Site visit – Heidelberg Weighbridge Station, N3
20 members took the opportunity to visit this unique site where UTCRCP is being used to rehabilitate the traffic lanes entering the weighbridge facility. Hugh Crofford, Senior Contract Manager of King Civil Engineering Contractors (Pty) Ltd, the main Contractor for the project, described to members the project in some detail.
The client, SANRAL had specified the installation of 400 metres of an ultra-thin, continuously reinforced concrete pavement on the ‘screening’ lane approaching the main weighbridge at the site. The specification included a 65mm thick concrete slab, reinforced with steel mesh, a fast setting time to allow minimum traffic down-time, a compressive strength of 40 MPa at 3 days and 80 MPa at 28 days.
King Civil staff spent many hours designing the concrete mix which ultimately met the criteria set, and ultimately gained approval from the client 3 months after initiating the design work. The final mix comprised 3 sands, 6-7 mm stone, CEM 1 52,5 cement, superplasticiser and steel fibres at an addition rate of 80 kg per m3.
In view of the fast setting time requirement, the contractor had no choice but to mix the concrete on site. In fact the final mix only allowed 15 minutes working time once poured.
Consequently, they designed their own mobile batch plant with an 800-litre capacity pan mixer, generator, admixture storage tank and dispensing equipment, all mounted on the back of their own flatbed truck. The sand, stone and cement were mixed off-site and delivered in 300-litre capacity bulk bags. These were emptied into the pan mixer, after which the superplasticiser, steel fibres and water were added to make one homogenous mix.
Asphalt first had to be removed from the lane, repairs made to isolated base patches, and then the screed could be laid on top. Once mixed, the concrete was poured into place with the truck riding over the reinforcing mesh, which was designed to sit in the centre of the concrete slab. The slump of the concrete was 90 mm, flow was good, but the mix was very sticky due to the high cement content. This resulted in a lot of labour to work the material into position. Poker vibrators were used to compact the concrete.
Finally, the concrete was cured with the use of a resin-based curing compound.
Members spent some time inspecting the lane in question, and watching the mixing and placing of the concrete mix. In conclusion to the visit, Andrew Schmidt, Inland Branch Chairman thanked King Civil Engineering Contractors for the very interesting site visit and a perfect opportunity to see concrete in action. He also thanked AfriSam, the cement suppliers to the project, who had provided some very welcome refreshments on the day.
Site Visit - Heidelberg Weighbridge Station, N3 - Photo Gallery
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