Friction Surface Treatment Selection: Aggregate Properties, Surface Characteristics, Alternative Treatments, and Safety Effects S. Li Indiana Department of Transportation, and 2Purdue University

1. objectives To evaluate the long-term performance of the selected friction treatments HFST with calcined bauxite and steel slag, and Preservation treatments such as chip seal, micro-surfacing, UBWC, and diamond grinding To determine the crash-friction correlation to establish crash modification factors (CMFs) To provide original data on HFST aggregates that can be readily implemented by State DOTs Standard specifications, and Evaluation of alternative aggregates

Micro-Deval Abrasion Loss, % Apparent Specific Gravity 2. Aggregate Properties Laboratory tests Mechanical properties: Los Angeles abrasion (LAA), Micro-Deval abrasion, & polished stone value (PSV). Chemical/physical properties: Al2O3 content, fine aggregate angularity (FAA), and others Recommendations for aggregate properties Property Test Method Aggregate Size Calcined Bauxite Steel Slag LAA Loss, % ASTM C131 Grading D 12.5 max 14.0 max Micro-Deval Abrasion Loss, % ASTM D6928 6.39.5 mm 5.5 max 6.5 max PV-10 ASTM D3319 35.0 min 26.0 min 13 mm 55.0 min 49.0 min Al2O3, % by Mass, % ASTM C 311 N.A. 86.5 min 5.0 min Apparent Specific Gravity ASTM C 127 3.30 min 3.50 min Water Absorption ASTM C 127 3.0 max 2.0 max FAA AASHTO 304 48 46

3. surface friction Characteristics Evaluation methods Laboratory accelerating polishing, and Actual traffic polishing on test strips Major factors Cost: single or double layer application Appearance/tire wear: aggregate size and gradation Recommended surface friction characteristics Property Test Method No. 6 Calcined Bauxite No. 8 Steel Slag DFT Friction Coefficient @20 km/h, 90 days ASTM E 1911 0.90 min 0.65 min MPD (mm), 90 days ASTM E 2157 or E 965 1.45 max 1.35 min

4. Pavement preservation Treatments Evaluation methods Long-term field friction testing on chip seal, micro-surfacing, UBWC, and diamond grinding Evaluation results Chip seal can provide satisfactory friction for five years or more. Microsurfacing can provide durable friction for six years or more. UBWC can maintain durable and sound friction under high traffic conditions. Diamond grinding can provide durable friction for both concrete and asphalt pavements.

5. Crash-friction models Major distinguishing features Based on well documented historical crash records and friction test results Ability to allow for a dynamic evaluation of the CMF due to friction surfacing for life-cycle cost analysis (LCCA). Prediction models Road Category Linear Regression Fitted Regression 𝐿𝑛 𝛽 0 𝛽 1 R Square Interstate 0.5779 -0.0456 0.8057 𝑦 𝑖 =1.782 𝑒 −0.046 𝑥 𝑖 State Road 0.4378 -0.0813 0.7669 𝑦 𝑖 =1.550 𝑒 −0.081 𝑥 𝑖 US Route 1.3781 -0.1507 0.9133 𝑦 𝑖 =3.967 𝑒 −0.151 𝑥 𝑖

6. benefits Provide more realistic estimates on HFST crash reduction. High friction surface treatments are capable of providing crash modification factors of 0.727 for state roads, 0.567 for U.S. highways, and 0.348 for Interstate highways Provide quantitative friction performance on pavement preservation treatments, including chip seal, microsurfacing, UBWC, and diamond grinding that can be used to address friction concerns at locations with less extreme friction demands. Provide first-hand data on the mechanistic properties of aggregates for HFST that can be readily implemented by State DOTs. Provide realistic models that makes it possible to perform life cycle cost analysis (LCCA) for surface treatments