A research group from the University of Granada has discovered the secret of the ancient Maya masons, who produced lime mortars and stuccoes of extraordinary durability: plasters with plant extracts.
Scientists analyzed the materials used to build the Maya site of Copán, in Honduras. The ruins of this Maya city built between the 4th and 9th centuries were declared World Heritage Site by UNESCO in 1980.
Despite the multiple studies carried out on these construction materials, “until now it was not known why the monuments built by the Mayans, in many cases, currently present an excellent state of conservation, in spite of having been exposed for more than a thousand years to a very aggressive tropical climate”, explains the main author of this work and professor of the Department of Mineralogy and Petrology at the UGR, Carlos Rodríguez Navarro.
Now, these materials have been analyzed with high resolution analysis techniques such as transmission electron microscopy and X-rays diffraction, at the MSPD beamline of ALBA. Synchrotron X-rays enabled to know exactly the chemical composition and structure of the materials. It has been discovered that ancient lime mortars and stuccoes include organic compounds and have a calcite crystals cement (CaCO3) with meso-to-nanostructural features matching those of calcite biominerals (for example, shells). That fact allowed the Maya masons from Copán to obtain materials with such high performance.
Researchers wanted to prove that organic compounds in lime mortars could play a hardening role similar to that of (bio)macromolecules in calcite biominerals (which have much higher mechanical strength than purely inorganic calcite), following the advice of current local masons from Copán that have inherited the construction tradition of the ancient Maya civilization from which they descend.
“To do this, we prepared replicas of lime mortars dosed with extracts rich in polysaccharides from the bark of common trees in that Maya area, such as chukum (Havardia albicans) and jiote (Bursera simaruba) -explains Rodríguez Navarro-. Our analytical results demonstrate that the replicas have similar features to those of ancient Maya mortars and stuccoes containing organic compounds. In addition, we have shown that, as in biominerals, both the historical Maya mortars and the replicas present a calcite cement that includes intercrystalline and intracrystalline organic compounds (polysaccharides) that impart to the mortar matrix a marked plastic behavior and a greater toughness and resistance to breakage, while increasing its resistance to chemical alteration, since they reduce its dissolution rate”.
Read more on the ALBA website
Image: Maya site of Copán (Honduras). The ruins where the “Rosalila” structure is located, the best example of a complete classical temple in the Mayan area, is decorated with pink lime plaster and stucco masks.