Bosch Holdings Enginuity November 2011 - Page 12

page ENGINUITY 12 page Bosch Stemele N2 Overlay In The Eastern Cape 13 Bosch Stemele Roads Division Rise To The N10 Upgrade Challenge Construction of high fill in Phase 2 N2 overlay under construction Bosch Stemele, in joint venture with BCP Engineers, was successful in a tender to SANRAL to undertake special maintenance of a 15km section of the N2 to the west of Port Elizabeth. This portion of dual carriageway, from Van Stadens River Bridge to the St Albans Interchange, had last received structural maintenance in the mid-nineties, and the surfacing was exhibiting severe forms of distress. Investigations showed that with minor exceptions, the layerworks below the surfacing were adequate for the design life traffic if they were kept dry. This necessitated upgrades to the surface drainage as well as subsoil drainage in both the median and outer edges of the carriageways. As much of the surrounding terrain is very flat, particular attention had to be paid to ensuring free flowing side drains, resulting in the requirement for concrete lining. This was followed by extensive repairs of the distressed roadway surfacing by milling out the top layer of asphalt and replacing it with new asphalt. This was restricted generally to the slow lanes. Selected deep structural patches were also undertaken. In a deviation from more recent practice, SANRAL requested that a semi-gap graded asphalt be investigated for use in the overlay, as this grade of asphalt provides better resistance to moisture ingress amongst other beneficial properties. A shortcoming of se