The Purpose of the Road

The main purpose of the road structure is to provide a means of

reducing the stress or pressure due to a wheel load to a value

which the ground under that structure can support.

The Structure of the Pavement

This usually consists of four layers of road construction material, these being built up on the formation

The four layers of the road structure have been re-named since 1 January 2004 and are:

1 The sub-base, (a) assists in load-spreading, (b) assists in subsoil drainage and (c) acts as a temporary road for construction traffic.

2 The base/road base (formerly road base), is the main load-spreading layer of the structure.

3 The binder course (formerly base course), which supports the wearing course and also assists in protecting the road.

4 The surface course (formerly wearing course), which (a) provides a skid-resistant surface, (b) waterproofs the pavement and (c) withstands the direct loading of the traffic.

The term ‘sub-grade’ is used to define the natural foundation or fill which directly receives the loads from the pavement.

COMMON

DISTRESSES

ON PAVEMENTS

Factors affecting pavement performance

Subgrade soil

Pavement materials characteristics

Asphalt cement

Aggregate

Modifiers for asphalt cement (e.g., rubber and polymers)

Additives or stabilizing agents for aggregates (e.g., lime

and cement)

Traffic loading

Environment

Moisture; and Temperature

Common Pavement Distresses

LONGITUDINAL CRACKINGCracks that are approximately parallel to pavement centerline and are not in the

wheel path. Longitudinal cracks are non-load associated cracks..

FATIGUE CRACKING

Cracks in asphalt layers that are caused by repeated traffic loadings. The cracks indicate fatigue failure of the asphalt layer.

TRANSVERSE CRACKINGCracks that are predominately perpendicular to pavement centerline .Thermal cracking is typically in this category.

RUTTINGLongitudinal surface depression that develops in the wheel paths of flexible pavement under traffic. It may have associated transverse displacement

CORRUGATION

Transverse waves appear at regular intervals due to the unstable surface course caused by stop-and-go traffic

SHOVINGIt is generally caused by braking or accelerating vehicles, and is usually located on hills or curves, or at intersections.

OVERLAY BUMPSCracks in old pavements were recently filled.

This problem is most prevalent on thin overlays.

DELAMINATIONLoss of a large area of pavement surface. Usually there is a clear separation of the pavement surface from the layer below. Slippage cracking may often occur as a result of poor bonding or adhesion between layers.

STRIPPINGThe loss of the adhesive bond between asphalt cement and aggregate, most often caused by the presence of water in asphalt concrete, which may result in raveling, loss of stability, and load carrying capacity of the pavement or treated base

PUMPING

Leaking or ejection of water and fines from beneath the pavement through cracks.

SEGREGATIONSeparation of coarse aggregate from fine aggregate as a result of mishandling of the mix at several points during mix production.

BLEEDING/FLUSHING Excess bituminous binder occurring on the pavement surface. May create a shiny, glass-like, reflective surface that may be tacky to the touch. Usually found in the wheel paths.

ROCK LOSS

Wearing away of the pavement surface in seal coats.

BLEEDING / FAT SPOTSExcess binder occurring on the surface treated pavements. May create a shiny, glass-like, reflective appearance. Fat spots are contained bleeding.