EFFECT OF AGGREGATE GRADATION AND BINDER ON DURABILITY AND PERFORMANCE OF BITUMINOUS MIXES

Abstract

Bituminous mixtures are used as base and wearing course in a pavement structure to distribute stresses caused by loading and to protect underlying unbound layers from the effects of water. To adequately perform both of these functions over the pavement design life, the mixture must also withstand the effects of air and water, resist permanent deformation, and resist cracking caused by the loading and environment. Bituminous mixtures consist of aggregate and binder. Properties of component materials play important roles in resulting structural characteristics of a pavement. Performance of a bituminous mixture can be defined by its ability to resist permanent deformation, fatigue cracking, moisture induced damage, thermal cracking, and the mixture's overall stiffness. Aggregate gradation can affect these and other properties such as skid resistance, field constructability, and the asphalt binder aging characteristics. A bituminous mixture has different types of distresses like: fatigue cracking, rutting, thermal cracking, friction, and moisture susceptibility. All of these distresses can result in loss of performance but rutting is the one that is most likely to be a sudden failure as a result of unsatisfactory hot mix asphalt. Other distresses are typically long term failures that show up after a few years of traffic. Some of the factors causing distresses in bituminous pavements are high pavement temperatures, heavy axle loads, high tyre pressure and possibly inadequate binder and mix specification. For a major portion of India highways, low temperature cracking is not an issue while it is one of the main modes of failure of bituminous materials considered in some countries. This thesis presents a study on the effects of aggregate gradation and type of bitumen. binder on the properties and performance of bituminous mixtures. Two layers Bituminous Concrete (BC) mix for surface layer and Dense Bituminous Macadam (DBM) mix for binder layer are selected in this study. Three types of aggregate gradation (Upper limit, Mid limit, ii Lower limit) are selected for each of these mixes per MORTH — 2001 specifications, and two types of bitumen binders are selected. One of them is conventional bitumen binder (VG30) and other is modified bitumen binder (PMB40). The mixes are designed as per Marshall method of mix design which is currently used in India. Durability of bituminous mixtures is studied through retained stability, indirect tensile strength, and tensile strength ratio. Performance of bituminous mixtures is studied through static creep test, static triaxial tests, wheel tracking test, and portable skid resistance test. The results of experimental work indicate that the performance of BC mix is better than DBM mix in most of the tests. The performance of mixes prepared with PMB-40 is superior to the mixes prepared with VG-30 and it was observed in all the tests. The finer gradation mix has higher indirect tensile strength (ITS), horizontal tensile strain (HTS), retained stability, tensile strength ratio (TSR) than mid and coarser gradations mix, while the coarse gradation mix has higher resistance of permanent deformation, shear strength, skid resistance, and less rut depth than finer gradation mix. Further, the BC mix has higher compressive strength and stiffness and less effect of moisture than DBM mix. Gradation parameters like 61 and Gradation Ratio (GR) are defined in this thesis and these are estimated from particles size distribution curves of aggregate. These parameters are correlated with durability and performance parameters of a mix to predict later from aggregate gradation curve alone. Keywords: Aggregate Gradation, Performance Parameters, Durability, Binder Type, Gradation Ratio. iii