Producion of concrete

The concrete

Concrete production

Concrete is an artificial conglomerate consisting of a mixture of binder, water and aggregates (sand and gravel) and with the addition, as required, additives and / or added minerals that affect the physical or chemical characteristics of the concrete is fresh hardened.

Currently, the binder used to manufacture concrete and cement, but in the past have been made ??using concrete with different binders such as lime or hydraulic.
Rarely was also used chalk to make concrete "poor."
The fresh concrete is cast in the formwork and compacted with vibrators, but there are those modern formulations of self-compacting concrete (SCC) that do not require constipation.
The cement hydration with water, get a grip and give the mixture hardens strong enough to make it comparable to a rock.
Today it is used for making structural parts of a building and is the most widely used building material in the world

 

The concrete
Superficie del calcestruzzo
Surface of the concrete
Calcestruzzo fresco
  Frech concrete
General characteristics
Composition Conglomerate consists mainly of a binder, water and aggregates
Aspect dull gray
State of aggregation (of c.s.) solid
Physical and chemical properties
Density (g/cm3, of c.s.) 2,4
Porosity 0÷40% by volume

 

 

THE HISTORY OF CONCRETE

History of Concrete
The invention of concrete and its improvements over time
Recognized the great value to the concrete by its first users was the ability to obtain any form of artificial rocks.
It is difficult to clearly identify the origins of the technique of building in concrete, because it seems that already the Assyrians and the Egyptians to realize buildings using small material. The Greeks knew this technique, having used for the construction of the aqueduct of Argos, of Sparta Tank and other buildings of which still remains a trace.
But the Romans were to give great impetus, using it to build a considerable number of works still in good condition. The Romans employed in the concrete construction of roads, building foundations and retaining walls. The techniques incertum opus, the opus reticulatum and opus caementicium are described by Vitruvius in his De Architectura. The opus caementicium consisted in raising walls depositing layers of mortar and aggregates. The external facings of brick or hewn stone, which served as permanent formwork, were quickly filled with mortar, in which were embedded scrap of stone or brick.
The invention of the binder is not Roman, as it can be traced back to the third millennium BC, when Egypt was used malta plaster wall hangings for the construction of blocks of stone. As long as the binder of the mortar was made up only of lime, hardening of the concrete was done very slowly, because the progressive consolidation of a lime-based mortar is caused by reaction of calcium hydroxide with carbon dioxide present in 'air with the subsequent production of calcium carbonate. Since almost no possibility of contact between the inner opus caementicium hydrated lime and carbon dioxide in the air, the reaction occurred very slowly with low resistance end products. In some ancient masonry buildings, concrete made with lime-based binder have been found, even after several centuries, significant amounts of lime not yet transformed into calcium carbonate and not yet hardened.
The opus caementicium was brought to the highest degree of perfection from the first century BC when the sand forming the mortar was replaced in part or in whole by pozzolan (pulvis Puteolana) or earthenware. The discovery of pozzolana marked a revolution in the construction of masonry work. For he says in Book II of Vitruvius' De Architectura that the Bay of pozzolan or vigorous Cuma is not only every kind of construction but particularly those who are at sea underwater. Thanks to the behavior of pozzolan pozzolanic concrete and earthenware was made and hardened, even in water without the need of contact with air, allowing the production of high-strength mortars and rapid hardening.
With the fall of the Roman Empire began, especially away from Rome, an inexorable decline in the quality of buildings and how to make concrete as the Romans did was forgotten because it was abandoned the use of pozzolan. This decline continued throughout the Middle Ages. During the Middle Ages was gradually forgotten concrete technology in favor of more simple construction methods, the ligand by replacing cement with lime.
With the awakening of the humanities, especially after the fourteenth century, and rilessero translated Latin texts of Pliny the Elder and Vitruvius. It is the 1511 edition of the De Architectura edited by a Dominican, John Monsignors (Fra 'Giocondo). This followed numerous other translations, which helped to clarify the secret of making more concrete according to the Romans. Thus, especially in eighteenth-century France, he rediscovered the art of well-built concrete structures.
In this continuous approach to today's cement concrete, there was the revolutionary discovery of hydraulic lime by the British engineer John Smeaton. These, in the realization of the Eddystone lighthouse used, instead of mixing lime - pozzolana, the first hydraulic lime obtained by him from firing limestone containing a fair amount (about 11%) of clay impurities.
The discovery of hydraulic lime concrete marks the shift from Roman to modern, as investigators, especially with the help of the new science of chemistry with Lavoisier newborn are capable of governing a new process of synthesis that will lead to the first artificial hydraulic lime and later to modern Portland cement. In fact, once discovered that the impurities of silica and alumina present in the clay of course some accompanying limestones, are responsible for the formation of silicates and calcium aluminates capable of hardening under water, they began firing trials in artificial mixtures of limestone and clay at a temperature higher and higher until you reach a rudimentary scarification of the final product.
Especially in England and France, between the late eighteenth and early nineteenth century, flourished inventions, patents and industrial initiatives that led to the production of the first industrial hydraulic binders, called cements. In particular, in 1796 Parker manufactures the first quick-setting cement (cement or concrete roman Parker), cooking in his lime kilns contained in the concretions marly clays of the Thames, while Lesage in 1800 obtained a material highly resistant hydraulic calcining limestone pebbles of Boulogne sur Mer
In general the watershed that marks the transition between the hydraulic lime and Portland cement of Smeaton made is fixed to 1818, the date on which the engineer defines the Vicat formula of artificial hydraulic lime.
The first industrial building to have slow-setting hydraulic cement seems to have been, in 1824, a kilnmen of York, Joseph Aspidin, who gave the name to the product of Portland cement, because of the similarity between Malta and the conglomerate formed with the Compact concrete with a limestone island of Portland in England.
In 1844 J.C. Johnson emphasized the importance of high-temperature cooking processes that led to the formation of clinker, the final product of the proceedings. In fact, while the firing of hydraulic lime you require from 600 to 700 ° C, we must reach 1600 ° C and more to get the slow-setting cements, as a principle of vitrification should occur.
In 1860 M. Chatelier established the chemical composition of the concrete allowing the industrialized production of concrete.

