Construction World October 2017

COVER STORY

AFRISAM is building new life into HOPETOWN bridges The passage of motorists and pedestrians over the bridges north of Hopetown is about to get safer. This is due to a South African National Roads Agency SOC Ltd (SANRAL) bridge widening project currently underway by contractors Botes & Kennedy Manyano with perfor- mance-based concrete mixes designed by AfriSam.

slump requirements,” says Croney. “These included designs for 15 MPa, 30 MPa, 40 MPa and 50 MPa in both standard concretes and the ‘W’ concretes that must meet certain durability indices for oxygen permeability, sorptivity and chloride conductivity.” These tests were conducted at AfriSam’s CPE, SANAS accredited laboratories in Roodepoort. New piers Placing new piers in the flow of the Orange River required the construction of a causeway out into the watercourse, while being careful not to unduly affect the river level. As it was, the water level presented one of the key risks in the project, according to Botes & Kennedy Manyano site agent Jeann van Tonder. The construction plan was based on a study of the river’s high water marks over the past 100 years, and daily contact with the water authorities upstream at the Gariep and Vanderkloof dams. “Earthworks were undertaken down to bedrock so that a mass concrete base could be anchored, onto which a 1,7 metre deep concrete base is constructed for each new pier,” says Van Tonder. “The piers are then cast in three lifts of 3,6 metres each and

The R88-million project – which began in mid-2016 and is on track for completion by the end of February 2018 – is focused on the 312 metre Hopetown bridge (B2482) that crosses the Orange River north of the town en route to Kimberley. There is also a much smaller and lower bridge being widened (B2483) which traverses the 30 m over what used to be Langford Stream. This substantial piece of engineering will see the current Hopetown bridge widened from 9,28 m to 15,4 m, according to Botes & Kennedy Manyano contract manager Deon Douglas. “While the road will remain a single lane carriageway over the bridges, this improvement will allow a 2,5 m shoulder on either side, as well as a dedicated asphalt surfaced pedestrian walkway along the eastern side, protected from the traffic by a concrete balustrade,” says Douglas.

The original bridge comprises 11 concrete piers – each measuring some 12 m in height – between a north and a south abutment. The road widening project requires 11 new piers to be built, alongside the existing ones and to similar dimensions. It is therefore unsurprising that the project should consume as much as 4 000 m 3 of concrete and almost 500 tonnes of reinforcing steel. Performance based concrete SANRAL’s specification of a performance- based concrete – rather than providing a prescriptive specification – put the ball in the court of the concrete designer to meet their requirements, according to Brendan Croney, technical consultant at AfriSam’s Centre of Product Excellence (CPE). “AfriSam designed a range of concrete mixes for the project to ensure optimal durability and meet certain workability or

The road widening project requires 11 new piers to be built, alongside the existing ones and to similar dimensions.

Another indication of the scale of the concrete works was the fact that almost 9 700 m 3 of formwork was used.

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CONSTRUCTION WORLD OCTOBER 2017