Ordinary Portland cement 42.5 is the standard grade of cement used in the majority of ordinary cement applications, such as pavements, residential buildings, and pipes. OPC 42.5 comes in two sub grades, OPC 42.5 R, and OPC 42.5 N.

OPC 42. 5 R develops high strength early in the curing phase, whereas OPC 42.5 N develops high strength at the normal rate. OPC 42.5 R is suitable for applications where high strength is needed relatively quickly after pouring and setting. Both types of OPC 42.5 will attain a minimum compressive strength of 42.5 MPa on the 28th day after pouring, however OPC 42.5 R will gain strength more quickly than its N rated counterpart.

The Secret of OPC 42.5 R Cement

OPC is a blend of lime, silica, iron and aluminum. These elements must be mined, extracted and crushed so that they can be mixed in the correct proportions. Though made from rough and jagged rocks, precision is the key to making OPC.

Source materials are deposited from separate silos onto a conveyor belt by computer controlled feeds, and the batch, known as ‘raw mix’, is sent to a blending chamber, where it is mixed and analyzed to ensure that the correct amounts of each material are present. This can be either a wet or a dry process, and plants differ greatly from one another as to how they manage this stage of manufacturing.

The R rating of OPC 42.5 R is conferred by blending the base ingredients in certain precise portions. An adjustment of just a few percent of any raw material can lead to large variances in strength and other qualities of the resulting product. This is why chemical analysis at the raw mix stage is carried out so very rigorously.

The bulk of OPC is made up of calcium and silicone, which together form 66% of the total mass of the product. Iron and aluminum act as flux materials, lowering formation temperatures for the calcium silicates which make up OPC.

When analysis is complete, the raw mix is sent to a kiln where it is heated gradually along its length to between 1400 and 1450 degrees Celsius at its hottest point. As the raw mix travels through it, it begins to melt and calcium silicates begin to form. The end result of this firing are small nodules of calcium silicates called ‘clinker’.

Clinker is ground down in a rotating chamber until it becomes a fine powder known as OPC. The size of the final particles determine the grade of OPC. OPC 42.5 is a relatively coarse type of OPC, with the grains of the final product being around 40 microns in diameter.

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Both Portland cement and Blended cements are hydraulic cements, which means that they require the addition of water in order to form the bonds which make them set hard and strong. Once formed, the bonds are not soluble in water, which means that hydraulic cements can be used in situations where they will be exposed to water (such as rain water, drainage water, or sea water) without fear of them breaking down and washing away.

There are six main types of hydraulic cements, and both Portland and Blended cements can be categorized into these types.

Type GU – General Use. Suitable for general applications, except those where ground water may be involved, or where moderate to low heat of hydration is required. Heat of hydration is a term referring to the amount of heat that is given out as bonds are formed within the cement. The reactions which form the bonds in cement are exothermic, which means they give out heat. In some projects, such as large scale dams, it is advantageous to use a cement that has a low heat of hydration, as cements which release a great deal of heat whilst setting and hardening can cause major problems.

Type HE – High Early Strength. High early strength cements set and harden quickly, and can be used as load bearing structures much more quickly than their counterparts. These types of cement are ideal for projects which must be finished quickly.

Type MS – Moderate Sulphate Resistance. Moderate sulphate resistance makes cement suitable for use in applications where the concrete will be exposed to normal levels of sulphates which are present in ground water.

Type HS – High Sulphate Resistance. High sulphate resistance is useful for projects where the cement will be exposed to unusually high levels of sulphates.

Type MH – Moderate Heat of Hydration. Moderate heat of hydration cements are suitable for large applications, such as small bridges, or retaining walls.

Type LH – Low Heat of Hydration. Low heat of hydration cements are designed for relatively rare major construction projects.

Blended Cements

Blended cements are produced by blending two types of materials together to produce a new type of cement. Portland cement, natural pozzolanic compounds, blast furnace slag, silica fume, calcined clay, and fly ash are all common components of blended cements. Blended cements have been developed in response to various needs and market pressures, including the need to find means of recycling materials left over from other processes, such as the production of iron, which leaves blast furnace slag. Blended cements also have certain properties that make them more useful in some cases than ordinary Portland cement, and they quite often reduce the cost of cement as well.

There are five main types of blended cement:
Type IS – Portland blast furnace slag cement, where Portland cement has been ground with blast furnace slag. Blast furnace slag content is usually between twenty five and seventy percent of Type IS cement by mass.

Type IP or P – Portland pozzolan cement, where Portland cement has been ground with pozzolanic material. Pozzolan content is usually between fifteen and fourty percent of total mass.

Type I (PM) – Pozzolan modified Portland cement.

Type S – Slag cement.

Because there are no restrictions on the makeup of blended cements, they can be designed with specific properties in mind to fit specific construction applications.

