8 main cement ingredients & their functions - civil engineering
Cement, as a binding material, is a very important building material. Almost every construction work requires cement. Therefore, the composition of cement is a matter of great interest to engineers. For understanding cement composition, one must know the functionality of Cement ingredients. By altering the amount of an ingredient during cement production, one can achieve the desired cement quality.
Please note that the information in Civiltoday.com is designed to provide general information on the topics presented. The information provided should not be used as a substitute for professional services.
the chemical composition of concrete
Concrete is an important part of modern infrastructure. It is used in buildings, roads, bridges and dams. It is known for its high compressive strength and versatility, which makes it an ideal material for the basis of most structures.
Concrete is actually a mixture of cement (the binder), water and some form of aggregate (the filler). This means that concrete is a composite material. In addition to this, cement is also a compound material, as it is a mixture of limestone and clay. It is made by burning the two compounds together at extremely high temperatures ranging from 1400 - 1600C.
While there is a range of cements available on the market - in addition to new research into sustainable alternatives - the most popular type of cement is known as Portland cement. Portland cement uses crushed CaCO3 (also known as limestone), mixed with clay, sand and iron ore to form a homogeneous powder.
This powder is heated to the high temperatures discussed previously. To achieve these temperatures, the mixture is poured into kilns which consist of long steel cylinders that are rotated on an incline. Depending on the size of the kiln, the materials can take up to 2 hours to pass slowly through the cylinder. The slow process allows the different elements of the material to react. The reaction of these materials involves the following processes:
The cooled clinker is then ground once more, and a compound known as gypsum is added to the mixture. This is in order to regulate the setting of the mixture. In Portland cement, 5% of its chemical composition is the gypsum mineral.
The major compounds that make up Portland cement are tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite and gypsum. Once this process is complete, the cement is packaged and stored for use in concrete at a later date.
Concrete can be created on site with the use of a rotating metal drum, known aptly as a cement mixture. The cement is rehydrated with water to make a thick consistency and large or fine aggregate is added depending on its intended use.
Aggregates are an important part of the concrete mixture as they determine the desired characteristics of the concrete. All aggregates are known to be chemically inert but vary in shapes, sizes and materials. The most commonly used are a mixture of fine sand and coarse stone. They also make up the largest portion of the concretes material composition, ideally between 70-80% of the volume. Concrete then must be vibrated, in order to release any air bubbles which may compromise the structural integrity of the material. Once poured, concrete needs at least 28 days to cure to full strength.
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cement | definition, composition, manufacture, history, & facts | britannica
Cement, in general, adhesive substances of all kinds, but, in a narrower sense, the binding materials used in building and civil engineering construction. Cements of this kind are finely ground powders that, when mixed with water, set to a hard mass. Setting and hardening result from hydration, which is a chemical combination of the cement compounds with water that yields submicroscopic crystals or a gel-like material with a high surface area. Because of their hydrating properties, constructional cements, which will even set and harden under water, are often called hydraulic cements. The most important of these is portland cement.
This article surveys the historical development of cement, its manufacture from raw materials, its composition and properties, and the testing of those properties. The focus is on portland cement, but attention also is given to other types, such as slag-containing cement and high-alumina cement. Construction cements share certain chemical constituents and processing techniques with ceramic products such as brick and tile, abrasives, and refractories. For detailed description of one of the principal applications of cement, see the article building construction.
Cements may be used alone (i.e., neat, as grouting materials), but the normal use is in mortar and concrete in which the cement is mixed with inert material known as aggregate. Mortar is cement mixed with sand or crushed stone that must be less than approximately 5 mm (0.2 inch) in size. Concrete is a mixture of cement, sand or other fine aggregate, and a coarse aggregate that for most purposes is up to 19 to 25 mm (0.75 to 1 inch) in size, but the coarse aggregate may also be as large as 150 mm (6 inches) when concrete is placed in large masses such as dams. Mortars are used for binding bricks, blocks, and stone in walls or as surface renderings. Concrete is used for a large variety of constructional purposes. Mixtures of soil and portland cement are used as a base for roads. Portland cement also is used in the manufacture of bricks, tiles, shingles, pipes, beams, railroad ties, and various extruded products. The products are prefabricated in factories and supplied ready for installation.
what is cement? manufacturing, composition & their functions | civildigital
Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve. The mix will be turned into form of slurry by adding 30 40% of water. It is then heated to about 2750F (1510C) in horizontal revolving kilns (76-153m length and 3.6-4.8m in diameter. Natural gas, petroluem or coal are used for burning. High fuel requirement may make it uneconomical compared to dry process.
Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve. Mixture is fed into kiln & burned in a dry state. This process provides considerable savings in fuel consumption and water usage but the process is dustier compared to wet process that is more efficient than grinding.
The rotation and shape of kiln allow the blend to flow down the kiln, submitting it to gradually increasing temperature. As the material moves through hotter regions in the kiln, calcium silicates are formed. These products, that are black or greenish black in color are in the form of small pellets, called cement clinkers. Cement clinkers are hard, irregular and ball shaped particles about 18mm in diameter. The cement clinkers are cooled to about 150F (51C) and stored in clinker silos.
When needed, clinker are mixed with 2-5% gypsum to retard the setting time of cement when it is mixed with water. Then, it is grounded to a fine powder and then the cement is stored in storage bins or cement silos or bagged. Cement bags should be stored on pallets in a dry place.
chemical composition of cement - construction how
Ancient Romans were probably the first to use concrete a word of Latin origin based on hydraulic cement that is a material which hardens under water. This property and the related property of not undergoing chemical change by water in later life are most important and have contributed to the widespread use of concrete as a building material.
Portland cement is the name given to a cement obtained by intimately mixing together calcareous and argillaceous, or other silica-, alumina-, and iron oxide-bearing materials, burning them at a clinkering temperature, and grinding the resulting clinker.
The definitions of the original British and new European Standards and of the American Standards are on those lines; no material, other than gypsum, water, and grinding aids may be added after burning.
These compounds interact with one another in the kiln to form a series of more complex products, and, apart from a small residue of uncombined lime which has not had sufficient time to react, a state of chemical equilibrium is reached.
The properties of this amorphous material, known as glass, differ considerably from those of crystalline compounds of a nominally similar chemical composition. Another complication arises from the interaction of the liquid part of the clinker with the crystalline compounds already present.
Calculation of the compound composition of commercial cements: the potential composition is calculated from the measured quantities of oxides present in the clinker as if full crystallization of equilibrium products had taken place.
