Strength and Elastic Properties of Air–Cement-Treated Clays Under Cyclic and Monotonic Compression Tests

Using air–cement-treated clay (ACTC) as a subgrade material for flexible pavements has gained widespread interest and acceptance. The mechanical properties of ACTC, including its compressive strength and elastic modulus (i.e., equivalent elastic modulus, E_eq ) are required to realistically model its behavior in simulating pavement structure. This paper investigates the impact of different mixing proportions, particularly cement content and unit weight, on the mechanical properties of ACTC. These properties include its unconfined compressive strength ( q_u ) and elastic moduli (initial modulus ( E_0 ), secant modulus ( E_50 ), and E_eq ). The aim of the current study is to develop an equation for estimating the E_eq , which is essential for analyzing pavement structures under cyclic loading. The study involves applying continuous monotonic and cyclic loads to evaluate the mechanical properties of ACTC mixtures with varying cement contents (35–135 q_u and the elastic moduli are significantly influenced by cement content and unit weight, and are well described using the effective void ratio ( e_st ) parameter. The ranges for q_u , E_0 , and E_50 were 51.9–411.2 kPa, 42.8–289.4 MPa, and 33.9–183.1 MPa, respectively. E_eq varied between 37.6 and 289.4 MPa, depending upon the cement content, unit weight, and applied stress level. Notably, E_eq values decreased with increasing vertical stress. A simplified equation, accounting for the combined effects of cement content and unit weight on the E_eq variation under different stress levels, is developed and recommended for practical use in designing ACTC mixtures for pavement analysis.