Relating In Situ Properties of Cement-Bound Bases to Their Performance

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.