The critical path is the two bridges, joined by a 1000 mm stitch to resemble a single structure.
Cape contractor Haw & Inglis Construction has, since July 2021, been undertaking an upgrade of Cape Town’s Refinery interchange, supported by construction materials from AfriSam.
The project is due for completion in early 2024, delivering two new higher and wider bridges over the N7 highway – a new road-over-rail bridge alongside the existing bridge, which is undergoing rehabilitation works, and upgraded access ramps.
Haw & Inglis construction manager Leiton Chan says the new bridges double the capacity of the interchange and provide an additional 1.7 m clearance from the existing bridge for vehicles travelling on the N7.
To accommodate existing traffic, the westbound carriageway was built alongside the existing eastbound carriageway.
Once completed, the traffic was diverted onto the new carriageway to complete the eastbound carriageway.
The existing bridge was demolished in December 2022 to make space for the new bridge, which is currently under construction.
“Each bridge deck over the N7 was cast in two, consisting of a dual-spine, post-tensioned structure. The project is currently on schedule, with the estimated completion date for the eastbound carriageway bridge over the N7 being August 2023,” says Chan.
AfriSam is providing about 6 300 m3 of readymix concrete, as well as material for layer works, according to AfriSam territory sales manager Bradley Thomas.
The company is also supplying about 15 000 t of aggregate to the project’s asphalt supplier, Much Asphalt.
“An important application of our readymix was for the piling under the bridges, which required almost 1 500 m3 of high-strength 40 MPa concrete. A priority here was to avoid any jointing in the piles, so it was essential that each pour – about 3.5 m3 per pile – was continuous,” explains Thomas.
He notes that the decks on the two main bridges over the N7 also require continuous pours, amounting to substantial volumes of 500 m3 of W50 MPa concrete per deck.
Placement is carried out using a high-capacity 36 m boom placer.
The readymix is supplied from AfriSam’s Contermanskloof plant in Durbanville, located 8 km from the site, with support from the company’s other nearby plants at Woodstock and Bellville.
The spreading of supply sources allows for further mitigation of project risk related to readymix deliveries, says Thomas. For instance, large continuous pours leave little room for error, and unforeseen events such as traffic congestion have to be factored into the resource planning.
“On the smaller-scale aspects of the project’s readymix requirements, our flexibility also allows us to effectively supply the smaller subcontractors on the project. We have therefore also been able to play a role in enterprise development, supplying the kerb mix to small, medium-sized and microenterprise contractors installing the precast kerbs,” he outlines.
According to Chan, Haw & Inglis has been able to incorporate a considerable amount of recycled material in the road fill.
He points out that the westbound carriageway fill was made up of in-situ G7 sand material excavated from the bridge and mixed with recycled asphalt product (RAP). The RAP is milled material from the various road contracts conducted by the Western Cape government.
In addition to carefully facilitating the traffic flow through the interchange during construction, the project has also had to navigate underground and overhead services from high-voltage power lines and diesel pipes to sewer networks and optical fibre lines, he says.
A further environmental priority was not to disturb two small wetlands within the road reserve.