Title: Slump Loss, Air Loss, and Field Performance of Concrete
Author(s): George R. U. Burg
Publication: Journal Proceedings
Appears on pages(s): 332-339
Keywords: admixtures; air entrainment; coefficient of variation; compressive
strength; concrete durability; concrete pavements; freeze-thaw durability; fresh
concretes; hardened concretes; microscopy; retempering; slump tests; standard deviation.
Field and laboratory experience demonstrates that when concrete loses slump, there is generally a loss of entrained air content. Results obtained from tests made in conjunction with a large concrete roadway and parking lot paving project may give the answer to the often asked question, "Is slump loss due to the loss of air, or is air loss due to the loss of slump?"The purpose of these tests was to study the accuracy of current recommendations for durable concrete pavement, the history of air-entrained pavement-type concrete as it matures from the time it was freshly mixed to after it has been in service for several years, and the degree of confidence that can be expected when using Standard ASTM Test Methods to obtain certain selected concrete qualities. Tests were made on randomly selected truckloads of freshly mixed concrete at three different times: I) at the central mix plant, "as mixed" 2) at the job site, "as received" and 3) at the job site, "as retempered. " The concrete was adjusted for slump at the job site by retempering with water. Samples of hardened concrete from test cylinders and cores cut from hardened concrete pavement were microscopically analyzed. A comparison of all test data obtained from loads of freshly mixed concrete and from hardened concrete are presented, indicating the concrete’s qualities as it matures over a three-year period. The coefficient of variation and standard deviation were calculated for each series of tests conducted on the concrete.