The History of Concrete

University Degree Architecture, Building and Planning

THE HISTORY OF CONCRETE

Concrete has been used in construction for over 2000 years. The Romans used it for their Roadways & Aqueducts. The Romans used a primitive mix for their Concrete. Mortar consisted of small gravel & coarse sand mixed together with hot lime and water. To reduce shrinkage horsehair was used, much like we use polypropylene fibres today. They even added animal’s blood to created small air bubbles in the concrete, making the mix more durable. The Romans used concrete extensively; they built over 5000 miles of roads. This is more than the total length of interstate highways in America today.

Ancient roman concrete has withstood the attack by the elements for over 2000 years. The basic construction techniques of the Romans must be better than those of modern practice as judged by comparing the products.

Roman concrete consisted of just three parts: Hydrate Lime, pozzolan ash form nearby Volcano, and a few pieces of fist sized rock. If these parts were mixed together in the manner of modern concrete and placed in a structure, the result wouldn't pass the test of the ages.

One of the most significant ancient buildings was built by the Romans this Building is called the Pantheon in Rome it is a brick faced building that has withstood the ravages of weathering in near perfect condition. The purpose for the building was to honour the gods, it is said to humble the most brilliant of Engineers due to the fact it has no steel rods to counter the high tensile forces such as we need to hold modern concrete together. The building is circular in form it was designed to hold a fictional ball, and is 143 feet in diameter with a wall in the form of skirts dropping from its circumference. In the centre of the dome is a 19-foot opening held in place by a bronze backed by a brick ring integrated into concrete dome. The opening admitted sunlight to brighten the interior. The slightly curved marble floor provided drainage and the complex notches in the walls and ceiling tell only a few features of its meticulous design.

It has been studied that the Romans hand mixed there components (wet lime & volcanic ash) in mortar box with very little water to give a nearly dry composition; carried to the job site in baskets placing it over a previously prepared layer of rock pieces; and then proceeded to pound the mortar into the rock layer. We have proof that Vitruvius the noted Roman Architect (20 BC) mentioned this process in his history formulas for his concrete, plus the fact special tamping tools were used to build a cistern wall. This is important because close packing of the molecular structure by tamping reduced the need for excess water, which is a source of voids and weakness. But also close packing produces more bonding gel and might be normally expected. In America today the Bureau of Reclamation has built the Upper Still Water Dam using the same methods as Virtruvius with the hope of it lasting 2000 years?

Other famous buildings built by the Romans which are still standing using their methods of concreting are Appian Way, Roman Baths, The Coliseum and the Pont du gard aqueduct in South France.

The use of a primitive concrete can even be traced back to the Great Wall of China and this old man made structure is still standing and can be seen from the moon.

1200 - 1300 AD

The Middle Ages, the quality of cementing & concreting materials deteriorated. The use of burning lime and pozzolan (admixture) was lost, but reintroduced ...

This is a preview of the whole essay

Other famous buildings built by the Romans which are still standing using their methods of concreting are Appian Way, Roman Baths, The Coliseum and the Pont du gard aqueduct in South France.

The use of a primitive concrete can even be traced back to the Great Wall of China and this old man made structure is still standing and can be seen from the moon.

1200 - 1300 AD

The Middle Ages, the quality of cementing & concreting materials deteriorated. The use of burning lime and pozzolan (admixture) was lost, but reintroduced in the 1300's.

In 1824 Joseph Aspdin of England invented Portland Cement by burning finely ground chalk with finely divided clay in a LimeKiln until carbon dioxide was driven off. The sintered product was then ground and he called it Portland cement named after the high quality building stones quarried at Portland, England. In 1828 I.K. Brunel is credited with the first engineering application of Portland Cement, which was used to fill a breach in the Thames Tunnel.

In 1887 Henri Le Chatelier of France established oxide ratios to prepare the proper amount of lime to produce Portland cement. He named the components: Alite (tricalicium silicate), Belite (dicalcium silicate), and Celite (tetracalcium aluminoferrite). He proposed that hardening is caused by formation of crystalline products of the reaction between cement and water.

In 1889 the first reinforced bridge was built.

In 1890 the addition of gypsum when grinding the clinker to act as a retardant to the setting of concrete was introduced in the USA. Vertical shaft Kilns were replaced with rotary kilns and Ball Mills were used for grinding cement.

In 1891 George Bartholomew placed the first concrete street in the USA in Bellefontaine, OH. It still exists today.

In 1900 Basic cement tests were standardised.

In 1903 the first concrete high rise was built in Cincinnati, USA

In 1930 air-entraining agents were introduced to improve concrete’s resistance to freeze/ thaw damage.

In 1936 the first major concrete dams, Hoover dam and the Grand Coulee Dam, and were built.

In 1970 Fibre reinforcement in concrete was introduced.

In 1973 The Sydney Opera house in Australia was built, perhaps the most famous building in the world, the ditintive shell roofline owes much to UK engineers, Ove Arup & partners.

In 1975 The CN tower in Toronto, Canada, the tallest slip form building was constructed.

In 1977 The M40 Motorway Interchange was built which relied heavily on Concrete

In 1980 superplasticizers were introduced as admixtures.

In 1985 Silica Fume was introduced as a pozzolanic additive.

As we now know concrete has moved on

Concrete making has moved on from its earliest beginnings some 9000 years ago but the principle is still broadly the same – pieces of an inert hard material, such as gravel or crushed rock, together with sand to fill the gaps, are mixed with a paste of cement and cement and water. This hardens over time to bind it all together, producing an extremely durable solid mass.

