An advanced experimental investigation of size effect on flexural fatigue behaviour of cement-bound granular materials

This paper investigates the effect of specimen size on the flexural fatigue behaviour of two different locally-sourced pavement materials stabilised with 3% general purpose (GP) cement, viz., cement-stabilised Holcim road base (CSHRB) and cement-stabilised quartzite (CSQRT). Three different sizes of geometrically similar beams were tested under both static and dynamic four-point loading conditions. A suitable load pulse shape that simulates the critical stress response of the cement-treated base (CTB) under standard axe loading was generated for each beam size to perform stress-controlled flexural fatigue tests. The flexural fatigue test results showed the existence of a fatigue endurance limit in cement-stabilised pavement materials (CSPMs) at 28 days curing period. The analysis of experimental data revealed that the flexural properties of CSHRB (i.e. flexural strength and flexural fatigue performance) are appreciably affected by the size of the beam specimen employed in the flexural test while the flexural properties of CSQRT did not show a clear trend for increasing beam size. Bažant’s size effect law is in good agreement with the flexural strength results obtained in this study for CSHRB. For materials that exhibit size dependence on flexural strength, an empirical relation is proposed in this study to determine the flexural strength of any given beam size using the flexural strength of standard beam size or indirect tensile strength of the beam material. Furthermore, a stress-based fatigue model incorporating the size effect is proposed to predict the flexural fatigue life of CSPMs in service. The factors that give rise to erroneous strain-based fatigue models were critically discussed on the basis of the results of this study.