To make cement, the Nabataea located the deposits and scooped up this material and combined it with lime, then heated it in the same kilns they used to make their pottery, since the target temperatures lay within the same range.
By about BC along the Danube River in the area of the former country of Yugoslavia, homes were built using a type of concrete for floors. Around BC, the ancient Egyptians used mud mixed with straw to form bricks. Mud with straw is more similar to adobe than concrete. However, they also used gypsum and lime mortars in building the pyramids, although most of us think of mortar and concrete as two different materials.
The Great Pyramid at Giza required about , tons of mortar, which was used as a bedding material for the casing stones that formed the visible surface of the finished pyramid.
About this same time, the northern Chinese used a form of cement in boat-building and in building the Great Wall. Spectrometer testing has confirmed that a key ingredient in the mortar used in the Great Wall and other ancient Chinese structures was glutenous, sticky rice. Some of these structures have withstood the test of time and have resisted even modern efforts at demolition.
By BC, the Greeks had discovered a natural pozzolan material that developed hydraulic properties when mixed with lime, but the Greeks were nowhere near as prolific in building with concrete as the Romans. It was not a plastic, flowing material poured into forms, but more like cemented rubble. The Romans built most of their structures by stacking stones of different sizes and hand-filling the spaces between the stones with mortar.
Above ground, walls were clad both inside and out with clay bricks that also served as forms for the concrete. The brick had little or no structural value and their use was mainly cosmetic. True chemical hydration did not take place. These mortars were weak. For marine structures and those exposed to fresh water, such as bridges, docks, storm drains and aqueducts, they used a volcanic sand called pozzuolana.
These two materials probably represent the first large-scale use of a truly cementicious binding agent. Pozzuolana and harena fossicia react chemically with lime and water to hydrate and solidify into a rock-like mass that can be used underwater.
The Romans also used these materials to build large structures, such as the Roman Baths, the Pantheon, and the Colosseum, and these structures still stand today. As admixtures, they used animal fat, milk and blood -- materials that reflect very rudimentary methods. On the other hand, in addition to using natural pozzolans, the Romans learned to manufacture two types of artificial pozzolans -- calcined kaolinitic clay and calcined volcanic stones -- which, along with the Romans' spectacular building accomplishments, are evidence of a high level of technical sophistication for that time.
Built by Rome's Emperor Hadrian and completed in AD, the Pantheon has the largest un-reinforced concrete dome ever built. The dome is feet in diameter and has a foot hole, called an oculus, at its peak, which is feet above the floor.
It was built in place, probably by starting above the outside walls and building up increasingly thin layers while working toward the center. The Pantheon has exterior foundation walls that are 26 feet wide and 15 feet deep and made of pozzolana cement lime, reactive volcanic sand and water tamped down over a layer of dense stone aggregate.
That the dome still exists is something of a fluke. Settling and movement over almost 2, years, along with occasional earthquakes, have created cracks that would normally have weakened the structure enough that, by now, it should have fallen.
The exterior walls that support the dome contain seven evenly spaced niches with chambers between them that extend to the outside. These niches and chambers, originally designed only to minimize the weight of the structure, are thinner than the main portions of the walls and act as control joints that control crack locations. Stresses caused by movement are relieved by cracking in the niches and chambers.
This means that the dome is essentially supported by 16 thick, structurally sound concrete pillars formed by the portions of the exterior walls between the niches and chambers. Another method to save weight was the use of very heavy aggregates low in the structure, and the use of lighter, less dense aggregates, such as pumice, high in the walls and in the dome.
The walls also taper in thickness to reduce the weight higher up. Another secret to the success of the Romans was their use of trade guilds. Each trade had a guild whose members were responsible for passing their knowledge of materials, techniques and tools to apprentices and to the Roman Legions.
In addition to fighting, the legions were trained to be self-sufficient, so they were also trained in construction methods and engineering. During the Middle Ages, concrete technology crept backward. After the fall of the Roman Empire in AD, the techniques for making pozzolan cement were lost until the discovery in of manuscripts describing those techniques rekindled interest in building with concrete.
He used limestone containing clay that was fired until it turned into clinker, which was then ground it into powder. He used this material in the historic rebuilding of the Eddystone Lighthouse in Cornwall, England.
Finally, in , an Englishman named Joseph Aspdin invented Portland cement by burning finely ground chalk and clay in a kiln until the carbon dioxide was removed. During vitrification, materials become glass-like. Aspdin refined his method by carefully proportioning limestone and clay, pulverizing them, and then burning the mixture into clinker, which was then ground into finished cement.
Before Portland cement was discovered, and for some years afterward, large quantities of natural cement were used, which were produced by burning a naturally occurring mixture of lime and clay. Because the ingredients of natural cement are mixed by nature, its properties vary widely. Modern Portland cement is manufactured to detailed standards.
Some of the many compounds found in it are important to the hydration process and the chemical characteristics of cement. Eventually, the mix forms a clinker, which is then ground into powder. A small proportion of gypsum is added to slow the rate of hydration and keep the concrete workable longer. Between and , systematic tests to determine the compressive and tensile strength of cement were first performed, along with the first accurate chemical analyses.
In the early days of Portland cement production, kilns were vertical and stationary. In , an English engineer developed a more efficient kiln that was horizontal, slightly tilted, and could rotate. The rotary kiln provided better temperature control and did a better job of mixing materials. By , rotary kilns dominated the market.
Top of the page Go to content Back to home page. Le site Planete-TP. Partner websites. Ministry of Ecology. High relative strength. High toleration of tensile strain. Good bond to the concrete, irrespective of pH, moisture, and similar factors.
Thermal compatibility, not causing unacceptable stresses in response to changing temperatures. Durability in the concrete environment, irrespective of corrosion or sustained stress for example. Coignet was the first to use iron-reinforced concrete as a technique for constructing building structures.
In Coignet built the first iron reinforced concrete structure, a four story house at 72 rue Charles Michels in the suburbs of Paris. Coignet's descriptions of reinforcing concrete suggests that he did not do it for means of adding strength to the concrete but for keeping walls in monolithic construction from overturning.
Joseph Monier, a French gardener and known to be one of the principal inventors of reinforced concrete, was granted a patent for reinforced flowerpots by means of mixing a wire mesh to a mortar shell.
In , Monier was granted another patent for a more advanced technique of reinforcing concrete columns and girders with iron rods placed in a grid pattern. Though Monier undoubtedly knew reinforcing concrete would improve its inner cohesion, it is less known if he even knew how much reinforcing actually improved concrete's tensile strength.
Before the use of concrete construction, though dating back to the Roman Empire and reintroduced in the mid to late s, was not yet a proven scientific technology. His work played a major role in the evolution of concrete construction as a proven and studied science. Without Hyatt's work, more dangerous trial and error methods would have largely been depended on for the advancement in the technology.
Wayss, was a German civil engineer and a pioneer of the iron and steel concrete construction. Up until the s Wayss and his firm greatly contributed to the advancement of Monier's system of reinforcing and established it as a well-developed scientific technology. Ernest L. Ransome, was an English-born engineer and early innovator of the reinforced concrete techniques in the end of the 19th century.
With the knowledge of reinforced concrete developed during the previous 50 years, Ransome innovated nearly all styles and techniques of the previous known inventors of reinforced concrete.
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