Citi-Con’s specialist concrete repair capabilities are being harnessed by a leading agricultural company to refurbish its silos at three sites. Their useable lives are also being extended, a critical intervention considering the strategic nature of this infrastructure.

“Silos are very costly to demolish and reconstruct, which often involves specialist construction techniques to reduce build time and costs. Even so, it is not always possible to decommission this infrastructure without negatively impacting operations. This is considering the strategic role that silos play in preventing post-harvest losses by providing efficient and reliable storage capacity,” Andrew Rudolph, Technical Manager of Citi-Con, says.

Considering the age of these silos, they require extensive concrete repairs. The work scope includes waterproofing the bin roofs and ceilings, as well as sealing the drip ends. Citi-Con is also sealing the ring-beams; vertical wall joints; wind inlets; and manholes.

This is in addition to comprehensive repairs to the concrete walls, each about 33,5m in height and 49m in diameter. Rudolph says that the process starts with thorough preparation of the concrete substrate, removing a thin layer of concrete via high pressure cleaning at 200 bar. This exposes the many vertical and horizontal cracks in the walls, after which a comprehensive structural investigation is undertaken. Cracks greater than 1mm in width are addressed first. A chip hammer is used to identify honeycombing and spalling due to steel reinforcement corrosion and the compromised concrete then marked for attention.

Thereafter, square cutting is undertaken to prepare the compromised concrete for repair. This entails cutting the edges of the cracks to about 120mm on either side and widening the bases. They are opened to about 20 mm behind the reinforcement to create a shelf for the repair material to lock in. “This level of preparation is key to ensuring durable concrete silo repairs. In many instances, premature failure of concrete repairs can be attributed to poor preparation practices to save time and costs,” Rudolph says.

As part of the process, the steel reinforcement is treated with StonCor Africa’s Pro-Struct 688 Zinc Rich Primer. It was specified for this application because of its durable and corrosion resistant properties. He says that this is a sound example of how Citi-Con is also extending

the useable life of the infrastructure, considering that corrosion is one of the leading causes of degradation of reinforced concrete structures.

Thereafter, the exposed concrete is saturated with water ahead of the application of StonCor Africa’s TAMMS structural mortar, which provides high strength and increased adhesion due to its proprietary formulation. The structural mortar consists of Portland cement; graded aggregates; unique fibres; and polymers, while also containing a corrosion inhibitor.

Cracks that are less than 1mm in width are chased with V-joint/V-groove cutting discs and then reinstated with ProStruct 506 Flexicoat. This is a high quality elastomeric waterproofing membrane.

“Completing the concrete silo repairs entails also treating the other repair areas with Pro-Struct 506 Flexicoat. The wall is first saturated with water using a hose. The first coat is applied horizontally from right to left and the second perpendicular, starting from the top. This approach ensures proper adhesion of the 2mm-thick waterproofing membrane,” Rudolph concludes.