The calculation of the potential composition of Portland cement is based on the work of R. H. Bogue and others, and is often referred to as Bogue composition. Bogues equations for the percentages of main compounds in cement are given below. The terms in brackets represent the percentage of the given oxide in the total mass of cement.
They have been found to react with some aggregates, the pro ducts of the alkali-aggregate reaction causing disintegration of the concrete (see page 267), and have also been observed to affect the rate of the gain of strength of cement.
Two terms used in require explanation. The insoluble residue, determined by treating with hydrochloric acid, is a measure of adulteration of cement, largely arising from impurities in gypsum. BS EN 197-1 limits the insoluble residue to 5 per cent of the mass of cement and filler; for cement, the ASTM C 150 limit is 0.75 per cent. The loss on ignition shows
the extent of carbonation and hydration of free lime and free magnesia due to the exposure of cement to the atmosphere. The specified limit both of ASTM C 150-05 and of BS EN 197-1 is 3 per cent, except for ASTM Type IV cement (2.5 per cent) and cements with fillers of BS EN (5 per cent). Since hydrated free lime is innocuous, for a given free lime content of cement, a greater loss on ignition is really advantageous.
what is concrete? composition & types of concrete - civil engineering
An ever-evolving world needs constantly developing construction ways. In the present world, concrete is one of the most widely used construction materials. This can be due not alone to the large choice of applications that it offers, however, besides, its behavior, strength, affordability, durability, and flexibility play vital roles. Therefore, constructing-building works have faith in concrete as a secure, strong, and simple object. It is utilized in all sorts of buildings (from residential to multi-story workplace blocks) and infrastructure comes (roads, bridges, etc). Concrete is used for the development of foundations, columns, beams, slabs, and different load-bearing components. So, then let us dig into detail:
Concrete, an artificial stone-like mass, is the composite material that is created by mixing binding material (cementor lime) along with the aggregate (sand, gravel, stone, brick chips, etc.), water, admixtures, etc in specific proportions. The strength and quality are dependent on the mixing proportions.
Concrete is a very necessary and useful material for construction work. Once all the ingredients -cement, aggregate, and water unit of measurement mixed inside the required proportions, the cement and water begin a reaction with one another to bind themselves into a hardened mass. This hardens therock-like mass is the concrete.
Concrete is powerful, easy to create, and could be formed into varied shapes and sizes. Besides that, it is reasonable, low cost, and is instantly mixed. It is designed to allow reliable and high-quality fast-track construction. Structures designed with the concrete unit of measurement plenty durable and should be designed to face up to earthquakes, hurricanes, typhoons, and tornadoes. This is an incredible advancement. With all the scientific advances there are in this world, there still has not been a way of preventing nature's injury.
Binding material is the main element of a concrete mix. Cement is the most commonly used binding material. Lime could also be used. When water is mixed with the cement, a paste is created that coats the aggregates within the mix. The paste hardens, binds the aggregates, and form a stone-like substance.
Water is required to with chemicals react with the cement (hydration) and to supply workability with the concrete. The number of water within the combine in pounds compared with the number of cement is named the water/cement quantitative relation. The lower the w/c quantitative relation, the stronger the concrete. (Higher strength, less permeability)
Concrete is employed for various projects starting from little homemade comes to large subject field buildings and structures. It is used for sidewalks, basements, floors, walls, and pillars at the side of several alternative uses. Many sorts of concrete are utilized in the development works.
Lime concrete uses Lime as the binding material. Lime is usually mixed with surki and khoa or stones in the proportion 1:2:5 unless otherwise specified. The khoa or stones are soaked in water before mixing. Lime concrete is used mainly in foundation and terrace roofing.
Most engineering construction uses cement concrete composites as the main building material. It consists of cement, sand, brick chips, or stone chips of the required size. The usual proportion is 1:2:4 or 1:3:6.After mixing the required amounts of materials, the concrete mix is cured with water for 28 days for proper strength building.
For enhancing the tensile strength of concrete, steel reinforcements are added. Sometimes, RCC is prestressed under compression to eliminate or reduce tensile stresses. The resulting concrete is known as Prestressed Concrete.
This is the combination that may be found at most home improvement and hardware stores. It comes in baggage typically starting from sixty to eighty pounds. Dry ready mix is simple to combine and this is often the combination that almost all homemade comes would require. The tools needed for the mixture are a bucket or cart, shovel or hoe, trowel, and a measured quantity of water.
The distinction between dry ready mix and ready-mix concrete is that the water is already supplementary to ready combine. This concrete comes pre-mixed and is for larger homemade comes or for people who do not need to combine their own concrete. It is typically brought in an exceedingly little trailer, typically with an intermixture drum connected to stay it dampish and mixed. The ready combine is usually costlier and might be troublesome to search out. It additionally should be used quickly as an alternative it will set while not unfolding properly.
It is price effective to purchase dry materials in bulk. This may let the project be custom-built to the particular wants and usage of the concrete. The drawback of shopping in bulk is that there will be much space for the materials to be kept before getting used. The materials will over probably be delivered to the positioning.
This is the mix that almost all cast-in-place concrete comes can use. it is typically trucked in using concrete trucks that have the massive drum that keeps the concrete from setting up whereas in transit. It permits for one continuous pour so fewer seams and stronger concrete overall. For big comes, transit combine is a far additional value effective than getting bulk materials or ready-mix since in each those the workforce to combine the concrete would get to be patterned into the value.
The most common type used is the regular concrete that is referred to as traditional weight concrete or traditional strength concrete. This pertains to the concrete that is promptly on the market within the retailers marketplace for personal and residential usage. This includes usage directions that are written within the packaging of the product. It utilizes sand and different materials to function aggregates and is consolidated in temporary vessels.
High strength concrete combine possesses compressive strength that is over six thousand pounds per area unit. This can be processed by lowering the water-cement quantitative relation to a minimum of 0.35 or lower. The low water-cement quantitative relation makes this sort of cementless feasible. to combat this weakness, superplasticizers are other to the present concrete combine.
Stamped concrete is a subject area concrete wherever realistic patterns almost like natural stones, granites, and tiles will be obtained by inserting the impression of skilled stamping pads. This stamping is applied on the concrete once it is in its plastic condition. totally different coloring stains and texture work can finally provide an end that's terribly almost like costlier natural stones. A high aesthetic look will be obtained from a sealed end economically. This is often utilized in the development of driveways, interior floors, and patios.
High-performance concrete refers to a freshly developed concrete combine that has properties that are a notch higher compared to regular concrete mixes. This includes increased strength, durability, and workability, simplicity of usage, compaction while not segregation, long-run mechanical properties, porosity, density, toughness, and volume stability. Air-entrained agents may be utilized to customize this concrete combine for severe environments.
