Three types of aggregate—a dolomitic limestone, a granodiorite, and a gravel—were studied to investigate the relationship between the particle properties and their performance in terms of strength, elastic behavior, and resistance to permanent deformation. Particles of each material were assessed for their geometry at both coarse and fine scales. This was quantified using several different measures including particle shape, roughness factor, roundness, sphericity, surface friction characteristics, and angularity. Laboratory tests, using a large shear box (300 × 300 mm) and a large (280-mm-diameter) repeated-load triaxial apparatus, were carried out to understand the significance of the geometry of the particles as well as of their surface friction characteristics and the effect of grading and of compaction. Roundness and angularity are considered to be the major factors affecting ultimate shear strength and permanent deformation. The degree of compaction and consequent density also has a great effect on the shear strength and resistance to permanent deformation. However, an increase in surface friction and surface roughness tends to improve the resilient shear stiffness. A pavement trial on the three aggregates, 300 mm thick over a subgrade, was constructed. Subsequent trafficking indicated that the limestone and the granodiorite performed significantly better than the gravel. It confirms that high roundness and low angularity have a much greater impact on performance than does surface friction when rutting is the chief distress mechanism.

No abstract

No abstract

A rationale for explanation of the in situ layer modulus expected from a cementitious base is presented. It is assumed that all such bases crack to various degrees, depending on material strength and other pavement parameters, under the influence of shrinkage, temperature changes, and trafficking. The layer modulus is shown to be a function of hinge and slip effects at cracks, as well as the intrinsic material modulus, and simple, practical, but fundamental-based equations are given for its prediction. The point that any given layer modulus could, in principle, be due to any of several different combinations of material modulus, crack spacing, and condition is made, and so careful interpretation is vital. The use of the predictive equations is then demonstrated in six selected cases, covering materials ranging from cracked pavement-quality concrete to lime- and cement-stabilized clay, and the equations are seen to enable the measured layer moduli to be interpreted sensibly. Finally, two examples are given. In these examples similar layer moduli relate to two quite different materials and conditions, which have given rise to different pavement performances. The weaker material resulted in a better combination of crack spacing and condition and a longer-lasting pavement, whereas the stronger material resulted in a pavement very susceptible to reflective cracking. The conclusion is drawn that, for optimum pavement performance, the key is to limit the amount of slip at cracks by ensuring good interlock as well as adequate intrinsic material strength and stiffness. A slowly curing material is ideal.

No abstract