The Maya invention of hydraulic cement predated the patent for Portland cement in 19th century England by 1500 years. This enabled the construction of cast in-place concrete structures to build the Mayan great high-rise cities. This durable material allowed the structures to withstand the ravages of time and the environment. They resisted the forces of earthquakes, hurricanes, and prying jungle growth to enable their survival after 2000 years. The grand buildings towering over the rainforest, the infrastructure of the large cities, water reservoirs, paved roads and long span bridges were made possible through the use of cast in-place concrete in unique structures built by creative Maya engineers.
Mayan cement was produced using native materials in combination with an ingenious firing kiln process. The cement kiln was constructed of timber components. The top of the kiln supported the limestone raw material. The timber served as fuel to produce the high temperatures required for the chemical conversation of limestone into cement “clinkers.”
With their ingenious design of the cement kiln the Maya developed a thermodynamic reactor that emulated the modern blast furnace. The kiln assembly was configured in a circle of approximately ten meters in diameter; the height of the kiln was approximately four meters. A circular open shaft was located in the center of the kiln. The kiln assembly was elevated above the ground to permit the free flow of cool, oxygen-rich air from the exterior of the kiln into the low pressure of the open shaft, thus increasing the temperature. A windless day would be chosen for the burn and the kiln would burn for about 48 hours.
The fire was initiated at the bottom of the center shaft. Heated air from the fire flowed rapidly upward through the fire shaft. The heat of the fire and the upward movement of heated air created a negative pressure zone at the center of the kiln. This low-pressure zone drew large amounts of oxygen-rich fresh air from the exterior into the center. The inflow of oxygen-rich air increased the heat of combustion and increased the temperature of the air flowing upward in the vertical shaft. This cycle of superheated air interfaced with the limestone on the top to initiate the chemical process of conversion into cement. The temperatures developed by this Mayan blast furnace reached temperatures of 1400 to 1600 degrees Celsius. During this process, chemical change was induced and the limestone converted into cement clinkers. The process produced hydraulic cement. Hydraulic cement reacts with water to form calcium silicate hydrate crystals. The tentacle-like growth of these crystals, when mixed with water, creates an interlocking interface with aggregate to produce cast in place concrete.
Mayan engineers enhanced their concrete technology by improving the properties of their cast in concrete through the addition of admixtures to improve the quality of the concrete. These admixtures included latex and the juice of the morning glory vine.