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New-generation plasticiser used on Musina bridge project

Home Engineering Engineers, Consulting Engineers & Project Management New-generation plasticiser used on Musina bridge project

AN advanced water reducing plasticiser has been used in the concrete mixes for the new Nancefield bridge, which forms part of the SA National Road Agency’s (SANRAL’s) Musina Ring Road Project in Limpopo Province.

The R640-million project, which allows the N1 to bypass Musina, is due for completion in Q2 2022. The N1 will pass under the 77-metre-long bridge.

SANRAL wanted visitors from Zimbabwe and South Africa travelling on the N1 to experience a feeling of being welcomed and the bridge therefore features a prominent pair of 13-metre-high ‘hands’ – which are essentially extensions of the centre piers – which express this message. The deck is supported by the columns of the hands and the bridge is aesthetically held on the palms of the hands.

Matthew Barker, General Manager at CHRYSO for technical, mining and export at the company’s centre of excellence said one of the main reasons their Plast Omega 174 plasticiser was selected for the project was that it countered the problem of slump loss.

Based on the available aggregate, ambient temperature and distance from site, the plasticiser was tested and found to be the most suitable admixture, Barker added.

Another challenge was presented by the hot temperatures – up to 45°C – typical of Musina in summer. The concrete temperature needed to be kept under 30°C to prevent thermal cracking. This was achieved by a combination of measures, which included keeping the concrete under shade and cooling it with sprayers, which involved installing a cooling tower to keep the water cool.

CHRYSO Plast Omega 174 allowed the mix designs to be optimised, giving more open time on the fresh mix concrete.

It was the primary product supplied for the Nancefield bridge and was used for the bridge decks, balustrades and the bridge piers with hands.

Just over 3 000 m3 was required for the concrete of the bridge. The use of CHRYSO admixtures for the mix design was implemented by Jacques Marais, senior plant foreman for the production of concrete at OMV, part of the Raubex Group. The consulting engineers for the project were KBK Engineers.

Ben Myburg, Technical Consultant at CHRYSO Southern Africa said the company’s personalised technical service offering and logistics were the deciding factor in OMV using CHRYSO as the main admixture supplier for the project.

“CHRYSO Plast Omega 174 is a multi-dose admixture, which allows concrete to exhibit extended workability characteristics. It improves the cohesion and lowers the viscosity of a concrete mix, which results in an improved homogeneity and compaction, allowing for superior off-shutter finishes thereby eliminating the risk of repairs. By reducing the need for extra water, it increases the durability of concrete by reducing permeability.”

The product is part of the wider CHRYSO Plast Omega range. The company says products in the range are ideal for applications such as underwater concrete, pumped concrete, large pours and flowing concrete.

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