Press release from Jan de Beer, cell 082 456 3677:

B&KM COMPLETES CHALLENGING IRON ORE RAIL SIDING CONTRACT Local civil engineering contractors, Botes & Kennedy Manyano (B&KM), has completed a challenging R12,7m contract for the concrete structures required for a new iron ore export railway siding for the new Khumani Iron Ore Mine in the .

Morné van der Merwe, director of B&KM, says the project involved the construction of a rail-over-road bridge with post-tensioned, precast beams as well as all the other concrete structures including in-situ culverts, precast pipe and portal culverts on the siding. Work started on the Assmang contract in July last year and was completed in May this year.

Van der Merwe said the bridge is one of few in with the capacity to carry the individual loads of 120t iron ore wagons, or full train loads of 41 000t, over the R325 road to onto the Sishen-Saldanha railway line. “These exceptionally heavy loads, and the long 20m span of the bridge, called for a 1m wide bottom flange for the beams as well as more reinforcing and cable sleeves for post-tensioning. B&KM had to get the required 50MPa concrete fully compacted to all corners of the beams. This was achieved through a special concrete mix designed by Chryso SA, and a special Chryso admixture for self-compacting concrete.”

Hennie van Heerden, Chryso SA Technical Services Manager, says the project called for self-compacting concrete because of the intricate shape of the structure and highly congested reinforcement at very narrow spacing. “The available local aggregates were not suitable for pouring the concrete and distributing it without vibration, or other means of consolidation. The admixture selected was Chryso’s proven Chrysoplast Optima 100 which is specially formulated to provide a concrete mix that is cohesive without being sticky. Optima 100 also extended concrete workability up to three hours, which was essential in view of the congested steel reinforcement, and the sweltering Northern Cape temperatures - prohibitive conditions for other admixtures,” van Heerden explained.

B&KM’s van der Merwe said the admixture had played an invaluable role and achieved maximum concrete density into the one meter wide flanges at the bottom of the 1,36 m deep beams.

Describing the other challenges involved in the project, van der Merwe said high temperatures, no running water and electricity were available on site which necessitated special temporary arrangements. “The bridge structure was entirely constructed on site, as well as the 11,3m and 20m precast post-tension beams. This was achieved with 70% local labour from Dingleton, , , and and the rest from other parts of the Northern Cape. All materials were locally sourced, except the bearings from Freyssinet Posten and VSL post-tensioning system from Tsala-RMS on site, under supervision from R&H Railway Consultants.”

Other challenges include the fact that rock was encountered to a level of 4m below the base levels and that one of the 4m deep excavations was within a metre of the Department of Water Affairs and Forestry (DWAF) regional water supply pipeline.

“In addition, the abutment foundation of the bridge partially fouled the Gamagara DWAF main water pipeline which itself posed challenges to both contractor and consultant,” stated Henk Bester, R&H Railway Consultants. “The scope of the contract was changed to include 794 cubic metres mass concrete and a new DWAF culvert constructed over, and under, the existing pressurised water pipeline next to the western abutment. To minimise the time delay of the scope change, BKM constructed the bridge piers, abutments and DWAF culvert simultaneously. The temporary bypass road was then removed to start earthworks and the installation of the precast beams. ‘Stop-go’ traffic controls were used during the day until the suspended cantilever scaffolding was in place to bring traffic back to normal under the bridge while earthworks, deck slab and parapet walls were completed,” Bester added.

The concrete requirements of the project were 120cu m (50MPa precast beams), 574cu m (40MPa bases, piers, abutments, deck), and 794cu m (15MPA mass concrete under bases, not in the original scope). Holcim OPC 42,5 cement from Ulco was used.

Concor Roads was the main contractor and handled all earthworks. Botes & Kennedy Manyano civil engineering contractors hold a 7CE CIDB grading. ends

Captions

DSC00116: Suspended formwork allowed construction of the bridge deck and parapet walls to continue while the road was open to traffic. ends

“Completed bridge”: The completed rail-over-road bridge. ends

Issued for Chryso SA, Jet Park/ Further info: Hannes Engelbrecht, tel 011 395 9700