Effect of Aggregate Gradation and Compactive Efforts on Marshal Properties of Dense Bituminous Macadam Mix Grade II

Abstract

India has a road network of over 4.69 million kilometers, second large roadways in the world. The road transport carries close to 5% of passenger traffic and 70% of freight transport. The bituminous mix design aims to determine the proportion of bitumen, filler, fine aggregates, and coarse aggregates to produce a mix which is workable, strong, durable and economical. An aggregate’s particle size distribution, or gradation, is one of its most influential characteristics. In hot-mix asphalt, gradation helps to determine almost every important property including stiffness, stability, durability, permeability, workability, fatigue resistance, and resistance to moisture damage. Gradation is usually measured by a sieve analysis. Dense Bituminous Macadam is a binder course in the highway pavement. Bituminous mixes are most commonly used in flexible pavement construction. Marshall properties of bituminous mix vary from binder to binder. DBM. mix is a heterogeneous material that consists of aggregate, filler, bitumen binder, stone dust and air voids. Marshall mix design method is used to decide the optimum bitumen content (OBC) and Marshall properties were determined at optimum bitumen content. Gradation is one of most important factors influencing the Marshall Properties of DBM mix, so it is required to select best aggregates gradation. The optimum gradation is the one that which gives the highest density. When fine particles are properly packed between coarser particles, this reduces the voids space between to specified limit. Thus improves the density and is called the optimum gradation. The present study aims to determine the Marshall properties of DBM mix, such as Stability, Flow, density, Voids in mineral aggregate, Voids filled with bitumen and Air voids percentage by using three types of aggregate gradation (MORTH, ASTM and Kandhal gradation) and three types of compactive effort (50 blows, 75 blows and 100 blows) for each gradation according to low, medium and high traffic at 4%, 4.5%, 5% and 5.5%. It is important to analyze that how the variation in aggregate gradation can affect the Marshall Mix properties of DBM without affecting the durability of pavement. The Maximum Marshall Stability is 27.44 obtained at 5% of bitumen content at 100 blows of MORTH Gradation. For the ASTM Gradation the maximum Marshall Stability is 18.43 at 5% of bitumen at 50 blows.