Portland Cement

See also: Cement & Concrete

Portland cement is the primary ingredient used to make concrete, mortar, or plaster.^[1] A carefully controlled mixture of chemicals consisting of calcium (limestone), silicon (clay or sand), aluminum, iron, and other various ingredients, Portland cement is referred to as a hydraulic product because gypsum is added during the final grinding process and then mixed with water. The gypsum is what gives the cement the ability to harden or set once water is added.^[2]

The process for making Portland cement is carried out by heating limestone and clay in a special rotary kiln and then pulverizing the resulting material, known as clinker, into a fine granular powder.^[3] Portland cement is reputed for its high quality, and the term is used interchangeably to describe any cement. In fact, 98 percent of cement produced in the U.S. today is Portland cement.^[4]

There are different variations of Portland cement. For example, white Portland cement, known as ASTM C 150, has the same properties as gray Portland cement, but is distinctive in its white color. Portland cement can also be colored by adding different pigments, or aggregate material can be mixed in with it to alter its texture or achieve various surface finishing treatments.^[5]

[edit] History

[edit] The Origins of Portland Cement

In 1824, British bricklayer Joseph Aspdin received a patent for the first prototype of Portland cement, which he created when he burned limestone and clay in his kitchen stove.^[6] His method for creating Portland cement involved mixing controlled proportions of limestone with clay, grinding them down, and burning the mixture into clinker that was then ground once more into a finished powder. He named his cement after a similarly colored type of building stone called Portland stone, quarried off the Isle of Portland in Dorset, England.^[7] Aspdin developed his first Portland cement manufacturing plant near Wakefield. The new cement product caught on quickly in the U.K. and was used in the 1828 construction of the Thames River Tunnel and eventually in the building of London’s sewer system between 1859 and 1867.^[8] Joseph Aspdin’s son, William Aspdin, eventually refined his father’s product in 1843; this led to the wide-scale adoption of Portland cement as a product in many building projects in Germany, Belgium, and the U.K. By 1878, Portland cement was commonplace in Germany to the point that the German government outlined a number of product standards for it.^[9]

[edit] Production of Portland Cement in North America

The first recorded shipment of Portland cement in the U.S. was in 1868. European manufacturers were shipping cement as ballast in tramp streamers at very low freight rates. This volume increased to a peak of nearly three million barrels in 1885.

The manufacturing of Portland cement within the U.S. didn’t occur until the 1870s when a man by the name of David O. Saylor built the first Portland cement production plant at Coplay, Pennsylvania. Another U.S. manufacturer to emerge around the same time as Saylor was Thomas Millen. Millen and his two sons experimented in manufacturing Portland cement using a piece of sewer pipe as a kiln to burn the materials into clinker. The sewer pipe was the first example of a rotary kiln used in North America. Using a coffee mill, clinker was then crushed into a fine powder. In 1871 he experimented with different kinds of rocks extracted from his quarries to produce Portland cement.^[10]

In Canada, Portland cement was first imported in wooden barrels from Europe. The first actual recorded production of Portland cement in Canada occurred in 1889 in Hull, Quebec. Other cement plants had been established in Ontario, Quebec, and British Columbia by 1893.^[11] 

In 1874 American Robert W. Lesley founded Lesley & Trinkle, a cement broker. The firm dealt in natural and Portland cements. Lesley used his business contacts to devise both time- and labor-saving apparatus in Portland cement manufacturing. One method entailed pressing the pulverized raw materials into “eggettes” for burning in the kiln. The invention of the rotary kiln led to a jump in the volume of Portland cement produced in the U.S. in the late 19th century—production increased from 42,000 bbl. to 335,000 bbl. a decade later. This was due in large part to the development of the more efficient rotary kiln, which could be run continuously in contrast to the earlier vertical stationary kilns that had to cool after each use.

In 1902 Thomas Edison, owner of the Edison Portland Cement Works in New Jersey, improved upon the design of the rotary kiln by introducing long kilns measuring 150 feet (46 m) in place of the standard 60- to 80-foot (18- to 24-m) kilns that had been previously used. Over the years, the size of kilns increased to more than 500 feet (152 m) long. Substantial improvements were also made to crushing and grinding equipment.^[12]

[edit] Process

Portland cement is produced using a dry and wet process. In both processes, the first step involves crushing rock material extracted from a quarry in large industrial crushers. Rocks are fed into the crusher and reduced to a size of six inches (15 cm) in the first crushing. The rock then goes through a second crushing phase using secondary crushers and hammer mills, reducing it to a size of three inches (8 cm) or smaller. In the wet process, the raw materials are proportioned and then ground with water and fed into the kiln as slurry. The dry process involves feeding a raw ground mixture of dry materials into a kiln.

The huge cylindrical-shaped steel rotary kilns used to manufacture Portland cement are big enough to fit an entire automobile and can be as high as a 40-story building, and are mounted on a slightly inclined horizontal axis. The slurry or dry materials are fed through an opening at the top. Near the bottom is a roaring blast of flame that heats the slurry or dry mixture to a temperature of 2,700 degrees Fahrenheit. The kiln is heated using coal, oil, or gas.

As the material moves through the kiln, particular elements are driven off as gases. The elements that remain combine to form clinker, a new, marble-sized material, exhibiting completely different chemical and physical attributes.

The clinker is so hot it has to be discharged through the lower end of the kiln and cooled down in industrial-sized coolers. The heated air from these coolers is then funneled back into the kilns to save fuel and increase burning efficiency.^[13] After the clinker has cooled, it is ground down with a small amount of gypsum into a fine powder to make Portland cement.

[edit] References

1. ↑ Definitions. Boston Brick and Stone, 2008-10-14.
2. ↑ ToolBase Services, 2008-10-14.
3. ↑ What is Cement? What is Concrete?. The Artistic Garden, 2008-10-14.
4. ↑ A History of Cement. Traditional Mortars, 2008-10-14.
5. ↑ What is White Portland Cement. Portland Cement Association, 2008-10-14.
6. ↑ How Portland Cement is Made. Portland Cement Association, 2008-10-14.
7. ↑ Definitions. Boston Brick and Stone, 2008-10-14.
8. ↑ Definitions. Boston Brick and Stone, 2008-10-14.
9. ↑ What is Portland Cement? WiseGeek, 2008-10-14.
10. ↑ A History of Cement. Traditional Mortars, 2008-10-14.
11. ↑ Cement Industry. The Canadian Encyclopedia, 2008-10-14.
12. ↑ A History of Cement. Traditional Mortars, 2008-10-14.
13. ↑ How Portland Cement is Made. Portland Cement Association, 2008-10-14.