Expansive Cements

Expansive cements are a type of hydraulic cement which expand as they begin to harden. Expansive cements are designated with an ASTM label of E-1, and come in three categories, K, M, and S, though in certain regions, such as the United States, only K may be available. E-1(K) cement contains lime, calcium sulphate, anhydrous tetracalcium trialuminosulfate, and Portland cement as its main ingredients.

Expansive cements are exceedingly useful in construction applications where structural cracks must not develop. Normal cement types shrink during drying, which can cause problems in some construction applications. Expansive cements compensate for this shrinkage by expanding slightly. There are three main uses for expansive cements the first one being crack resistance, the second being induction of tensile stress in reinforcement applications, and the third being as a means to ensure that dimensions of post tensioned concrete structures remain static.

Portland Cement
There are many different types of cement available on the market today, but by far and away the most popular type of cement is Portland Cement, which comes in a range of specifications to suit various conditions. The basic ingredients of Portland cement are calcium and silicone, along with iron, aluminum, and very small amounts of other substances. Gypsum is also a component of Portland cement, added at the very end of production in order to control the rate at which the cement will set. Gypsum (the lay term for calcium sulfate) has been used since Egyptian times to regulate setting of cement like substances.

ASTM Standards For Portland Cement
As has been mentioned, there are various types of Portland cement which posses different properties which make them suitable for different applications. The American Society for Testing and Materials has classified eight different types of Portland Cement.

Type I Portland Cement
Type I Portland cement is general purpose cement with no particularly special attributes. It is suitable for use in general applications, however it should not be used in applications where the cement will be in contact with the ground, or with ground water, as these substances tend to contain sulphates which can attack the cement and make it expand and distort out of shape.

Type II Portland Cement
Type II Portland cement has some sulphate resistance, and releases less heat during setting and hardening than Type I Portland cement. Type II cement is therefore suitable for construction projects which involve exposure of the cement to ground water, such as pavements and drainage systems. Type II cement can also be used for large scale work such as retaining walls and other such masses.

Type III Portland Cement
Type III Portland cement develops strength much quicker than other types of Portland cement. The trade off is that its final strength tends to be slightly less than other forms of Portland cement which take longer to set and harden. Type III Portland cement is very useful for projects which must be completed quickly.

Type A Portland Cement
Type A Portland cement refers to Type IA, Type IIA, and Type IIIA Portland cements. These cements are simply cement types of the aforementioned categories which have had special additives added to them which cause small pockets of air to be trapped inside the cement in a uniform fashion. This provides greater freeze/thaw resistance to the cement, preventing it from cracking in conditions which experience large variances in temperature.

Type IV Portland Cement
Type IV Portland cement is a relatively rare type of Portland cement which is specially designed to release heat slowly during setting and hardening. Designed for use on very large scale projects, such as dams, Type IV Portland cement can generally only be obtained by special order in very large quantities.

Type V Portland Cement
Type V Portland cement was designed to be used in high sulphate conditions, where Type I and Type II Portland cement cannot successfully be used. It is not typically necessary to use Type V Portland cement, except in extreme conditions. Most applications requiring contact with water are adequately satisfied with Type II Portland cement.

White Portland Cement
Whilst not truly a separate type of cement, white Portland cement is a unique kind of Portland cement that can be produced to meet the specifications of most types of Portland cement. It is different from ordinary Portland cement in that it has a white coloration, instead of a dull grey one. This effect is achieved by limiting the amount of iron and magnesium oxide in the mix during production. White cement can also be colored to achieve various effects, and is quite popular as an alternative to the traditional drab grey coloration of ordinary Portland cement, especially in projects which have a strong aesthetic component.

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Just as there are various types of Portland cement available for different applications there are also various grades of cement existing within ordinary Portland cement. Ordinary Portland cement can be classified as being either 33 grade, 43 grade, or 53 grade, though sometimes the latter grade types are referred to as 42.5 grade or 52.5 grade.

Each grade type corresponds to the compression strength which is attained on the 28th day after pouring, with 53 grade having a minimum compressive strength of 53 MPa, or 530 kg/cm2. It should be noted that the number associated with a particular cement grade is the lowest strength allowable at the 28 day mark. Many cements far exceed the grade number in terms of compression strength. For instance, some 43 Grade OPCs can have a strength over 500 kg/cm2 on the 28th day.

OPC 43 and OPC 53 do not differ in chemical content, OPC 53 is simply ground much finer than OPC 43 during the final grinding process. This creates a product that is much stronger and more durable than less finely ground cements.

33 Grade Ordinary Portland Cement (OPC 33)

33 Grade Ordinary Portland Cement is now very rarely used, as higher strength cements have become increasingly popular. It is suitable for general uses such as general paving and mass concreting, but may be hard to find as it has been phased out in many areas of the world and replaced with either OPC 43 or OPC 53.

