Jobsite description
A range of CHRYSO products contributed to the success of a bridge project near the historic city of Paarl in South Africa, involving the largest precast beams cast to date in the Western Cape.

CHRYSO expertise
CHRYSO® Premia 310 Superplasticizer & CHRYSO® Dem Bio 10 environmentally friendly release agent was supplied to Cape Concrete for the casting of huge prestressed beams, large facing panels, coping and culverts for the construction of Val de Vie Berg River Bridge. The 18 precast beams supplied are 35.62 m long and 2 m high. They are Western Cape’s largest precast beams to date, weighing 64 tons a piece. Concrete pouring commenced once all the beam strands were evenly stressed. A combination of external and poker vibration was used to compact the concrete. This provided a very good surface finish with minimal blow holes. As soon as the pouring was completed, a tarpaulin was placed over the mould and steam was injected under the cover to accelerate the hydration process. This meant that a strength of 40 MPa could be achieved in 20 hours and enabled Cape Concrete to produce one beam a day. The final strength required was 60 MPa which was achieved within 28 days. CHRYSO® Retarder paste was applied at the end of each beam after casting and was washed off with water the next day to create a rough exposed aggregate finish. This provided a good bonding surface for the assembly of the bridge. The facing panels were also steam cured, the largest units measuring 4 m x 3 m. These panels were cast with a glass-smooth finish and attached with cleverly designed fingers that eliminated the use of visual fixing on the front face. Some of the panels were curved, for example those which were used for cladding of the central viewing cove.

PRODUCT USED
- CHRYSO® Premia 310
- CHRYSO® Dem Bio 10
- CHRYSO® Retarder paste
- CHRYSO® Plast Omega 126
Project technical challenges:
Once all 18 precast beams were in position, five diaphragm transverse beams were cast in-situ between the precast beams. Permanent deck shutters were cast in Empa’s site yard and were used to close the remaining gaps between the precast beams. Measuring 1.2 m x 300 x 50 mm they rested on recesses which had been cast into the beams for that purpose. Afrimat readymix concrete comprising of CHRYSO® Plast Omega 126 was then poured onto the shutters to create the deck. It comprised a 250 mm thick road section and a 335 mm pavement section. Heavily reinforced, it included a substantial quantity of Y32s. The casting of the pavements was especially challenging because provision had to be made for the attachment of the precast cladding on each side of the bridge. This involved the use of box-outs to create holes into which the panels’ concrete fingers could be inserted. Once the fingers of a panel were inserted and tied temporarily to the deck, final lining adjustments were made using jacks before final grouting took place.

Project participants
Client:Val de Vie Developments
Contractor: Empa Structures
Supplier: Cape Concrete Works & Afrimat Readymix (Cape)
Technical Advisor: CHRYSO SAF