WHO'S WHO IN ROADS
Why do some seals work and others don’t?
When water gets into a road surface, it results in an unwanted pothole pandemic
The headline is meant to be an attention grabber. In fact, all sprayed seals or chip seals work but some are just more appropriate than others. It all depends on the correct selection criteria, substantiated by the fundamental principles any design engineer must employ in order to ensure the success of any seal type specified. By Johan Muller
ABOUT THE AUTHOR: Johan Muller, founder of Bituminist Consulting, has an MSc in Organic Chemistry and has worked in the roads industry for more than 27 years. He started to live his passion as an independent road binder specialist in 2018. Knowledge transfer and training form key components.
T
he central theme for the roads feature in the April 2021 issue of IMIESA is repair and maintenance interventions. It is therefore imperative that when we discuss the most appropriate process for seal selection, important aspects are included in this discussion; however, it is inevitably impossible to include all the details involved in the design process of surface seals. Two things that bituminous binders do not adhere to at all are water and dust. Therefore, if you want a successful seal, these two culprits must be dealt with prior to any construction attempt. Obviously, road owners must assess the condition of the existing roads to be repaired and maintained. Often, we reseal over existing asphalt layers, but reseals can also be done on top of aged seals. Some, but not all, important criteria to consider are: • Cracks, and type of cracking: the magnitude, severity and extent are all important. When water gets into a road surface, it results in an unwanted pothole pandemic. Sadly, the costly result of insufficient attention to maintenance and repair strategies is all too visible in most municipalities. • Rutting/deformation creates another collection point for water, which results in unsafe driving conditions, with excessive mist spray. Worst-case scenarios cause aquaplaning.
• Stone or chip loss is a result of construction errors or ageing over time. This needs to be corrected before your next reseal intervention. • Bleeding and punching go hand in hand. Care must be taken before attempting your next maintenance intervention. Technical Methods for Highways (TMH) 9 Manual for Visual Assessment of Road Pavements Part A and Part B, issued by the Committee of Transport Officials (COTO) in May 2016, describe the process to assess surface seals both visually and with instrumentation. Visual assessments include surface failures (de-bonding), surface cracking, surface ravelling (aggregate loss) and bleeding, whereas
