Construction World December 2023

INFRASTRUCTURE REHABILITATION: SARNIA ROAD BRIDGE PROJECT

S arnia Road Bridge (B112) is a vehicular bridge over the N2 and carries traffic along the M10 route, within the eThekweni municipality, located between the suburbs of Bellair and Hillary. In 2017, a vehicle accident took place on the N2 Northbound carriageway, beneath the bridge and a fuel tanker truck subsequently caught alight resulting in significant damage to the underside of the structure. South African Roads Agency Limited (SANRAL) put together the scope of works for the N002-250-2020/3-The rehabilitation of B112, Sarnia remedial works tender, and put the project out to tender in 2022. Afrostructures, a construction company located in KwaZulu-Natal with a Grade 9CE and a Level 1 BBBEE rating, emerged victorious in the competitive bidding process and secured the contract in April 2022. Naidu Consulting Engineers oversaw the engineering works and supervision of the project, while the specialist company Structural Maintenance Works was contracted to handle the repairs for fire damage, spalling, and coating of the bridge. In the world of construction and infrastructure rehabilitation, innovation is the driving force behind safer, more durable, and longer-lasting structures. The rehabilitation of the Sarnia Road Bridge (B112) serves as testament to how cutting-edge construction technology can elevate the quality and longevity of concrete refurbishment. Step 1: High-Pressure Cleaning (350 bar pressure) The process begins with a thorough high-pressure cleaning of the damaged concrete surfaces. At a 350-bar pressure, this technique removes debris, contaminants, and compromised concrete, preparing the structure for restoration. Step 2: Sounding Survey Precision is key. A sounding survey is conducted to assess the concrete's integrity. This step ensures that only compromised sections are addressed, optimizing efficiency and resource utilization. Step 3: Exposing Sound Undamaged Concrete Breaking out the fire damaged concrete until exposing sound undamaged concrete. This selective approach minimizes the need for extensive reconstruction, reducing both cost and environmental impact.

Step 4: Rebar Preparation and Substrate Dampening Exposed rebar is meticulously cleaned, and the substrate is pre-dampened to ensure a strong bond. This precise preparation ensures that the subsequent layers adhere securely to the surface. Step 5: Application of Structural Repair Mortars Following substrate preparation, Sika MonoTop®-1010 ZA, a bonding primer and reinforcement corrosion protection, cement-based polymer modified slurry containing recycled waste materials, which leads to a reduced carbon footprint, is brush applied. Step 6: Spalling Repairs 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 applied with a trowel to the affected areas. In the case of more extensive repairs, a shutter and pour method was executed using the Sikacrete®-214, a cementitious high Concrete blistering was 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, a R3 cementitious pore filler and levelling mortar with reduced carbon footprint, is meticulously trowelled on in a 1 mm - 5 mm layer thickness. " Innovation doesn't stop here. Protective coatings also play a vital role in the careful refurbishment of concrete structures.  early strength structural micro concrete. Step 7: Addressing Concrete Blistering

PROJECT INFORMATION

• Company entering: Sika South Africa • Client: South African Roads Agency Limited (SANRAL) • Main Contractor: Afrostructures • Principal Agent: Naidu Consulting Engineers • Subcontractor: Structural Maintenance Works

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22 nd Best Projects Awards 2023