Page 8 - Sept-Oct2023 Vol 41 No 3

Red Bank from page 7 FIGURE 1
UT Red Bank Field Test Report (excerpts)

Location Information
As shown in Figure 1, the outer lane was chosen for the
pavement skid test. The outer lane was subject to heavy traffic
resulting in a rapid loss in pavement friction. The distance
between each test spot is 20 feet to finish relative tests at the test
lane efficiently.
As shown in Figure 2, two segments in Red Bank were tested.
Segment 1 was tested at the outer lane of Ashland Terrace in both FIGURE 2
wheel paths. Segment 2 was tested at the shoulder to represent the
initial pavement skid resistance for comparison.
The outer lane of Ashland Terrace was tested, including the left
wheel path and the right wheel path. The shoulder was tested on
Morrison Spring Road including the left wheel path and the right
wheel path.
Test Device
A Dynamic Friction Tester (DFT) is a portable device to
measure the coefficient of friction. It consists of a rotating circular
disk attached with three rubber sliders to interact with the
pavement surface. The disk rotates at tangential velocities up to
80 km/h. Water flows over the pavement surface being tested to
simulate the wet conditions.
The DFT measures the friction-speed relationship with speeds
ranging from 0-80 km/h to evaluate the micro-texture. The
coefficient of friction at 20 km/h (DFT20) is commonly used for
evaluation. Additionally, the content of SiO2 has larger value of standard
The circular track meter (CTM) was used to measure the deviation compared with CaO content, showing that carbonate-
macro-texture of pavement. CTM is a laser-based non-destructive rich aggregates can present more reliable results of CaO than
device, which can achieve a quick measurement. It uses a laser SiO2. Most of the SiO2 contents are greater than 15%, which can
displacement sensor mounted on an arm that rotates at a fixed provide acceptable pavement skid resistance.
elevation from the measured surface. Mean profile depth (MPD) Conclusion
and root mean square (MSE) were tested by CTM to evaluate the • The DFT20s at segment 1 are lower than average values,
skid resistance at high speed. indicating lower polish resistance compared to the segment 2.
DFT and CTM are commonly used devices in the laboratory as • The polish resistance of pavement is strongly related to
well as in the field. Traffic control was provided during the field the silica dioxide content of aggregates. Polishing-resistant
test. Eighteen field spots were tested to evaluate the pavement aggregates with higher silica dioxide content are recommended
skid resistance. for pavement wearing courses.
The average MPD of tested spots is about 0.4mm, which • Macro-texture-based MPD is smaller due to the fine gradation
represents the asphalt mixture containing more fine aggregates. of asphalt mixtures. Asphalt mixtures with higher content of
It is recommended to consider increasing the contents of coarse coarse aggregates may be suitable for improving pavement skid
aggregates. resistance.
Coring Analysis Based on the results of the joint investigation, Red Bank is
Six samples were cored in the field. Mineral analysis was evaluating its alternatives. These include:
conducted to determine the polishing resistance. Poor skid • Milling the segment in question and overlaying with either a
resistance could be a result of the low polishing resistance of standard TDOT D mix or an open graded mix
coarse aggregates. Siliceous aggregates are less prone to polishing. • Using one of several available surface treatments for increasing
Therefore, the collected cores were prepared for silica dioxide skid resistance.
(SiO2) and calcium carbonate (CaO) content tests. • Using a thin lift overlay with the appropriate aggregate.
Selected cores were coated with asphalt binder that influenced Multiple Entities Contributed to A Successful Study
the test results of SiO2. Chemical solution Trichloroethylene The project was an interesting case which involved
(TCE) and extractor were used to remove asphalt binder to collaboration between the Red Bank Police Department, the Red
expose the virgin aggregates for the chemical composition test. Bank Public Works Department, the Signal Mountain Public
The SiO2 and CaO contents were analyzed by X-ray Works Department, the Municipal Technical Advisory Service,
Fluorescence (XRF). From the results of the original and washed the Center for Transportation Research, and the Department
mixtures, aggregates with thinner asphalt binder film can have of Civil & Environmental Engineering at the University of
higher SiO2 and CaO contents. Tennessee, Knoxville.

8 TPW September/October 2023