Cement and Concrete

In 1824, acquired Joseph Aspdin, a British stone mason, a patent for cement he produced in his kitchen. Inventor heated a mixture of finely ground limestone and clay in his kitchen stove and ground the mixture into a powder create a hydraulic cement-one that hardens when mixed with water. Aspdin named product Portland cement because it resembled a stone mined on the Isle of Portland off the British coast. With this invention, there Aspdin foundation for today's Portland cement industry.

Manufacturing Process:

Portland cement, the fundamental ingredient in concrete, is calcium cement made with a combination of calcium, silicon, aluminum and iron. Cement that meet specific chemical and physical characteristics requires careful control of the manufacturing process. The first step in Portland cement manufacturing process is the extraction of raw materials. Generally, raw materials, which consist of combinations of limestone, shells or chalk and slate, clay, sand or iron ore from a quarry near the plant. At the quarry, the raw material was reduced by primary and secondary crushers. Stone is first reduced to 5-inch size (125 mm), then to 3/4-inch (19 mm). When raw materials arrive at the cement plant, the materials that are sized to create cement with a definite chemical composition. Two different methods of dry and liquid used in the manufacture of Portland cement. In the dry process, dry ingredients are proportioned, ground to a powder, mixed together and fed to the kiln in a dry state. In the wet method, slurry is formed by adding water to the properly proportioned raw materials. The grinding and blending operations are then supplemented by materials in the slurry form. When the mixture is a mixture of raw materials incorporated in the upper end of a tilted rotating, cylindrical kiln. The mixture passes through the furnace at a rate controlled by the slope and rotational speed of the oven. Burning fuel consisting of powdered coal or natural gas is forced into the lower end of the kiln. Inside the oven when the raw temperatures 2600ÞF to 3000ÞF (1430ÞC to 1650ÞC). On 2700ÞF (1480ÞC), a series of chemical reactions that cause the materials to fuse and create cement clinker-grayish-black pellets, often the size of marbles. Red-hot clinker is discharged from the lower end of the oven and transferred to various types of coolers to lower the clinker to handling temperatures. Cooled clinker is combined with gypsum and ground into a fine gray powder. The clinker is ground so fine that nearly all of it passes through a No. 200 mesh (75 micron) sieve. This fine gray powder is Portland cement.

Types of Portland Cement:

Different types of Portland cement are manufactured to meet various physical and chemical requirements. The American Society for Testing and Materials (ASTM) Specification C-150 contains eight types of Portland cement. Type I Portland cement is normal, general purpose cement suitable for all uses. It is used in general construction projects such as buildings, bridges, floors, sidewalks, and other precast concrete products. Type IA Portland cement resembles type I with the addition of air-entraining properties. Type II Portland cement generates less heat at a slower pace and has a moderate resistance to sulfate attack. Type IIA Portland cement is identical to Type II and produces air-entrained concrete. Type III Portland cement has high early strength cement and causes concrete to set and gain strength quickly. Type III is chemically and physically similar to Type I, except that its particles have been ground finer. Type III is air-entraining, high early strength cement. Type IV Portland cement has a low heat of hydration and develops strength at a slower pace than other types of cement, making it ideal for use in dams and other massive concrete structures where there is little chance for heat to escape. Type V Portland cement is used only in concrete structures that will be exposed to severe sulphate action, principally where concrete is exposed to soil and groundwater with a high content of sulphate.

Portland cement can also be made to ASTM C1157 and includes the following: Type GU hydraulic cement for general construction, Type HE-high early strength cement, Type MS-moderate sulfate resistant cement, Type HS-high sulfate resistant cement, Type MH-moderate heat in the hydration of cement, and Type LH-low heat of hydration cement. These cements can also be designated for low reactivity (option R) with alkali-reactive aggregates.

White Portland cement:

In addition to the eight types of Portland cement, a series of special purpose hydraulic cements are produced. Among them are white Portland cement. White Portland cement is identical gray Portland cement, except in color. During the manufacturing process, manufacturers select raw materials which contain only negligible amounts of iron and magnesium oxides, the substances that give cement its gray color. White cement is used when architectural considerations specify white or colored concrete or mortar.

Blended hydraulic cement:

Blended hydraulic cement is produced by thoroughly mixing two or more types of cementations' material. Primary composite materials are Portland cement, ground granulated blast furnace slag, fly ash, natural pozzolans, and Silica fume. These cements are commonly used in the same manner as Portland cement. Blended hydraulic cement in accordance with the requirements of ASTM C595 and C1157. ASTM C595 cements are as follows: Type IS Portland blast-furnace slag cement, IP and Type P-Portland-pozzolan cement, Type S-slag cement, Type I (PM) pozzolan-modified Portland cement and Type I (SM) slag modified Portland cement. Of blast furnace slag content of type is between 25 percent and 70 percent of the mass. The pozzolan content of type IP and P is between 15 percent and 40 percent of the mass of the mixed cement. Type I (PM) contains less than 15 percent pozzolan. Type S contains at least 70 percent slag by mass. Type I (SM) contains less than 25 percent slag by mass. The supplementary materials in these cements are explained on page 28 These mixed cement can also be described as air-entraining, moderate sulfate resistant, or with moderate or low heat of hydration. ASTM C1157 blended hydraulic cement comprises the following: Type GU-blended hydraulic cement for general construction, Type HE-high early strength cement, Type MS-moderate sulfate resistant cement, Type HS-high sulfate resistant cement, Type MH-moderate heat of hydration cement, and Type LH-low heat of hydration cement. These cements can also be designated for low reactivity (option R) with alkali-reactive aggregates. There are no restrictions on the composition of C1157 cement. The manufacturer can optimize ingredients, such as pozzolans and slag, in order to optimize certain properties. The most commonly available mixed cement, Type IP and IS. U.S. spends a relatively small volume of mixed cement in relation to countries in Europe or Asia. This may change with consumer demand for products with special properties, together with environmental and energy concerns.

Expansive Cements:

Expansive cement is hydraulic cement, which expands a bit in the early hardening period after setting. They meet the requirements of ASTM C845, designated as Type E-1. Although the three varieties of expansive cement standard designated as K, M and S, K is only available in the U.S. Type E-1 (K) contains portland cement, anhydrous tetra calcium trialuminosulfate, calcium sulfate, and uncombined calcium oxide (lime).

Expansive cement used to make shrinkage-compensating concrete is used:

(1) To compensate for the volume decrease due to drying shrinkage. 

(2) To move in reinforcements. 

(3) To stabilize the long-term dimensions of post-tensioned concrete structures. One of the great advantages of using expansive cement is in control and reduction of drying-shrinkage cracks. In recent years, shrinkage-compensating concrete was of particular interest in bridge deck construction, the crack development is minimized.