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Customer: KwaZulu-Natal Department of Transport

Location: KwaZulu-Natal, South Africa

Service: Surface and sub-surface pavement evaluation (iPAVe)

Completed: 2019

In addition to network level use, the iPAVe enables optimised data acquisition at project level and has recently been used to undertake ‘forensic’ investigations on roads under construction. One such project is the major rehabilitation of a 20 Kilometre portion of Provincial Main Road P21-1, a major link between two freeways, located between Durban and Pietermaritzburg in the KwaZulu-Natal Province of South Africa.

The construction of the new road commenced in 2016 and progressed well until industrial action and other issues resulted in an 8-month delay. During this period, it was necessary to open the road with a number of newly constructed sections being exposed to traffic without the 40mm surfacing layer ie, running on the reconstructed sub-base and new asphalt base course.

The 8-month premature trafficking, together with an even longer period where the comparatively porous base mix asphalt was exposed, resulted in fatigue and block cracking occurring over certain sections. Following detailed visual inspections, it was clear the affected areas would require remedial action, the only question was how much of the new pavement structure would have to be reconstructed.

Based on visual assessment alone, together with the presence of block cracking which would suggest the stabilised base was cracked, the initial consensus was the entire 380mm thick base and sub-base should be removed and reconstructed – at a significant cost to the Road Authority.

KwaZulu-Natal Department of Transport (KZN DOT) made the decision to contract ARRB Systems Africa to undertake an iPAVe survey of the entire length of the road, with interesting results.  The portion of the road under consideration was in comparatively sound condition. The areas with concerning deflection measurements were on sections of the project that had not yet been rehabilitated or were the subject of rejection due to quality control issues.

Simultaneous roughness, rutting and crack detection measurements were also undertaken and subsequent analysis of the combined data sets indicated that the rehabilitated sections of the contract had a bearing capacity exceeding the design traffic loading, including the areas exhibiting the fatigue and block cracking and that full depth reconstruction of the latter would not be required.

Instead, selective asphalt base ‘mill and fill’ repairs were carried out at a significantly reduced time and financial cost to the KwaZulu-Natal Department of Transport.

The capability of iPAVe technology to produce continuous integrated road structural and surface measurement, enables precise identification of critical pavement sections thereby eliminating potential wasted expenditure.