Contractors building two of the elevated grade separated interchanges were able to accelerate construction and keep costs down by bypassing the installation of complicated temporary formwork systems.
They used sand instead.
'It's not pioneering stuff - it is done quite a bit here, ' says Halcrow project manager Jim Richardson. 'The foundations (750mm reinforced concrete piles) are placed fi rst, piers and abutments are cast and then sand is placed up to the finish level of the piers. The soffit of the plywood forms for the concrete deck are then supported on the sand.
'Concrete is cast across the full 22m width of the bridge, and it takes three pours to cover the length.' Bridges vary in lengthy between 16m and 30m.
Despite the fierce heat, which can soar to over 50°C in the summer, the concrete box sections are poured insitu. 'In the heat of summer the pours were done at night but we use plasticisers in the mix to keep it workable. We also add ice to keep the temperature down, ' says Richardson.
Once the steel cables in the deck are stressed and grouted in place, the top slab of the deck is cast in one operation.