Geomechanical Characterization of Experimental Mud Bricks from La Joya Archaeological Site: Effect of the Addition of Additives on Their Mechanical Properties

This paper focuses on the study of earth-based building techniques from the pre-Columbian site of la Joya in Mexico, which use soils containing a high proportion of fine fraction (loam and clay) stabilized with bitumen, a combination considered inadequate by modern building standards. Experimental mud bricks were manufactured emulating the ancient technique representative of the construction in that region by using the raw earth of the archaeological zone mixed with additives of different nature. The bricks' cohesion was analysed by submitting them to mechanical stresses in compression mode. The effect of the inherent heterogeneity of hand-made bricks, along with the effect of the additive concentration on their mechanical behaviour, is discussed. Techniques such as determination of particle size, X-ray diffraction, X-ray fluorescence, Scanning Electron Microscopy and total inorganic carbon-organic carbon were implemented for quantitative and qualitative measurement of the soil characteristics. Results indicate that synthetic additives provide better cohesion. Fracture analysis was monitored in real time by using acoustic emission technique in order to understand the mechanisms of failure. The main result is that the pre-Columbian recipe improves the mechanical performance of mud bricks, a knowledge important both for the conservation of the archaeological heritage architecture as well as for modern construction.