Refurbishment of silo complex sets new benchmark

In constant operation since the 1940s, Pioneer Foods’ grain silo complex at its Malmesbury Mill has delivered faithful service, with the concrete standing up well to the passage of time. Now, a recent overhaul has given the silos a new lease on life.

Repairs were carried out on the spalled concrete areas of the silo complex and, in some cases, badly corroded rebar had to be removed and replaced

Specially designed scaffolding enabled the installation of the external repairs, with internal repairs carried out via rope access

After some 77 years, a degree of wear and tear can be expected on any structure, and this became evident during 2018 when large vertical cracks started to form in some areas. Given the silos’ strategic importance to sustained mill operations, an urgent repair solution needed to be found since a complete demolition and rebuild was not possible from a time and cost perspective. Making use of the latest state-of-theart infrared and high-resolution scanning equipment, LNW Consulting Engineers and Project Managers was appointed to collect evidence of the typical distress patterns to

Due to the existing state and surface imperfections of the concrete, Sikalastic-152 was chosen as a cementitious, flexible, fibre-reinforced mortar for waterproofing and concrete protection, and was applied on the entire external surface as a protective coating complete a thorough structural analysis. The insights gained from this investigation indicated ring tension failure of the horizontal reinforcing with large areas of fatigue within the concrete walls. This information enabled the engineers to design and develop a silo rehabilitation repair methodology employing specified Sika products.

The decision was made to repair the entire silo complex, utilising external structural reinforcement methods such as horizontal carbon fibre composite strapping, along with various types of mortars, epoxies and protective coatings.

To execute the works, Redec Industrial and Engineering Solutions was appointed as the repair contractor. Specially designed scaffolding enabled the installation of the external repairs, with internal repairs carried out via rope access.

As the work would take place within an operational grain silo storage facility, it was crucial to select products and processes that would not pose a risk of food contamination or potential health and safety risks to the applicators. The silo storage levels were constantly monitored as repair work took place, and silos needing internal work had to be emptied.

Since the silos are situated next to Malmesbury Mill, innovative preparation techniques also had to be adopted to minimise dust pollution.

Crack repairs

Due to the age of the structure and its low concrete compressive strength, the evidence of cracking was extensive. These cracks needed to be reamed open, stitched and repaired. Some of the minor cracks were saw-cut and sealed with Sikaflex® PRO-3, an I-Cure polyurethane sealant with high mechanical and chemical resistance. Sika® Primer-3 N, an epoxy primer for porous substrates, was also utilised for this purpose.

Sikadur-Combiflex® SG-20 P, a high-performance movement joint and crack sealing bandage system, was applied over all expansion joints to seal and waterproof. This Sika product uses the Sikadur®-31 DW structural epoxy as its adhesive for enhanced performance.

For crack repairs on the concrete roof slab floors, Sikadur-43 ZA was used. This solvent-free, three-component repair and filling mortar was applied prior to application of the modified structural steel, which was fortified with the new SikaCem®-810 additive.

Coating application

Because all the repairs were vertically oriented, the method adopted needed to make use of either trowel-applied mortars, or a letterbox shutter and pour system. Following consultation with technical specialists at Sika South Africa, SikaTop® Armatec®-110 EpoCem® was employed as the primary rebar protective coating.

Additionally, SikaTop Armatec-110 EpoCem and Sika MonoTop®-610 were used as bonding primers for the concrete substrate. In turn, Sika MonoTop-615HB was utilised as an R4 high build repair and reprofiling mortar due to its unique Ferrogard corrosion inhibitor and excellent lightweight properties. These and other specialised Sika solutions all came together to form a highly sustainable refurbishment solution, meeting and exceeding the required 20-year design service life.

AfriSam’s slagment operation was established in 1955 and has supplied product to flagship projects that include the Gariep Dam