in accordance
with Vicroads Section 610.07 f, the chloride diffusivity may have reduced by
up to 65% between 7 and 90 days whereas the VPV reduced by up to 10%.
Whiting (1988) compared different penetrability parameters with the
90-day ponding test (AASHTO T259) where chloride penetration is due
to the combined effect of absorption, wick action, and chloride diffusion.
Six concrete mixes with w/cm ratios ranging from 0.26 to 0.75 were tested
and cured for 1 or 7 days before testing. Five of the mixes were pure ordi-
nary Portland cement (OPC) mixes and one contained 11.7% silica fume.
The correlation coefficient between the total chloride penetration into the
concrete (2-40 mm) and VPV% was 0.90 as seen in Figure 7.12. Because
Whiting did not measure the chloride profiles, it is not possible to estimate
the chloride diffusion coefficients of the concrete mixes and the correla-
tion with the measured VPV. The tests were also confined to concrete with