Sentech Tower Concrete Rehabilitation Project

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Sentech Tower Concrete Rehabilitation Project

This successful concrete rehabilitation project, located in Johannesburg, South Africa was undertaken by Stefanutti Stocks Inland: Civils Discipline between 6 July 2020 – 30 November 2021 and achieved a LTIFR of zero.

Background: Construction of the 237-metre-high Sentech Tower (originally called Brixton or Albert Hertzog Tower) was completed in 1962. The TV tower (built to withstand winds of 186km/h and gusts up to 200km/H) was constructed using reinforced concrete coated with an approximately 50mm thick sacrificial gunite layer. Over its sixty-year lifespan the tower has been exposed to harsh local climatic conditions, abrasive airborne materials from mine dumps, and chemical attacks by pollutants, resulting in the deterioration of the gunite. The external refurbishment of the Sentech tower was undertaken to prevent the possibility of falling debris becoming a public hazard, as well as extending its lifespan.

The Project Scope

The external refurbishment of the Sentech Tower included the access systems and temporary works required to access the tower externally.

Concrete rehabilitation, repair, and protection was undertaken to provide short to medium term solution of prolonging the tower’s lifespan. This included preparation (concrete demolition to vertical

surfaces), in-situ concrete repair, applying protective coating, replacing existing fenestration, installing new stainless-steel handrails, closing port holes, and waterproofing the Rotunda roof slab.

A purpose-built access system – consisting of two landing platforms, temporary suspended platforms (TSPs), and a monorail – accommodated the increased loads and provided a continuous work face around the tower. Repair work was conducted from the top platform down to the middle of the tower, and from the middle platform down towards the ground. The TSPs were suspended from the platform, in line with the temporary works design. The TSP platforms on the middle platform were installed alongside one another to create a continuous working platform that can be moved around the tower on a Monorail. The concrete repair and protection, as far as practicable, were undertaken from these TSPs. Repair and protection to areas not accessible from the TSPs was undertaken either from the landing platforms or via rope access.

Quantities

  • Concrete demolition (50m3)
  • 30MPa self-compacting concrete (15.5m3)
  • SikaGrout-212 (11 800 litres)
  • Sikacrete-214 (9 900 litres)
  • SikaSwell S-2 (60 litres)
  • Sika MonoTop-412 NFG (11 760 litres)
  • Sikagard-550W Elastic Primer (1 750 litres)
  • Sikagard-550W Elastic Topcoat (3 200 litres)

Working at heights and the exposed working area on the side of the 237-metre-high tower meant that progress on the project was highly dependent on weather.

The 25 days originally allocated for weather delays were consumed within the first three months of the project, mainly due to rain and lightning (work had to stop when lightning struck within a 16km radius).
A further 65 days were accumulated due to high winds (windspeed more than 38km/h).

Interesting Facts About the Structure:

  • The TV tower offers some of the best views of Johannesburg.
  • Ove, Arup and Partners designed the tower and Christiani and Nielsen SA built it.
  • The first transmission took place 22 December 1961.
  • Presently Sentech broadcast 18 FM programmes and 7 TV stations.

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