The concrete combine once placed can compact by its own weight is considered self-consolidated concrete. No vibration should be provided for an equivalent individually. This combination has higher workability. The slumping price is going to be between 650 and 750. This concrete because of its higher workability is named flowing concrete. In the areas wherever there is thick reinforcement, self consolidating concrete works best.
Concrete with water content quite the desired amount is poured into the formwork. The surplus water is then removed out with the assistance of an air pump while not looking forward to the concrete to endure setting. Thus, the concrete structure or the platform is going to be able to use earlier in comparison with traditional construction technique. These concretes can attain their 28 days compressive strength inside an amount of 10 days and therefore the crushing strength of this structure is 25 you bigger compared with the standard concrete sorts. To learn more about vacuum concrete read-Vacuum Concrete | Definition, Procedure and Advantages
Shotcreting refers to a method within which compressed air forces mortar or concrete through a tube and tap onto a surface at a high speed and forms structural or non-structural parts of buildings. Shotcrete is currently applied to the wet-mix method and has gained universal acceptance in several countries. In wet-mix application cement, aggregate, admixture, and water are mixed along before being wired through a hose and atmospherically designed. On the opposite hand, in dry-mix applications cement, aggregate, and admixture are mixed along, sent pneumatically through a tube so, at the tap via a water ring, water is injected equally throughout the combination because it is being designed.
This type of concrete has been placed and compacted with the assistance of earthmoving instrumentality like serious rollers. This concrete is principally utilized in excavation and filling wants. These concretes have cement content in lesser quantity and are stuffed for the realm necessary. once compaction, these concretes give high density and eventually cure into a powerful monolithic block.
The recycled glass may be used as aggregates in concrete. Thus, we tend to get concrete of recent times, the glass concrete. This concrete can increase the aesthetic appeal of concrete. They can give long strength and higher thermal insulation.
Asphalt concrete may be a material, the mixture of aggregates and asphalts ordinarily accustomed surface roads, parking tons, airports, yet because of the core of mound dams. Asphalt concrete is known as asphalt, blacktop, or pavement and tarmac or bitumen, macadam, or rolled asphalt in other countries.
As the name implies these concretes can acquire strength with few hours once it's manufactured. Therefore, the formwork removal is created simple and the building construction is roofed quickly. These have a widespread application within the road repairs, as they'll be reused once in some hours.
In polymer concrete, the aggregates are restrained with the polymer rather than cement. The assembly of polymer concrete can facilitate the reduction of the volume of voids within the mixture. This may cut back the quantity of polymer that is necessary to bind the aggregates used. Hence, the aggregates are ranked and mixed consequently to attain minimum void. This kind of concrete has totally different classes:
The cement is replaced by lime during this concrete kind. The most application of this product is on floors, domes, likewise as vaults. These not like cement have several environmental and health advantages. These products are renewable and simply clean.
Concrete that has a density lesser than 1920kg/m3 are classified as light-weight concrete. The utilization of lightweight aggregates in a concrete style can provide us lightweight aggregates. Aggregates are the vital part that contributes to the density of the concrete. The samples of lightweight aggregates are stone, perlites, and scoria. The lightweight concrete is applied for the protection of the steel structures and is used for the development of the long-span bridge decks. These are used for the development of the building blocks.
To conclude with, concrete is the basic need for building or other constructional works. Thus, the knowledge of different types of concrete should use wisely by consumers to take advantage of its properties for their construction engagements.
Please note that the information in Civiltoday.com is designed to provide general information on the topics presented. The information provided should not be used as a substitute for professional services.
cement types, composition, uses and advantages of nanocement, environmental impact on cement production, and possible solutions
S. P. Dunuweera, R. M. G. Rajapakse, "Cement Types, Composition, Uses and Advantages of Nanocement, Environmental Impact on Cement Production, and Possible Solutions", Advances in Materials Science and Engineering, vol. 2018, Article ID 4158682, 11 pages, 2018. https://doi.org/10.1155/2018/4158682
We first discuss cement production and special nomenclature used by cement industrialists in expressing the composition of their cement products. We reveal different types of cement products, their compositions, properties, and typical uses. Wherever possible, we tend to give reasons as to why a particular cement type is more suitable for a given purpose than other types. Cement manufacturing processes are associated with emissions of large quantities of greenhouse gases and environmental pollutants. We give below quantitative and qualitative analyses of environmental impact of cement manufacturing. Controlling pollution is a mandatory legal and social requirement pertinent to any industry. As cement industry is one of the biggest CO2 emitters, it is appropriate to discuss different ways and means of CO2 capture, which will be done next. Finally, we give an account of production of nanocement and advantages associated with nanocement. Nanofillers such as nanotitania, nanosilica, and nanoalumina can be produced in large industrial scale via top-down approach of reducing size of naturally available bulk raw materials to those in the nanorange of 1nm100nm. We mention the preparation of nanotitania and nanosilica from Sri Lankan mineral sands and quartz deposits, respectively, for the use as additives in cement products to improve performance and reduce the amount and cost of cement production and consequent environmental impacts. As of now, mineral sands and other treasures of minerals are exported without much value addition. Simple chemical modifications or physical treatments would add enormous value to these natural materials. Sri Lanka is gifted with highly pure quartz and graphite from which silica and graphite nanoparticles, respectively, can be prepared by simple size reduction processes. These can be used as additives in cements. Separation of constituents of mineral sands is already an ongoing process.
This paper is an extended version of the Conference Paper published in the Proceedings of the 28th International Symposium on Transport Phenomena, 2224 September 2017, Peradeniya, Sri Lanka . As described in it, cement is a powdery substance made with calcined lime and clay as major ingredients. Clay used provides silica, alumina, and iron oxide, while calcined lime basically provides calcium oxide. In cement manufacturing, raw materials of cement are obtained by blasting rock quarries by boring the rock and setting off explosives . These fragmented rocks are then transported to the plant and stored separately in silos. They are then delivered, separately, through chutes to crushes where they are then crushed or pounded to chunks of 1/2 inchsized particles . Depending on the type of cement being produced, required proportions of the crushed clay, lime stones, and any other required materials are then mixed by a process known as prehomogenization and milled in a vertical steel mill by grinding the material with the pressure exerted through three conical rollers that roll over a turning milling table. Additionally, horizontal mills inside which the material is pulverized by means of steel balls are also used. It is then homogenized again and calcined, at 1400C, in rotary kilns for the raw material to be transformed to a clinker, which is a small, dark grey nodule 3-4cm in diameter. The clinker is discharged from the lower end of the kiln while it is red-hot, cooled by various steps, ground and mixed with small amounts of gypsum and limestone, and very finely ground to produce cement .
