The busy N7 highway on the west coast of the Western Cape province will soon be even safer when H&I Construction completes the Van Schoorsdrif interchange about 15 km north of Cape Town’s suburb of Milnerton.
This project removes one of the last at-grade intersections on the N7, which have increasingly presented a safety hazard as the fast two-lane highway becomes increasingly well-used by commuters, tourists and industry. Commissioned by the Western Cape Department of Infrastructure, the safety improvement project includes 5 km of greenfields road and six bridge structures, Willem Olivier, Contracts Manager for H&I Construction, explains.
The company is partnering with AfriSam for the approximately 10 000 m3 of 50 MPa readymix concrete required for the bridge builds and ancillary road works such as concrete drains. The 36 month project began in March 2024 and is due for completion in March 2027.
“The new road links Frankdale Road in the west and Vissershok Road in the east,” Olivier says. “The new interchange also necessitates the construction of a new weighbridge facility 600 m north of its current location.”
Importantly, the vertical and horizontal alignment of the new road is designed to be compliant with the latest speed and safety requirements, making for a safer driving experience and more efficient logistics. It is generally a two lane carriageway with lanes of 3,7 m widths and 2 m of surfaced shoulder in each direction.
“The alignment has meant that a significant portion of the road is in fill with over 500 000 m3 of fill constructed,” he explains. “Where the road crosses the Diep River, for instance, high approach fills were required due to the depth of the river valley, combined with the required vertical alignment.”
A major focus of the project has been the work on the six bridges, of which the largest were the four span road-over-road bridges spanning the N7 national road and the 156 m long road-over-river bridge crossing the Diep River.
Spanning the N7 highway, the B6113 is a four span bridge designed with three piers consisting of trestle beams supported on 750 mm diameter friction-type piles.
According to Lucien Smith, H&I Construction’s Project Manager, the bridge consists of 32 prestressed precast U-beams with diaphragms over the piers and abutments. The beams were successfully installed using mobile cranes over a single weekend in April 2025.
“The in-situ deck is supported on permanent shuttering between beams with cantilevers at the edges on conventional shuttering,” Smith says. “The in-situ slab was constructed in stages, ensuring that the deck is continuous over the diaphragms, with a sidewalk and balustrades.”
AfriSam supplied 870 m3 of readymix for this bridge from its batching plants at its Bellville, Woodstock and Peninsular Quarry sites, and the structure was strengthened with over 210 t of reinforcing bar.
The B6116 bridge over the Diep River is an in-situ concrete three span structure supported on 1 200 mm diameter end-bearing piles. It is underpinned by piers 12 m high and 900 mm diameter end-bearing piles on perched abutments. The deck comprises two spine post-tensioned arched spine beams of 2,6 m to 4,5 m deep. The deck itself varies in depth from 250 mm to 450 mm and has 2,2 m cantilevers supporting the balustrades.
Smith highlights that the risk of flooding required some innovative thinking to ensure a safe and streamlined work programme on the Diep River bridge. While the initial plan was to stress the whole deck as one structure, this would have required the formwork to be erected during two rainy seasons.
“To reduce the risk to the temporary support when the Diep River floods, we opted for a temporary stressing design which allowed us to remove the formwork from the first two outer decks and construct the central deck before stressing the whole deck as one,” he says.
AfriSam supplied close to 3 000 m3 of readymix concrete for the Diep River bridge, which was reinforced by 408 t of rebar and cast using 5 402 m2 of formwork.
Shaughn Smit, AfriSam’s Regional Sales Manager – Construction Materials Cape, highlights the complex logistics behind the large continuous pours involving a coordinated effort by about 60 staff at AfriSam’s three batching plants.
“With the pour ramping up to between 60 to 70 m3/h during the day, we augmented readymix from our Peninsular Quarry with supply from our Bellville and Woodstock quarries,” he explains. “Optimising the cycle times from our different batch plants required intense focus and meticulous systems. Readymix had to arrive exactly on time to keep the two concrete pumps continuously fed with its water-cement ratio actually delivering up to 64 MPa strength.”
The concrete’s slump was critical and also required adjustment during the pour, notes Douw De Vos, Cluster Manager for AfriSam’s Cape-based readymix operations.
“It was vital to achieve a consistent 200 mm slump to prevent excessive pressure on the formwork while maintaining adequate flow,” De Vos explains. “Adding to the complexity during the pour, the slump had to be reduced on short notice to 175 mm in areas with less congested reinforcement to prevent the concrete from spreading too rapidly. This would otherwise have increased the exposed plastic surface area, leading to premature drying and potential cold joint formation. AfriSam’s laboratory and plant teams coordinated this effectively to ensure these slump adjustments were implemented accurately.”
Constant communication with the client was also vital to alert the batching plants and on-site laboratory to change the slump throughout the day, taking into account that about 45 m3 of concrete was on route to site at any one time. De Vos adds that AfriSam used 25 to 30% fly-ash in the mix to help control the heat of hydration and to contribute to durability.
Another significant bridge is the B6112 road-over-road portal structure that links the two sections of the City of Cape Town landfill site on the western side of the N7 highway. This landfill site will be cut in two by the new Vissershok road. The portal is built with a 1 m deep solid deck spanning 15 m with 1,2 m thick abutments and will be 11 m high, supported on a 1 m thick raft foundation.
“The design of the structure allows for future extension northwards, with the deck being constructed to the current end of the wing walls which are 1,2 m thick,” he says. “Due to the high abutment walls, the wing walls to the south are 1,2 m thick up to a height of about 6 m, once the cantilever wing walls are constructed.”
This substantial structure consumed 3 336 m3 of readymix from AfriSam and was supported by 323 t of reinforcing and 3 340 m2 of formwork.
“AfriSam’s strong relationship with H&I Construction dates back to their founding 35 years ago,” says Smit, who has been a key link from the start.
