Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. It is by now common knowledge that the old Concrete Pavement Design and Construction
Manual (Manual M10, 1995) has been upgraded to a design process based on mechanistic
design principles, in the form of a software package, cncPave. The aim of this paper is to
present the results of a study, conducted at the University of Pretoria to improve the aggregate
interlock equation used in the software, as it was identified that the previous relationship
modelling the mechanism of concrete joints in shear (aggregate interlock) was not accurate,
especially for the smaller sized coarse aggregates used in the construction of concrete.
A main objective of the study was to investigate existing methods for modelling aggregate
interlock shear transfer efficiency and use that as the basis to develop a mechanistic model
simulating variations in joint load transfer efficiency with joint opening, load magnitude,
subbase characteristics, and concrete aggregate properties. A secondary objective was to
investigate the difference in pavement response to static and moving impulse or dynamic loads
(equivalent to traffic loads) in terms of deflections across the joint in the pavement.
The specific contribution of the study to the improvement of the aggregate interlock equation
used in the new mechanistic concrete pavement design method, cncPave, is highlighted in the
Of the conclusions reached after interpretation of experimental results were that the
deflection load transfer efficiency was greater during dynamic than static loading, and that
larger maximum sized coarse aggregates in the concrete mix (37.5 mm) had lower deflections
at the same crack width than smaller sized coarse aggregates (19 mm).
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