History - Evolution

Cement and concrete although two different products, are not really distinguished in the mind of the ordinary consumer, who practically knows the end product, which is concrete. Their historic evolution therefore is parallel. The existence of an artificial solid material derived from the mixing of natural raw materials with binding mortars and water to become a solid body, which has now evolved to the concrete of today, has a background of 9000 years.

What is considered today to be the oldest concrete dates back to 7000 BC and is located in south Galilee, Yiftah El, in Israel. It was discovered in 1985 while opening a street and forms a kind of floor. It is made of a mixture of lime with stones. Lime when mixed with water and sand forms a kind of slime - mortar which in contact with the carbon dioxide of the atmosphere becomes stiffer and forms a solid compound. If this mortar is mixed with stones, it bonds-sticks together the stones and forms a type of concrete.

Another old concrete finding exists in the shores of Danube in Lepenski Vir in Yugoslavia and dates back to 5600 BC. It constitutes the ground of a prehistoric hut.

In the big pyramid in Giza, Egypt (2500 BC), the stones used are interconnected via a certain type of mortar made of lime or gypsum. In the same country, in ancient Thebes, there is a fresco which depicts the works for the preparation of a lime mortar and the application of this material.

This mastery of building seems to have been transferred to ancient Greece as well, where various mixtures of lime were used for construction and for coating bricks made of clay and dried out in the sun.

The Roman architect-writer Vitruvius is considered to be an important information source concerning the ancient Greek architecture and masonry. He uses the Greek word “emplekton” to describe a material, precedent of today's concrete, consisting of a binding mortar in which small pieces of stone are mixed. In his manuscripts traced down to the first pre-Christian years (around 13 BC) and discovered in a Swiss convent in 1414, he included instructions to architects for the preparation of a mortar that sets in open air as well as submersed in water. It is well known that mortars consisting of lime and water in order to set and harden need to remain in the open (aerated mortars) for the chemical reaction of lime with the carbon dioxide of the atmosphere to take place. Ancient Greeks were probably the first to use hydraulic mortars, in other words, mortars which when mixed with water can set and harden in the air as well as into the water. It is therefore self-evident that mortars and concrete produced with hydraulic mortars have a much higher degree of durability against constant environmental impacts. Such hydraulic mortars were used by ancient Greeks of which the main ones are:
  • A blend of lime and volcanic earth from the island of Thira or Nisiros in Greece or from Dikearchia (Pozzuoli) in the Greek colony in Italy, close to Napoli. This blend has the ability to set and harden into water (hydraulic mortar) not dissolving as lime mortars do. In that sense, the blend of lime and volcanic earth is very relevant to cement and could be considered as a precedent of contemporary cement.(Today, Portland cement with the addition of pozzolana is being produced and widely used, the so-called pozzolanic portland cement). It appears that a blend of this type was used to construct a waterproof tank of 600 m3 capacity in the temple of Athena in ancient Kamiros in Rhodos island and in the port of Piraeus (Zea). In addition, blends of lime, milled volcanic earth and marble powder were extensively used in the construction of plasters, special coatings to form painting surfaces (stucco), but also for “bonding of broken marble pieces” (ancient temple of Artemis). These materials are mentioned by the ancient authors Theophrastus, Stravon and Vitruvius and also by contemporary researchers (Tassios, Banteca, Haegerman Botticher, Bullard, Efstathiadis, Wilski and others).
  • Milled clay tiles with lime mainly in maritime constructions (Delos, Rhodos villa of Hellenistic period).
  • Various other materials, like ashes (Kortys in Arcadia), iron waste (Athens Agora), lead oxide (Lavrio).
It seems that Romans obtained this knowledge probably from the Greeks populating the Greek colonies in Italy, and as early as 300 BC significantly developed it regarding either lime mortars (aerated mortars) or the use of the lime and volcanic earth blend (hydraulic mortars). Volcanic earth was taken from the village Pozzuoli close to Vesuvius. This village gave the name «pozzolana» to volcanic materials, but also to artificial ones with the same approximate properties (several fly ashes – silicate fume), widely used today (Pozzolanic cements – pozzolanic chemical reaction). One of the first important works of Romans is the ancient theater of Pompeii accommodating 20.000 spectators (75 BC). A number of admirable works both from technical and architectural perspective follow: Coliseum (82 BC), Pantheon (123 BC) and several water reservoirs, for example the one in the city of Nimes in France (150 AD).

It is also well known that Romans used to add sometimes various materials to “concrete” to improve its properties and these materials can be considered as “forerunners” of the chemical additives used today. For instance, they used blood whose action is similar to that of air entraining agents (materials importing air into concrete, aiming to improve its resistance to frost and increase its workability).

Of interest is also the addition of horse hair during the mixing process, “forerunner” of the plastic and steel fibers used today (fiber reinforced concrete). A similar material was also used for the construction of the cavities and arches of Aghia Sofia, around 540 AD.

No development exists during the medieval period. Bringing Vitruvious’ manuscripts to light in 1414 AD though, warmed up the interest to concrete and a few years later, in 1500 pozzolanic mortar is used for the footings of Notre Dame in Paris, that being the first verified use of concrete in the new era.

The first essential step for the development of cement in the form it is used today could be attributed to the British engineer John Smeaton in the middle of the 18th century. The engineer had undertaken the construction of a lighthouse close to Plymouth, previously made of wood which had been destroyed twice, the first time from fire and the second from a storm. It had been evident that the lighthouse would have to be constructed with stones but the vicinity with sea and the slow setting and hardening of the lime mortars did not allow a safe construction. Smeaton started investigating the various materials and came to the conclusion that lime mortars made of lime produced from the burning of limestone containing clay (i.e. silica and alumina) could set both in the air as well as –more importantly – into the water. This observation is considered to be the first essential step for the production of cement in the form in which it is produced today. Similar developments during that period come from France and are attributed to Vicat and Lesage. Several other “inventions” will follow respectively patented, such as the “Roman cement” of the parish priest James Parker. The most systematic preparation of cement is attributed to the English engineer Joseph Aspdin who gave the material (for which he obtained a patent) the name used today, “Portland cement”. This name was given because the color of hardened cement was very similar to the color of the rocks in Portland. Today (in the installations of a British Cement Industry) one of the stone kilns used by Aspdin’s son William, for the production of cement is still preserved.

Since that time, cement production spread all over the world and continuously evolved, to reach the current development stage.

At the same time the development of concrete continued and the first construction of the first bridge from unreinforced concrete is reported in France (1816) and in 1818 the British engineer Ralph Dodd obtained a patent for the placement of forged iron bars into concrete. Thus the concept of reinforcement of concrete is introduced and soon broadened with the use of steel beams with concrete for the construction of floors (Francois Corgnet, 1855) and steel wire for the enforcement of concrete pots (Joseph Monier, 1850-1861), which constitutes the more advanced form of reinforced concrete until then. In 1902 August Rerrert built in Paris a block of flats using a “reinforced concrete system” as he called it. This was the first building with bearing structure of columns, beams and slabs without bearing walls.

The evolution of technology has been impressive in what regards the construction building systems, with the use of higher steel qualities, prestressing systems, fiber reinforcement and in what regards concrete, through the evolution of the production process and quality control and the use of improving chemical additives.

Today the annual quantity of cement produced worldwide is app. 3,0 b tons and that of concrete app. 10 b m3 making cement and concrete the most important structural materials of our era.

Today concrete with compressive strength exceeding 200 MPa is produced as well as concrete with predetermined properties (low strength, high durability, self-compacting, absorbing NOx for ambient improvement).