Some of the first uses of concrete in the UK were influenced by the idea that it should resemble Portland Stone, but with the advances in construction techniques has come the realisation that concrete can be any shape and any colour.

The only thing restricting its appearance is the imagination of the designer, as moulds of the desired shape and texture can produce concrete, and modern pigments and paints can impact all colours of the rainbow.

The exploitation of concrete’s unique properties has resulted in some of the most exciting buildings as well as many striking and beautiful works of art.

The architectural advantages of using concrete are its strength and resistance to vandalism.

TYPES OF CEMENT

The main types of cements in use in the UK.

Portland cements:the predominant constituents in all portland cements are calcium silicates, formed by clinkering materials rich in calcium and silicon respectivley in specially designed kilns.

Ordinary Portland cement(OPC): this has a medium rate of hardening and is suitable for most types of work and so is the most widely used.

Rapid-hardening Portland cement(RHPC): this is similar in production as ordinary Portland cement but is ground more finely. This does not make it quick-setting and it remains workable for periods similar to concretes made with ordinary Portland cement.The finer grinding increases the rate of hydration at an early stage and this leads to the increased rate of hardening as implied by the name.The increased rate of heat evolution associated with this cement may also be useful when concreting in cold weather.

Ultra-rapid-hardening Portland cement: the grinding of this is even finer than either ordinary and rapid hardening Portland cements so it has an exceptional rate of hardening.

Sulphate-resisting Portland cement(SRPC): the permissable tricalcium aluminate (C3A) content of this cement is limited by BS 4027. In most respects this resembles ordinary Portland cement, except that it may be necessary for the concrete to contain less than a stipulated amount of cement if it is to resist sulphates to the required degree.

Low heat Portland cement(LHPC): this contains less tricalcium silicate and more dicalcium silicate than ordinary Portland cement. It hydrates more slowly and loses heat less rapidly. It is intended for use in massive constructions, where the rate of heat loss in ordinary Portland cement at an early stage might cause unwanted thermal stresses which might lead to cracking in the immature concrete.

White portland cement: this is used mostly where a coloured concrte is required for visual effect.It complies with BS 12 so it is suitable for all applications where ordinary Portland cement can be used. It is made from raw materials such as china caly and high grade chalk.

Blended Portland cements:Portland-blastfurnace cement:this is made the same way as ordinary Portland cement but with selected granulated blastfurnace slag added. The proportion of slag must not exceed 65% by weight. This cement evolves less heat and hardens more slowley than ordinary Portland cement.The resistance of this cement to sulphates is said to be intermediate between sulphate resistant cement and ordinary Portland cement.

Low heat Portland-blastfurnace cement: this cement has a reduced rate of hydration and heat evolution which is achieved by modifying the mineral comosition and adding slag similar in composition to that in Portland –blastfurnace cement.

Portland cements with additives: special additives are added to Portland cement to produce oil-well cements, hydrohobic cement and water-repellant cement.

Masonry cement: it is customary to add lime to mortar mixes in order to overcome the mixes lake of cohesiveness and the water retion desirability for laying bricks and blockwork. Ordinary mortar may also be to rigid.

ADDITIVES.

Additives are materials which are added to concrete during the mixing process. All portland cements contain at least one interground additive,gypsum without which it would be difficult to control the stiffening of a mix within a reasonable period of time. The low cost of many additives is offset by the problems associated with handling and dispensing the additive accurately at the concrete mixer. Adding to much is to be avoided because excessive doses have adverse effects on the properties of the concrete. Sometimes the benefits to be obtained by using an additive can more easily be obtained adjusting the other constituents of the mix. There are many sorts of additives on the market but the active materials in them are relatively few in number. The commonly used additives generally fall into four main categories; air-entrained agents, accelerators, retarders and water reducers. In each class there is generally just one widely used active material.

ACCELERATORS.

The most commonly used accelerator is calcium chloride. It is used either on its own or contained in a propiertary admixture. One serious drawback with calcium chloride is that it may lead to corrosion of embedded steel such as reinforcement and prestressing wires.It should never be used in prestressed concrete and should not normally be used in reinforced concrete.It should also not be used with sulphate resistant portland cement because the sulphate resistant properties are then impaired.

Accelerators should not be used in mortars because they can cause efflorescence and the quanity of cement in mortar joints is to small to protect it from frost by heat evolution.It may also lead to dampness in walls and accelerate the corrosion of wall ties.

Accelerators are sometimes called hardeners, anti-freezes, frostproofers and even waterproofers. Calcium chloride can be purchased in solid form and dissolved in water before being added to the concrete.

WATER-REDUCING ADITIVES.

Some surface active chemicals have the property of inducing a repelling force between cement particals and therefore act as dispersing agents of concrete. The dispersed particles require less water to lubricate them, so for a given workability a lower water content is required when used with these chemicals. These are sometimes know in the trade as densifiers, hardeners, water-proofers and plasticizers. The most frequently used raw material for water-reducing is calcium lignosulphnate, a by-product of the wood processing industry. The material is also know as sulphite lye or lignin in the trade. If 0.20% of the additive by weight of cement of the mix will, in a typical case, enable the water content to be reduced by10% without the loss of workability. This in turn allows the cement content of a mix to be reduced without loss of ultimate strength. However to ensure that there is sufficient durability, a minimum cement content may be specified.

AIR-ENTRAINING ADDITIVES.

Peter Irwin Page