mining infrastructure projects
The Matla Headgear Rehabilitation project for Exxaro Coal was completed in September 2018. The silos and headgears at the mine were nearing their design life span and of the mine’s four silos and three headgears all four of the silos and two of the headgears required maintenance. The scope included sealing cracks to extend the life span of the reinforced concrete structures and protect against corrosion; delamination and cleaning of concrete structures to achieve a contaminant free open textured concrete followed by the treatment of the steel/reinforcement and then closing the area; as well as cleaning and coating the surface. A range of relevant and effective Pro-Struct systems were used on the project.
The Majuba Coal Silo Recovery project followed the Majuba Silo Recovery Anchors and Demobilisation project and was completed for Eskom in March 2017. The recovery project included the reconstruction of the main feed silo (silo 20), the lift shaft and the overland conveyor columns, as well as the reinforcement of silos 10 and 30. The construction methodology utilised for the three silos was very unique. A concrete skin was slid to the first ten metres of silo 20 and the complete silos 10 and 30 using a single-sided shutter. The remaining forty-four metres of silo 20 were slid using a conventional slide.
The Majuba Silo Recovery Anchors and Demobilisation scope of works was completed in September 2016. The project entailed the power washing of three silos in order to install 5 800 Y12 dowels into the silo and demolish/cut bad concrete on Majuba’s main feed silo (silo 20). The specialised concrete repair project included rope access technicians who power-washed (350 bar) and installed the dowels to a height of sixty metre. A concrete wire cutting machine (hydrocut) was used to cut the uneven top of the demolished silo into a horizontal working service. The concrete was cut into three- to four-ton sections and removed by crane. The bottom twelve metres of the silo was structurally intact, so was not removed. During the Majuba Coal Silo Recover project eight twelve-metre-high columns were constructed on this foundation to support the new concrete skin.
The silo repair at the Greenside Colliery for Anglo Operations Limited was undertaken in 2016. The project began with the identification of delaminated and spalled areas by means of hammer tests. Further tests, including reinforcement cover readings, carbonation tests and Schmidt hammer tests were conducted on each structure. Temporary suspended platforms were used to access to the inside of the silos. The scope of work on the project also included the removal of the delaminated and spalled concrete via mechanical breakers; thorough high-pressure washing of all areas to achieve an open textured surface exposing the aggregates; inspection of the reinforcement for corrosion and high-pressure washing of the reinforcement with grit entrainment to achieve a Swedish standard; injection of a low-viscosity epoxy into cracks on the concrete substrates of each structure; and the coating of the silos and take-up tower with a migrating corrosion inhibitor and a cementitious mortar.
The NAMDEB diamond mine in Namibia required minor rehabilitation works within an existing active plant in the mine’s ‘Red Area’. The project was completed between February and May 2014. The damaged structure required a complete face lift, and the work was executed within the active plant. Access was strictly controlled by the mine’s security and employees had to pass through a four-system security check when entering and exiting the area.
Matla Mine’s ROM 2 silo was repaired for Exarro between November 2012 and February 2013. Stefanutti Stocks Technical department designed and developed a hydraulic access system solution that reduced the installation and dismantling time by 60 per cent.Due to production pressures the worked was scheduled on a 24-hour per day basis. The inside of the silo (spalled areas of concrete) needed to be repaired during a short wall move underground and was accessed by means of a platform suspended from eight hydraulic jacks, operated with a single power pack. A migratory corrosion inhibitor infused repair mortar was used to reinstate the silo.
The Impala No 4 Penstock Pipe Rehabilitation project, undertaken in late 2011, involved strengthening a 1.25 metre-diameter Northern Penstock Pipeline by resleeving the entire two kilometres with a 1.1 metre diameter steel pipe of walls ten millimetres thick. Stefanutti Stocks chose not to use conventional methods to re sleeve the pipeline as these did not address major safety concerns. Instead, a world first, custom developed option involving the use of a 48 Volt DC motor to power a pipe vehicle through the two-kilometre pipeline, was implemented to execute the project.
The rehabilitation of Geita Mine’s primary crusher’s supporting base at the Anglo Gold Ashanti’s mine in Northern Tanzania involved a five-day, around the clock rehabilitation programme with minimal disruption. The cracks in the base were repaired by injecting a low viscosity epoxy resin into the cracks and a high-strength reinforced grout skin was added to the outer face of the base. The spalling concrete on the outer face was removed and the outer face repaired and re-profiled. Material and equipment was shipped in three months prior to the scheduled shut-down in 2010.
The repair of a concrete silo for Harmony Gold was undertaken in 2009 and included the removal of damaged and loose concrete, the replacement of missing reinforcing steel (12 ton); the installation of new rail liner brackets; guniting (180m3) the silo wall to its original profile; installation of new rail tracks and post tensioning of the silo.