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In the early 1900s, the farmer that wanted to improve their farm by putting in a concrete floor in their barns, build a root cellar, or have a dry spot in front of a hog lot had to do it themselves. There were no concrete batch plants and few rural concrete contractors, so the farmer had to learn how to make and place concrete. Many cement companies and farm organizations developed publications that took the farmer through the process. We have more sophisticated equipment and improved materials today but the process remains much the same. I have worked in many third world countries and found that some of the techniques that the early farmers used are as useful today and can keep the contractor out of trouble. Part one of this series of discuses how to get clean concrete sand.
How to get clean sand
In most cases, the farmer was on his own to find a suitable sand to use in concrete. They knew that dirty sand (sand with clay and silt) would result in weaker concrete. Thus most publications presented a simple test to determine if the sand was usable in concrete. To do this test, you need a see-through container. The self help books of the time recommended a quart canning jar with a top - probably because they were available on most farms. I have used soda and juice bottles when doing this test. The bottle or jar should be about 8 inches high with straight sides. To do the test:
Silt test, from Permanent Farm Construction, Portland Cement Association, 1916.
If the test has over the 1/8 inch of silt and clay, the farmer has to make a decision. They can look for a different source of sand, wash the sand, or use this sand and add extra cement to maintain the required strength of the concrete.
I have used this method in Mexico and Mongolia when examining sands. I used a soft-drink bottle and followed the steps outlined above. It was a quick way to determine if the sand was acceptable or needed more detailed laboratory testing.
Two other steps are required to make sure the sand is acceptable for use. The farmer should examine the sand to see if it has organic content. The farmer should do a visual inspection looking for tree roots, leaves, animal waste, and construction waste in the sand. In most cases, this will be adequate. If there is doubt, a laboratory test that requires the use caustic chemicals can be performed. This is best done in the laboratory by experienced technicians. The sand piles or where the sand is stored should also be inspected.
Here are three examples of how inspection of the sand and sand piles easily identified a problem and one example where an inspection could not catch the problem.
The farmer is now ready to move to the next step of gathering the other materials needed to make concrete.
To read Part 2, Materials, click here.
To read Part 3, Concrete Mixtures, click here.
To read Part 4, Mixing the Concrete, click here.
To read Part 5, Placing the Concrete, click here.
Luke M. Snell is a concrete historian and Emeritus Professor at Southern Illinois University Edwardsville.