Testing - Concrete Mix Design, Quality Control and Specification - page 176

0.12

0.1

0.08

0.06

y = 0.012x - 0.072
R 2 = 0.90

0.04

0.02

0

0 5 10 15

VPV %

Figure 7.12 The relationship between chloride penetration (% by mass 2-40 mm) and
VPV%. (From Whiting D., Permeability of Selected Concretes, ACI Special
Publication, SP 108-11, 195-222, 1988.)

limited curing and not containing cementitious materials with significant
binding capacity which would reduce the long-term reduction in chloride
penetration as discussed earlier.
Sherman et al. (1996) tested concrete with w/cm ratios of nominally 0.32,
0.37, and 0.46 with and without silica fume. The concretes were exposed
to different curing regimes—water, burlap, or heat curing—before testing.
Plotting the chloride diffusion coefficients against VPV% showed no clear
relationship (Figure 7.13). An interesting result from this research was the
effect of the curing regime on VPV. Water curing compared to burlap, for
7 days reduced the average VPV by 8.4% as would be expected. However,
concrete exposed to a heat curing regime that involved 7.5 hours at 63°C
and storage at 50% RH after 24 hours reduced the VPV by an average of
25% compared to water curing for 7 days (see Figure 7.14). Elevated tem-
perature curing is typically associated with reduced long-term performance
of concrete and therefore a lower VPV demonstrates the limitations of
using indirect indicators. This unusual temperature effect may be one of the
reasons for the much lower maximum VPV requirement of 7% for severe
exposure in the Middle East (Summers, 2004) compared to a maximum of
11% for Vicroads. However, other requirements such as a maximum binder
content of 400 kg/m³ rather than a minimum binder content of 470 kg/m³
and a ternary blend should help improve durability and reduce VPV.
In our opinion, porosity tests provide additional information on the
penetrability of concrete. Variations in measured porosity in a particular
concrete mix will help detect a change in quality. The concerns with the
porosity tests for performance specification are that they have limited dis-
crimination, they are affected by concrete temperature, and they can be
poorly correlated to key transport properties such as chloride diffusion and