Visit ShapedbyConcrete.com to learn more about how cement and concrete shape the world around us. Portland cement is the basic ingredient of concrete. Concrete is formed when portland cement creates a paste with water that binds with sand and rock to harden.
- Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients.
- Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore.
These ingredients, when heated at high temperatures form a rock-like substance that is ground into the fine powder that we commonly think of as cement. Bricklayer Joseph Aspdin of Leeds, England first made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove.
With this crude method, he laid the foundation for an industry that annually processes literally mountains of limestone, clay, cement rock, and other materials into a powder so fine it will pass through a sieve capable of holding water. Cement plant laboratories check each step in the manufacture of portland cement by frequent chemical and physical tests.
The labs also analyze and test the finished product to ensure that it complies with all industry specifications. The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials.
- After quarrying the rock is crushed.
- This involves several stages.
- The first crushing reduces the rock to a maximum size of about 6 inches.
- The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.
- The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln.
The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building.
- The large kilns are mounted with the axis inclined slightly from the horizontal.
- The finely ground raw material or the slurry is fed into the higher end.
- At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft.
As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles. Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers.
The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency. After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that 1 pound of cement contains 150 billion grains. The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.
Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln.
- 1 What is used for making cement?
- 2 What is the main compound in cement?
- 3 Is caco3 raw material for cement?
What is used for making cement?
Different minerals need to be mined in order to make cement. Limestone (containing the mineral calcite), clay, and gypsum make up most of it. The US Geological Survey notes that cement raw materials, especially limestone, are geologically widespread and (luckily) abundant.
Domestic cement production has been increasing steadily, from 66.4 million tons in 2010 to about 80.5 million tons of Portland cement in 2014 according to the U.S. Geological Survey 2015 Cement Mineral Commodity Summary, The overall value of sales of cement was about $8.9 billion, most of which was used to make an estimated $48 billion worth of concrete.
What are the Raw Materials Used at Cement Industry ??? Let’s Know
Most construction projects involve some form of concrete. There are more than twenty types of cement used to make various specialty concrete, however the most common is Portland cement. Cement manufacturing is a complex process that begins with mining and then grinding raw materials that include limestone and clay, to a fine powder, called raw meal, which is then heated to a sintering temperature as high as 1450 °C in a cement kiln.
- In this process, the chemical bonds of the raw materials are broken down and then they are recombined into new compounds.
- The result is called clinker, which are rounded nodules between 1mm and 25mm across.
- The clinker is ground to a fine powder in a cement mill and mixed with gypsum to create cement.
The powdered cement is then mixed with water and aggregates to form concrete that is used in construction. Clinker quality depends on raw material composition, which has to be closely monitored to ensure the quality of the cement. Excess free lime, for example, results in undesirable effects such as volume expansion, increased setting time or reduced strength.
- Several laboratory and online systems can be employed to ensure process control in each step of the cement manufacturing process, including clinker formation.
- Several laboratory and online systems can be employed to ensure process control Laboratory X-Ray Fluorescence (XRF) systems are used by cement QC laboratories to determine major and minor oxides in clinker, cement and raw materials such as limestone, sand and bauxite.
Read Analysis of Clinker and Cement with Thermo Scientific ARL OPTIM’X WDXRF Sequential Spectrometer to learn why XRF is the technique of choice for elemental analysis in cement industry. Combination X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) systems accomplish both chemical phase analysis for a more complete characterization of the sample.
- Clinker phase analysis ensures consistent clinker quality.
- Such instrumentation can be fitted with several XRF monochromators for major oxides analysis and a compact diffraction (XRD) system which has the capability of measuring quartz in raw meal, free lime (CaO) and clinker phases as well as calcite (CaCO 3 ) in cement.
Read XRF/XRD Combined Instrumentation Can Provide Complete Quality Control of Clinker and Cement to learn more about technology that combines the advantages of both XRF and XRD together. Cross Belt Analyzers based on Prompt Gamma Neutron Activation Analysis (PGNAA) technology are installed directly on the conveyor belt to measure the entire material stream continuously and in real time to troubleshoot issues in pre-blending stockpile control and quarry management, raw mix proportioning control, and material sorting.
Read PGNAA Improves Process and Quality Control in Cement Production to learn what makes PGNAA particularly suited for cement analysis. Accurate cement production also depends on belt scale systems to monitor output and inventory or regulate product loadout, as well as tramp metal detectors to protect equipment and keep the operation running smoothly.