In the calcination process, in the kiln, at high temperatures, the above oxides react forming more complex compounds . For instance, reaction between CaCO3, Al3(SiO3)2, and Fe2O3 would give a complex mixture of alite, (CaO)3SiO2; belite, (CaO)2SiO2; tricalcium aluminate, Ca3(Al2O3); and ferrite phase tetracalcium aluminoferrite, Ca4Al2O3Fe2O3 with the evolution of CO2 gas in the Portland cement clinker . However, there can be many other minor components also since natural clay also contains Na, K, and so on. In the chemical analysis of cement, its elemental composition is analyzed (e.g., Ca, Si, Al, Mg, Fe, Na, K, and S). Then, the composition is calculated in terms of their oxides and is generally expressed as wt.% of oxides. For simplicity, if we assume that the clinker contains the above four main oxides, they can be simply represented by the Bogue formulae where CaO, Al2O3, Fe2O3, and SiO2 are denoted as C, A, F, and S, respectively . In this notation, alite (tricalcium silicate) [(CaO)3SiO2], belite (dicalcium silicate) [(CaO)2SiO2], celite (tricalcium aluminate) [Ca3Al2O6=3CaOAl2O3], and brownmillerite (tetracalcium aluminoferrite) [Ca4Al2Fe2O10=4CaOAl2O3Fe2O3] are represented by C3S, C2S, C3A, and C3AF, respectively. If we analyze the elemental composition of Ca, Al, Fe, and Si, usually from X-ray fluorescence spectroscopy, then we express them as wt.% of their respective oxides. For example, if the experimentally determined clinker composition is CaO=65.6%, SiO2=21.5%, Al2O3=5.2%, and Fe2O3=2.8%, then Bogue calculations would give C3S=64.7%, C2S=12.9%, C3A=9.0%, and C4AF=8.5%, respectively . However, cement contains water (H2O), sulphate (SO3), sodium oxide (Na2O), potassium oxide (K2O), gypsum (CaSO42H2O), which are denoted as H, S, N, K, and CSH2, respectively. Note that gypsum (calcium sulphate dihydrate) is considered as CaOSO32H2O and hence its notation is CSH2. As such, approximate composition of the cement clinker is different from the above values and is depicted in Table 1.
There are several different types of cements of which Portland cement, Siliceous (ASTM C618 Class F) Fly Ash, Calcareous (ASTM C618 Class C) Fly Ash, slag cement, and silica fume are the major types [9, 10]. They differ from their chemical composition. Table 2 gives the compositions of the above cement types in terms of SiO2, Al2O3, Fe2O3, CaO, MgO, and SO3, and the remaining can be other materials such as Na2O and K2O. Note that SO3 stands for oxide of S, where S is derived from gypsum (CaSO42H2O). Given in Table 2 are also important physical properties such as specific surface area (surface area per unit mass, SSA) and specific gravity (SG) of these different types of cements [11, 12].
General use of the Portland cement, Siliceous (ASTM C618 Class F) Fly Ash, Calcareous (ASTM C618 Class C) Fly Ash, slag cement, and silica fume in concrete is as primary binder, cement replacement, cement replacement, cement replacement, and property enhancer, respectively .
There are over ten different types of cements that are used in construction purposes, and they differ by their composition and are manufactured for different uses. These are rapid-hardening cement (RHC), quick-setting cement (QSC), low-heat cement (LHC), sulphate-resisting cement (SRC), blast furnace slag cement (BFSC), high-alumina cement (HAC), white cement (WC), coloured cement (CC), pozzolanic cement (PzC), air-entraining cement (AEC), and hydrophobic cement (HpC). RHC has increased the lime content compared to the Portland cement (PC) [17, 18]. Purpose of having high lime content is to attain high strength in early days. It is used in concrete when formwork is to be removed early. Since hardening of cement is due to the formation of CaCO3 by absorbing atmospheric CO2 by CaO, increased CaO results in increased CaCO3 formation even at the early stage to result in rapid hardening .
QSC is produced by adding a small percentage of aluminium sulphate as an accelerator and reducing the amount of gypsum used with fine grinding. This cement is used when the work is to be completed very quickly as in static and running waters. LHC has reduced the amount of C3A, which is used to produce massive concrete constructions like gravity dams. LHC has compressive strength to heat of the hydration ratio of at least 7 at the age of 13 weeks. The usual wt. ratio of CaO to SiO2 is between 0.8 and 1.5, but Al2O3 wt.% is less than 10% . This is prepared by grinding the CaO, SiO2, and Al2O3 materials, melting the mixture, quenching the melt, and grinding the quenched matter to have mainly amorphous material of the above composition. Alumina is a hydratable material and reduced alumina gives reduced hydration to produce less heat of hydration. This is important in the construction of large structures to avoid possible thermal cracking during concrete setting .
Sulphate attack on concrete is a chemical breakdown mechanism, where sulphate reacts with C3A and/or Ca(OH)2 components of the hardened cement forming ettringite, which is hexacalcium aluminate trisulphate hydrate [(CaO)6(Al2O3) (SO3) 32H2O=C6ASH32]. Sulphate ions can react with C3A and/or Ca(OH)2 in hardened concrete in the presence of water forming gypsum. These newly formed ettringite and gypsum crystals occupy empty spaces of concrete, and as they grow, they tend to damage the paste by cracking. The most important parameters determining the sulphate attack are C3A, C3S/C2A ratio, and C4AF. It has been reported that the addition of pozzolonic admixtures such as fly ash reduces the C3A content of cement  when sulphate is present in water and soil used; in places like canal linings, culverts, retaining walls, and siphons, it is important to use SRC. SRC is prepared by maintaining C3A content below 6%.
