There are five types of hydraulic cements. The first, Portland cement, is the most common and has been the standard for over a century. However, the other four types of hydraulic cements have their own unique applications and benefits. Let us take a closer look at each one and their uses.
Portland cement is made from limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore. These materials are crushed and combined with other ingredients (including iron) in a rotating cement kiln at 2,600 degrees Fahrenheit. The resulting substance is a marble-like ball called clinker that is ground into powder along with gypsum to create what is known as Portland cement (Type I).
There are several variations of Portland cement that include Type II – sulfate resistant; Type III – high early strength; Type IV – low heat of hydration; and Type V – high sulfate resistance.
There are five different types of hydraulic cement:
1. Cement based on Portland cement
2. Calcium aluminate cement
3. Slag cement
4. Type K cement
5. Geopolymer cement
Portland cement is the most common type of hydraulic cement used worldwide. It is made by grinding limestone and clay into a fine powder, mixing them together in the correct proportions, heating them in a rotary kiln to 1400 °C (2550 °F) and then grinding the resulting clinker to a fine powder to make portland cement. Portland cements are usually grey in colour, but white portland cements are also available. Clinker is finely ground with gypsum to produce ordinary portland cement; clinker may also be ground alone to produce Portland blast-furnace slag cement. Portland pozzolana cements are made by including pozzolanic materials such as fly ash, volcanic ash or other natural materials that contain silica and alumina (and possibly small amounts of iron oxide) in the production process for ordinary portland cement or Portland blast-furnace slag cement. The inclusion of these supplementary materials produces blended cements that have properties similar to those of ordinary portland
While there are several different types of hydraulic cements, portland cement is the most common. As such, this article will focus on the properties and characteristics of portland cement and how it is made, as well as its uses.
Portland cement is made from a combination of raw materials. The primary raw material used in the production process is limestone. Limestone contains calcium carbonate (CaCO3). Other raw materials may include shells, chalk, marl, shale, clay, blast furnace slag, slate, fly ash, and silica sand. In addition to these raw materials, other ingredients are also added to the mix to ensure the product has specific chemical properties once cured.
Portland cement manufacturing is a four-step process: 1) crushing and pre-homogenization; 2) raw material preparation; 3) clinker production; 4) cement grinding.
Crushing and Pre-homogenization: Raw material preparation involves crushing and pre-homogenization. Crushing is accomplished by compression of the rock against rigid surfaces or by impact against surfaces in a constrained motion path. Crushing is done dry or with water spray applied on the surface to prevent dusting. The crushed rock is stored in stockpiles where it undergoes further homogenization
There are four main classes of hydraulic cements. They differ in their chemical compositions, the rate at which they set, and the amount of expansion they produce when setting.
The first class is known as ordinary Portland cement, or just Portland cement. This cement is made by heating limestone with clay or shale to 1450 °C in a kiln. The resulting hard substance, called clinker, is then ground with gypsum into a fine powder to make ordinary Portland cement, the most commonly used type of cement (often referred to as OPC).
The other three classes are called hydraulic cements because they contain certain compounds that will react chemically with water to form a product that will harden under water.
A second class is known as pozzolanas or pozzolans, named for the town Pozzuoli near Mount Vesuvius in Italy. These cements contain silica, alumina, and iron oxide as major ingredients. They set rapidly by reacting chemically with water and harden under water. The Romans used these cements to build many structures such as the Pantheon in Rome more than 2,000 years ago using volcanic ashes from Mount Vesuvius and other volcanoes as the major ingredient for their hydraulic cement.
The name “hydraulic cement” comes from the fact that it hardens when water is added. It is called hydraulic because water is one of the components. The hydraulic cement was first made by a British bricklayer named Joseph Aspdin in 1824, who cooked ground limestone and clay together in his kitchen oven. He called it Portland Cement because the finished product resembled a type of building stone quarried on the Isle of Portland off the coast of England.
Hydraulic cements are made from clinkers produced by calcining limestone with small amounts of other ingredients, such as sand, shale, clay, and iron ore. The most important properties are strength, durability and low permeability to liquids and gases.
The main difference between ordinary portland cement (OPC) and other types of hydraulic cements is the amount of Tricalcium aluminate (C3A) it contains. C3A is responsible for the initial set or rate at which concrete hardens. Hydraulic cements contain less than 5% C3A while OPC contains more than 5%.
The “hydraulicity” of a cement is determined by the hydration reaction between the cement and water. As the reaction proceeds, crystals of hydrates form that bond to each other and lock together. If a cement has good “hydraulic” properties, it will harden underwater or when exposed to moist conditions.
In order to be considered hydraulic, a cement must:
• Contain an appreciable amount of lime (CaO)
• Contain an appreciable amount of silica (SiO2)
• Contain less than 5% alumina (Al2O3)
• Be free from alkali sulphates.
Portland Cement: Is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding Portland cement clinker (more than 90%), calcium sulfate, usually gypsum (less than 5%) and other materials to control the setting properties of the finished material. It may also be mixed with gypsum plaster, finely ground blast furnace slag, silica fume or metakaolin.
Portland Pozzolana Cement: Is a variation of ordinary Portland cement. It is mixed with fly ash, a waste product from coal burning power stations, ground granulated blast furnace slag and hydrated lime.
Portland Slag Cement: Is made when iron ore or iron pellets are cooked in a furnace at 2,600 degrees fahrenheit. They are then ground up and mixed with limestone. The result is what we call slag cement. There are two types of slag cements: Type IS (slag cement) and Type IP (portland-slag cement). Type IS is used for most applications.
Portland-Limestone Cement: Is for structural applications and is used in