Pavement Distress: Fatigue: Rut: Bleeding: Cracks by Prof Dr Asim Farooq скачать в хорошем качестве

Pavement Distress: Fatigue: Rut: Bleeding: Cracks by Prof Dr Asim Farooq

Lecture Content What is Pavement Distress/Cracks Alligator or Fatigue Cracking Block Cracking (Thermal Cracking) Joint Reflection Cracking from Concrete Slab Lane/Shoulder Drop-off or Heave Longitudinal Cracking Water Bleeding & Pumping Fatigue and Rut Bleeding Slippage Alligator or Fatigue Cracking Initiates at the bottom of AC layer or stabilized base. Cracks propagate to the surface and connect to form many-sided, sharp angled pieces Occurs only in areas subjected to repeated loading (wheel path) Block Cracking (Thermal Cracking) Block cracks divide the asphalt surface into approximately rectangular pieces. Caused mainly by the shrinkage of hot mix asphalt Not load induced, although load can increase its severity Caused by low temperatures and improper grade of asphalt Joint Reflection Cracking from Concrete Slab Occur on pavements that have an asphalt surface over a jointed concrete slab. Cracks occur over transverse and longitudinal joints – were pavement was widened. Caused by the movement of the slab beneath because of temperature and moisture changes Generally not load initiated Longitudinal Cracking Longitudinal cracks are running parallel to the pavement centreline, while transverse cracks extend across the centreline. Main Causes Shrinkage of asphalt surface (low temperature cracking) Asphalt hardening Reflective cracks other than the joints Poor construction of paving lane joint Usually not load associated Water Bleeding & Pumping Water bleeding occurs when water seeps out of joints or cracks or through an excessively porous HMA layer. Pumping occurs when water and fine material is ejected from underlying layers through cracks in the HMA layer under moving loads. Main Causes: Porous pavement as a result of inadequate compaction during construction or poor mix design High water table Poor drainage Rutting Rutting is characterized by depressions that form in the wheel paths. Main Causes: High asphalt content Rounded aggregate Low air voids Structural problems – insufficient thickness design Asphalt cement grade – ‘soft’ binder Consolidation Rutting The result of excessive consolidation of the pavement along the wheel path due to either reduction of the air voids in the asphalt concrete layer, or the permanent deformation of the base or subgrade. Bleeding Bleeding is characterized by excess asphalt binder on the surface of the pavement. Main Causes: Excess prime or tack coats Excess asphalt content in mixture Drain-down Contamination with diesel or similar Slippage Slippage is characterized by crescent or half-moon shaped cracks generally having two ends pointed into the direction of traffic. Main Causes: Thin Layers Insufficient/too much tack coat Wrong tack coat material Tracking of tack coat with equipment Contamination – sand, dirt, organics Rolling process 00:00 Pavement Distress 03:00 Alligator Cracking 06:00 Thermal Cracking or Block cracking 08:45 Joint Reflection 12:35 Bleeding & Pumping 15:25 Fatigue & Rut 20:19 Slippage