Bitumen coating should be applied above the neutral plane.
Likewise, the visual inspection of the degree of bitumen coating on loose mixtures exposed to water in a "rolling bottle" test, and further surface free energy measurements, showed that the bitumen modification by the isocyanate-based prepolymer seems to reduce moisture-induced damage on siliceous aggregates.
Most of the design guidelines limit the amount of RAP in the base course up to 30% by weight of the virgin aggregates, in lieu of the aged bitumen coating present on the RAP aggregates and lack of understanding of the long term performance of the material.
After analyzing water samples, the water company concluded that the complaints may have been a result of PAHs in the drinking water, which were assumed to have originated from the bitumen coating in the cast iron mains.
We categorized the type of coating [no coating, bitumen coating, coal tar coating, or unidentified (i.e., there was a coating, but there was no certainty of it being coal tar or bitumen)]; the thickness of the coating [thin (< 1 mm) or thick (≥ 1 mm)]; and the coverage of the main [none, less than one-half, more than one-half, and full (0%, > 0% to 50%, > 50% to < 100%, or 100%)].
Because water companies do not know which of their cast iron mains have bitumen coatings and which have coal tar coatings, the effect of coating type is of no practical value.
To summarize, PAHs may leach from bitumen coatings into drinking water, and the erosion of bitumen coatings may release particles that contain PAHs.
It is important to understand the behavior of bitumen before designing bitumen-coated piles.
We found bitumen, coal tar, and some unidentified coating types of varying thickness and coverage.
Historically, substances such as coal tar or bitumen were used to coat the insides of iron water pipes, which reduces corrosion by forming a water-resistant barrier on the pipe walls (Maier 1998; Miller et al. 1982; van den Hoven and van Eekeren 1988).
