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Skip Navigation LinksHome > Products > Knowledge Center > General Information > Concrete Information

Concrete Information 

HISTORY: The Egyptians used a mixture of mud and straw to make bricks in 3000 B.C. They also used gypsum and lime mortars in the construction of the pyramids, an early form of concrete.

The statement that all roads lead to Rome is well known. Lesser known is that the 5300 miles of those roads were built from concrete. From 300 B.C. to 476 A.D. the Romans used Pozzolana cement from Pozzuoli, Italy, to build the Apian Way, as well as the Roman bathes, the Coliseum, the Pantheon, and the Pont du Gard aqueduct in southern France.

 


Properties of concrete: Concrete is known as manmade stone. Concrete is everywhere. Sidewalks, roads ,water tanks, bridges, buildings, sewer pipes, swimming pools, bank vaults, railroad ties, foundations, parking garages, airport runways, patio bricks, light poles and prison cells to name just a few.

It is strong, inexpensive, friendly to the environment, able to be recycled and plentiful. Concrete is found all around the world. Every year more than a ton of concrete is produced for every man women child on this planet.

 

Concrete BlockWHAT IS CONCRETE ? Concrete is an Artificial Rock. It is a construction material composed of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel limestone or granite, plus a fine aggregate such as sand), water, and chemical admixtures.  The word concrete comes from the Latin word "concretus", which means "hardened" or "hard". Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. Source: From Wikipedia, the free encyclopedia

 

HOW IS CEMENT MADE? The basic ingredient of concrete is cement.."Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum)." Source: From Wikipedia, the free encyclopedia

 

MAKING CEMENT:

  • cement is basically limestone or calcium carbonate
  • simple formula is 1 cup of limestone blended with ¼ cup pulverized shale and a pinch of iron Cementore.

Limestone is mined from quarries; run through a primary then a secondary crusher; blended with above ingredients; heated in a blast furnace up to 2700°F for several hours and clinker is formed.  The blending and grinding process may be wet or dry.  After the clinker is stored and cooled in a silo, it is again blended with gypsum (3-4% by weight) to regulate pre-set.  Without gypsum (CaSO4), cement would set almost immediately, thus preventing us from getting concrete out of the mixer; into the bucket; into the forms and placed and finally finished.

  1. 80% Limestone , 20% Shale
  2. Burned in a kiln at high temperatures ( 2700 degrees Fahrenheit)
  3. Produces clinker
  4. Clinker is ground and Gypsum is added to produce cement. Gypsum controls setting properties, without it we would get "flash set"
 
 

Why is cement referred to as Portland Cement?

In 1824, an Englishman named Joseph Aspden invented a cement that strongly resembled the natural limestone cliffs of the Isle of Portland in the southeast English Channel, thus the name Portland has continued to describe modern day cement

 

Fresh Concrete

What is hydration?

Hydration is the chemical reaction that takes place when cement and water come into contact.  New compounds are formed and heat is generated. As the reactions proceed, the products of the cement hydration process bond together to form a solid mass, concrete.

Supplementary Cement "Cementitious Materials"(SCM) : Fly ash, slag cement, and silica fume are industrial by-products that are used as a partial replacement for portland cement in concrete. SCMs are used in at least 60% of ready mixed concrete. These supplementary cementitious materials (SCMs) are pre-consumer materials. The use of SCM increases the durability and can also lower the cost of concrete.

  • Fly Ash & Silica FumeFly Ash, 10 times as fine as cement (also called PFA), is a waste by-product of coal fired electricity generating stations. Fly Ash reacts with free lime created from the hydration process
  • Slag, 10 times as fine as cement, is also called ground granulated blast furnace slag. Slag is a waste by-product of iron manufacturing. Slag reacts with water, using the free lime catalyst.
  • Silica Fume, 100 times as fine as cement, is a by-product of the production of silicon and ferrosilicon alloys. Ferrosilicon is used in steel making as a source of silicon in the production of carbon steels, stainless steels. The use of Silica Fume in the production of concrete creates a very dense and strong concrete.
 

Use of Aggregates: Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. Recycled aggregates (from construction, demolition and excavation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.Cement paste must coat all particles and fill small voids. The use of fine sands make for a thirsty mix- high surface area. The use of coarse aggregates makes a boney mix with a lot of voids.

 

Exterior Vibrators on MoldConcrete Consolidation/Compaction: "The finishing of quality precast concrete products depends on the consolidation and compaction of the concrete. Consolidation is the even distribution of all ingredients throughout the mix. Compaction refers to the packing of concrete and removal of entrapped air. [1]" Mixing and placing entraps air in the concrete mix. This air needs to be released. Vibration is used to drive the entrapped air out. "The vibrations separate the aggregate particles and reduce friction between them. This action releases entrapped air and increases density. Fresh concrete must be properly vibrated so that, once hardened, its strength and durability potential are maximized[1]".

