DESIGN AND VISCOELASTOPLASTIC CHARACTERIZATION OF A LIME-DUNE SAND-ASPHALT MIX (REPLACING AGGREGATE, MATERIAL LAWS, CREEP COMPLIANCE, RUTTING).

Abstract

Viscoelastic and viscoelastoplastic characterization of pavement materials by means of simple testing and simple equipment is of great concern to pavement technologists. Another area of great concern is the replacement of premium aggregates by local materials after improving the engineering properties of the local materials. Such replacement is for the avoidance of the high costs of hauling the well-graded aggregates whose resources are also being depleted. These two research areas were combined in this study. A uniformly graded dune sand which is abundant in desert-like areas was upgraded with hydrated lime and stabilized with asphalt to improve its engineering properties. By variation of some of the mix design variables, a mix that complied with Marshall and Hveem stability criteria was produced. The effect of lime on the engineering properties of the mix was studied, and substantial improvements due to the addition of lime were observed. A mix that contained 10% Type S lime was found to have engineering properties that were comparable with those of conventional asphaltic concrete. Also, the effect of lime on the thermorheological, thermal, and elastic properties of bituminous mixes in general was studied. In addition to complying with the above-mentioned stability criteria, the lime-sand-asphalt mix was characterized by creep compliance, over wide ranges of time and temperature, so that the mix is available for thickness design by both the empirical and the theoretical methods of pavement design. New, simple equipment by which repeated as well as constant load creep tests can be easily performed was introduced and used to develop a viscoelastic-plastic constitutive law of the designed lime-sand-asphalt mix. Both the equipment and the testing are simple and gave repeatable measurements. Models for the elastic, plastic, viscoelastic and viscoplastic responses of the designed mix were derived from measurements taken by this equipment and by using computerized regression analysis techniques. Generalized models for the viscoelastic strain during the N-th loading and the N-th recovery period were developed. A FORTRAN computer program was written for computing the four strain components mentioned above separately, and for computing the total strain component for large numbers of load repetitions.