Highway Engineering

Section CHART – a summary indicating the average and maximum ratings

Treatment length CHART – only shows those sections where treatment has been

recommended (separate lists are compiled for each form of treatment)

Subsection rating and treatment CHART – lists the sections recommended for

treatment. Main recommendations for treatment are given.

A computerised system such as CHART has not yet been developed for rigid

pavements. Nonetheless, the aim of the procedure in this instance must be to

accurately record all relevant features observed, be that the condition of the car-

riageway itself or related matters such as drainage or earthworks problems.

HD 29/94 (DoT, 1994a) provides guidance on how the information from

visual surveys should be interpreted. A summary of these interpretations is given

in Tables 9.1 and 9.2.

254 Highway Engineering

Observations Interpretation

Single longitudinal cracks in Indicate the onset of structural failure in

wheelpath pavements greater than 200 mm thick. These do

not heal and deterioration will be progressive

Multiple wheelpath cracking Narrow cracks imply condition is not near failure. Wider

and crazing cracks imply advanced failure of a thicker structure

Longitudinal cracking outside In all likelihood the location of a construction joint

the wheelpath

Short transverse cracks Unlikely to be structurally significant. Has probably

started at the surface and will progress slowly

Long transverse cracks Indicate a discontinuity in a lower layer, possibly

a construction joint in a bituminous material

Table 9.1Interpretation of visual data for bituminous surfaces

Observations Interpretation

Longitudinal cracks Indicate either the onset of structural failure, differential

settlement or compression at the joints. Deterioration is

likely to be rapid. Sealing cracks can reduce the rate of

propagation

Mid-bay/third bay cracks These are thermally induced in URC pavements, a

consequence of a joint malfunctioning. They can result in

serious distress if left unsealed

Joint damage Sealant damage and spalling indicate excessive movement at

the joint. Foundation damage and voiding may have

occurred

Table 9.2Interpretation of visual data for concrete pavements

It should be noted that narrow (non-structural) ruts indicate that the wearing

course is probably deforming under traffic. No effect on the lower layers will

result. With wide (structural) ruts, however, deformation is taking place deep

within the pavement and structural damage is occurring. It is possibly the result

of too much moisture in the unbound granular layers and excessive stress inci-

dent on the subgrade.