Admix enhances concrete workability for interchange bridge

Work in progress on one of the bridge decks which were launched incrementally to complete the King Shaka International Airport interchange, north of Durban. Chryso’s regional KwaZulu-Natal office supplied one of the company’s popular ‘new generation’ admixtures to NPC Concrete for the concrete mix used in the bridge deck of the new R70-million King Shaka International Airport interchange. The bridge was constructed by Stefanutti Stocks Civils KZN.

Vishnu Beeput, regional manager of Chryso in KZN, says Chrysofluid Optima 175 was included in the concrete mix. “This is a super-plasticiser, formulated from polycarboxylate and modified phosphonate. It has been developed to reduce the water content of a concrete mix considerably and to increase concrete workability, without compromising setting time. The product is especially suitable for readymix and fluid concretes which require high short- and long-term strengths,” says Beeput.

Chryso also supplied its Deco Lav PO5 surface retarder for the project. Deco Lav P is a range of eight ‘positive’ aqueous surface retarders. The product delays the hydration of cement on exposed surfaces of concrete. After cleaning the treated surface, the aggregate in the concrete is exposed.

“No solvents are used in the formulation of Deco Lav, so it is easier to use and environmentally friendly. When it’s applied, it is not necessary to protect any surrounding area, except painted facades and porous surfaces,” Beeput adds.

Rolf Schutte of NPC Cimpor, who designed the concrete mix for the bridge, says Chrysofluid Optima 175 was chosen after in-depth consultations with Beeput. “We needed highly workable concrete, with low shrinkage and high early strength, as well as extended workability to allow for the sometimes slow discharge times. The use of the admixture proved most successful,” Schutte says.

Bruce Ivins, site agent for Stefanutti Stocks Civils KZN, says the Chryso Deco Lav PO5 surface retarder helped tremendously in saving time in completing the interchange’s various construction joints. “Use of the surface retarder reduced the equipment and manpower required for the preparation of the various joints,” he says.

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