43 Grade Ordinary Portland Cement (OPC 43) / (OPC 42.5)

This type of cement is commonly used in construction work, such as residential, commercial, and industrial structures. In addition to this, most pre-cast cement objects such as pipes and tiles are made from OPC 34 cement. Because OPC 33 has now been phased out in most areas of the world, OPC 43 is also quite often used in plastering, flooring and other non structural applications.

Unless a project requires very high strength cement, most experts generally recommend the use of 43 Grade Ordinary Portland Cement. OPC 43 has a set time of around 30 minutes, and develops a minimum compression strength of 230 kg/cm2 after three days, 330 kg/cm2 after seven days, and 430 kg/cm2 after twenty eight days.

53 Grade Ordinary Portland Cement (OPC 53) / (OPC 52.5)

This cement is used for projects where a high level of strength is needed, such as in the construction of skyscrapers, bridges, and other heavy load bearing structures. Not only is this type of cement stronger than other types it is also more durable, and in lower stress applications, can be substituted for lower cement grades. If OPC 53 is substituted for a lower grade cement, overall savings in the amount of cement used can sometimes be made. OPC 53 grade cement often has a compression strength of over 580 kg/cm2 after 28 days.

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The concept of cement has been with humanity virtually since the first attempts at construction began over 600,000 years ago when man moved out from the caves and began to construct his own housing from wood and wattle, and then later on, from mud bricks.

Wood and wattle houses (also known as post houses, because of the wooden posts which were often erected to give them structural integrity) were made by weaving wattle and wood together, and then daubing them with a mixture of materials containing cow dung, lime, and mud. This daub sealed the houses as it dried, due to the reaction of certain chemicals present in the cow dung with the lime in the mixture. The substance produced by this reaction made a strong, solid coating which protected the inhabitants of the building from the elements.

The bricks of mud brick homes were also joined together with a kind of primitive cement, a clay based slurry that dried hard and kept the bricks in place. Both so called ‘cow dung’ and mud brick techniques are still used by some tribal populations when building homes to this very day, and evidence of the relative efficacy of these techniques can be observed in many small tribal villages in Africa.

In many parts of the world however, as mankind evolved from primitive societies towards more technologically advanced ones, better techniques were evolved for the making of bricks. Fired bricks, heat treated in kilns were used in in construction applications in Egyptian and Mesopotamian societies, and as the buildings built by these, and other advanced socities, became larger and more complicated, a need arose for a better kind of binding agent with which to join the bricks together. Various cultures and societies began to experiment with different types of cement like substances to be used as mortar in their buildings. Lime became a popular choice throughout much of the world as an additive which added strength and durability to existing types of cements and mortars. The Egyptians also used gypsum, which is still used in modern cement as an additive which controls how quickly cement sets.

Modern Cement

Modern cement was not invented until the Industrial Revolution which took place in Europe in the late 18th century. Technology was booming during this time, and the need for new and better materials with which to build structures was high. Modern cement was developed in response for a need for stronger concretes, and for cements which could be used in structures which were commonly exposed to water, such as those near the sea, and those in rainy climates.

Prior to this time, stone had been the primary building material, but supplies of stone suitable for building were beginning to run low, and prices were higher than ever before. Some ingenious builders and designers began to build buildings from brick instead, and finished them with a type of stucco that made them appear to be made out of stone. Because these large British buildings had to be completed on strict schedules, there was no time to wait around for weeks on end for cement to dry. In response to this need, a range of quick drying cements were developed.

One of the most popular early quick drying cements was known as ‘Roman’ Cement. It was developed in the 1780’s by a man named James Parker, and was manufactured by burning a specific type of clay deposit known as septaria, a substance which contains both clay and chalk, and grinding the post firing material down into a very fine powder. When combined with sand this cement made for a very quick setting mortar which could dry in just 15 minutes.

The next major development in cement technology was a strong type of hydraulic cement. Hydraulic cement is a type of cement that needs to be mixed with water in order for it to set, and is not soluble in water once it has set and dried.

Prior to the 1820’s, most all cements had been non hydraulic in nature, meaning that they were dry mixtures which had to remain dry in order to develop the necessary strength which was needed for construction applications. This was obviously a problem in many respects, especially in construction projects which involved a great deal of water. The first step towards truly effective hydraulic cements was taken by an English engineer called John Smeaton in 1755 , who was building a lighthouse, and during his investigations into possible construction materials which might be suitable for the building of a lighthouse, discovered that the more clay that was present in the cement, the more hydraulic it was.
For the next seventy years or so, various people worked on the problem of creating a strong cement which could withstand the rigors of being rained on, or washed up against by waves without dissolving away leaving buildings which used it nothing more than untidy piles of bricks.

