Bridges

The Roads and Traffic Authority of NSW (RTA) has had various concerns regarding the quality of the “cover concrete” produced by contractors and suppliers using certain types of bar chairs in the manufacture of concrete products for RTA bridges. There is particular concern with precast concrete products. Plastic and Aspro concrete bar chairs are manufactured in various shapes and size configurations for use in reinforced concrete products. As a result of these concerns, bans have been imposed on the use of certain bar chair types until testing confirms that the concrete products can fully comply with RTA requirements. This paper will highlight some of these concerns and the verification process proposed for certain types of bar chairs. The verification process objectives are:

• To validate concerns regarding the use of strip plastic bar chairs
• To assess the concrete’s susceptibility to specific durability deterioration mechanisms
• Compare & assess precast “cover concrete” quality with different variations of bar chairs and with 2 alternate concrete mixes.

The paper will also explain the testing process undertaken to verify the above objectives. Testing undertaken includes standard compressive and density tests from concrete batch samples and of core specimens. Subsequent testing includes visual assessment followed by non-destructive and destructive durability testing of concrete specimens and core samples. Finally the results of testing and recommendations on the use of specific bar chairs for certain scenarios will be highlighted, with comments included on different variations of concrete mix and bar chair type.