August 23, 2017

Impala Platinum Mine undergoes concrete repairs

In 1924, platinum was discovered in the Bushveld Igneous Complex, an area containing some of the world’s richest ore deposits, lying just north of Pretoria near Rustenburg. Ninety years later in the same area, Sika was involved in a major refurbishment project at the Impala Platinum Mine, a fourteen-shaft mining complex with concentrating and smelting plants.

Engineers from Blue Consult specified 11 Sika products for the project whose scope of works consisted of general concrete repairs, spalling repairs, external reinforcing, waterproofing, and protection. The contract was awarded to concrete repair and corrosion specialists, Hindle Mason Projects.

For general concrete repairs, Sikagrout-212, a high performance, cementitious grout, was used. Easy to apply with an adjustable consistency, this fluid grout expands by gas generation whilst in the plastic state of curing. It is non-corrosive with high final strengths.

For large-scale structural repairs, the free-flowing, high strength cement-based micro-concrete, Sikacrete-214 was used. With a maximum aggregate size of 9mm, it is an economical option, providing excellent adhesion and high resistance to freeze/thaw cycling. It is shrinkage compensated and provides rapid strength development. Sikacrete-214 is ideally suited for casting sections or members where the volumes required are too large for conventional grouts or too small and inaccessible for normal concreting procedures.

Corroding rebar were first grit blasted and then coated with SikaTop Armatec-110 EpoCem, an easy to mix, cementitious, three-component epoxy resin bonding primer with corrosion inhibitors. Boasting Sika’s EpoCem technology, it provides excellent adhesion to concrete and steel, and extended open times for repair mortars. SikaTop Armatec-110 EpoCem may be applied by brush or spray gun and provides high shear strength as well as good resistance to water and chloride penetration.

To complete the spalling repairs to the columns and beams, Sika Rep LW, a cement-based, multi-purpose patching and repair mortar was applied. With excellent adhesion, non-sag properties, Sika Rep LW is shrinkage compensated, permeable to water vapour and provides a high resistance to freeze/thaw cycling.

Prior to structural strengthening of the actual storage silos, the strength and ductility of their support columns was increased by first applying Sikadur-330, a two-part, thixotropic epoxy-based impregnation resin, followed by SikaWrap-230 C, a unidirectional, woven carbon fibre fabric, designed for installation using the dry application process. SikaWrap-230 C is a multi-functional fabric that increases flexural and shear loading capacity in many different strengthening applications. Available in varying widths, it is lightweight, flexible and accommodating on various surface planes and geometry. Compared to traditional strengthening techniques, SikaWrap-230 C is an extremely cost effective option.

Sikadur-30 was used as a structural adhesive for bonding Sika CarboDur Plates onto the silos as external reinforcement. Sikadur-30, a high strength, two-part, thixotropic adhesive based on a combination of epoxy resins and special filler. It hardens without shrinkage and provides high abrasion and shock resistance. Sika Carbodur Plates manufactured from pultruded, carbon fibre reinforced polymer (CFRP), these world renowned, high strength laminates are extremely durable with outstanding fatigue resistance. Despite their robustness, Sika CarboDur Plates are lightweight, easily transported and very simple to install. The numerous combinations of high strength and modulus of elasticity available, makes this exceptional product highly versatile. Prior to the end of the project, approximately 3500m of Sika CarboDur Plates S512 had already been installed on the silos.

Since this active platinum processing facility could afford no stoppages, the project was carried out under a highly restrictive schedule, with some work only being performed during scheduled plant shutdowns. Further challenges included a closed working environment and limited access to certain working areas.

Another structure at the mine requiring refurbishment was the main clarifier, the interior surface of which was protected and sealed with solvent-free Sikagard-720 EpoCem (150 kits), a three-part, epoxy modified, thixotropic, fine textured mortar. Providing better chemical resistance than a PCC mortar, Sikagard-720 EpoCem is impervious to liquids but permeable to water vapour, and provides an excellent bond to green or hardened concrete, whether damp or dry.

Prior to the final protective coating, the interior of the clarifier was primed with Sikafloor-161, a two-part, low viscosity epoxy resin providing good penetration and excellent bond strength. This was followed by a coating of Sikalastic-841 ST (approx. 400m2), a two-part, elastic, pure polyurea liquid applied membrane with very good chemical resistance. Applicable in a wide range of temperatures, it is 100% solids with zero VOC and provides outstanding crack-bridging properties. Importantly for this project, Sikafloor-161 requires short waiting times, whilst the very fast reactivity and curing time of Sikalastic-841 ST, allowed for almost immediate return-to-service time.

It was credit to these outstanding Sika products, many of which meet the most stringent international standards, that this lengthy project at the world’s second largest platinum producer, remained on schedule with no major delays incurred.

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