Page 140 - Lecture Notes DCC3113

Possible causes of cracks include: depression, age embrittlement, fatigue life has been exceeded,
reflection cracks from underlying layers, pavement shrinkage, insufficient thickness, poor bonding,
braking and turning and poor construction joints.

Possible treatment depends on the causes but may include: pavement strengthening, reconstruction, cut
and patch, improve drainage, crack sealing, thin overlay, reconstruction of joint, widen and strengthen
pavement edge and use stiffer mix.

Cracks can be divided into six types based on their shape:
i. Longitudinal crack: Cracks parallel to the pavement’s centerline or laydown direction, can be
isolated or in series with limited branching.
ii. Transverse: Cracks perpendicular to the pavement’s centerline or laydown direction.
iii. Edge crack: Crescent shape or continuous, parallel and usually 300 to 600mm from the road edge.
Usually occur along unpaved shoulder.
iv. Block crack: A series of interconnected cracks caused by fatigue failure of the MHA surface under
repeated traffic loading. As the number and magnitude of loads becomes too great, longitudinal
cracks connect forming many-sided sharp-angled pieces with size between 100 to 300 mm
v. Crescent shape: Crescent or half-moon shaped cracks generally having two ends pointed into the
direction of traffic, usually related to shoving and occur only on bituminous layer. Also known
as slippage cracks.

Surface Deformation

Posibble causes : inadaquate pavement thickness, inadequate compaction, low stability mix, low stability
base/sub-base, change in subgrade volume, settlement of layers, lack of adhesion between surface
layers, stop and start of vehicles at intersections or rounabouts, settlement of trenches/service line.

Possible treatments: strengthening overlay or reconstruction, mill of and replace surface with stiffer mix,
reconstruction or strengthening of road base, improve subsurface drainage and reconstruction of
subgrade or base.

Types of surface deformation :
i. Rutting : longitudinal depression in the wheel paths after repeated application of axle loading.
ii. Shoving : an abrupt wave or bulging of road surface where braking or acceleration movements
occurs, cause by traffic pushing against the pavement. Transverse shoving may occur with
turning movements.
iii. Corrugation : a form of plastic movement typified by closely spaced ripples resulting in rough
ride and becomes worse with time. The distortion is perpendicular to the traffic direction.
iv. Depression : loacalized pavement surface areas with slightly lower elevations than the
surrounding pavement. Depressions are very noticeable after a rain when they fill with water.

Surface Defect

Posibble causes : excessive application of binder, paving over flushed or excessively primed surface,
insufficient binder content, poor adhesion of binder to aggregate, inadequate tack coat, seepage of water
into pavement and adhesion of binder to vehicle tires.

Types of surface defects :
i. Bleeding : the presence of film of asphalt binder on the pavement surface, likely to occur in the
wheel paths. It usually creates a shiny, glass-like reflecting surface that can become sticky when
dry and slippery when wet.
ii. Raveling/Stripping : the progressive disintegration of the pavement surface due to loss of bond
between aggregates and asphalt binder resulting in dislodgement of aggregate particles.

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