Coatings World - November 2015

Waterborne Traffic Markings
November 2015 www.coatingsworld.com Coatings World | 39

driver safety have failed to be developed.

In an effort to reduce the time and cost associated with developing higher performance traffic marking paints, other methods for assessing product performance and numerous accelerated methodologies have been proposed for evaluating the durability of traffic markings, and indeed transverse striping on the NTPEP test deck is itself a form of accelerated testing. No matter the technique a correlation must be established between accelerated test results and real world performance. An ideal accelerated testing protocol would be highly correlated to real world performance, but also must be inexpensive, reproducible, accessible and significantly shorten the time interval to yield results.

Of all the accelerated methods pro-
posed, Abrasion Resistance, as described
by ASTM D2486-96, most closely meets
this set of criterion. It is probably the least
expensive and most common technique
for evaluating the wear resistance of
coatings. The technique is highly repro-
ducible and results
for dozens of different traffic markings
can be obtained in a week’s time. The
use of abrasive scrub media simulates the
abrading action of sand and salt embed-
ded in tires. One obvious concern is that
traffic markings are not usually evalu-
ated with embedded traffic beads and
so the question may arise as to whether
a correlation exists between abrasive
wear and the loss of retroreflectivity.
Retroreflectivity is defined as the light
that returns to the light source.

In an attempt to establish a correlation between abrasion resistance, durability and retroreflectivity, data from NTPEP trials were compared to laboratory test results.

Experimental

Paint Formulations

Traffic marking paints utilized in this work were prepared using the formulas shown in Table 1. Three latexes (A, B and C) with varying abrasion resistance were included in the study.

N TPEP Test Deck

Transverse traffic paint pavement markings were applied to test decks as a part of the NTPEP; paints were tested on both asphalt and concrete.

Test decks were located on straight, flat roadways that were not likely to have areas of excessive wear caused by braking or turning, were fully exposed to sunlight during daylight hours, and had good drainage. Average daily traffic (ADT) was approximately 15,000.

All lines were applied in the transverse direction, or perpendicular to the flow of traffic, using a walk-behind striping machine with traction drive and spray guns similar to those used on commercial striping trucks. Lines measured four inches in width and either 15 ± 1 or 30 ± 1 wet mil in thickness. To calibrate the spray application of each paint, the four-inch wide stripe was sprayed onto a test panel of known dimensions, which was then weighed. To calculate the line’s thickness,