A Study of the Cuase of Nonuniformity in the Compressive Strength of Concrete Pavement Cores
V. L. Glover
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It is common knowledge that the individual compressive strengths of cores from concrete pavements are less uniform than those of cylindrical test speci-mens made in the laboratory. This more pronounced nonuniformity is believed to be due to variables encountered in field practices which are not present in the laboratory. The Illinois Division of Highways had occasion to test a large number of pavement cores and the nonuniformity found in the test results was such as to make these results wholly unsatisfactory for the desired comparisons. termine the causes. A study was made to de-An attempt was made to duplicate the nonuniformity known to exist in field concrete, proceeding on the theory that segregation might influence nonuniformity. Results indicate that the position of the coarse aggregate particles in the specimen does not affect greatly the uniformity of the compressive strenqth; that the . amount ot coarse aggregate particles in the specimen, that is, the degree to which separation of the aggregate particles and the mortar has taken place, does have an effect; that segregation of the coarser particles of aggregate from the finer ones also has an effect; and that part of the nonuniformity of compressive strength is due to the difference in age of the specimens at the time of test, oavement cores usually being tested at ages considerably greater than the usual standardized age of laboratory speci-mens.