Scientists from the University of Granada (UGR) managed to unlock the secret of the ancient Mayan builders, who produced extraordinarily durable lime mortars and plasters, which have survived to this day in excellent condition: they include floor extracts. His work is published today in the scientific journal advances in science.
Researchers analyzed the materials used in the construction of the Mayan archaeological site of Copán, located in western Honduras, 14 kilometers from the border with Guatemala, whose ruins were declared Archaeological Heritage of Humanity by UNESCO in 1980. Ancestors The Mayan Indians built this city between o 4th and 9th centuries on a narrow strip of land that separates the Caribbean from the Pacific.
The Mayan constructions are currently in an excellent state of conservation.
Carlos Rodríguez, Professor of Mineralogy and Petrology at the UGR
“Until now, it was not known what was the secret by which the monuments erected by the ancient Mayan builders, in many cases, currently present an excellent state of conservation, even though they have been exposed to a tropical climate for more than a thousand years. very aggressive”, explains the main author of this work, the professor of the Department of Mineralogy and Petrology of the UGR Carlos Rodríguez.
Using high-resolution analysis techniques such as transmission electron microscopy (TEM) and high-resolution X-ray diffraction using synchrotron radiation, the research group showed that ancient lime mortars and stuccos from the Mayan archaeological site of Copan include organic compounds and have a cement of calcite crystals (CaCO3) with nano and mesostructural characteristics (structure of said crystals from atomic and molecular to micrometric scale) similar to those of calcite biominerals (for example, bivalve shells).
The builders of Copan inherited the Mayan architectural tradition, the civilization from which they descend.
The researchers wanted to prove in this work that organic compounds in lime mortars could play a hardening role similar to that of (bio)macromolecules in calcite biominerals (which have much greater mechanical resistance than purely inorganic calcite), following the indications of builders Copan sites that inherited the building tradition of the ancient Mayan civilization from which they descended.
“For this, we prepared replicas of lime mortars dosed with extracts rich in polysaccharides from the bark of trees common in the Mayan area, such as chukum (Havardia albicans) and jiote (Bursera simaruba)”, explains Rodríguez. “Our analytical results show that the replicas have similar characteristics to ancient Mayan mortars and stuccos that contain organic compounds,” he adds.
“Like the biominerals, both the historic Mayan mortars and the replicas present a calcite cement that includes intercrystalline and intracrystalline organic compounds (polysaccharides) that give the matrix mortar a marked plastic behavior and greater tenacity and resistance to breakage, at the same time that it increase resistance to chemical alteration, as they reduce the speed of dissolution”, highlights the professor.
The replicas have similar characteristics to ancient Mayan mortars and stuccos that contain organic compounds.
Taken together, these effects, similar to those that allow calcite in mollusc shells or sea urchin spines to be enormously resistant, made the mortars and stucco used in the buildings of the ancient Maya civilization survive until the present day. in excellent condition.
Apparently, the lime technology developed by the ancient Maya and probably other ancient civilizations using natural organic additives to prepare lime mortars and plasters accidentally explored a biomimetic (i.e. mimicking nature) route to improve lime performance. the binders of these lime-based materials.
“The use of plant extracts today can help us to develop new mortars, plasters and plasters based on lime that are optimized and compatible for the preservation of historical-artistic heritage and modern and sustainable construction”, comments the researcher.
“Our results pave the way for the design of new lime-based biomimetic binders that include natural or synthetic organic compounds with specific functionalities, or with known hardening effects, such as the organic compounds present in calcitic biominerals”, he concludes.
Rodríguez-Navarro, C. et al. “Revealing the secret of ancient Mayan masons: biomimetic lime plasters with plant extracts”. advances in science (2023)