Prestressed Concrete Replaces Steel for Railway Poles in Durban
A number of 880 prestressed concrete poles, manufactured by INFRASET Infrastructure Products, have been installed in place of steel masts for the support of overhead electrical equipment OHTE at Transnet’s Bayhead marshalling yard in Durban. The steel masts had been in service for 35yr and were falling prey to steel’s major coastal adversary, corrosion. They would have become a logistical and safety liability had they been allowed to remain in service for much longer.
Contract manager and Transnet Projects overhead track and equipment manager, Mahomed Sayid, observed that concrete poles were primarily chosen because of their long-term durability and rust-free properties. “We were able to source the concrete poles from INFRASET’s factory in Effingham and having witnessed the effects of corrosion on the steel masts, we wanted to avoid it on the new generation of poles. This was why we asked INFRASET to galvanise the steel strands which were used for prestressing the poles. We also took the precaution of requesting that the poles be cast with condensed silica foam (CSF), an additive which yields a dense concrete far less prone to moisture absorption.
“All the associated steelwork and fittings were supplied in rust-proof 3CR12 steel. Our overall aim was to lengthen the life-cycle of the support masts and to reduce the amount of maintenance that would be required during this period. We are confident that we have achieved this objective,” explained Sayid.
Pole installation began in January 2005 and was completed in September 2007. Installation work was executed in two phases, 1A and 1B and INFRASET supplied four pole variants poles, 12m and 13m units rated at 64kN as well as 12m and 13m units rated at 85kN.
“We placed our pole orders in manageable batches and INFRASET met all our deadlines. They also installed plastic plugs into the masts for the fastening of bonding cables,” said Sayid.
Excavation coring and mast erection were outsourced to Sub-Contractor Meyker Reteng Construction and all installation work was certified by an engineer. Using a rail-mounted rig, poles were planted in foundations holes ±3m deep and 800mm wide and, once inserted, were stabilised with channel jacks and cast in concrete rated at 20MPa. All other work was undertaken as a joint venture by Transnet Projects’ OHTE teams.
INFRASET’S pole product manager, Sizwe Mkhize, said that the poles have been designed to provide 50yr maintenance-free service and that only beyond that point should minor maintenance be required.
Sayid concluded by saying that the yard lighting had also been upgraded as part of the project. This was executed by the EL7#38;P division of Transnet Projects Port and & Pipe Lines, Durban. The receiving yards were completed in September 2004 and the classification yard in August 2006.