The invention of reinforced concrete
The widespread use of concrete, however, has had with the advent of reinforced concrete. In fact, the compound has excellent compressive strength but poor tensile strength and this has limited use for decades.
The date of birth of the reinforced concrete is difficult to detect, but it is certainly in the nineteenth century, thanks to the industrial revolution that led to an outstanding production of the two constituent materials: steel and concrete, which has had its large-scale deployment.
From a strictly technical point of view, the idea of ??using iron as a material tensile strength in combination with other materials resistant to compression, such as stone, can be found already in the seventeenth and eighteenth centuries in France. Examples of this combination are the East Colonnade of the Louvre designed by Perrault and the portico of the church of Saint Genevieve in Paris created by Rondelet. The obvious difficulties inherent in the union of steel and stone have limited the use of such technology to a few works of particular interest and commitment. The idea of ??static, however, subsequently found practical implementation when it is combined with the steel to a plastic material which is concrete. Already in the late eighteenth century, the principle is described and tested by many manufacturers such as Loriot, Fleuret, and Raucourt de Charleville. However, only since 1845, with the beginning of the industrial production of cement artificial attempts become more important.
In 1847 he designed the first cover Coignet concrete formwork and cast in concrete with profiled irons. Also in 1847 J.L. Lambot designing a boat whose hull is obtained by casting a thin shell of concrete on a mesh of flat irons. The hull is exposed at the Universal Exposition in Paris in 1855.
The key idea of ??the concrete: the role assigned to the reinforcement theory of elements in a beam subject to bending to be done anyway back to the patent of November 3, 1877 by Joseph Monier, a gardener at the Orangerie at Versailles. With the insole Monier, Monier system states in Europe at the turn of the century. The Monier system, however, is not based on any theory or experimental approach. Only in 1886 the first theoretical analysis - systematic experiments on reinforced concrete structures were published by Ing. Matthias Koenen on a German technical magazine. The following year, and Mr. Koenen. G.A. Wayss finished the writing Das System Monier, the first publication on the theory of reinforced concrete structures.
In the early years of the use of reinforced concrete reality, the leadership was taken over in its commercial development, especially in Germany and Austria, the company Wayss and Freytag with the Monier system. This situation remained unchanged from 1892 when they began an apprentice bricklayer in Paris, François Hennebique. In 1892, fifty years, Hennebique Hennebique patented system, which collected the main ideas of the author, selected in its years of operation. In this system, the beam was reinforced with iron rods on the lower face streamers and some of them, in the vicinity of the supports were raised to cope with the inevitable setbacks. But the most salient feature of the system was the presence of iron plates shaped to U, who are willing to connect with the concrete in compression reinforcement taut, had the function of brackets, designed to absorb the shear efforts. With these features the patent Hennebique best summarized the findings of the previous twenty years of activity in the field. On its patent Hennebique built a business empire and in 1896 he founded the magazine Le Beton Arme, which were published informative articles on high scientific content.
As a result of problems arising from the construction of artifacts built for the Exposition Universelle of 1900, the Commission developed the Concrete Ministerial Circular of 20 October 1906. Institutions with Ministerial material was removed so the control of the holders of patents, and was then made available to every entrepreneur.

The modern era
A strong evolution of the quality of the concrete has taken place with the transition from concrete to assay in which the designer showed quantitatively the main features of the mixture to guarantee a predetermined Rck (m3 of sand, gravel m3, kg, type and strength class cement) to concrete resistance in which the designer showed only the class of concrete strength (Rck).
Recently it comes to concrete performance [4], as it is necessary to ensure the concrete is also a suitable durability and workability.
In this case, the designer must specify in addition to the class of concrete strength and also the consistency of exposure, and the maximum nominal size of aggregate.
As will be seen as a result of these classes are limit values ??of the main components of the mixture.
This evolution has occurred with the transition from concrete prepared on site, where workers had limited staff to enter into the mixer components of the mixture in the proportions shown in the design documents, to the pre-industrially produced at concrete batching plants, which appropriately dosing the mixture a cycle of production certificate, which will include testing of samples hardened, guaranteeing a product that meets hi-tech classes of concrete required by the designer.
The quality of the mix has evolved following the introduction of additions and additives, they affect behavior and performance of the mixtures.
Today they are produced in the factory also manufactures finished goods (prefabricated), also prestressed, such as beams and slabs for the construction of brick and concrete floors.

 

The products