The term D-cracking has been used for many years to describe a form of deterioration which is periodically observed in concrete pavements. In this article, D-cracking will refer to a series of closely spaced cracks that appear at a pavement wearing surface adjacent and roughly parallel to transverse and longitudinal joints and cracks, and the free edges of pavement slabs, and also to associated cracking preliminary to that appearing at the wearing surface. As such, D-cracking is defined by a characteristic crack pattern and, as will be shown later, indicates a particular source of distress.
D-cracking normally first appears at transverse-longitudinal joints and transverse cracks and at the outside corners of a pavement slab. As cracking progresses along the joints, the resulting crack pattern forms a nearly continuous network that is confined to the peripheral areas of the slab. With continued deterioration, the crack pattern encroaches rapidly on the remaining central portion of the slab. This stage of deterioration is seldom observed since maintenance operations have either removed the deteriorated concrete or overlaid the entire pavement, thus obscuring but not terminating the further development of cracking.
In a final report produced as a result of an extensive study completed in the state of Ohio, the authors make three recommendations, two of which are of great importance to the aggregate industry. They recommend that gradation of coarse aggregate, with particular reference to maximum particle size, be considered the single most important factor affecting the development of D-cracking, and that coarse aggregate specifications require that each source be evaluated on an individual basis, as regards its potential for causing D-cracking.