Flowable Fibrous Concrete for Thin Concrete Inlays

A thin concrete pavement wearing surface has been developed using a flowable fibrous concrete (FFC) as a 50 mm (2 in.) inlay on a milled asphalt concrete pavement. The flowable concrete mixture incorporating a hybrid of synthetic fibers was optimized for rapid placement and consolidation. An objective of the wearing surface was to construct reasonable slab sizes and crack widths while ensuring economic feasibility. Laboratory testing demonstrated the FFC has a slump flow diameter value of 400 mm (15.5 in.) and post-cracking residual strength ratio over 47 percent with 0.5 percent volume fraction of synthetic macrofibers. A full-scale demonstration project was cast to evaluate constructability and concrete material performance including placement issues, crack spacing and width development, and interface bonding conditions. Different slab sizes were explored from 1.2 to 3.3 m (4 to 11 ft) with the longer slabs having the earliest and widest cracking up to 1.25 mm (0.05 in.). The joints cracked before day one reside as the largest crack widths measured at later ages. In-situ bonding tests confirmed a good bond between the asphalt and concrete, except in locations where debris from the asphalt layer was not adequately removed.