Abstract
The problem of reflection cracking through the conventional asphalt concrete overlays has increased the need to find new materials which could resist cracking or fracture more effectively. It is for this reason that polymers (Styrelo are added to the neat asphalt to improve the fracture resisting properties of asphalt concrete. In this study three different asphalt concrete mixtures with and without polymer (Styrelf) were used to study their fracture toughness. With four different binders and different combinations of mixtures, 18 different overlay systems were tested for their fracture toughness. Each overlay was made up of two different layers with asphalt rich sand anti-fracture (SAF) mixture as the bottom layer. Fracture mechanics concepts were used to compare the fracture properties of polymer (Styrelo modified asphalt concrete with the corresponding conventional neat asphalt concrete. Rate of crack growth is correlated with the energy line J*-integral. Crack growth rates were determined from laboratory experiments conducted on TTI overlay tester. Analysis of the experimental results showed that crack growth rate and J*-integral are correlated. In this study it was observed that the relation between the fracture material constants log(A) and (n) is not linear. A new fracture material constant (S) relating to crack speed was developed. The relationship between log(A) and (n) was found to be linear when combined with constant (S). Results showed that this new material constant (S) could lead to a better characterization of fracture toughness. Crack speed when calculated using (S) has shown better correlation with the observed experimental fatigue life. It is speculated that this new material constant (S) could be related to healing of the asphalt concrete or the plasticity effects due to unloading of the sample in overlay test.
Reddy, Praveena Gutha (1996). A comparison of the fracture properties of conventional and polymer-modified two-layer asphalt concrete overlay systems. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -R43.