Distinctive mechanism and model for whole-life ratcheting of cement-stabilized aggregates in tensile fatigue tests

Abstract

In light of the limited research on the fatigue damage and plastic strain evolution of cement-stabilized aggregates (CSA) despite their widespread application, this study aims at modeling the ratcheting of CSA, which provides better characterization of fatigue by counting plastic strain accumulation. Uniaxial and indirect tensile fatigue tests were conducted to obtain the plastic strain accumulation and stress-strain curves. A bar system was constructed to describe the ratcheting mechanism of CSA, which considers the non-homogeneity of CSA's components and composes parallel bars with a distribution of plastic-damage properties. The ratcheting rate variation was attributed to the strength distribution of the bars. Then, to prevent complex and hard-to-implement parameter fitting, a predigested ratcheting model was proposed, which focuses only on the secant modulus and simplifies the generation of ratcheting to the difference between reloading and unloading secant modulus. The test results revealed a three-stages characteristic in the ratcheting evolution of CSA. The non-coincidence of reloading and unloading curves was deemed the intuitive cause of the ratcheting. The numerical implementation of the proposed mechanism indicated that the strength and modulus discrepancies between weak and strong bars can lead to ratcheting. By comparing with the experimental results, the effectiveness of the proposed model was verified in describing the ratcheting evolution of CSA and to characterizing the non-linearity of the accumulation curves. Moreover, the parameter fitting process requires the results of the current fatigue test instead of parallel tests or other loading tests, successfully eliminating calibration difficulties resulted from significant property discrepancies among CSA specimens.