Comparative Study Of Semi-Rigid Pavement Reflection Cracking Preventive Measures

In our country, to get stronger base and reduce the thickness of HMA layers, semi-rigid base is widely used in highways. In time of maintenance and working, semi-rigid base may crack due to thermal shrinkage and drying shrinkage. Then, when traffic loads pass the fractures or pavement temperature reduces, strain and stress are very high in HMA layer near these fractures. Eventually, cracks will initiate at the bottom of the HMA layer and then propagate to the surface. We call this kind of cracks reflection cracks. Reflection cracking not only reduces the soundness of pavement, but also makes water enter into pavement easily. Eventually, local distress will occur in pavement.Reflection cracking has been one of the main distresses of our country's pavements. Reflection cracking has been studied for decades, but most of the studies are separate lacking colligation and general comparison. It is necessary to study the reflection cracking preventive measures systemically and compositively.The reasons of reflection cracking and mechanisms its preventive measures are studied. Then, effectiveness of several reflection cracking preventive measures is evaluated. Finally, technological requirements of different measures are put forward.Five reflection cracking preventive measures are studied: adding polyester fibers to asphalt mixes, geofabric interlayer, glass fiber grid interlayer, stress absorbing membrane interlayer and asphalt treated base. Three means were used in this study: mechanical analysis, material experiments and simulative experiments, experimental roads. In mechanical analysis, three dimensional liner elastic finite element method, two dimensional elasto-viscous finite element method and fracture mechanics were used to analyze the mechanisms of reflective cracking and the mechanisms of cracking preventive measures. Low temperature bending beam tests of several types of asphalt mixtures were done to evaluate crack resistance of deferent asphalt mixtures. Simulative experiments were done to evaluate the effectiveness of reflective cracking preventive measures. Finally, experimental roads were constructed in order to compare the effectiveness of different cracking preventive measures through pavements survey.Some conclusions were drawn: Adding polyester fiber into bituminous mixture can improve mixture's cracking resistance substantially. glass fiber grid interlayer prevent reflective cracking through absorbing stress; geofabric interlayer has partition function; SAMI which are thick and has lower modulus prevents reflective cracking through absorbing strain; asphalt treated base prevents reflective cracking through separating surface and semi-rigid base. the effectiveness of different reflective cracking preventive measures: Adding polyester fiber and asphalt treated base are better than SAMI which are better than geofabric and glass fiber grid interlayer. Bituminous mixture which has small nominal maximum size of aggregate, more binder and more fine aggregate has better low temperature performance and fatigue resistance. It is shown that"Accumulative Dissipated Energe"can de used to evaluate mixture's fatigue resistance, and"Reduced Dissipated Energe Ratio"is a proper parameter to analyse fatigue experimental data. Finally, the construction experiences are summarized.