Quiet Concrete Pavements in Belgium: a Tale of Two Aggregates

10/25/2007

Thanks to the assistance of FEBELCEM and the Road and Traffic Administration, testing in Belgium was completed last week with the evaluation of three test sites. Two of these sites were located along the N49 (E34) highway – the primary artery between Antwerp and Brugge in the northern part of the country (Flemish region). Both sites were constructed with exposed agrgegate concrete surfaces.

One site, labeled BE02, is located near the town of Zelzate or more specifically, HERE. It was constructed as a 23-cm Continuously Reinforced Concrete Pavement (CRCP) inlay of an existing asphalt section. The concrete aggregate consisted of 4 fractions: a blend of two porphyry coarse aggregates and two sands. The maximum aggregate size is 20 mm. Here are a coupleof photographs of these surfaces. Click on either image to view more detail:

concrete surface concrete surface

The second site, BE03, is just outside Antwerp near the town of Melsele, HERE. It was reportedly constructed as a two-lift concrete pavement using techniques similar to the those used in Austria. The top lift on this section used a much smaller coarse aggregate though, with a maximum aggregate size of 6 mm. The following are two photographs of this surface. Again, click on either image to expand it:

concrete surface Concrete surface

The results of the On-Board Sound Intensity testing of these two pavements was, as expected, very different.

Theory tells you that the concrete with the smaller aggrgeate should fare better in terms of measured sound levels. The measurements made under the National CP Tech Center program validated this fact. In fact, the OBSI level of the exposed aggregate surface on BE03 averaged 101.7 dBA compared to 105.3 dBA on the BE02 section.

OBSI levels graph OBSI levels graph

Comparing the spectra of the two sections is also revealing. The biggest differences can be found in the lower frequencies… those that “rumble”. However, this too is not surprising in that the larger aggregates on the BE02 section lead to a corresponding increase in texture size. This, in turn, should lead to an increase in low frequency content.