The Cement Manufacturing Process flow chart sums up where in the process each type of technology is making a difference. NOTE: Need a Belt scale system for your bulk material handling? To help you decide which belt scale system is best for your mining operation, we’ve outlined the options in an easy-to-read belt scale system selection guide so you can decide which belt scale system is right for you. Click on the image, take a look at the chart, and see if it helps you decide.
What are the two raw materials of cement?
Extracting raw material I: blasting and ripping – The most important raw materials for making cement are limestone, clay, and marl. These are extracted from quarries by blasting or by ripping using heavy machinery.
What is the main compound in cement?
🕑 Reading time: 1 minute Compounds in cement mainly are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium alumino ferrite. Not only do these compounds control most of cement properties but also reacts with water to produce new materials (cement hydration) and consequently responsible for concrete strength.
For instance, tricalcium silicate hydrates and hardens rapidly, hence generates heat greatly whereas hydration of the other three compounds are slow and consequently heat of hydration would be much lower. It is demonstrated that tricalcium silicate and dicalcium silicate provide most of concrete strength, but the contribution of tricalcium aluminate and tetracalcium alumino ferrite to the concrete strength are considerably low both at early strength and at ultimate strength.
It is worth mentioning that tricalcium silicate is the only compound that provide high early strength to concrete.
How cement is made step by step?
Manufacture of cement – There are four stages in the manufacture of portland cement: (1) crushing and grinding the raw materials, (2) blending the materials in the correct proportions, (3) burning the prepared mix in a kiln, and (4) grinding the burned product, known as ” clinker,” together with some 5 percent of gypsum (to control the time of set of the cement).
The three processes of manufacture are known as the wet, dry, and semidry processes and are so termed when the raw materials are ground wet and fed to the kiln as a slurry, ground dry and fed as a dry powder, or ground dry and then moistened to form nodules that are fed to the kiln. It is estimated that around 4–8 percent of the world’s carbon dioxide (CO 2 ) emissions come from the manufacture of cement, making it a major contributor to global warming,
Some of the solutions to these greenhouse gas emissions are common to other sectors, such as increasing the energy efficiency of cement plants, replacing fossil fuels with renewable energy, and capturing and storing the CO 2 that is emitted. In addition, given that a significant portion of the emissions are an intrinsic part of the production of clinker, novel cements and alternate formulations that reduce the need for clinker are an important area of focus.
How many ingredients are in cement?
Ingredients of cement: What is the composition of cement? – The main ingredients in cement are sand, clay and water. These three ingredients are mixed to form a paste. The paste is then mixed with other additives, such as lime or silica fume, which helps make concrete stronger. The blend is then poured into moulds, where it hardens into concrete.
Is coal used in cement?
What is Cement? – Cement is made from a mixture of calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina. A high-temperature kiln, often fuelled by coal, heats the raw materials to a partial melt at 1450°C, transforming them chemically and physically into a substance known as clinker.
This grey pebble-like material is comprised of special compounds that give cement its binding properties. Clinker is mixed with gypsum and ground to a fine powder to make cement. Coal is used as an energy source in cement production. Large amounts of energy are required to produce cement. Kilns usually burn coal in the form of powder and consume around 450g of coal for about 900g of cement produced.
Coal combustion products (CCPs), such as Fly Ash also play an important role in cement manufacture and in the construction industry generally.
Is caco3 raw material for cement?
Raw Materials. Minerals of natural origin as well as industrial products/by-products can be used for cement production as long as the main components of cement (Cao, SiO2,Al2O3,Fe2O3)are present in a required proportion on mixing and the impurities or undesirable components like alkalies, sulfur, chlorides, Mgo etc are below the allowable levels to ensure cement quality and operational stability.Cement mixes vary from ‘natural cement rock’, a single component which, as mined, contains appropriate proportions of all the required minerals, to 2- or 5- component mixes comprising one or two grades of limestone, shale or clay/silcastone, and one or more additives to augment SiO2, Al203 or Fe2O3 levels.
- Raw meal typically contains 78-80% CaCO3 so that lime- stone can only fall close to this level to the extent that it also contains the other ingredients.
- It is essential to have sufficient flux/liquid (Al, Fe, Mg, F) to promote fusion in the kiln, but MgO should not exceed 4-5% or the cement may be expansive.
Excess alkalies (K, Na) affect both kiln operation (build-ups) and product quality (alkali-aggregate reactivity). Excess sulfur causes kiln build-ups and limits the addition of gypsum which may result in setting problems. The stoichiometric ratio of alkalies to sulphur is normally kept between 0.8-1.2.
