Impact of clay content on the fracture behavior of rammed earth: Experimental and nondestructive assessment

Abstract

Understanding the fracture behavior of rammed earth (RE) is critical, as cracking and brittle failure often govern the structural performance and durability of rammed earth elements, particularly under extreme loading conditions. The present study investigates the fracture behavior of unstabilized rammed earth as a function of clay content, using both destructive and nondestructive testing approaches. Three-point bending tests were conducted on four unstabilized RE mixtures, with increasing clay contents of 25 %, 40 %, 65 % and 100 %, to characterize fracture behavior. Results demonstrate that increasing clay content improves stiffness, peak load and fracture energy. Despite the inherent heterogeneity of RE, results showed consistent trends and variability levels comparable to those reported in the literature. Maximum average fracture energy of 26 N/m was obtained for 65 %-clay specimens. A piecewise linear-exponential model was fitted to the load–displacement curves, with its parameters expressed as functions of clay content, enabling extrapolation to other mix designs. Nondestructive techniques (free–free resonant column and ultrasonic pulse velocity) showed good correlation with fracture energy, particularly through longitudinal natural frequency. A multivariable regression combining parameters from both nondestructive tests improved prediction accuracy (R2 = 0.80 ), supporting the combined use of nondestructive methods for reliable assessment of rammed earth behavior. These findings contribute to improved diagnostics of existing RE structures and more effective mix design and quality control in new RE construction.