Coatings World - November 2015

Waterborne Traffic Markings
November 2015 www.coatingsworld.com Coatings World | 41

the impact of 10 months of road wear on the appearance of traffic marking paints applied at 15 ± 1 wet mils line thickness. These paints differed only in the latex used in their formulation. Differences in line durability are already apparent even after this short period of time.

Figure 2 illustrates the impact of 24 months of road wear on lines applied at 15 ± 1 and 30 ± 1 wet mils line thickness. The thinner line is quite worn and would be considered in need of re-striping. The thicker lines are more intact, but a clear difference can be seen between different latex types.

The durability rating of the traffic
marking paints over the 24 month test-
ing interval is depicted in Figure 3. The
rate of degradation was found to be a
function of line thickness and latex type.

Unless otherwise specified, traffic markings with a durability rating less than 4 (less 40% remaining) are considered in need of replacement.

Figure 4 illustrates the skip-line ret-
roreflectivity of the traffic markings. The
retroreflectivity of the traffic marking
can be expected to decrease as beads are
lost or damaged. Below 100-150 milli-
candales/m2/lux markings are not easily
seen by drivers. The higher initial retro-
reflectivity of the 30-mil lines is a result
of the use of larger Type IV beads and
the higher application rate of 12 lbs/gal
of paint. White lines also generally have
higher initial retroreflecitvity than yellow.
The rate of degradation of retroreflectiv-
ity was also found to be a function of line
thickness and latex type.
It was found that the degradation in the
skip-line retroreflectivity was highly cor-
related to the wheel-track durability rating
with a correlation coefficient of 0.94. This
finding suggests that durability and retrore-
flectivity degrade in a similar manner and
higher durability markings will tend to re-
tain an acceptable level of retroreflectivity
longer. Figure 5 outlines the skip-line ret-
roreflectivity predictive formula developed
with data from the NTPEP trials, showing
the correlation to wheel track durability.

From this data it is clear that the life expectancy of a traffic marking can be enhanced simply by applying a thicker line.

Abrasion Resistance Testing

Standard durability traffic marking paints are applied at 15 wet mils and durable markings at 30 wet mils. Abrasion resistance testing protocol specifies films be applied with a 7-mil drawdown applicator which, depending on paint rheology, yields a film only 4-5 mils thick. Thus abrasion testing does not directly provide information on the durability of thicker films. To establish the impact of film thickness on abrasion resistance, a series of films of varying thicknesses were cast and their performance tested.

Figure 6 illustrates the scrub performance of the traffic marking paints applied to the NTPEP test deck. Clearly film thickness has a dramatic impact on abrasion resistance. This finding is not surprising since the test involves the removal of material with an abrasive media, so it would be expected that doubling the film thickness would double the number of abrasive cycles required to remove the paint film.

Since both paints passed 1 year durability testing when applied at 15 ± 1 wet mils and 2 year durability testing when applied at 30 ± 1 wet mils on the NTPEP deck, a correlation between abrasion resistance and durability can be inferred. It would appear that to achieve 1 year durability on the NTPEP test deck a minimum abrasion resistance of 5,000 cycles is required. It follows that 2 year durability