Site batching is the norm in Algeria because ready-mix is not available.
Not all parts of the world have the luxury of relying on consultants to prepare organization plans to create a more efficient organization. In some parts of the world, just batching concrete is painstaking.
While in Algeria recently, we visited some jobsites and saw the batching procedures. Here, as in many parts of the world, site batching of concrete is the norm because ready-mixed concrete is not available.
In the United States, site batching of concrete also was common in areas which did not have access to ready-mixed concrete. Before World War II, much of the concrete used for farm buildings was made onsite. Many cement companies and the Portland Cement Association wrote pamphlets on how to make and place concrete on the farms.
Since it was not easy to weigh the cement, sand, and stone, batching was done by volume. To make batching easier, cement was put in 1-cubic-foot bags. This made measuring the volume of cement unnecessary. The farmer would simply determine how much concrete he needed and add the appropriate number of bags of cement. The sand and the rock would be measured in convenient-sized containers of a known volume so that they achieved the desired ratio of materials in their concrete.
A bag of cement in Algeria weighs 50 kilograms or 110 pounds. This is slightly larger than the U.S. cement bag of 94 pounds. They add the cement by the bag. The coarse and fine aggregates are added by volume into the hopper.
The Algerian procedure of site batching concrete for reinforced concrete structures is to use a ratio of cement: fine aggregates: coarse aggregates of 1:1.8:2.7. This is almost identical to the 1:2:3 mixture used in the United States.
They specify a slump of 4 inches, with strength of 3500 psi. Obviously, there are many mix designs used in Algeria. The one that we witnessed would be typical for structural concrete.
The material is put into a hopper and mechanically lifted into the mixers. The contractor blends the two coarser aggregates. The first is sized from ¼ inch to ½ inch; the second from ½ inch to 1 inch. This blending of aggregates is recommended so they get a uniform distribution of aggregate and a more efficient mixture.
Concrete can be batched in many ways, requiring attention to details and a need for consistent procedures. Algerians have developed an improved way of site batching their concrete. By following a consistent procedure and using modern equipment, they produce good quality concrete.
Snell is the director of the Concrete Industry Management Program at the Del E. Webb School of Construction at Arizona State University. Baghli is an assistant professor at the University of Aboubekr in Tlemcen, Algeria.