Optimum Design for Sustainable, ‘Green’ Concrete Overlays. Part I: (a) Mix-Design, (b) Controlling Flexural Failure

The goal of ‘Green Overlays’ is a cost effective, minimal disruption, sustainable and environmentally friendly alternative to the wholesale demolition, removal and complete reconstruction of the existing structural concrete pavement.
A new mix design method for steel fibre reinforced, roller compacted, polymer modified, bonded concrete overlay has been developed. ‘Placeability’ and ‘compactability’ of the mix were two dominant issues. Hence, the mixes established were suitable to be placed by an asphalt paver and compacted by a roller. They were also characterized of high flexural strength, and bond strength with the old concrete substrate.
An innovative approach for establishing the relationship between Stress and Crack Face Opening Displacement for steel fibre reinforced concrete beams under flexure, using test data of a notched beam under three-point bending was developed.
The bridging laws obtained using this method disclosed the mechanism of flexural strength development of roller-compacted, polymer modified, fibre-reinforced concrete. The fibre efficiency of the latter was compared against fibre-reinforced conventional concrete.
A new test specimen, complete with its loading configuration for measuring interfacial fracture toughness (IFT) for concrete overlay pavements was proposed. The IFT of a steel fibre-reinforced, roller compacted, polymer modified, composite concrete beam, bonded on conventional concrete and undergoing flexure, was assessed.
Finally, a new innovative method for calculating the Strain Energy Release Rate at the interface of an overlaid pavement was developed. This method can be readily and easily used by practising engineers.