Evaluation of bituminous mixes in pavement structures interim report III - A preliminary study of the use of the stiffness concept in minimizing

Abstract

Transverse cracking in flexible highway pavements is considered to be a serious and extensive problem by the asphalt paving technologist. There is a wide adreement that these cracks are caused primarily by the thermal contraction of the pavement structure at low temperatures and appear in the surface when asphalt concrete pavement has been unable to absorb the strains generated by the thermal contraction forces. This cracking of the asphalt concrete is related to the rheological properties of the bitumen, and it sppears necessary that a state highway department be able to specify bitumens which can accomodate the thermal strains imposed by the various environmental conditions encountered. To accomplish this, numerous investigations have been directed towards characterizing the rheological and consistency properties of the bitumens at low temperatures. These studies indicated that the most satisfactory parameter to characterize the low-temperature response of binders and mixtures is the "stiffness modulus". The use of a lmiting stiffness value, or what is called a "critical" stiffness value, seems to be a very useful quantitative guide in selecting asphalt cements that will enable low-temperature transverse pavement cracking to be avoided during a pavement's service life. This report reviews the literature related to the different direct and indirect methods of determining the stiffness modulus of asphalt binders and/or mixtures. The concept of limiting stiffness in selecting asphalt binders was extensively reviewed and the main findings are included.