The ancient Mayas built thousands of cities throughout their 125,000 square mile realm. Ruins of huge Maya cities have been dated back to 300-400 BCE. No doubt smaller cities were being built centuries before, but the fragile wood and thatch building materials degraded over time. By the Late Preclassic Period (400 BCE—250 CE) the technology for building stone structures had been perfected. This technology created tall pyramids, expansive palaces that reached five stories, and complex residences with interlocking passages and plazas. These strong and durable structures were able to withstand 3,000 years of harsh environment, earthquakes, and hurricanes. Even the encroachment of jungle roots and vines since the great cities were abandoned around 1,000 CE could not bring down most of these buildings. Hundreds of high-rise Maya cities remain standing today; a tribute to their building technology.
What substance was strong enough to “glue” the building stones together for so many centuries? The answer is found in Maya cement. Maya technicians invented a method for producing hydraulic cement from native limestone before 250 BCE. How they discovered this process is a mystery, since it requires extremely high temperatures in a type of “blast furnace” to convert limestone into cement. Archeologists surmise they used trial-and-error over many years, perhaps a millennium, to get the formula right. We can imagine ancient Mayas watching a huge conflagration from lightning strikes in forests, or set off by volcanic flow or cinders, that created super-heated fire. After the burning was reduced to coals and ashes, they saw peculiar round globules sitting on top, where before there were chunks of limestone. As rain moistened the globules, they puffed up into a grey-white powder. Curious, the Maya collected the powder and started experimenting with its properties. After mixing it with pebbles or clay or other substances, and adding water, they found that it made a very hard, durable bonding material. Claro que si! Cement was converted to concrete.
Maya cement was used for making cast-in-place concrete, the “glue” that held together their stone buildings and the base material for stucco that coated Maya structures, roads, cisterns, and plazas.
Hydraulic cement – the Mayas made true hydraulic cement, first used by the Romans. This cement reacts with water to form silicate hydrate crystals; these grow and interlock creating a bond between aggregate mixtures (pebbles, ground limestone, clay) to produce hard, durable construction material called concrete. The cement paste glues together the aggregate mixture, fills voids, and increases strength as it stiffens, called “setting up.” As the concrete hardens, it continues increasing in strength and durability. Maya cement is similar in chemical makeup to modern Portland cement, which is the current standard.
Maya cement kiln – the Maya cement firing kiln has similar thermodynamic and chemical properties to a blast furnace. Calcium is the essential chemical component for cement, and the Mayas had an abundant supply of limestone. When heated to 1450-1600 degrees C (2642-2912 F) the limestone melts, inducing a chemical reaction to form calcium silicate. These take the shape of globules called “clinkers.” Wood was the Maya fuel source, and generally it does not produce high enough temperatures, normally
reaching 300-400 degrees C (572-752 F). Learning that a higher temperature was needed, the Mayas invented a kiln. They stacked wood in a circular design set on an elevated platform of spaced rocks. The center of the circle was left open. The kiln diameter was around 6 meters (19.7 feet) across and 2 meters (6.6 ft) height. Logs were stacked horizontally in a radial pattern, larger logs filled in with smaller ones and chinked solid with chipped wood. A vertical shaft was left open up the center, 8 inches diameter, extending from ground level to the top of the pile. To keep the kiln burning the required 24-30 hours, the wood had to contain enough moisture. It was either green wood or it was moistened with water. Readily combustible material such as dry leaves and dry decayed or resinous wood was put at the shaft base to ignite the kiln.
Raw limestone was cut into small blocks and stacked on top of the wood pile, to a height of 0.75 meters (2.5 ft.). The dry tinder was set afire, and its rapid burning sucked in cool, oxygen-rich outside air through the elevated base of the platform. As this air entered it increased the temperature in the center core while reducing ambient pressure. In turn, the reduced pressure induced a rapid flow of cooler, oxygen-rich air which then increased the temperature even more. This super-heated air was exhausted upward into the limestone, in a chimney-like effect. This cycle kept raising temperature and burning the stacked wood at temperatures that reached 1600 C (2912 F). When the kiln was at peak operation, a narrow tongue of flame soared skyward to a height of 30 meters (98.4 ft.). As heat increased, the flame color changed from red to orange, then yellow and finally to blue, which indicates 1600 C.
When the burn was complete, a collection of clinkers sat upon a pile of cinders. These were allowed to cool. Exposure to dew and rain caused the clinkers to expand into a dome of fluffy grey-white powder, 5-6 times the bulk of the limestone. This powder was hydraulic cement, and could be ground finer as needed. The cement was combined with the aggregate mixture and water to make cast-in-place concrete: one part cement, 3 parts loosely ground limestone or other aggregate, and water. Five tons of wood were required to produce one ton of cement.
Weather conditions had to be just right to make cement: clear weather with zero chance of precipitation, and no wind. Wind would cause higher burn rates at the windward side leading to collapse of the kiln structure.
Rituals accompanied the kiln burning. Women were not permitted near the kiln during the burning, since the kiln, considered to be feminine, would become jealous and refuse to operate properly.
Studies have shown that Maya cement has almost the same chemical composition as Portland cement, meeting strict international standards for manufactured cement. Maya cast-in-place concrete has higher strength than needed by the loads superimposed on Maya structures. It has remarkable ability to resist severe environmental exposure. Its high compressive strength is greater than building materials of any other ancient American culture.
Conclusion: Maya cement is a true cement, a building material very similar to modern cement. Its properties produce concrete with a strong matrix, similar to modern concrete.
James A. O’Kon, PE. The Lost Secrets of Maya Technology. Career Press: New Page Books, Pompton Plains, NJ. 2012. In depth explanations of many types of Maya technological achievements, by an “archeoengineer” who spent 40 years investigating at over 50 remote Maya sites.