Effects of Aging on the Mechanical Characteristics of Bituminous Binders in PAC

Abstract

Wearing courses of porous asphalt concrete (PAC) are widely used in The Netherlands for noise reducing purposes. Because these mixtures have a very high void content (>20%), they are sensitive for damaging effects of climate and traffic. Especially, aging is a major concern because it makes the mixture brittle and prone to raveling. In order to be able to do meaningful tests and analyses based on laboratory produced specimens, it is important to mimic field aging as well as possible. This paper describes the results of an investigation in which the effects of well known short-term and long-term laboratory aging procedures on the rheological characteristics and chemical composition of binders, are compared with the rheological characteristics and chemical composition of field aged binders. The results obtained on field aged binders are also compared with the results of laboratory aging protocols in which a special weatherometer was used. The results clearly show that none of the laboratory procedures is capable of simulating long-term field aging. At best 2 years field aging could be simulated. Furthermore, the study showed that the way bitumens are aged in the laboratory affects the chemical composition of the binder. The paper also discusses the effect of aging on the mechanical characteristics of bituminous binders in porous asphalt concrete. It is shown that due to aging, the binder will start to behave brittle at temperatures above 0°C. Furthermore, it is shown that aging increases the tensile strength of the binder and the bituminous mastic (mixture of bitumen and filler). The strain at break however decreases as a result of aging. Fatigue testing showed that aging initially increases the fatigue resistance of the binder. However long-term aging occurring in the field after a period of more than 7 years results in a significant decrease of the fatigue resistance. Although not discussed in detail, the results show that aging reduces the stress relaxation capacity of the binder. This will negatively influence the behavior of the binder in case temperature stresses occur together with traffic induced stresses. Also, the healing capacity will be negatively influenced by aging.