Rut potential determination of marginal asphalt with low traffic volumes on a regional airport in Southern Africa Emile Horak KUBU Consultancy Pty Ltd, Centurion, South Africa Stephen Emery KUBU Australia, Pty, Ltd, Perth, Australia Bing Walker Bing Walker & Associates, Cape Town, South Africa Abstract—Asphalt production and paving in remote regions of Africa can be problematic in terms of logistics, material sourcing and production quality. Airport planning also tend to project high growth rates of aircraft movements which don’t always realize. A further complication is the tendency to use roads design and specifications on airports in such remote regions. A recent airport runway upgrade and asphalt overlay on the west coast of Africa taxed these realities. Dynamic creep modulus was specified as main criteria for rut resistance. The dynamic creep modulus gave variable results partly due to the proven inherent unreliability aspects of the test procedure. Therefore the asphalt had to be evaluated against fit-for-purpose criteria. Actual asphalt thicknesses were variable and in some instances significantly thicker than the specified 50mm. The thicker asphalt, in particular, raised questions about perceived rut propensity. The air traffic movements at this remote airport are low and in future will also be low, which potentially lowers the potential impact of excessive rut development. A number of additional tests including the Light Weight Falling Weight Deflectometer (LFWD) and Falling Weight Deflectometer (FWD) were done to determine and confirm the overall structural pavement strength. . Asphalt rut propensity was evaluated with Model Mobile Load Simulator (MMLS) tests. MMLS tests were done on site and additional MMLS tests were done in South Africa on cores from site. Constant Height Repeated Simple Shear Tests (CH-RSSTs) were also done.. The latter test allowed comparison of data obtained from Heavy Vehicle Simulator (HVS) tests and associated CH-RSST data base developed in California, USA. All these tests to determine rut potential have different quirks and positives. A comparative triangulation approach had to be followed to arrive at a weighted best evaluation of this asphalt surfacing. The net result was positive. Key words: Rut resistance Repeated Simple Shear Test at Constant Height, Model Mobile Load Simulator, Heavy Vehicle Simulator , (Light) Falling Weight Deflectometer, Triaxial testing I. INTRODUCTION Walvis Bay is approximately in the middle of the long and arid coast of Namibia, on the west coast of Africa. The upgrade of Walvis Bay International Airport (WBIA) was planned in the late 1990s after the handover of Walvis Bay from the South African government to the then recently independent Republic of Namibia. Walvis Bay was identified as a gateway with the existing harbour facilities and airport in need of upgrade. The original plan was to upgrade the former Rooikop military airport runway by lengthening and widening it. The later planning stages coincided with the emergence of the new Airbus 380 size super wide body aircraft. It was thus decided to upgrade this new longer runway to an ICOA 4F standard [14 & 19]. Regional airports in remote regions of Africa often suffer from a number of planning, design and construction peculiarities. A first and common problem is a tendency of over estimation of air traffic movement (ATM) figures. Traffic forecasts with airport upgrades or development generally has a high probability to be wrong to start with due to various extraneous factors. It is often found that traffic figures are overestimated or projected at an inflated growth rate during the planning stage. Socio-political motivations for airport upgrades are often linked with misplaced national pride. The expectancy level therefore often drives a positive over estimation of ATMs. The decade trend of long term down turn in world air travel figures have thus also showed a number of projects world- wide up to be over optimistic in their planning. In this regard Walvis Bay International Airport (WBIA) experienced a similar dichotomy in planning scenarios versus actual realised future traffic figures. WBIA was designed in 2006 [14 & 19] to be upgraded from an ICAO 3C to a 4F runway. There is clear wisdom gained in hindsight in comparing original planned growth rates versus actual ATM growth rates experienced. In Fig. 1 the actual versus planned air traffic movement (ATM) figures trends are shown. The gap in the published ATM figures of 2005 and 2006 is when actual construction commenced. This negative impact in ATMs due to construction activities clearly lingered until at least 2007 due to prolonged contractual difficulties and eventual late completion date. The actual CAPSA 2015 – Peer reviewed published papers