BFSC is prepared by grinding the clinkers with 60% slag. BFSC resembles properties of the Portland cement and is used for works in which economic considerations are predominant. HAC is obtained by melting a mixture of bauxite and lime and grinding the mixture with the clinker. Since it contains high alumina content, it is rapid-hardening cement with initial and final setting times of about 3.5h and 5h, respectively . HAC is used in works where concrete is subjected to high temperatures, frost, and acidic conditions. WC is prepared from raw materials free from iron oxides and oxides of other transition metals such as Cr, Mn, Cu, V, and Ti. The colouring effect takes the order Cr2O3>Mn2O3>Fe2O3>V2O3>CuO>Ti2O3. As such, the amounts of these transition metal ions, particularly Cr3+, Mn3+, and Fe3+, should be minimized to form white cement. Usually, Cr2O3, Mn2O3, and Fe2O3 are kept below 0.003%, 0.03%, and 0.35%, respectively, in the clinker . Cheap quarried raw materials usually contain Cr, Mn, and Fe. For example, lime stones and clays usually contain 0.31% and 515% Fe2O3. Keeping Fe2O3 below 0.5% is desirable to make WC, and as such, kaolin and sand are used instead of other clays in making WC. The abrasiveness of sand particles with size <45m also ensures less wearing of chrome-steel grinding mill used to grind raw materials, which would otherwise contaminate the mixture with Fe and Cr. Usually, sand is ground separately using ceramic grinding media to avoid chromium contamination. WC is costly and hence used in aesthetic applications such as precast curtain wall and facing panels and terrazzo surface. Contrary to WC, CC is prepared by deliberately adding mineral pigments to cement. CCs are widely used in decorative works on floors. Iron oxides are used to get red, yellow, and black base colours, and several mixed colours such as browns-terracotta-tuscany-sepia-beach. Standard green and blue pigments are chrome oxide and cobalt aluminium oxide, respectively. TiO2 is the usual white pigment. PzC is prepared by grinding the pozzolanic clinker with the Portland cement . It is used in marine structures, sewage works, and for laying concrete under water such as in bridges, piers, and dams.
AEC is produced by adding air-entraining agents that are surfactants such as alkali salts of wood resins, synthetic detergents of the alkyl-aryl sulphonate type, calcium lignosulphate derived from the sulphite process in paper making, and calcium salts of glues and other proteins obtained in the treatment of animal hides, animal and vegetable fats, oil and their acids, wetting agents, aluminium powder, and hydrogen peroxide, during the grinding of the clinker . They are added in 0.0250.1% in either solid or liquid form. At the time of mixing, AEC produces tough, tiny, discrete noncoalescing air bubbles of 10500m in diameter in the body of the concrete. These bubbles can compress to some extent, and hence, they can absorb stress created by freezing.
HpC is prepared by adding water-repellent chemicals . They are prepared particularly for use in high-rainfall regions to prevent water absorption during storage. Particles of HpC are coated with nonpolar substances, usually by adsorbing oleic acid, stearic acid, and so on, to cement particles [27, 28]. When adsorbed, these surfactant molecules self-assemble by coordinating with surface cations through their carboxylic acid groups thereby allowing the nonpolar hydrocarbon chain to extend from the particles. When a water drop falls on them, they are stuck on hydrocarbon chains and stay as spherical particles as does by the lotus leaf. The cement particles are then not wetted, and water drops roll off when slightly slanted. These hydrophobic coatings prevent the attacks by chloride and sulphate ions, and hence, they resist to deterioration of concretes by these ions .
Measured data of the European cement kiln emissions show that cement industry contributes substantially to environmental pollution. Table 3 lists main environmental pollutants emitted by the European cement kilns in tonnes per year.
TOC/VOC, PCCD, and PCDF indicate total organic compounds including volatile organic compounds, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans, respectively. It has been reported that toxic metals such as Hg, Cd, Tl, As, Sb, Pb, Cr, Co, Cu, Mn, Ni, and V are also emitted in considerable amounts. For example, masses of Hg, (Cd, Tl), and (As, Sb, Pb, Cr, Co, Cu, Mn, Ni, V) emitted in kg per year are 01311, 01564, and 09200, respectively . In addition to material pollutants, noise emission is also associated with almost all the processes involved in cement manufacturing. These environmental impacts contribute to abiotic depletion, global warming, acidification, and marine ecotoxicity .
Cement is produced by utilizing an extensive amount of raw materials treated and reacted at extreme conditions such as high temperatures. The high-temperature processes are called pyroprocessing processes where raw materials are heated at high temperatures for solid-state reactions to take place, which utilize fuel sources such as coal, fuel oil, natural gas, tires, hazardous wastes, petroleum coke, and basically anything combustible . Some cement manufacturing plants utilize the organic waste generated in other industries such as rubber processing industries. As such, cement industry contributes to a significant extent of anthropogenic carbon dioxide emissions, which is in the range of 57% of total anthropogenic carbon dioxide emissions . In the clinker burning process, in order to produce 1 tonne of clinkers, 1.52 tonnes of raw materials are used on average. The balance of 0.52 tonne of raw materials is converted mainly to carbon dioxide by the processes such as CaCO3 CaO+CO2. This is a serious global environmental problem since increase in carbon dioxide in the atmosphere has direct consequences on global warming. In addition to CO2, other key polluting substances emitted to air by the cement industry include dust, other carbon oxides such as carbon monoxide (CO), nitrogen oxides (NOxs), sulphur oxides (SOxs), polychlorinated dibenzo-p-dioxins, dibenzofurans, total organic carbon, metals, hydrogen chloride, and hydrogen fluoride, which are serious health-hazardous substances and some are hilariously odorous . However, the type and amount of air pollution caused by the cement industry depend on various parameters, such as inputs (the raw materials and fuels used) and the type of process used in the industry.
As for water pollution, the contribution from cement industry may be insignificant through the storage and handling of fuels that may contribute to soil and groundwater contaminations . In order to reduce the amount of raw materials, particularly in the manufacturing of specialized cement types as described above, supplementary cementitious materials such as coal fly ash, slag, and natural pozzolans such as rice husk ash and volcanic ashes are used. This will not only reduce the waste materials generated for landfilling but also the cost of cement production .
However, cement is an essential material for human survival nowadays. As such, there is no alternative, but the production of cement is mandatory. At the same time, controlling pollution created by cement industry is also very important. In the next section, we discuss ways and means of controlling pollution resulting from cement industries.
The air pollution occurs in the excavation activities, dumps, tips, conveyer belts, crushing mills, and kilns of cement industry. Minimizing air pollution is a mandatory legislative requirement, which also contributes to minimizing wastage and survival of the industry . Dust particles emitted at sites other than kilns can be captured using a hood or other partial enclosure and transported through a series of ducts to the collectors. The dust collected can be fed to the kiln provided that it is not too alkaline not exceeding 0.6% as per the Na2O (N) content. However, if the alkalinity is higher than this value, then the dust must be either discarded or pretreated before feeding to the kiln. Flexible pulse jet filters, electrostatic precipitators, wet scrubbers, and baghouse method can be used to collect dust from flue gas . The US Environmental Protection Agency has reviewed the available and emerging technologies for reducing greenhouse gas emissions from Portland cement industry. The primary greenhouse gas emitted in the cement industry is carbon dioxide, but in lower quantities, NOxs and SOxs are also emitted as detailed in Table 3 .
