Kwa-Zulu Natal

The Sarnia Road Bridge (B112), located within the eThekwini municipality between the suburbs of Bellair and Hillary, is a vehicular bridge that runs over the N2 and carries traffic along the M10 route. 

A familiar sight for many motorists, the bridge incurred significant damage in 2017, especially to the underside of the structure, when a vehicle accident took place on the N2 Northbound carriageway, resulting in a tanker truck catching alight directly beneath the bridge. 

The South African Roads Agency Limited (SANRAL) put the project out to tender in 2022, with the scope of work as N002-250-202/3-The rehabilitation of B112, Sarnia remedial. 

Project Requirements

The process begins with a high-pressure cleaning at 350-bar to remove debris and compromised concrete, preparing for restoration. Sounding Survey conduct a precision sounding survey to assess concrete integrity, streamlining the process by addressing only compromised sections. We than break out the fire damaged concrete, exposing only sound undamaged sections to minimize reconstruction needs which reduces costs and environmental impact.
The exposed rebar is meticulously cleaned, and the substrate pre-dampened for a strong bond, ensuring the subsequent layers adhere securely.

Application of Structural Repair Mortars

The MonoTop®-1010 ZA was applied to both the rebar and the substrate as both a protective coating for reinforcing steel and a bonding agent. After the primer has completely cured, the Sika MonoTop®-412 NFG is wet sprayed applied. Small parts of the bridge required spalling repairs due to chloride ingress, the substrate preparation process mirrors the one mentioned earlier, with a minor adjustment of Sika MonoTop®-412 NFG now being trowel applied to the affected areas. In the case of more extensive repairs, a shutter and pour method was executed using the Sikacrete®-214. There was concrete blistering in the centre of the bridge where the heat of the fire was less intense. This was addressed by following the same preparatory steps, and a layer of Sika MonoTop®-3020 ZA, was meticulously trowelled on in a 1 mm - 5 mm layer thickness.

Protective Coating Systems

The Sika® FerroGard®-903 Plus was applied via low pressure spray to the entire bridge soffit to not only delay corrosion but to reduce the corrosion rate. Thereafter the Sikagard®-550 W Elastic system was used on abutments, piers, and sides which enhances durability and guards against chloride and carbonation ingress. The final step in the protection process is the application of the Sikagard®-850 AG, an antigraffiti coating. This coating was applied on the lower 3 meters of abutments and the pier to remain pristine, to deter vandalism with any graffiti easily washable with water.

Project Participants

South African Roads Agency Limited (SANRAL)

Main Contractor:
Afrostructures (PTY) Ltd

Naidu Consulting Engineers

Specialist Contractor:
Structural Maintenance Works (PTY) Ltd

Specialist Product Supplier:
Sika South Africa (PTY) Ltd

Image: Side view of bridge before repairs.
Bridge Soffit before repairs
Image: Bridge Soffit before rehabilitation.
After Rehabilitation of Sarnia Bridge in KZN.
Image: After Concrete Repair and Protection of Sarnia Bridge.
Bridge Soffit | Civil Engineering
Image: Bridge soffit after rehabilitation.

Photo Gallery

The Sarnia Road Bridge (B112) rehabilitation project demonstrates that even in the realm of rehabilitation, there’s room for innovation and improvement. The successful completion of the project contributes to the safety and functionality of the bridge and the overall transportation infrastructure in the area.