"Technology and Us"
School of Technology
Centennial Symposium
An Extended Celebration

Fall Semester 2002

Technology and US:
From Cement to Concrete

Anthony M Sorcic
Peter Bohme

Cements are considered hydraulic since they set and harden by reacting with water. Hydraulic cements are binding materials generally classed as adhesives. These substances are capable of holding other materials together by paste to aggregate bond.

The origins of hydraulic cements go back to classical Greece and Rome, when lime and volcanic ash were mixed to form a hard monolithic mass. However, the invention of Portland cement is widely credited to Joseph Aspdin, an English mason. Aspdin patented it in 1824 and named his product Portland cement because its gray color resembled the color of limestone quarried on the Isle of Portland in Great Britain.

The manufacturing processes of today generally consist of raw materials extraction, blending and clinkerization and grinding and distribution. Typically limestone, marl and clays as well as other materials containing the required proportions of calcium, silicon, aluminum and iron oxides are extracted using drilling and blasting techniques from quarries located near the plant. The quarried materials are then reduced in size by compression and/or impact in various mechanical crushers. These selected materials are then proportioned in such a way that the resulting mixture has the desired chemical composition. Mixing is an important step in the process to ensure an even distribution of the properly proportioned components of the raw mix so that the clinker will be of a uniform quality. This process is accomplished by either a dry process method, which entails the grinding and blending of materials in a dry state or a wet process method were the grinding and blending operation utilizes a slurry. After blending, the prepared mix is fed into a kiln, which operates at temperatures of approximately 2700 degrees Fahrenheit. During this process, several reactions occur resulting in the transformation of the raw materials into stone called clinker. The clinker is then set to the finish mill where it is ground to produce a fine grey powder. Gypsum (controls the rate of hydration) is blended with the ground clinker, along with other materials, to produce finished cement. Final cement may be transported pre-bagged or as a bulk powder.

Concrete is a structural material consisting of a hard, chemically inert material, such as sand and gravel (aggregate), bonded together by cement and water (paste). Among the ancient Assyrians and Babylonians, the bonding substance most often used was clay. The Egyptians developed a substance more closely resembling modern concrete by using lime and gypsum as binders.

Concrete is characterized by the type of aggregate or cement used, by the specific qualities it manifests, or by the methods used to produce it. The mixture must have just enough water to ensure that each aggregate particle is completely surrounded by the cement paste, that all the voids are filled, and that the concrete is plastic enough to be placed, compacted, and screeded effectively. Quality of hardened concrete is determined by the amount of water used in relation to the amount of cement.

The chemical reaction between the cement and water, know as hydration, gives Portland cement paste its binding quality. During the hydration process two new compounds are formed, calcium hydroxide and calcium silicate hydrate. The engineering properties of concrete-setting and hardening, strength and dimensional stability depend primarily on the calcium silicate hydrate gel.

Portland cement literally shapes the world we live in. Concrete, which is the result of cement, water and aggregate is the second most consumed material on the globe after water. For every person on the plant there is one ton of concrete produced. It would be difficult to walk outside and not view concrete in one form or another.