Excess Cl causes serious build-up problems for preheater operation. Apart from chemistry, grindability is also a factor in selecting raw materials. In particular, silica additives containing large-grain quartz are very difficult to grind and can result in hard burning and high fuel consumption. If quartz silica is employed it should, preferably, have a natural grain size of less than 50% µ.
Generally, cement plants are located on limestone deposits and shale or clay is sufficiently abundant for most plants to mine this locally. Additives are usually brought in small quantities. An approximate analysis for raw mix on ignited basis, or for clinker, is:
|Si O2||20- 23%|
Lime Component Limestone: Common forms of calcium carbonate used as raw material for cement manufacturing are limestone and chalk.Limestone is of predominantly fine grained crystalline structure, its hardness is between 1.8 to 3.0 of the Mohs scale of hardness and specific gravity 2.
- To 2.8. Limestone usually contains admixtures of clay substance or iron compounds, which influences its color.
- Only the purest varieties of limestone are white.
- Chalk: Unlike limestone chalk is characterized by a soft earthy texture.
- It is a sedimentary rock which was formed during the cretaceous period in geological time, it is relatively young geologically.
Blasting is not required for quarrying of chalk, and the crushing process can also be omitted which will reduce considerably cement production cost. Marls: Limestone with admixtures of silica, clay substance and iron oxide are called marls. Marls form the transition element to the clay.
Because of the wide distribution of marls, they are frequently used as raw material foe cement production Clay Component The second important raw material for cement production is clay.The main component of clay is formed by hydrous aluminium silicates.The chemical composition of clay may vary from those close to the pure clay, to that containing a significant amount of admixtures as iron hydroxide, iron sulfide, sand, calcium carbonate, etc.
Clay is used as an argillaceous component of raw mix. Corrective Ingredients If the primary components needed in the cement raw mix are not present in the required percentage, the corrective materials are used as additives. For example to augment SiO2 component, sand, high silica clay, etc., is used as additive.
Similarly to augment Alumina content in raw mix, bauxite or alumina rich clay is used and to augment for iron component, Iron Ore, pyrite cinders, etc are used as additives. Auxiliary Components Some of the most important auxiliary components whose quantities in the cement are curtailed either by standard specifications or by manufacturing experience are discussed here.
Magnesium Oxide (MgO) 0-5%: MgO combines up to 2% by weight with clinker phase and beyond that it appears as free MgO (periclase). Crystalline matured periclase reacts with water to form Mg(OH)2, but this reaction is proceeds slowly, while the other hardening reactions are already concluded.
Since the Mg(OH)2 occupies a large volume than the MgO and is formed on the same spot where the periclase particle is located, it can split apart the binding of the hardened cement paste, resulting in expansion cracks. Fast cooling of clinker (quenching) in cooler helps to freeze MgO in a glassy form which remains as it is and does not get hydrated to give expansion problem in cement paste.
Alkalies: Some of the Na2O (Sodium oxide) and K2O (Potassium oxide) is built into the clinker menials C3A, C4AF and C4AF.Most of the remaining will remain water soluble. An increased percentage of alkalies, particularly water soluble alkalies influences adversely the strength (28 Day).
Low alkali cements should have Na-equivalent below 0.6% by weight. If alkalies are not balanced by sulfates, they will remain highly volatile and can accumulate in the circulation between kiln and preheater increasing troubles of kiln inlet, kiln riser coatings. Main sources of alkalies are raw materials and coal.
Sulfur (SO3): Sulphates may be present in clinker up to about 3%. Sulphur in raw materials increases SOx emission and cause build-up in preheater. Sulphate can form a stable compound with Potassium (K2SO4) and to lesser extent Sodium (Na2SO4). The sulphates in the clinker comes from raw materials and fuel.
- Sulphates must be balanced with alkalies otherwise an excess or deficiency of sulphates with respect to alkalies will increase volatile circulation phenomena.
- Cl Chlorides: Chlorides form stable compounds with the alkalies and are more volatile than sulphates.
- About 1% in hot meal is considered maximum for smooth operation.
Clinker can contain about 0.012 to 0.023% Cl. A bypass generally known as alkali bypass may be required to vent out chlorides from kiln system. : Raw Materials.
What is used in making cement Class 10?
Limestone is the main raw material. The location of a cement plant depends mostly on the limestone deposits. The other raw materials are seashells, slag from steel plants and slag from fertilizer, silica, and aluminium are important ingredients.