Why friction testing for asphalt mixes matters — and how to ensure a reliable outcome
Friction testing helps ensure pavement safety by increasing the amount of polish-resistant aggregates in the asphalt mix. Testing evaluates the pavement’s ability to provide adequate tire grip and reduce the risk of skidding or hydroplaning.
There are a variety of methods for testing skid resistance on existing pavements, but once a pavement becomes too slick, the remedies — ranging from various surface texturing or overlay treatments — add up to extra time and money that’s best avoided by first developing a skid-resistant mix.
States like Kentucky, Texas, Ohio, Florida, and Tennessee have begun to focus on asphalt pavement friction testing in an effort to increase the amount of polish-resistant aggregates in asphalt mixes, save money on maintenance, and make roads safer. They’re advancing new specification requirements, and that means future bids may need to include the results of friction testing on proposed mixes.
The complex testing required by states to meet polish-resistant specifications needs to be performed by experienced technicians and intuitive testing equipment like the Dynamic Friction Test (DFT), which
can travel from the lab to the field for real-time data and correlation. Below are some best practices to consider when searching for asphalt mix testing services to test both in the lab and on existing pavement.
FRICTION TESTING BEST PRACTICES
Test under realistic conditions
o Ensure friction tests account for typical conditions (wet/dry surfaces).
o Test at different speeds since friction changes with speed.
o If testing in the field, clean the pavement to remove debris, oils and loose materials that can affect results.
Establish testing locations and patterns
o In the field, select representative locations that cover different pavement sections, such as curves or intersections.
o Conduct spot checks in high-risk areas and areas prone to heavy braking.
Calibrate and maintain equipment
o Regular calibration of all testing equipment is critical to ensure reliable results. Rubber pads should be checked regularly for wear and proper thickness.
o Perform validation checks on equipment using established references to test for accuracy. BATT tests repeatedly in the same area of pavement in the field and in the lab runs three to five tests to ensure replication of results.
Ensure accurate data collection and analysis
o Data must be recorded accurately and include conditions, locations, speeds, and surface temperatures. Use GPS mapping in field tests for precise documentation of test locations.
o Compare friction data over time on existing pavements to identify trends, degradation rates and the effectiveness of different asphalt mixes.
o Conduct multiple tests at each location and calculate the average to account for variability, as single-point measurements can be unreliable.
Adhere to standards and guidelines
o Follow ASTM/ASHTO standards in all testing and utilize certified personnel to ensure the quality of data collection and interpretation.
Follow safety protocols
o Ensure proper traffic management when testing in the field to protect both the testing crew and road travelers.
o Equip personnel with the necessary safety gear and training for testing on active roads.
BATT rigidly adheres to these best practices, ensuring that our testing will yield reliable and actionable data for our clients. As one of the few labs in the nation capable of delivering test results from aggregate to asphalt, BATT has been instrumental in helping contractors acquire an extensive understanding of friction testing and how to accurately apply the results. Visit friction testing services for more information.
Please let us know if agencies in your area are updating friction specifications.
