Building techniques and materials for 500-year-old long-lived earth monuments: Chullpares in Huayllani-Condor Amaya (La Paz, Bolivia)

This work presents a first approach to compositional and structural aspects of the building material in some chullpares in Huayllani-Condor Amaya (La Paz, Bolivia). A multi-technique method is proposed and tested in order to explore the raw material selection and technical choices, seeking for a better understanding of the chullpar's builders' technological knowledge and the long preservation of these ancient monuments. As a corollary, it could provide valuable information concerning the chullpar heritage conservation programs. Three of this earthen buildings were examined using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD) and Fourier Transform Infrared-Attenuated Total Reflection (FTIR-ATR), Laser Diffraction Grain Size Distribution, Polarized Light Microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). The results describe the chullpar building material as a prepared admixture of plant fibers -Poaceae- and selected sedimentary components - clayey phyllosilicates and sand and silt sized grains, the latter dominated by quartz and feldspars, with smaller amounts of lithic fragments of sandstone, limestone, quartzite, altered metapelite, chert and quartz-schist, non-crystalline silica with vesicular texture and cryptocrystalline aggregates of limonite, leucoxene and phyllosilicates. The fabric reflects a mixing procedure by which superposed layers of plant fibers and composed, pre-treated inorganic substrates were 'kneaded'. The final product is a low porous 'suspension-like' blend, where the coarser elements are floating into a profuse phyllosilicate matrix. The whole attributes of this material combine to create a resistant structure and an efficient system able to control the saturation and circulation of water through the chullpar walls. This mechanism might contribute to mitigate the degradative effects of water flow and humidity and concomitantly help in the preservation of the monuments. However, contrasts in the composition and structure of the building material were observed across the samples. This promotes a differential efficiency of the porous system which results in variations in the type and magnitude of the effects of degradative processes for each chullpar . & COPY; 2023 Consiglio Nazionale delle Ricerche (CNR). Published by Elsevier Masson SAS. All rights reserved.