Portland cement, a hydraulic cement which is still in popular use today was invented by Joseph Aspdin who patented the product in 1824, however it was his son, William Aspdin who developed the strength and durability of Portland cement by adding a compound called ‘alite’ to it, which is still used to strengthen cement today.

William had a difficult time at first convincing people of the usefulness of his product, as it contained much more lime than the original Portland cement, and so needed to be fired at much higher temperatures. Also, due to its hardness, the resulting clinker developed during the firing process caused problems during grinding because it would wear down the millstones much more quickly than other types of cement.

The saving grace of Portland cement was the fact that the end product was a slow setting, high strength cement which could be mixed with concrete to create structures which developed strength quickly, unlike earlier cements which could take weeks to develop enough strength for timber framing to be able to be removed.

Portland cement is now the most popularly used type of cement in the world, although since the 19th century, many different types of cement have been developed for use in different kinds of applications. A few of these cements include expansive cements, which do not shrink during drying like typical hydraulic cements, colored cements, for decorative uses, and masonry cements, which have been developed for used solely in masonry applications and which are not suitable for use in concrete.
Cement continues to evolve, though admittedly at a much slower pace than it did during the boom years of the Industrial revolution. Necessity will always be the mother of invention, and as long as we encounter new needs which are unfulfilled by cement products currently available on the market, it is certain that new types of cement will be developed.

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Cement is a fine ground powder which when mixed with water forms a paste which quickly dries and hardens. Cement is an excellent binding agent and is often used in construction applications to create a bond between the surfaces of two or more objects. Cement is also used heavily in the manufacturing of both concrete and mortar, where its binding properties are used in conjunction with various aggregates to form strong and durable building materials. The most commonly used type of cement today is Portland cement, patented in 1824, and so named by its inventor, Joseph Aspdin, because he thought that the color of the cement was very similar to the limestone which was mined at the time from the Isle of Portland in the English Channel.

Cement Ingredients

Long story short, cement is made by transforming quarry rock into a powder so incredibly fine that it will even pass through a sieve capable of holding water. The most commonly used type of modern cement, Portland cement, is made by blending iron, aluminum, silicone, and calcium. These are extracted from one or more of the following sources: limestone, chalk, silica sand, iron ore, shale, shells, clay and blast furnace slag.

Though cement appears to be a fairly dull and simple substance, a great deal of effort must be expended in the manufacturing process to ensure that the raw material mix contains the correct amounts of each element, and that production conditions such as temperature and pressure remain within acceptable predetermined limits throughout the process. Deviations in any of these elements could jeopardize the quality of the entire batch.

A major part of the cement producing process is microscopy, a science which involves analyzing the structure of materials on a microscopic level, and which allows producers to know the precise amounts of each of the elements present in a sample, and how these elements are bound together. Without the ability to tell exactly what elements are present in a sample, and in what quantites they are present, it would be almost impossible to create a homogeneous cement product that could be relied upon to behave in the same fashion, and possess the same chemical and physical properties as other cement batches when mixed and poured. This could be potentially disastrous in construction applications where strength tolerance, chemical resistance, and other factors must be consistent and predictable from batch to batch.

Making Cement

The actual production of cement involves crushing large amounts of rock, reducing it little by little until no piece exceeds roughly three inches in diameter. Usually this takes place in two stages, with large rocks being crushed and broken up, and then the smaller pieces being hammered until they reach the desired size. In some operations, this crushing is undertaken in a one step operation which reduces large chunks of rock into small fragments relatively quickly.

Once the rocks are crushed there are two possible means of processing the raw materials further. The first process, the ‘dry’ process, involves grinding the rock up into a very fine powder and sending it into a kiln in a dry state. In the second type of process, the ‘wet’ process, the raw rock and other materials are mixed with care to predetermined specifications, and mixed with water before being ground up and fed into the kiln wet.

Of course, it is not so simple as merely grinding up rock and then heating it in a kiln. The ground rock must first be analyzed to determine its content, and then blended in correct proportions before it is sent on to the kiln. In order to get to the kiln, the ground rock is sent through a preheated tower, where the raw material is preheated by the gases exiting the kiln, speeding the process up and saving the plant a great deal of energy and expense.

Once inside the kiln, which is a very large structure, sometimes over three meters in diameter and over sixty meters tall, the materials are heated to tremendous temperatures of 2,700 degrees Fahrenheit or more. The firing process melts the materials and causes waste gases to be released, (the same gases which are then used to preheat the raw material entering the kiln), and as the gases are released, the various elements form entirely new compounds, and emerge from the kiln in the form of pebble type structures called ‘Clinker’. To the clinker is added gypsum, a chemical which helps control the way that cement sets. The clinker is then ground down in a rotating chamber into the very fine power that comprises cement, packed into bags, and sent off for mixing and use in construction applications.

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