Paper and Presentation by Arvo Tinni and John Hodgkinson from ASCP 5th Concrete Pavements Conference 2019
Road Authorities commonly require detailed 40 year design traffic loading (DTL) estimates and concrete pavement thickness design calculations. The purpose of this paper is to draw attention and to demonstrate that detailed concrete pavement design in accordance with the Austroads Pavement Design Guide and RMS Supplement can be a time consuming effort with limited value as 7 out of the 9 input parameters are assumptions and minimum base thickness requirements are set out in State Authority supplements to Austroads. These latter thicknesses usually exceed detailed design results. Until recently, design estimates of heavy vehicle Design Traffic Loading (DTL) was based on initial traffic counts with an arbitrary 4% annual growth continuing for then design period, usually 40 years. The procedure did not take into account carriageway saturation and lane capacities that would probably be exceeded within the design period. Previous design traffic loads exceeded that capacity of typical lane numbers to provide appropriate level of service. This paper considers lane capacity. A suitable methodology is proposed. Concrete base thicknesses are given for various flexible concrete strengths and corresponding compressive strengths. Comparisons are provided for concrete strength against required slab thicknesses by design and also flexural concrete strength and design traffic loading using lane capacities for different Levels of Service. Discussion and recommendations are included for lowering of design concrete strength and also strength for opening the pavements to traffic. The paper demonstrates that pavement thicknesses, particularly when using road agency supplement minimum thicknesses, can be simplified without detailed design assessed on design traffic load classifications only and then fitted into a small number of traffic classifications with design loads that take into account lane capacity. No detailed thickness calculations would then be necessary.