Testing of the affinity to bitumen of limestone and basalt using several different testing methods

Abstract

The fact that good adhesion between bitumen and aggregate is a key ingredient for good performance is as old as the first bitumen bound asphalt pavements constructed. The bond of an asphalt mix depends on the characteristics and properties of the bitumen and aggregate and the presence of any adverse third component such as water or dust. Surface texture, porosity and absorption properties of aggregates also affect the bond of the interface under consideration. The viscosity of the bitumen is also very important. Bitumen must be in an enough fluid condition. For closest contact between bitumen and the aggregate surface, bitumen must be liquefied by heating, emulsifying, or by blending with petroleum solvent. There are six main theories of adhesion between bitumen and aggregate. These theories mainly are theory of fundamental forces of adhesion, theory of weak boundary layers, mechanical theory, electrostatic theory, chemical bonding theory and thermodynamic theory. The mechanisms of loss of bitumen-aggregate adhesion mainly are displacement, detachment, pore pressure, spontaneous emulsification and interfacial tension, hydraulic scour, pH instability and environmental effects on the bitumen aggregate systems. Many different loss of adhesion sensitivity testing methods have been developed until now, but it is necessary to keep in mind that no single testing method has been widely accepted because the repeatability and correlation to field performance is still unsatisfactory. It is very difficult to simulate field conditions in the laboratory. This study was based on three testing methods and other modified tests that are a combmat10n of two Mechamcal-lmmers1on tests (Marshall Immersion test and Compressive Strength test) and a Dynamic Immersion test (Rolling Bottle test). After these tests other modified Marshall Immersion tests where performed. Correlation between the different testing methods was found. But still each of the different testing methods has different advantages, disadvantages and limitations. The choice of aggregate type is the dominant factor affecting moisture sensitivity of the resulting mixtures. All testing methods indicate that stripping potential in asphalt mixtures using limestone aggregate is less than in basalt aggregate asphalt mixtures. It was concluded that the Rolling Bottle test because it is a quick and easily conducted test, should be used in production control of raw materials. The Marshall Immersion test (ASTM D-1559-89) and the Compressive Strength on Compacted Bituminous Mixtures test (ASTM D-4867-96) should be used in quality control testing. And the Modified Marshall Immersion tests should be used for job mix formula approval.