On roads that carry heavy traffic and where higher speed is allowed on the roundabout, conventional mixes may not work well. In the roundabout approach zone the forces due to braking can be very significant. On the roundabout itself, shear stress due to centrifugal forces can be high and regular asphalt mixes may not be able to cope with them. The pavements may shove in the roundabout approach zone and deform and shove and crack within the roundabout. Frequent maintenance including emergency repairs may be required. Frictional characteristics of the pavement in the approach zone can also be of concern.
The asphalt mixes to be used at roundabouts should offer better resistance to horizontal shear force than those used in other conventional roadway applications. Unfortunately, the shear resistance testing method for asphalt mixtures is limited in both laboratory and field work. An advanced asphalt technology developed for race track pavement appears to address high shear stresses successfully. A team including the University of Waterloo, Greater Toronto Airport Authority (GTAA) and Golder Associates Ltd. is carrying out a research project on evaluating airport asphalt mixes that can offer superior shear resistance. At minimum, the team will use a Uniaxial Shear Tester (UST).
The above mentioned research is focused on optimizing three main components that impact shear resistance: characteristics of asphalt cement; gradation of aggregates; and aggregate angularity. At the same time the mix is also required to offer good frictional characteristics. It is anticipated that as the results of this research, a mix design procedure can be developed that will allow the design of cost effective asphalt mixes that will offer superior shear resistance which could be beneficial to the performance of pavements at roundabouts.