This involves separation and capture of carbon dioxide from the flue gas, pressurization, and transportation via pipelines, injection, and long-term storage. In regard to this, several processes have been developed as detailed below.
This involves capture of CO2 from flue gas and conversion to carbonates. This utilizes a scrubber containing high-pH water with calcium, magnesium, sodium, hydroxide, and chloride as the scrubbing liquid. CO2 captured by this water is converted to CaCO3 and MgCO3, which are precipitated out of the solution. The precipitates can be filtered, washed, and dried for reuse as feed material for the kiln to make blended cement. Water used may be seawater or reject brine. Capture efficiency of over 90% has been reported in a 10-MW coal-fired pilot plant. It is interesting to note that when captured carbon is reused, the overall carbon footprint becomes negative since the carbon emissions avoided from the cement manufacturing process could be greater than those of carbon emissions from the power plant [39, 40].
In the oxy-combustion process, fuel is burnt with pure or nearly pure oxygen instead of air. Since there is no nitrogen gas, the fuel consumption is reduced due to the fact that there is no need to heat and burn nitrogen gas. Since air contains nearly 79% nitrogen gas and any combusted nitrogen comes as NOx in flue gas, the volume of flue gas and NOx in it is significantly reduced when pure oxygen is used for combustion [39, 41]. This process should utilize an air separation process to separate out nitrogen gas, which can be used for other processes such as for inflating vehicle tires. Nitrogen-removed air basically contains majority of oxygen, and it can be used for the oxy-combustion process. When oxy-combustion is used, the resulting kiln exhaust contains over 80% CO2 gas, which can be recovered by the Calera process. There are several technical issues as laid down in  that have to be tackled before implementing this process in cement industry.
When flue gas is passed through a column containing monoethanolamine, CO2 gas is selectively absorbed. High-pressure, low-temperature conditions favour the absorption. When CO2-rich MEA solution is subjected to low-pressure, high-temperature conditions, it releases absorbed CO2 which can be converted to some other product like CaCO3 or MgCO3 and the solvent recovered can be reused. One of the problems with this method is that acidic gases such as SOx and NOx present in the flue gas can react with MEA. Therefore, levels of these gases must be kept below 0.001% prior to absorption by MEA. Instead of regular amines, hindered amines can also be used. Hindered amines have special functional to prevent degradation of the amine .
Flue gas contains SOx, which could be separated using limestone-based compounds. They are then converted to slurries to use as CO2 absorbents. This way, both SOx and CO2 can be removed from flue gas .
Cryogenics is the science that addresses the production and effects of very low temperatures. In the cryogenic separation, all other gases except CO2 and N2 have to be removed prior to subjecting to low-temperature conditions. The triple point for CO2 is 256.68C and 7.4atm, and when these conditions are maintained, CO2 will condense while N2 will remain as a gas. N2 gas is then escaped through an outlet at the top of the chamber, and the dense liquid is taken from the bottom of the chamber. Refrigeration under pressure is an alternative method to cryogenic distillation but utilizes even harsh conditions such as higher pressures and lower temperatures. Cryogenic methods have distinct advantages over other separation methods. Since CO2 is separated as a liquid, it can be transported via pipelines for sequestration. Also, the recovery and purity of CO2 is very high (CO2 purity after distillation can exceed 99.95%) .
Suitable membranes can be used to separate or adsorb CO2 in the kiln exhaust gas. Poly(methoxyethoxy)ethanol phosphazene (MEEP) hollow fibre membranes are excellent CO2 separation and storing membranes, where (methoxyethoxy)ethanol groups attached P have strong interactions with CO2 . One such example is given in Figure 1.
Polymer blends with required properties such as strong interaction with CO2 can be used as CO2-selective membranes. For example, cross-linked thin-film composite of poly(vinylalcohol) (PVA)/polyvinylpyrrolidone (PVP) blend membranes doped with suitable amine carriers are excellent CO2-selective membranes as reported by Mondal and Mandal. The CO2 permeability of this membrane is 1396 Barrer at 2.8atm and 100C . Combination of grafting and cross-linking is an advanced technique capable of suppressing plasticization. In this respect, Achoundong et al. developed cellulose acetate (CA) membranes and grafted vinyltrimethoxysilane (VTMS) to OH groups, which due to subsequent condensation of hydrolyzed methoxy groups on the silane form cross-linked polymer networks. The modified membranes have an order of magnitude higher CO2 permeability than neat cellulose acetate membranes .
Polymers of intrinsic microporosity (PIMs), thermally rearranged polymers (TRPs), polyimides, and polyurethanes are advanced polymers with high selectivity for CO2 and hence are suitable membranes for CO2 separation. PIMs are ladder polymers with high free volume and high selectivity for CO2. These ladder polymer backbones can be prepared by polycondensation reaction of tetrahydroxy monomers containing spiro- or contorted centres with tetrafluoromonomers. One such example is the PIM-1 prepared by the polycondensation reaction of commercial monomers such as 5,5,6,6-tetrahydroxy-3,3,3,3-tetramethyl-1,1-spiro-bisindane with tetrafluorophthalonitrileo. Chemical structures of the monomers are given in Figure 2.
These polymers have high CO2 solubility and spirocentres, such as thianthrene , 9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene , ethanoanthracene , and pyrazine , and could be incorporated in PIM membranes for adjusting the gas permeation properties.
Thermally rearranging polymers (TRPs) are prepared by a thermal postmembrane conversion process of functionalized polyimides. They have uniform cavities with tailored free-volume elements with well-connected morphology in the amorphous state . For example, thermal rearrangement of poly(hydroxyimide)s is shown in Figure 3.
Separation of CO2 from a gas mixture by selective adsorption involves both thermodynamics (adsorption) and kinetics (diffusion selectivity), and designing adsorbents for CO2 in the presence of gases such as CH4 and N2 is challenging since all three gases have similar kinetic diameters of 3.30, 3.76, and 23.64, respectively . In this sense, sorbents such as zeolites and metal-organic frameworks (MOFs) stand out as adsorbents of CO2.
Zeolites are microporous aluminosilicate minerals such as analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. Figure 4 shows the microporous molecular structure of zeolite, ZSM-5. Synthetic zeolites are prepared by the slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates.
