Paper by BUITELAAR BRAAM DE WIT from ISCR 10th 2006 Brussels Belgium
Thin white toppings (TWT), as originally developed in the USA in 1918, are in majority placed as an overlay on deteriorated asphalt pavements. Usual thicknesses were 150 225 mm but since the last 30 years also ultra thin white toppings (UTWT) with thicknesses of 75 150 mm are used as an overlay on both asphalt- and cement concrete. Applications are not always successful; the problems are often related to the imperfect bonding to the layer underneath and to the thickness of the TWT or UTWT. A high shrinkage, curling, debonding, crack distribution and large crack widths are the most common problems. Load distribution is based on the effective thickness of the concrete layer placed and the stiffness and quality of the sub layers. Steel reinforcement and/or steel fiber reinforcement contribute only little to this. The development of High Performance Concrete (HPC; fc 100 150 MPa) and Ultra High Performance Concrete (UHPC; fc 150 >300 MPa) at the end of the seventies (Bache, 1981; Buitelaar, 1992, 1995) of the last century (Bache, 1970) made it possible to reduce the cover on the reinforcement and to utilize the reinforcement much more efficiently. The heavily reinforced ultra thin white topping (HRUTWT) as developed by Contec ApS makes new applications for UTWT possible. The HRUTWT not only functions as an independent overlay regardless the type, quality and condition of the sub base but can also give an additional strength to the underlying structure due to the very high stiffness and thus load spreading capacities in combination with bonding (anchors, intermediate layer, etc.). In this paper the development, research and applications of the HRUTWT are discussed.