COST 334

30first test pavement25295/60Practical Rut Depth (mm)201510second test pavement315/80385/65495/45500 5000 10000 15000 20000 25000 30000 35000 40000Loadcycles (N)Figure 4.46 – Development of ‘practical rut depth’ on the two tested pavements(based on Houben et al. 1999a and 1999b)From the measurement results, the following conclusions were drawn regarding thedifferences between the four tested tyres.First test pavement:• The prototype extra wide single tyre 495/45 R 22.5 showed the best behaviour, whichmeans that the rutting was smallest, while the rutting process remained stable.• On the contrast the standard wide single tyre 385/65 R22.5 showed the worstbehaviour, which means that the rutting was greatest while the rutting process becameunstable after about 20,000 load repetitions.• The standard dual tyre 315/80 R22.5 showed a similar behaviour as the prototype extrawide single tyre 495/45 R22.5 although the rutting was somewhat greater.• The alternative low diameter dual tyre 295/60 R22.5 showed the same ruttingbehaviour as the prototype extra wide single tyre 495/45 R22.5 up to about 20,000load repetitions, but after that an unstable rutting process occurred.Second test pavement:• At long term (i.e. for the relevant practical rut depths) the prototype extra wide singletyre 495/45 R 22.5 caused less rutting than the standard wide single tyre 385/65R22.5• The standard dual tyre 315/80R22.5 exhibited a remarkable good rutting behaviour(i.e. small practical rut depths) compared to both wide single tyres. A provisionalexplanation for this good behaviour is that through the combination of the great overallwidth of a dual tyre system and the stiff wearing course the stress levels in the StoneAsphalt Concrete layers are smaller than in the case of a wide single tyre, and byconsequence the permanent deformation in the Stone Asphalt Concrete layers causedby the standard dual tyre is much smaller than that caused by single tyres. Thisprovisional explanation is confirmed by the results of the performed layer thickness80version 29 November 2001