Zeolites are added to the Portland cement as a pozzolan and water reservoir to reduce chloride permeability and to improve workability. Siriwardane et al. have studied competitive gas adsorption properties of zeolites 13X, 4A, 5A, UOP-WE-G 592, and UOP APG-II with gas mixtures containing CO2 and found that all of them have good CO2 adsorption capacities down to ppm levels from a gas mixture containing 15% CO2, 3% O2, and 83% N2 . Zeolites are microporous and aluminosilicate minerals commonly used as commercial adsorbents. Zeolite has been used for trapping CO2 from ice or air . A zeolite trap was also used as an alternative to a cryogenic trap for collecting CO2 from oxidation of organic carbon. The selective gas absorption and desorption characteristics of zeolite as a function of temperature will be useful for simplifying the system for trapping CO2 and transferring the gas to a graphitization reactor .
Metal organic frameworks (MOFs) are yet another good sorbents for CO2. Their structures are composed of metal-containing nodes linked by organic ligand bridges, which are assembled through strong coordination bonds (Figure 5) .
Compared to other CO2 sorbents such as zeolites and activated carbon, MOFs have higher pore volume and surface area and hence have higher CO2 sorption capacity [60, 61]. Adsorption is the process of entrapping atoms or molecules which are incident on a surface; hence, the adsorption capacity of a material concerned increases with respect to its surface area. In 3D nature, the maximum surface area would be obtained by a structure that is highly porous such that molecules and atoms can access internal surfaces of the materials. It clearly suggests that the highly porous metal organic frameworks (MOFs) should have to have an excellent ability of entrapping CO2. Generally, the most successful MOFs demonstrate extremely high BET surface areas of 4,0007,000m2g1 with many also possessing coordinatively unsaturated metal sites . In order to gain high efficiency of CO2 entrapment inside the MOF and for the development of higher performance MOFs, the interior part of MOFs should be designed to have coordinative porosity, hydrophobicity, defects and embedded nanoscale metal catalysts, unsaturated metallic suitable sites, specific heteroatoms, and other building unit interactions . Some examples of MOFs capable of CO2 sorption are NiII2NiIII(3-OH)(pba)3(2,6-ndc)1.5 (MCF-19; pba=4-(pyridin-4-yl)benzoate, 2,6-ndc=2,6-naphthalenedicarboxylate), Zn4O(bdc)3 (MOF-5 or IRMOF-1, bdc=1,4-benzenedicarboxylate), Zn4O(btb)2 (MOF-177, btb=benzene-1,3,5-tribenzoate), and Zn4O(bte)14/9(bpdc)6/9 (MOF-210, bte=4,4,4-(benzene-1,3,5-triyltris(ethyne-2,1-diyl))tribenzoate, bpdc=biphenyl-4,4-dicarboxylate) .
Nanocement is the cement produced by mechanical activation of nuclear cement particles in the size range 2-3m by coating with 10 to 100nm-thick membranes of modifier materials. More than 65% of mineral supplements such as sand, ash, slag, and tuff and polymer additives are used as modifier materials . The development of modern cement and concrete industry seeks for the improvement of the durability of the materials by the addition of required amount of nanoparticles, or nano-based structure of cement-based materials can be improved. Frequently used nanoparticles are nanosilica, nanoclay, and carbon nanotubes [68, 69]. Improvement of durability of the materials is approached through alteration of the physicochemical properties of the binder. In addition, usages of nanoclay and carbon nanotubes can decrease the transport property, optimize microstructure, and decrease the volume instability of cement-based materials. The process of nanocement production is shown schematically in Figure 6. It has been reported that nanocement can be used to produce 500800 brands of high-strength concretes and 13001500 brands of heavy-duty concretes . US Patent on Method for producing nano-cement, and nano-cement  deals with the procedure developed to produce nanocement, which involves mechanochemical activation of dispersed grains of the Portland cement in the presence of a polymeric modifier. They used at least 60% by wt. of sodium naphthalenesulfonate and mineral siliceous additive containing at least 30 wt.% SiO2 and gypsum to form nanoshells around cement grins. Capsules of 20100nm thickness are formed around Portland cement grains, which are made of sodium naphthalenesulfonate and structured by calcium cations. Subsequent to mechanochemical activation, the resultant material is ground to a specific surface area of 300900m2kg1. Nanocement improves the technical quality of the Portland cement, reduces cost of production due to the use of 70 wt.% mineral additives, 1.22 times reduction of the fuel cost, and 2-3 times reduction of emission of NOx, SO2, and CO2 per tonne of cement. Nanocement has very high performance; for instance, the deflection strength of nanocement-based concrete and ordinary Portland cement-based concrete at 2-day hardening are around 6.37.1MPa and 2.9MPa with corresponding compressive strengths of 49.354.7MPa and 21.3MPa, respectively. At 28-day hardening, deflection strength improves to 8.28.7MPa and 6.4Mpa, respectively, while compressive strength improves to 77.582.7MPa and 54.4MPa, respectively .
Use of nano-graphite as an additive in cement is also currently under investigation. Use of graphite nanoparticles in cement is expected to not only improve mechanical properties but also improve faster curing time, inhibition of premature failure in concretes, and ability to withstand large external forces produced in earthquakes and explosions . The use of less concrete is also possible which means eventual contribution to the production of less Portland cement and hence reduction of consequent environmental problems associated with Portland cement manufacturing . Other nanofillers used to improve properties of Portland cement include nanotitania (TiO2), carbon nanotubes, nanosilica (SiO2) and nanoalumina (Al2O3), nanohematite/iron oxide (iii) (Fe2O3), nano-magnetite/iron oxide (ii) (Fe3O4), nano-ZnO2, nano-ZrO2, nano-Cu2O3, nano-CuO, nano-CaCO3, as nanotubes or fibres (carbon nanotubes and carbon nanofibers, and nano-clay).
According to the FeldmanSereda model, the cement paste consists principally of gel pores, capillary pores, and an interlayer of water. In the concrete, there is an interfacial transition zone between the cement paste and the aggregates, which establishes a weak link in the concrete, basically the site at which the first cracks occur. Hence, it is significant to generate crack-free concrete with the possible incorporation of nanosilica to pursue . Chen et al. demonstrated that TiO2 is an inert and stable compound during the cement hydration process, in which the total porosity of the cement pastes decreased, so that the pore size distribution is also changed. Normally, the acceleration of the hydration rate and the change in the microstructure also affected the physical and mechanical properties of the cement-based materials. The nano-TiO2 role is to work as a catalyst in the cement hydration reactions. Water absorption and capillary absorption show a significant decrease when TiO2 nanoparticles are included in the concrete, as the nanoparticles represent as nanofillers and thereby improve the concretes resistance to water permeability. Moreover, TiO2 nanoparticles can progress the filler effect, and also the great pozzolanic action of fine particles substantially rises the quantity of strengthening gel formed . Nanomontmorillonite (NM) is the most common member of the smectite clay family, which is sometimes referred to as nanoclay. This kind of clay belongs to a general mineral group of clays, which have particles with a sheet-like structure in which the dimensions in two directions far exceed the thickness.
