Aggregate absorption of bitumen in asphalt concrete mixtures

Abstract

The absorption of bitumen by aggregate is of importance to account for the loss due to absorption, because in the design of densely graded bituminous concrete mixtures, small variations in the bitumen content will affect the composition of the mix. Pore characteristics are the most important properties of the aggregate, especially in the absorption phenomenon. Absorption of bitumen by aggregate is one factor affecting the quantity of bitumen present on the surface of the aggregate and available as binder. The nature and amount of absorption thus influences directly the design of mixes (voids calculations) and the durability of asphalt concrete. In this research six different aggregates and a single asphalt cement have been used throughout. Sampling techniques were considered with attention, to ensure homogenous aggregate samples. Three different sizes of aggregate: 9.5mm, 12.5mm and 19mm were initially used to establish the aggregate characteristics, including the water absorption and specific gravity determination and Los Angeles abrasion test. The Mineral composition of rock used in the study was determined using X-Ray Fluorescence and spectroscopic techniques. Testing of bitumen absorption was carried out on a single aggregate size: passing 19mm and retained on 12.5mm. The bitumen absorption by aggregate has been determines using a variety of test methods, namely three variations of the Rice Method, and the Immersion Method. The insoluble content has been determined using the Modified Centrifuge Extraction Method and the Rolling Bottle Method. Different aging times were considered in the determination of the absorption of bitumen using the Rice Method. Finally the Salina Experimental Road was considered as a Case study. Marshall specimens were prepared and considerations of the bitumen absorption were made through a theoretical investigation of experimental results obtained.