Resilient modulus characteristics and model prediction of cement phosphogypsum under dry-wet cycling conditions

Abstract

The subgrade resilient modulus is a crucial parameter in pavement structure design, directly related to the safety and economy of the pavement structure. Currently, the subgrade resilient modulus used in pavement structure design is the static resilient modulus. To address this issue, this paper employs dynamic triaxial tests to analyze the effects of confining stress ( σ 3 ), cyclic dynamic stress ( σ d ), wet-dry cycles (N), and cement dosage (C) on the resilient modulus (M R ). It explores the relationship among the M R , static resilient modulus, and 7-day unconfined compressive strength ( σ c ), and proposes a predictive model for M R considering C and N. SEM and XRD methods are used to analyze the mechanism of the effect of wet-dry cycles on M R at the microstructural level. The results show that; (1) The M R of the PG mixture increases with the rise of σ 3 and decreases with the increase of σ d , is positively correlated with C, and negatively correlated with the number of N, with the decay of M R mainly concentrated in the first four wet-dry cycles and gradually stabilizing afterwards, which is explained through SEM and XRD analysis. (2) By comparing M R and the static resilient modulus, it is found that the M R of PG specimens under wet-dry cycles is 1.25–1.30 times that of the static resilient modulus, this ratio can be used to make a preliminary estimation of the M R of C-stabilized PG materials. (3) The model relating σ c and M R follows a linear relationship, with correlation coefficients for the fit all exceeding 0.94, indicating a good fit. (4) A model for predicting M R that incorporates N and C was proposed, and the reliability of this model was verified by comparing predicted values with experimental data. The predicted M R provides a reliable basis for pavement design and holds significant engineering value.