Cement concrete bases for pavements with bituminous surfaces are, of course, not new. However, it has been many years since concrete has served this purpose except as a pavement itself ultimately resurfaced after years of service. The outstanding qualities of many roads which developed in this way were obvious without any particular tests, and for many years there apparently was no attempt to evaluate them. Probably structural value was first investigated in tests on airfields in Florida, Ohio and California. Although the original concrete pavements in all cases were heavy in comparison with highway sections, the results of the tests have some bearing on highway considerations. In beefing up rigid pavements that had failed under heavy loads and running subsequent tests under moving wheels, the Army Engineers came to the conclusion that --treatments of as little as 3 inches of asphaltic concrete give astounding structural benefits. Accelerated traffic tests have shown overlays of less rigid material to be so beneficial that original designs utilizing a rigid slab of moderate thickness covered with a flexible type surface can and probably will be in cost competition where conditions are favorable