We have investigated the production of these nanoparticles from both top-down and bottom-up approaches. Top-down approach is more industrially viable since large quantities of bulk materials found naturally can be used to produce corresponding nanomaterials through particle size reduction. The top-down approach relies on reducing the size of bulk materials to the size of the nanorange of 1100nm. This can be done by crushing bulk materials to make powders, sieving to different fractions, further crushing of large size fractions, and finally milling to obtain sizes in the nanorange. Sri Lanka is gifted with very high-purity quartz, which contains almost 100% SiO2. This quartz can be used to obtain nanosized SiO2 particles. Our ongoing research in collaboration with the Sri Lanka Industrial Technology Institute (ITI) is very successful, and we are able to produce 50nm size SiO2 nanoparticles in large quantities by this top-down approach. We have also attempted converting ilmenite obtained from Sri Lanka Mineral Sand Corporation to produce nanotitania with great success. Birgisson et al.  summarized the key breakthroughs in concrete technology most probable to result from the usage of nanotechnology. Basically, it has shown the development of high-performance cement and concrete materials as measured by their mechanical and durability properties, development of sustainable concrete materials and structures through engineering for different adverse environments, reducing energy consumption during cement production and enhancing safety, improvement of intelligent concrete materials through the integration of nanotechnology-based self-sensing and self-powered materials and cyber infrastructure technologies, advancement of novel concrete materials through nanotechnology-based innovative processing of cement and cement paste, and also development of fundamental multiscale model(s) for concrete through advanced characterization and modeling of concrete at the nano-, micro-, meso-, and macroscale . The frost resistance of concrete comprising nano-Al2O3 is better than that comprising the same amount of nano-SiO2. The compressive strength of normal concrete containing nano-SiO2 is higher than that of the same amount of nano-Al2O3. The frost resistance of the concrete mixtures can be improved significantly by adding either nano-Al2O3 or nano-SiO2. These nanomaterials not only promote the pozzolanic reaction, but they also act as fillers, thereby improving the pore structure of the concrete and densifying the microstructure of the cement paste. The frost resistance of the concrete containing nano-Al2O3 is better than that containing the same amount of nano-SiO2.
Nanoparticles have a large surface area to volume ratio than their bulk counterparts, and due to their small size, they can fill in small cavities of the cement matrix, densifying the structure to result in improved strength and faster chemical reactions such as hydration reactions associated with cement setting. Further, the material requirement can be reduced drastically thus saving fast depleting natural resources and energy requirements for cement manufacturing and reducing associated adverse environmental consequences.
Basically, different types of cements and their chemical composition and applications in the current engineering and chemical world have been discussed in detail. Different types of enhancing materials and fillers developed using nanotechnology for the productive and effective cement manufacturing have been mentioned with the chemical background. The mechanical defects when concrete is concerned and possible solutions that can be given through chemistry and nanotechnology have been deliberated in detail. In addition, CO2-entrapping chemical compounds such as zeolites and metal organic framework and their contribution in making durability of the cement manufacturing have been illustrated with their chemistry. Environment effects of cement manufacturing and how to control the pollution of the environment when manufacturing processes that are being executed have been discussed using several standard processes, including the Calera process, oxy-combustion process, and monoethanolamide (MEA) process. Currently, the applications of nanoscience and nanotechnology have been gaining popularity in different fields of science and technology. The potential of nanotechnology to progress the performance of concrete and to lead to the development of novel, sustainable, advanced cement-based composites, and smart materials with unique mechanical, thermal, and electrical properties is promising, and many novel opportunities are expected to arise in the future. So finally, the newest trend of making nanocement and its development towards current developing and updating world is described in advance.
Copyright 2018 S. P. Dunuweera and R. M. G. Rajapakse. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
8 main cement ingredients composition and their functions
Cement is a very important building material as a binding element. Almost all building work needs cement. Accordingly, the cement composition is of great interest to engineers. To grasp the structure of cement, one has to learn the quality of the ingredients of cement. By adjusting the quantity of an element during cement manufacturing, the desired value of cement can be achieved.
The most important ingredient in cement is lime and calcium oxide. There is 60 to 70 % lime in the concrete. This comes from calcareous, limestone, shale, etc. Adequate quantities of lime in cement are helpful in the production of calcium silicates and aluminates.
If lime is added in excess quantity, the cement becomes unsound as well as cement expansion and decomposition occurs. If lime content is lower than cements minimum requirement strength, it will decrease and also decrease cement setting time.
The second-largest amount of concrete materials is silica and silicon dioxide, which is about 17 to 25 %. You can get silica from water, argillaceous soil, and so on. Adequate amounts of silica help to shape di-calcium and tricalcium silicates that offer the cement energy.
In the form of aluminum oxide, alumina throughout cement is available. The alumina level of cement should be between 3 and 8 %. Bauxite is extracted, alumina produces cement, etc. Alumina provides the cement with a quick setting quality.
In particular, to achieve the desired value of cement, a high temperature is needed. But when added with cement ingredients, alumina acts as a flux and reduces the temperature of clinkering that ultimately weakens the cement. Therefore, alumina should not be used in excess quantity to maintain a high temperature.
Concrete produces 1 to 3 % of magnesium oxide and magnesium oxide. Magnesia in small quantities of concrete gives the cement strength and color. If it reaches 3 %, the concrete becomes unsound and the cements intensity often reduces.
The sum of iron oxide in cement varies from 0.5 to 6%. It can be extracted from fly ash, iron ore, scrap iron, and so on. The main function of iron oxide is to give the cement color. At high temperatures, by reacting with aluminum and calcium, iron oxide forms tricalcium aluminoferrite. The resulting product supplies the concrete with the characteristics of strength and toughness.
Calcium sulfate is found in the concrete in the form of gypsum. Its packed along with calcareous. It ranges from 0.1%-0.5 %. The function of cement-based calcium sulfate is to increase the initial cement setting period.
The concrete includes alkalis such as soda and potash, which usually varies from 0% to 1%. At the moment of warming, most of the alkalis were carried away by the flue gases during the cement manufacturing process. Cement thus produces very small amounts of alkalis in it. Read More