 

Concrete CuringCuring of Concrete: After concrete is placed it is important to properly cure the concrete to achieve the best strength and hardness. A decrease in strength, shrinkage and cracks can occur if not cured properly. Water and temperature are the significant factors. The cement in the concrete mix requires moisture to gain strength and a consistent temperature. If the water dries out to quickly, there will be insufficient water available to hydrate the cement At the beginning, the longer the concrete is kept damp the more strength it will gain. The cement and water reaction goes on for years, but 95% of the strength is attained in the first 28 days ( 7 days for Type III).
Typically this is not a problem in precast concrete. The critical strength is stripping strength ( the removal of the concrete piece from the mold) . Adding heat accelerates the hydration and causes higher early strengths. This allows for an earlier removal of the concrete piece from the mold.

 
 

Types of Cement:

  • Type 1 - Normal Portland cement. Type 1 is general use cement.
  • Type 2 - Moderate sulfate resistant Portland Cement. Type 2 is used for structures exposed to soil or ground waters with higher than normal sulphate concentrations. Modified Type 2 cement is used to generate heat slower than Type 1.
  • Type 3 - High early strength. Used when high strength are desired at very early periods.
  • Type 4 - Low heat Portland cement. Used where the amount and rate of heat generation must be kept to a minimum.
  • Type 5 - High sulfate resistant Portland Cement. Used where the water or soil has high sulfate content.

CHEMICAL ADMIXTURES:

Chemical Admixtures are materials that are added to the concrete, during mixing, to obtain different characteristics than plain concrete mixes. The most common are:

  • Water Reducers: When added to the concrete mix reduce the demand for water by making concrete more fluid. Better flowing concrete can be placed more easily in the form.
  • Superplasticizers : Superplasticizers are added to the concrete mix to increase slump ( consistency of fresh concrete) and workability. Superplasticizers distribute evenly particles of cement throughout the concrete mix.
  • Air-entraining Agents : Air-entraining agents add and distribute air bubbles. This helps the workability of the concrete, but its primary function is to protect against freeze / thaw damage.
  • Accelerators: Accelerators speed up the hardening process of concrete. Do not use CaCl accelerator with rebar.
 

Rebar-steel reinforcing barSOME TERMS TO UNDERSTAND CONCRETE AND THE REINFORCING OF IT:

* compression - squeezing together
* tension - pulling apart

Concrete is excellent in compression yet poor in tension, a ratio of approximately 10 to 1.  (i.e. 6,000 psi compression = 600 psi tension)  Steel reinforcing bar or rebar is excellent in tension, yet poor in compression.  Rebar is 60,000 psi in tension.
Combining concrete and rebar you get the compressive strength of the concrete combined with the tension strength of the rebar making a very which is call reinforced concrete.

 

PRESTRESSING CONCRETE:

Post Tension CablePre stressing concrete minimizes the effect of cracks in concrete pieces. In regular reinforced concrete, steel  rods are used  to overcome low  tensile strength. They resist tensile forces and limit the width of the cracks which occur under design loadings. Pre stressing limits cracking in construction by placing the concrete in compression before adding  service loads. The Pre-stressing strand is used to put concrete into compression so that when tension is applied, the net effect is no tension. Pre stressed concrete has the ability to carry greater loads and span greater distances. It also enables both structural elements and structures to be formed from a number of precast units, e.g. Segmented and Modular Construction.

 

 

 
 

Hoover DamINTERESTING FACTS ABOUT CONCRETE:

Hoover Dam, the largest single public works project in the history of the United States, contains 3.25 million cubic yards of concrete, which is enough to pave a two-lane highway from San Francisco to New York. Source :www.concreteresources.net. Hoover Dam Photo source:=http://gocalifornia.about.com/bl_nvhdamphoto_dam.htm

America's first concrete street, built in 1891 in Bellefontaine, Ohio, is still in service today! Source www.concreteresources.net

If America's 47,744 miles of Interstate Highways were paved with concrete, 11,000,000 gallons of fuel would be saved EACH DAY!
Source :www.concreteresources.net

Human thigh bones are stronger than concrete.
Source: http://www.tealdragon.net/humor/facts/facts.htm

4 million pounds of concrete was used to construct the Spallation Neutron Source's 1000-foot linear accelerator. It is actually nearly perfectly straight, with an allowance of 7 millimeters to compensate for the Earth's curvature. A proton is accelerated down the linac from a stop to nearly the speed of light in 2 microseconds. http://www.physorg.com/news9309.html Article: Spallation Neutron Source Amazing Science Facts / Dec 22, 2005

The largest concrete structure in the world, the Grand Coulee Dam in the state of Washington, contains more than 21 million tons of concrete! Source: http://www.bigsiteofamazingfacts.com/what-is-concrete-made-from

Europe's Longest Water BridgeEurope's longest water bridge is made up of 24,000 metric tons of steel and 68,000 cubic meters of concrete. The huge tub to transport ships over the Elbe in Germany. Source: http://www.dw-world.de/dw/article/0,,990878,00.html /Article 10/10/2003

 

 


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