Top Down Cracking

Top Down Cracking

Top down cracking appears to be a common mode of HMA pavement distress in at least several states and countries.  Traditionally, pavement cracking is thought to initiate at the bottom of the HMA layer where the tensile bending stresses are the greatest and then progress up to the surface (a bottom-up crack).  Most traditional transfer functions used in mechanistic-empirical structural design are based on this concept.  However, the late 1990s saw a substantial focus on a second mode of crack initiation and propagation: top-down cracking.

Pavement Evaluation Categories

Pavement Evaluation Categories

Pavement performance is a function of its relative ability to serve traffic over a period of time.  Typically, a system of objective measurements is used to quantify a pavement's condition and performance.

Condition Rating Systems

Condition Rating Systems

Based on measurements of roughness, surface distress, skid resistance and deflection, pavements can be assigned a score that reflects their overall condition.  This score, sometimes called a pavement condition rating, quantifies a pavement's overall performance and can be used to help manage pavement networks.  By carefully choosing the rating scale (called the condition index), pavement condition scores can be used to (Deighton 1997):

Pavement Management

Pavement Management

“Pavement management” refers to a systematic process of maintaining, upgrading and operating a network of pavements and involves three major components: the pavement life cycle, the costs associated with this life cycle and pavement management systems.

Water Bleeding and Pumping

Water Bleeding and Pumping

Water bleeding (left two photos) occurs when water seeps out of joints or cracks or through an excessively porous HMA layer.  Pumping (right-most photo) occurs when water and fine material is ejected from underlying layers through cracks in the HMA layer or out the sides of the HMA layer under moving loads.

Transverse (Thermal) Cracking

Transverse (Thermal) Cracking

Cracks perpendicular to the pavement's centerline or laydown direction.  Usually a type of thermal cracking.