Civil Engineering September 2022 | Vol 30 No 8

construction due to the excessive pres- ence of chlorides in the area. For bridge construction, a durable concrete was specified to prevent chloride-induced corrosion of steel. This included limiting water to binder ratios, including ground- granulated blast-furnace slag in the concrete mix, and applying hydrophobic waterproofing on exposed concrete ele- ments. In addition to this, most gravel material along the road contains a high percentage of soluble salts and the project team had the challenge of preventing salt-migration in layer works, which could lead to de-densification of pavement layers and substantially damage the road surface through blistering of the seal. This was addressed by quick construction methods between constructed layers. Commercial water was sourced for the construction of layerworks since the only natural water source from the Swakop River was also laden with salt. WINDHOEK TO HOSEA KUTAKO INTERNATIONAL AIRPORT FREEWAY UPGRADE The Windhoek to Hosea Kutako International Airport Freeway Upgrade is split into three stages, namely WHK- HKIA Phases 1, 2A and 2B. Phase 2A is scheduled for completion in early 2024, and Phase 2B towards the end of September 2024, entailing the completion of the final dual-carriageway links to the east of the airport. Once the entire Western Bypass Freeway is complete, it is anticipated that there will be a significant reduction in heavy goods traffic in Windhoek with major cargo and commuter transport on the North-South corridor having a free flow route around the city centre. The very high geometric standard, which is necessary for a freeway align- ment, requires that the planning and proclamation of these freeways be completed some 30 to 50 years prior to the development of property adjacent to the freeway. Most of the route for the Windhoek to Hosea Kutako International Airport Freeway Upgrade had been pro- claimed in the 1970s and the preliminary geometric horizontal alignment was designed in 1978. It was only in the mid- 2010s, however, that the feasibility of the freeways in Namibia was revisited. Construction of WHK-HKIA Phase 1 is nearing completion. The geometric design included 9 km of freeway and 16 km of ramps and crossroads, as well as four interchanges of varying complexity. The road traverses flat to hilly terrain, requiring the construction of over 1.2 million m 3 over a 9 km long section. Also included was the structural design and supervision of seven twin-spine post- tensioned bridges, three river bridges, two road-over-rail bridges and two voided slab bridges. Construction of WHK-HKIA Phase 2A commenced in March 2020 through co-financing by the African Development Bank and the Namibian government. The project consists of a dual carriageway, split-level interchanges and river bridges for a length of approximately 20 km. A remarkable feature of this phase is the geometric alignment through the 16 September 2022  Civil Engineering Two bridges over the Klein Windhoek River, part of the Hosea Kutako International Airport Freeway Upgrade Early morning view of the construction of Sam Nujoma Interchange