Concrete has well earned its reputation as one of the most durable of all building and paving materials. In fact, the ancient Romans constructed buildings out of concrete that people can still visit today. Few other building materials can boast such compelling evidence of their strength and longevity.

Despite the universal role of concrete in the modern world, many people fail to understand the basic composition of concrete. Concrete consists of three principal ingredients: water, crushed stone aggregate, and cement. This article takes a closer look at the last of these ingredients, outlining three interesting yet little-known facts about cement.

Prior to the 19th century, concrete was made using natural cement — in other words, cement produced by burning naturally occurring mixtures of clay and limestone. The ingredients in such cement varied wildly depending on the properties of the local ingredients. As a result, not all concrete structures enjoyed the same level of strength and stability.

The production of cement changed drastically in 1824 when an English man named Joseph Aspdin created a specific blend of cement known as portland cement. Portland cement derived its name from color similarities with quarried stone from the Isle of Portland. The composition of portland cement has highly regulated proportions of chemicals such as aluminum, calcium, iron, and silicon.

Despite having been invented almost 200 years ago, portland cement remains the most common type of cement used in concrete. In fact, in the United States today, as much as 98 percent of all cement produced consists of portland cement. Manufacturers simply have not found a way to improve upon the performance characteristics of portland cement.

Even today, limestone and clay make up the two most common ingredients in portland cement. Other materials include everything from shells to chalk or iron ore. Many people assume that, once these ingredients have correct proportions, a manufacturer simply grinds them down into a power to produce cement.

Yet cement production actually involves applying extreme temperatures. A manufacturer heats the various ingredients that create cement inside of a giant cylindrical furnace known as a kiln. Temperatures inside of this kiln reach approximately 2,700 degrees Fahrenheit during the production process.

These temperatures act to purify the cement ingredients, driving off unwanted substances. In the process, the substances that remain fuse together into marble-sized grey balls known as clinker. Once the clinker has fully cooled, the manufacturer grinds it down into an incredibly fine powder. A single pound of ground cement contains a staggering 150 billion grains of material.

Concrete professionals continue to hunt for ways to tweak the performance characteristics of their product. While portland cement remains largely unchanged from its earliest days, producers have introduced subtle changes. Today, five different varieties of portland cement exist, each of which displays slightly different characteristics.

In terms of composition, the main difference between the five types of portland cement involves the amount of tricalcium aluminate used. Also known as C3A, tricalcium aluminate affects the heat of hydration — in other words, the amount of heat the concrete produces as it undergoes the chemical change that ultimately makes it hard and strong.

For general construction purposes, most contractors select Type I portland cement. Type II cement, by contrast, contains lower levels of C3A. This reduction gives the concrete more resistance to sulfate attack. Type II cement makes a good choice for building structures that face exposure to soil and/or water with high levels of sulfate ions.

A paving contractor must understand the distinctions between all five types of portland cement, in order to select the best one for a particular project. For more information about how to design the ideal concrete for your needs, please contact Albuquerque's paving pros at Star Paving Company.