Durability and Mechanical Properties of High-Performance Concrete for Ultrathin Whitetopping Pavements (05-2040) - MP-21
Brent Middleton, Lafarge North America
Robert Day, University of Calgary, Canada
Lynne Gradon Cowe Falls, University of Calgary, Canada

Increase in truck and bus traffic and vehicle sizes across North America has resulted in a consequent increase in asphalt pavement rutting and loss of performance. As agencies struggle to rehabilitate and maintain pavements with minimum disruption to traffic, Ultra Thin Whitetopping (UTW) has emerged as a viable new alternative. The use of a high performance concrete under highly-restrained geometric and very-severe exposure conditions constitutes the necessity for ultra-high performance. UTW is a pavement maintenance and rehabilitation strategy in which a 50 to 100 mm layer of concrete is placed over and bonds to an underlying asphalt pavement. UTW was initially intended for use on highways, streets, at intersections and at bus stops where severe rutting of the original asphalt pavement had developed. With the development of higher performance concrete materials, however, the potential exists to use UTW on high volume, heavily-loaded, roads exposed to severe winter environments. The use of UTW in Canada and the U.S. has grown since its first application in 1981. Many of these applications have occurred within the last 5 years and the majority have been fast-tracked in order to achieve a high early strength “fix” within 24 hours of placement. The number of UTW applications in cold climates is small; however, with further investigation of the response of UTW to freeze-thaw and scaling conditions, the potential for use is large. The paper outlines an investigation of the mechanical and durability properties of high early strength concrete for potential application in fast-tracked UTW construction in cold climates. An evaluation is made of the impact of different cement materials, synthetic fibre types, and curing procedures on compressive strength, flexural strength, shrinkage and scaling durability. High early-strength concrete containing ordinary or rapid-hardening cement in conjunction with a low water cementing-materials ratio (w/cm) gave excellent 1-day compressive and flexural strengths, and was highly resistant to scaling from de-icing agents. The use of a Class C fly ash at a 30% replacement level gave acceptable strengths for use in UTW applications, but as expected, early strengths were below those mixes without fly ash. This lower strength is offset by findings that the shrinkage of fly-ash concrete was significantly smaller than that of other mixes – an important consideration in maintenance of the concrete-asphalt bond in UTW application. The fly ash concrete showed poor scaling resistance. Discussion centres around possibilities to improve the performance of the fly ash performance by modifying mixing and curing specifications and employing other pozzolans, such as silica fume