Gas Permeability of High-Permeability of High-Performance Concrete Site and Laboratory Tests
Appears on pages(s):
bridges; high-strength concretes; laboratroy tests; permeability
The objective of this paper is to report test results of gas-permeability of high-performance concretes, measured on laboratory specimens and directly on site. The test refer to three concretes used in two projects: a tunnel (50MPa concrete) and a cable-stayed bridge deck (50 Mpa concrete) and pylon (75 MPa concrete). In particular, the investigation was focused on comparing the permeability of the "covercrete", measured on laboratory specimens, with that measured directly on the site concretes, I.e. subjected to strongly different placing, compaction and curing conditions. The air-permeability of the cover of the three concretes was measured with a non-destructive technique, which takes into account the effect of moisture. Cores were drilled from the same elements and the oxygen permeability measured on them. When core-drilling was not allowed, parallel tests were conducted on large cubes, site cured, cast with the same concrete mixture used for the actual construction. For the three structures investigated, the air-permeability of the site concrete was higher that that measured on the companion laboratory specimens. The largest difference was found for the 75 Mpa-strength concrete; this difference is attributed to thermal cracking in the pylon, the center of which exhibited 55 degrees C temperature rise. This indicates the risk of impairing the potential durability of HPC through inappropriate practices. The results presented show the importance of checking the quality of the concrete, not only on laboratory-prepared specimens, but also directly on site.