Your inspectors can take samples and make test cylinders. After 28 days, they can break the cylinders and determine the strength, with accelerated curing they can perhaps get roughly the same results in one or two days. But if a batch is not up to specifications you have wasted precious time in the curing and perhaps an even greater amount of time- and money- in tearing out and replacing the bad batch. The U.S. Army Corps of Engineers which is always involved with placing a fair amount of concrete, found itself faced with the same set of problems. As a result, it turned in 1974 to one of its field laboratories, the Construction Engineering Research Laboratory (CERL) in Champaign, Illinois, for some answers. A team from the Construction Materials Branch of CERL, led by Paul Howdyshell, screened the available literature on the subject and found a chemical technique originally proposed by two British researchers, R. T. Kelly and J. W. Vail, in the April 1968 issue of Concrete. The Kelly-Vail technique, which uses chemical analysis to determine the actual amounts of cement and water present in fresh concrete, was evaluated and modified in a number of ways by the CERL research team. The water test procedure involves intermixing the available water in a given weight of concrete with a chloride solution of given concentration and volume. The chloride concentration in the intermixed solution, which is determined by the Volhard back-titration method, is directly related to the water content of the concrete. In the cement test procedure, the aggregates and cement are separated by washing a concrete sample over a nest of sieves with a constant volume of recirculating water. The calcium concentration in the recirculating water indicates the cement content of the concrete.