Some senior engineering students asked about the price of concrete and what goes into it. Their guess of its cost was astonishingly high.
Check out the prices at a grocery store, or even better, ask about the current price of oil. Meat at $3 to $5 or more per pound. Several dollars for a partially filled box of breakfast cereal measurable in ounces. But for concrete delivered to a job-site, around $75 per cubic yard —about 2 cents per pound. What a deal! No cholesterol, built-in durability, and almost guaranteed to survive—if properly maintained—longer than we will. A true bargain by any standard!
Portland cement costs less than 4 cents per pound. How about becoming patriotic by diluting the cement with a less costly waste product like fly ash at 1½ cents per pound? Ready-mix companies used to get that stuff free. Not any more! Power plants not only don't pay you for taking it off their hands but actually make money selling it to you. So now why don't we become even more patriotic and frugal by throwing in something else cheaper than portland cement: ground granulated blast-furnace slag at about 3 cents per pound, or mix and match them and use a tertiary mixture of portland cement, fly ash, and ground granulated blast-furnace slag. People make a living selling those inexpensive materials!
Air entraining agents may make money for concrete supply companies by replacing some of the more costly fine aggregate. Including air can't be bad for anyone; it lubricates the mix, lightens the unit weight, and provides freeze/thaw durability with microscopic-sized air bubbles. And the reduced mix water decreases permeability, which increases resistance to chemical attack. Air weighs next to nothing and is almost free.
Gravel coarse aggregate costs about 5 mils per pound, and sand fine aggregate costs about 4 mils per pound.
So, the cost of an air-entrained 6-bag (564 lb) mix made using gravel coarse aggregate (1800 lb) and sand fine aggregate (1250 lb), as we previously mentioned, is about $75 per cubic yard even including the patriotic fly ash or ground granulated blast-furnace slag. The water is essentially free. Prices vary from state to state and region to region.
Portland cement manufacturing is an energy-consumptive industry, always has been and always will be. You can't heat and fuse materials at about 2700° F without a substantial fuel bill. In addition to the fuel, much of the cost of portland cement manufacturing is grinding the fused clinker that comes out of the kiln to face-powder fineness, and even finer for high-early strength-developing Type III portland cement. It then has to be hauled to its destination, stored in silos, and pass federal and state requirements found in ASTM C150, “Specifications for Portland Cement.”
A bag of portland cement weighs 94 pounds, about one bulk cubic foot of cement back in the days when batching was done by volume of materials. Actually, and keep this under your hat, the amount of portland cement in that cubic-foot bag is less than one-half a cubic foot: There is a lot of air between individual cement particles. Thomas Edison was the first to patent the long rotary kilns used to make portland cement at his Edison Cement Works facility in eastern Pennsylvania in the late 1890s and early 1900s. He must have been a Yankee and a Babe Ruth fan because 160,000 bags of his portland cement (about one-half of which is air) were used in the construction of Yankee Stadium, the house that Ruth built.
There are many other costs associated with concrete, like a variety of chemical admixtures that do all kinds of good things to concrete—most of the time. There are costs associated with form-work, placing, consolidating, and finishing concrete that drive up the cost of the final in-place concrete product. Unfortunately, that sometimes includes litigation.
Our world would be a far poorer place if concrete was not available to help make our lives easier, and certainly more enjoyable—and at less than 2 cents per pound for plain portland cement concrete (and just a little more with admixtures). What a bargain!
Mike Pistilli of Prairie Materials, Chicago, helped draft this column. Mike has been in the portland cement, fly ash, slag, chemical admixture, and concrete industries for decades, and well recognizes the price of concrete and concrete-making material and its impact on concrete and construction practices. We thank him for his valuable assistance.
- Bernard Erlin is president of The Erlin Company (TEC), Latrobe, Pa., and has been involved with all aspects of concrete for over 47 years.
- William Hime is a principal with Wiss, Janney, Elstner Associates and began working as a chemist at PCA 53 years ago.
