As a teenager way back in 1955, I placed concrete by operating a mono-wheeled cart known as a "wheelbarrow."
By that time, concrete had already changed quite a bit since 1824, when Joseph Aspdin invented portland cement. It is true that the Romans had a cementing material similar to portland cement, but during the middle ages the art of making this cementing material was lost. It was not until Joseph Aspdin's invention that the true concreting art was brought back to life.
By 1900, the first standardized testing procedures for portland cement had been written. Before that time very little testing was done, and very little cement was produced.
In 1909, Thomas Edison was issued a patent for the first rotary kiln. The rotary kiln revolutionized the production of portland cement. Prior to the rotary kiln, cement was produced by heating large caldrons filled with limestone and clay. Upon cooling a hardened mass would form. This hardened mass was then pulverized to produce portland cement. Production was not only slow, it was also very costly.
The rotary kiln is nothing more than a long cylinder-like tube about 300 feet long and about to 12 feet in diameter, lined with firebrick. It is inclined 15 to 20 degrees from the horizontal. Raw materials are loaded in at the upper end of the rotary kiln and heated to about 2400° F. As the rotary kiln turns, the raw materials flow "downhill." Along the way they are converted into thousands of golf ball sized, spherical cinders called "clinkers." These clinkers are mixed with gypsum and pulverized. The end product is portland cement.
The rotary kiln made it possible for portland cement to be produced as a continual flow-through process. Using the rotary kiln, large amounts of portland cement could be produced, and is in fact the way portland cement is produced today.
Thomas Edison anticipated that he would need large amounts of cement to produce concrete for the concrete houses he wanted to build. Unfortunately for Thomas Edison, concrete homes did not catch on. He did build a few such homes, however, some of which can be seen today in Union, New Jersey. I think he would be favorably impressed with the advancements in the construction of concrete homes today.
A key event in the early history of concrete was the introduction of air entrainment for freeze thaw protection in 1930. The discovery of air entrainment was a serendipitous event. As the story goes, some lubricant accidentally found its way into batch of portland cement. When the cement was used in concrete, the high pH of the concrete changed the lubricant into soap. The mixing action in making the concrete caused the soap to entrain air in the concrete. As luck would have it, this batch of concrete was placed in an area that was subject to freezing and thawing where it was found that it did not deteriorate. This was a big "Aha!" moment in the history of concrete.
In 1936, under the direction of FDR, the Hoover Dam project began. The two primary reasons for the project were flood control and jobs. This was the largest concrete project up to that date. The concrete pours were very large. The temperature rise during the early stage of hydration had to be addressed. This required the development of a portland cement with a lower heat of hydration. After this was developed, the temperature of the concrete was further controlled by placing conduit in the mass of the concrete and circulating cool water through it. If these steps had not been taken it would have taken 150 years for the dam face to cool to ambient temperature.
It is on a project such as the Hoover Dam that real progress is made. One little side note: the Hoover Dam project was a government project that came in ahead of the schedule and under budget. After being in service for a few years, the Hoover Dam paid for itself. I think steps have been taken to see that this does not happen again.
During the Second World War it was very difficult to ship war goods across the country. In 1956, President Eisenhower asked Congress for, and got, the Federal Interstate Highway Act. These highways would be built out of concrete. It was a good thing that by then we had a good understanding of the importance of air entrainment. Otherwise, our concrete highways would not have stood the test of time.
From the time I was a wheelbarrow jockey to the present, there has been a number of innovations that have affected the way concrete is produced and used. As late as the early 1970s, in some parts of the country, concrete was being specified by the number of bags of cement in a cubic yard of concrete. By the mid 1970s almost all concrete was being specified by the compressive strength produced after 28 days of curing. This change in the way concrete was specified allowed for the use of chemical admixtures in concrete, which further allowed for improvements in concrete in both the plastic and hardened state.
Today, both diamond polishing of concrete and decorative concrete are in vogue. Diamond polishing allows for the resurfacing of old worn out concrete floors, giving them new service life. Decorative concrete artists use concrete as a canvas on which art is produced. Concrete is not just the structural gray building material that typically gets covered up. It is now generating new architectural interest as decorative concrete makes a strong case for beauty as well as durability.
To bring concrete to its present state of art has taken the genius of the inventor of light bulb, two US presidents, a world war, and an accidental discovery, plus new innovations that are only a few years old. It has been said that concrete is man's oldest building material. Concrete has come a long way, and its history is being written every day.
There is a lot more to come.
© 2007 L&M Construction Chemicals, Inc. | ConcreteNews September 2007.