Introduction

Ancient civilizations that predated the Romans are often credited with early forms of concrete. However, their concrete was largely different from the modern version. This essay delves into the history of concrete, the ingredients used, and the formulas that enabled ancient builders to construct impressive structures.

Ingredients and Early Forms of Concrete

Before the Roman innovation, ancient builders primarily used mortar to bind stones, bricks, and tiles. Mortar basically consisted of two types of binder: lime and gypsum.

Lime Powder

Lime powder was a crucial component in early concrete. It was derived from heated materials such as sea shells, limestone, or marble. These materials were placed in a kiln, which decomposed them into calcium carbonate. The resulting white powder was then mixed with sand and water to form mortar. If no sand was added, the mixture would result in stucco.

Gypsum Mortar

Gypsum mortar was another early form of binder. It was first utilized in ancient Egypt and involved the use of gypsum to create a mortar that was similar to modern gypsum mortar.

Roman Innovation: Hydraulic Cement

The real revolution in concrete occurred during ancient Rome. The Romans or possibly the Etruscans discovered that adding pozzolana, a volcanic ash found near Naples, to lime could create a substance called concrete. This concrete was not only stronger but also more durable than previous types of mortar. It could bear the weight of buildings without the need for additional stones or bricks.

To make Roman concrete even more cost-effective, they added rough boulders inside wooden molds before pouring the liquid concrete. This method eliminated the need for skilled masons to trim stones, enabling faster construction.

The Secret of Concrete

The recipe for Roman concrete was lost during the Middle Ages and the Byzantine period. It wasn't until the 1840s that an analogous material called Portland cement was developed, bringing back the use of concrete. The development of this cement was closely tied to the widespread availability of fossil fuels.

The Evolution of Concrete

Tracing the evolution of concrete, we find that the oldest known recordings of concrete date back to 6500BC in the regions of Syria and Jordan, where the Nabataea traders used limestone dust, light sand, and water to create the beginnings of concrete. These structures included floors, housing, and underground cisterns.

The Roman Recipe

The Roman hydraulic cement was made from a mixture of equal parts of fired lime and pozzolana ash. To make concrete, this mixture was combined with an aggregate and about one-third water by volume. The mixture was then thoroughly mixed and poured into forms. After drying to the touch, it was left to cure for several days, becoming stronger with time, even under water conditions. It is imperative to note that concrete should not be mixed with salt water.

Conclusion

The ancient world's development of concrete marked a significant advancement in construction techniques. From simple lime-based mortars to the breakthrough of hydraulic concrete, these innovations enabled builders to create more durable and efficient structures. The legacy of these early forms of concrete still influences modern construction practices.