3.3.2. Water Permeability

The water permeability (WP) of concrete was tested using a uniaxial flow apparatus performed on cylinder specimens (ϕ150 mm × 50 mm) subjected to 0.29 MPa pressure for 3 h. The WP was calculated with following formula:

$$\text{Water permeability} = \frac{m\_2 - m\_1}{m\_2} \times 100\% \tag{3}$$

where *m*<sup>1</sup> = initial weight of specimen and *m*<sup>2</sup> = specimen weight after test.

Table 7 summarizes the measured WP of the concrete mixtures. It is seen that WP decreases with increasing compressive strength for both NAC and RAC mixtures. Incorporating BFS in concrete inherently reduces the WP of concrete at all ages. This is particularity found in mixtures NS 75 and RS 75 containing 75% BFS at curing age of 91 days, which has WP of 0.69% and 0.18%, respectively, comparably less with that of the reference mixture NS00 and RS00 of 0.46% and 0.79%, respectively. These results signify the fact that either NAC or RAC containing a high volume BFS at later ages may lead to lower water permeability, namely, superior durability to the concrete without BFS.

**Table 7.** Results of the concrete water permeability measurements.


Furthermore, the effect on the water permeability of concrete by adding BFS can also be seen from Figure 8, which illustrates the relations between water permeability and BFS content of RAC mixture at curing ages of 28 and 91 days. Note that the WP of concrete decreases with the increase of BFS content for the two curing ages, while the curve trend for the 91-day concrete presents a steeper decline than that for the 28-day concrete, indicating that BFS concrete may exhibit less WP at later ages.

**Figure 8.** Influence of BFS content on the water permeability of RAC mixtures.
