Surface run-off behaviour of bitumen emulsions used for the construction of seals

Abstract

Paper presented at the 33rd Annual Southern African Transport Conference 7-10 July 2014 "Leading Transport into the Future", CSIR International Convention Centre, Pretoria, South Africa.

The application of seals as surfacing on South African roads has increased due to its dual advantage in performance potential and sustainability. The field performance of spray seals depends on a number of factors, and its defects measured predominantly by bleeding and ravelling of the seals. During construction, viscosity is controlled such that the binder is sprayable, but not too low in viscosity as to run off the road surface. To avoid pavement distress resulting from loss of the binder or from inconsistent binder thickness after application, it is important to understand the run-off behaviour of seals. Run-off tests were conducted in the laboratory by constructing surfacing seals with varying texture depths. These seals were constructed on a surface that would allow the user to change the angle of application in order to simulate the spraying of the seals on different road gradients. A movable/mobile spraybar was used to simulate typical conditions as for a spray tanker during construction. Run-off was measured through a gutter system where the emulsions was collected and weighed. An analysis of the run-off results obtained from these experiments, revealed that the spray rate had the largest effect on run-off, followed by texture depth, and gradient.