Evaluating in situ shear strength of bituminous pavements

The friction transfer method described in this paper can be used to estimate the in situ shear strength of bituminous pavement layers. In this method a specially devised apparatus fits on the top of the partial core and is clamped to it. A torque is applied using an ordinary torquemeter, and the maximum shear stress at failure is calculated. Comparative studies of laboratory Marshall stability and friction transfer tests produced correlation coefficients of 0·72 and 0·82 for linear and polynomial best-fit curves respectively, and the respective linear correlation coefficient for the in situ tests was found to be 0·84. The measured values for Marshall and friction transfer tests ranged from 750 to 1100 kg and from 1·2 to 1·8N/mm² respectively. The average coefficients of variation of eight series of experiments were found to be 11·07% for Marshall stability tests and 11·39% for the friction transfer method. Based on the laboratory and site experiments, and considering such factors as versatility, simplicity, speed, applicability under any site conditions by untrained operators, very low cost, easily interpreted and understood results, and good accuracy, this new method is strongly recommended for the assessment of the in situ shear strength of bituminous materials.