||HISTORY OF CEMENT AND CONCRETE
The first prehistorical findings
Concrete in its broader sense, i.e. as a material made by man through the use of a binder in the mass of which other natural materials are being added and bonded together to form a new solid material, has a background of 7000 years.
What is today considered to be the oldest concrete dates back in 7000 BC and is located in south Galilee , Yiftah El, in Israel . It was discovered in 1985 when a bulldozer was opening a street and forms a kind of floor. It is made of a mixture of lime with stones. Lime when combined with water and sand forms a «slime» - mortar which coming into contact with the carbon dioxide of the atmosphere becomes more stiff and renders 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 prehistorical hut.
The first historical steps
In the big pyramid in Giza , Egypt (2500 BC) the cobble stones which were used are connected to each other through a certain type of mortar from lime or gypsum. In the same country, in ancient Thebes , there is a fresco which depicts the preparation works for a lime mortar and the construction works with this material.
This mastery of building seems to have been transported to ancient Greece as well, where various mixtures of lime were used for construction and for coating bricks made out of clay and dried out in the sun (500 BC, Krissos and Attalos' Palaces).
The Roman author Vitruvius is considered to be an important information source concerning the ancient Greek architecture and constructing technique. He uses the Greek word «emplekton» to describe a forerunner of today's concrete, a material made out of a binding mortar in which small pieces of stone are mixed.
All mortars consisting of lime and water in order to set and harden, need to remain on the air (aerated mortars) so that the chemical reaction of lime with the carbon dioxide of the atmosphere takes place. Ancient Greeks were probably the first to use hydraulic mortars, in other words, mortars which when mixed with water can set and harden both in the air and inside water. Therefore it is self-evident that mortars and concrete produced with hydraulic mortars have much higher durability against adverse environmental impacts. Such hydraulic mortars were being used by ancient Greeks and the main ones are:
A blend of lime and volcanic soil from the island of Thira
or Nisiros in Greece or from Dikearchia (Pozuoli) in the Greek colony
in Italy, close to Napoli. This blend has the ability to set and
to harden within water (hydraulic mortar) and is not dissolved by
water like lime mortars. Taking this into consideration, the blend
of lime and volcanic soil is very relevant to cement and could be
considered as a «forerunner» of contemporary cement.(Today,
Portland cement with the addition of pozzolana is being produced
and widely used, the so-called pozzolanic portland cement). This
type of blend was used to construct a waterproof tank of 600 m3
capacity in the temple of Athena in ancient Kamiros in Rodos island
and in the port of Piraeus (Zea).In addition, blends of lime, crumbed
volcanic soil and marble powder were extensively used in the construction
of plasters, special coatings to form a surface for painting as
well as for the «welding of broken marble pieces» (ancient
temple of Artemida).
- A blend of lime and volcanic soil from the island of Thira or Nisiros in Greece or from Dikearchia (Pozuoli) in the Greek colony in Italy , close to Napoli . This blend has the ability to set and to harden within water (hydraulic mortar) and is not dissolved by water like lime mortars. Taking this into consideration, the blend of lime and volcanic soil is very relevant to cement and could be considered as a «forerunner» of contemporary cement.(Today, Portland cement with the addition of pozzolana is being produced and widely used, the so-called pozzolanic portland cement). This type of blend was used to construct a waterproof tank of 600 m3 capacity in the temple of Athena in ancient Kamiros in Rodos island and in the port of Piraeus (Zea). In addition, blends of lime, crumbed volcanic soil and marble powder were extensively used in the construction of plasters, special coatings to form a surface for painting as well as for the «welding of broken marble pieces» (ancient temple of Artemida ).
- These materials are being mentioned by the ancient authors Theofrastos, Stravon and Vitruvius and also by contemporary researchers (Tasios, Banteka, Haegeman Botticher, Bulard, Efstathiadis, Wilski and others).
- Crumbed tiles or bricks with lime mainly in sea constructions (Dilos, Rodos villa of Hellenistic period).
- Various other materials, like ashes (Kortis in Arkadia prefecture), iron waste ( Athens market), lead oxide (Lavrio).
It seems that Romans from 300 BC got this knowledge probably from the Greeks residing in the Greek colonies in Italy, and developed it to a great extent both towards lime mortars (aerated mortars) as well as towards the use of a mixture of lime and volcanic soil (hydraulic mortars). Volcanic soil was being supplied from the village Pozzuoli close to Vesuvius. This village gave the name «pozzolan» to volcanic materials but also to technical materials with approximately the same properties (several fly ashes – silicate material finer than 70 µ ) which are widely used today (Pozzolanic cement – pozzolanic chemical reaction). One of the first important works of Romans is the ancient theater of Pompeii accommodating 20000 spectators (in 75 BC). Numerous works which are admirable from both technical and architectural perspective, follow, like Coliseum (82 BC), Pantheon (123 BC) and several water reservoirs, like the one in the city of Nimes in France (150 AD).
Worth mentioning is the written text which describes the preparation of this ancient cement and belongs to Vitruvius in 13 BC. In the text, directions are given to architects for the preparation of a mortar which «sets both in the air and in water».
It is also well known that Romans used to add sometimes various materials to «concrete» to improve its properties. These materials can be considered as «forerunners» of the «chemical additives» used today. For instance, they used blood the action of which is similar to the one of air entraining agents (materials which import air into concrete aiming to improve its resistance to frost action and to increase its workability).
Of interest is the addition of horse hair during the mixing process, «forerunner» material of the plastic and steel fibers used today (fiber reinforced concrete).
In medieval times there is no development.
The first fundamental step for the creation of cement in the form it is used today could be attributed to the english engineer John Smeaton in the middle of 1700 's AD. To this engineer was assigned the construction of a lighthouse close to Plymouth, which had previously made out of wood and had been destroyed twice, initially from fire and then from a storm. It became evident that the lighthouse should be constructed with stones but the small distance from the sea and the delay of 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 with lime which has been produced from the burning of limestone containing clay (silica and alumina) could set both in the air as well as –more importantly - in 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 of that period refer to France and are attributed to Vicat and Lesage. There also exist other «inventions» with respective patent diplomas, like 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 to the material (and obtained a patent diploma) the name which is also used today, « Portland cement». This name was given because the color of hardened cement was very similar to the color of rocks in Portland . Today (in the installations of a British Cement Industry) one of the stone kilns which was used by William, Aspdin's son, to produce cement is still preserved.
Since then, cement production spread throughout the world and continuously evolved so as to reach the contemporary development stage.
Today more than 1,5 b. tons of cement are annually produced worldwide, and the concrete which is produced from the cement exceeds 10 b. tons making cement and concrete one of the most important structural materials of our era. This has been accomplished following a number of significant developments having taken place within the last 80-100 years. The major ones are the combination of steel with concrete to form reinforced concrete capable to undertake tensile stresses, the introduction of pre-stressing steels, the use of fibers, non-metallic reinforcement, chemical admixtures (especially the high-range water reducers-superplasticizers) and very fine materials (pozolans).
Today concrete can be produced with compressive strength exceeding 200 Mpa. Furthermore, it is feasible to produce concrete with predetermined properties (low strength, high durability, self-compacting, absorbing NOx from the atmosphere).