R-curve behavior and crack propagation properties of asphalt concrete at low temperatures

Abstract

Fracture properties and crack propagation characteristics of asphalt concrete mixtures were studied by obtaining fracture resistance curves using three point single edge SE(B) notched beam specimens. Elastic-plastic approach is used in the calculation of the J-integral since the fracture process zone size is large enough to not use a linear elastic approach. Crack length measurements were obtained directly from high resolution images taken during the tests. A rising R-curve was observed in all the specimens which indicates ductility and a toughening mechanism in the ductile to quasi-brittle fracture of the mixture. Mixtures developed by limestone and siliceous aggregates with 4%, 4.5% and 5% binder contents were tested at temperatures ranging from +5°C to −20°C. Mixtures with 5% binder content showed greater crack resistant behavior at each temperature. Crack lengths at which crack propagation instability occurred were decreased by the reduction of temperature. A significant drop of this critical crack length is observed in temperatures below −15°C. As well, the elastic-plastic fracture toughness is increased by the reduction of temperature up to −15°C and starts to diminish thereafter.

Keywords:

• resistance curves
• unloading compliance
• fracture toughness
• stable crack growth

Additional information

Notes on contributors

Sepehr Ghafari

Sepehr GHAFARI. Received PhD degree in civil engineering from the Department of Civil and Environmental Engineering in Amirkabir University of Technology (Tehran Polytechnic) in 2013. He has been a teaching assistant for highway engineering and design as well as pavement engineering courses at the department of civil and environmental engineering in Amirkabir (Polytechnic) university from 2006 until 2013 and an assistant professor at Tehran Shahid Rajaee University from 2010 until now. He completed his Masters degree at Tehran Amirkabir (Polytechnic) university in highway engineering as well and had been in charge of the analysis and design of pavement systems, geotechnical structures, deep and shallow foundations at PASAR consulting engineers from 2007 until 2013. He is currently a project manager at NAVROOD Co., a leading civil construction contractor in Iran.

Fereidoon Moghadas Nejad

Fereidoon MOGHADAS NEJAD. Dr, is currently the consultant for Iran Road Maintenance and Transportation Organization and an associate professor at the Department of Civil and Environmental Engineering in Tehran Amirkabir University of Technology (Tehran Polytechnic). He completed his undergraduate education at Iran University of Science and Technology, where he received BSc. degree in civil engineering. He received his doctoral degree from the University of Sydney, Australia in 1997 followed by a one year post doctoral position researching on numerical modelling of the behaviour of Geosynthetics in pavements. His thesis discussed Geogrid reinforcement of pavements using experimental and numerical analyses. He has numerous articles and book chapters.