Yang Sheng Yeo

Mechanistic Classification of Cement Treated Base in Western Australia

In the past decade alone, the BITRE has indicated an increase of 40% in road users, escalating demands for quality pavements to service unprecedented traffic conditions. An abundance of crushed rocks are available in Western Australia but do not meet strength requirements for road construction. However, cement treatment of crushed rocks, forming Cement Treated Crushed Rocks (CTCR), improves the mechanical properties of the material, allowing wider application. In order to streamline the mix design of CTCR, the classification of its behaviour is pivotal. Austroad classifies cement treated pavement materials as either being modified or bound based on its Unconfined Compressive Strength (UCS) and performance attributes. Bound materials are defined by its susceptibility to fatigue failure which, in the mechanistic-empirical design for flexible pavements, is dictated by the flexural modulus. However, in the study of damage mechanics, fatigue life is suggested to be an accumulation of micro-scale damage in lieu of dependency to ultimate stresses. Strain dependent damage functions are used phenomologically to explain the evolution of fatigue for various engineering materials. This paper therefore investigates a theoretical relationship between strain and fatigue life prediction supported by a laboratory investigation on the use of UCS for classification. This is achieved by providing regression analysis with strain parameters used in fatigue life prediction. The Indirect Tensile Strength (ITS) test is also employed to this end. It is observed that strain at onset of micro-cracking coalescence (e30) is independent of test type undertaken and potentially capable of acting as a more superior blanket classification for cemented materials.