Rehabilitation of a section of the North-South Corridor Road, Zimbabwe

The North-South Corridor Road in Zimbabwe forms part of the trans-continental connector that ultimately connects Cape Town and Cairo. A 6.5km section of this road on the Zambezi escarpment between Makuti and Chirundu) was recently rehabilitated and upgraded with a foamed bitumen stabilised base. Loudon International assisted the contractor, Conduril – Engenharia, S.A., with the application of foamed bitumen technology.

The existing pavement consisted of a 150mm granular base, supported by 150mm of granular subbase and surfaced with a double seal. The existing road was widened from a 7m wide single carriageway with no shoulders to a 10.5m wide carriageway with a climbing lane, as well as a 2.5m shoulder on both sides, totaling a 15.5m wide surfaced road.

Once the subbase of the widening was constructed, the existing base was pulverized and spread over the full width before being supplemented with material imported from borrow pits. This material was shaped to line and level, pre-compacted and stabilised with foamed bitumen using a Wirtgen WR2000 recycler. Soon after construction, the layer was treated with a diluted bitumen emulsion fog spray and opened to traffic.

Two bitumen stabilised material (BSM) designs were adopted for different sections:

  • 210mm BSM layer (100mm existing with 110mm added material), stabilised with 2.5% bitumen.
  • 140mm BSM layer (90mm existing with 50mm added material) stabilised with 3.0% bitumen.

Both designs were carried out by BSM Laboratories (Pty) Ltd and met the requirements prescribed in the TG2 (2020) publication.

Loudon International carried out investigations of the pavement and mix designs, assisted with the application of foamed bitumen technology, onsite training and assisted with quality control procedures.