Density-Strength Decoupling in Compressed Earth Blocks: Insights from Mechanical, Ultrasonic, and Microstructural Characterisation

Résumé

This study investigates the effect of coarse sand grain correction on the coupled evolution of dry density, compressive strength, Ultrasonic Pulse Velocity (UPV), and microstructure of Compressed Earth Blocks (CEBs). Granular correction increased the Maximum Dry Density (MDD) from 1965 kg.m-3 to 2032 kg.m-3 (+3.4%); however, compressive strength decreased from 1.5 MPa to 1.25 MPa (-17%) and UPV from 0.873 km·s-1 to 0.737 km·s-1 (-16%). Conversely, a clay-rich soil exhibited the highest strength (2.42 MPa) and UPV (0.964 km·s-1) despite the lowest density (1890 kg·m-3). Scanning Electron Microscopy (SEM) and X-Ray Fluorescence (XRF) analyses revealed that strength evolution is governed primarily by the continuity of fines bonding rather than by density alone. A linear relationship between UPV and compressive strength was obtained with an R2 = 0.803. These findings demonstrate a density-strength decoupling induced by physical particle size correction and highlight microstructural bonding as the controlling mechanism for low-carbon CEB optimization.

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