AASHTO TP 130:2020 Standard Method of Test for Producing Drawdown Panels and Measuring the Coefficient of Retroreflected Luminance (RL) of Pavement Markings in a Laboratory Panel.
4.1. This test procedure is used to predict the retroreflectivity of M 247, Type I glass beads in waterbome paint using a laboratory simulation of a field striping operation. Measured quantities of glass beads are dropped on top of a repeatable, uniform thickness of paint on top of a glass panel. When the paint is dry (after 24 hours), the retroreflectivity is measured using a 30 m geometry portable retroreflectorneter.
5.1. One of the characteristics of a pavement marking is the coefficient of retro reflected luminance, RL. Under identical conditions of headlight illumination and driver viewing, larger values of RL correspond to higher levels of visual performance at corresponding geometry.
6.1. For waterborne paint, water for clean up;
6.2. 4 in. drawdown bar; thickness capability from 15-30 mils (375-750 microns);
6.3. Flat substrate 6 by 24 in. made of 1/8 in. glass, aluminum, or slate;
6.4. Support fixture to hold substrate firmly in place during drawdown;
6.5. Balance to 0,01 g accuracy;
6.6. Splitters to obtain representative glass bead sample (large 16:1, small 1:1);
6.7. Weighing dishes and containers for beads and paint;
6.8. Bead drop box (see Figure 1) with dimensions of approximately 5/2 by 19V2 in. by 14 in. (producing a 4 by 18 in. stripe) filled with 10 layers of V4 in. screening spaced 1 in. apart, with support bar to hold beads in swivel mounted on top;
6.9. Reflectometer, 30 rn geometry based on retroreflective measurements made with portable hand- operated instruments in compliance with ASTM E 1710;
6.10. Paint film thickness gauge, 5-30 mu (125-750 microns); and
6.11. Magnifying glass to check glass bead embedment.
7.1. A representative sample of glass beads meeting the requirements of M 247, Type 1, should be taken following T 346 procedures. The sampling shall be random in the following ratios: 100 lb (45 kg) of sample (in full bags) per 10,000 lb (4,535 kg) shipped. Upon arrival, material shall be reduced in a sample splitter to a size of approximately 2.2 lb (1 kg).
8.1. The drawdown procedure must be calibrated to ensure the correct thickness of paint is applied. The retroreflectometer must be calibrated in accordance with the manufacturer’s instructions. The rctroreflectivity is very dependent on the paint formula in addition to the glass bead quality. Use a control paint to compare glass bead retroreflectivity (Sherwin Williams TM2 152 White). Note 1—Use of this specific control product was chosen by NCHRP research team to minimize the test variables and compare testing and final retrorefiection performance. Users could consider alternate control traffic paints to suit their specific needs.AASHTO TP 130 pdf download.