Ultrathin Whitetopping Research Articles

Mechanical Properties and Durability of Bonded-Concrete Overlays and Ultrathin Whitetopping Concrete

Concrete overlays have been used for pavement and bridge-deck rehabilitation for many years. The mechanical properties and durability of several plain and fiber-reinforced concrete-overlay mixes were analyzed. Eight different concrete-overlay mix designs were investigated. The materials properties investigated were compressive and splitting tensile strength, modulus of elasticity, bond to concrete (with three different surface roughness characteristics), and durability. Freeze-thaw tests were performed to determine the durability of the concrete mixtures used. Strength and stiffness were investigated from 1, 3, 7, and 14 days. Laboratory tests on the strength and stiffness development of eight candidate concrete-overlay designs showed that high-strength concrete was appropriate for opening overlays to traffic in 24 h or less, but normal-strength concrete may be used if traffic loading may be delayed for 48 or 72 h. For larger projects, where paving continues over several days, normal-strength mixtures may be used when 48 to 72 h or more of curing can be achieved before traffic loading begins, with high-strength mixtures used for the last day's construction. All the high-strength concrete overlay-mixture designs tested appear to have satisfactory strength, stiffness, bond properties, and durability for use in bonded overlay construction. The normal-strength concrete is more economical than the high-strength concrete but develops its design properties more slowly.

Testing and Performance Evaluation of Ultrathin Whitetopping Pavements at Spirit of St. Louis Airport

To obtain a better understanding of ultrathin whitetopping (UTW) pavement behavior under traffic loading and environmental effects and to collect data for calibration and development of a mechanistic design procedure, a UTW test pavement was constructed, instrumented, and load tested. The UTW pavement test section is located at the Spirit of St. Louis Airport, a general aviation airport in Chesterfield, Missouri, and is designed to carry a light aircraft load of 56 kN. The results of analyses conducted on this test pavement and its performance to date are described. The UTW test section was constructed in February 1995 and consisted of six slabs with dimensions of 1.3 × 1.3 m and a design slab thickness of 89 mm. The load testing was conducted in May and September 1995. Load-induced strains, temperature distribution, and surface profiles were measured at different locations and at different times. Pavement core samples were also taken and subjected to laboratory testing. It was observed from the evaluation that ( a) there was very little vertical slab movement in spite of the temperature differential in the slabs, ( b) there was no apparent change in load-induced strains (stresses) with temperature changes, ( c) pavement exhibited high load transfer efficiencies across contraction joints, and ( d) an interface shear strength of 689 kPa was achieved by the commonly used technique for asphalt surface preparation, milling and cleaning. A recent performance review of this pavement also showed that it has performed extremely well after over 6 years in service. Of the 11620 m2 of UTW pavements (about 72,000 UTW panels), only 18 panels have cracked.

Performance, Analysis, and Repair of Ultrathin and Thin Whitetopping at Minnesota Road Research Facility

Thin and ultrathin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997 the Minnesota Department of Transportation constructed several thin and ultrathin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. Different techniques for repairing ultrathin whitetopping were investigated. Various techniques were also used to deter reflective cracking, including various bond-breaking materials and full-depth sawing at strategic locations along the longitudinal joint to prevent cracks from propagating into adjacent panels at misaligned transverse joints. Four of the six sections had present serviceability indexes (PSIs) greater than 3.5 before the repairs, showing that a good level of performance has been maintained after 4.7 million equivalent single-axle loads. The two sections that exhibited the largest drop in PSI were the overlays with 1.2- × 1.2-m (4- × 4-ft) panels. The repairs made in sections containing these panels have brought the PSI back up to an acceptable level (PSI > 3). The thin and ultrathin whitetopping test sections at Mn/ROAD have shown that whitetopping is a viable rehabilitation alternative for asphalt pavements. The importance of choosing an optimum panel size was exhibited. It has also been shown that when necessary, it is easy to repair ultrathin whitetopping sections. Various techniques for repairing each type of distress have been summarized.

Identification of Pavement Failure Mechanisms at FHWA Accelerated Loading Facility Ultrathin Whitetopping Project

In 1998 eight test lanes of ultrathin whitetopping (UTW) were constructed over existing hot-mix asphalt (HMA) pavements at FHWA’s Accelerated Loading Facility (ALF) located at the Turner-Fairbank Highway Research Center in McLean, Virginia. Various combinations of thicknesses, joint spacings, fiber reinforcement, and types of HMA base were used. In spring 2000 the loading experiment of these pavements was completed, and the analysis of behavior and performance was begun. A summary of some of the pavement distresses observed at the ALF is presented, and hypothesized failure mechanisms are identified, providing an addition to the state of the knowledge with respect to the actual life cycle of UTW pavements.

Repair of Ultrathin Whitetopping Pavements

Since its inception in 1991, ultrathin whitetopping (UTW) has moved beyond the experimental stage and has become a viable pavement rehabilitation alternative. Development of the mechanistic design procedure in 1997 represented a milestone in the development of this technology. Over 150 UTW pavements have been built in the past decade. With the use of UTW rapidly increasing, the next logical step in the development of this technology is to develop UTW repair and rehabilitation techniques. How does one repair UTW pavements? Can conventional concrete pavement rehabilitation materials and methods be used for UTW pavements? Construction of the UTW test sections at the FHWA Turner-Fairbank Highway Research Center, subjected to accelerated loading tests, provided an excellent opportunity for evaluating potential UTW pavement repair methods. These test sections were constructed in April 1998 and were subjected to accelerated load testing with FHWA’s accelerated loading facility (ALF) from May 1998 until November 1999. Some UTW panels exhibited distresses, with corner cracking being the most prominent. After discussions with state agency staff and industry representatives, panel removal and replacement was selected to repair some of the distressed panels of these test sections. The repair work was done in April 2000 and the repaired test sections were load tested with ALF from May to August 2000. Based on the results of ALF testing, it was observed that panel removal and replacement is an effective method for UTW pavement repair. Guidelines for UTW pavement repair by this method are proposed. A strong bond between the concrete and asphalt layers, even for distressed (cracked) panels, was observed. The time required for UTW panel repair was also documented and can be used for planning UTW repairs.

Characterization and Modeling of Axial Slab-Support Restraint

Slab-support interaction has long been established as an important consideration in the design and construction of concrete pavements for streets, highways, and airfields. With the current interest in design features such as open-graded permeable bases, unbonded concrete overlays, and whitetopping pavements, the need for an accurate and standard means for characterizing this behavior is evident. With respect to conventional concrete pavements, previous studies have concluded that excessive restraint between the slab and the support layers of a pavement structure can lead to pavement distresses that are ultimately detrimental to the per formance of the pavement. These studies have indicated that undesirable restraint characteristics typically are caused by improper subbase design or construction. The consequences of underestimating or neglecting the support restraint characteristics have been shown to result in uncontrolled slab cracking, excessive joint movements, and underdesigned reinforcement. However, in some cases a high degree of slab-support restraint is desired, such as for whitetopping pavements, especially ultrathin white-topping. Recent developments in characterizing and modeling axial slab-support restraint characteristics of concrete pavements are presented. Test procedures that have been developed to accurately assess the level of axial slab-support restraint present are identified, as are future enhancements to characterization and modeling of this phenomenon.

Rehabilitation of Ellaville Weigh Station with Ultrathin Whitetopping

The Florida Department of Transportation constructed the first ultrathin whitetopping (UTW) project at the Ellaville truck weigh station on I-10 in northwest Florida. This rehabilitation project included the placement of UTW on the existing asphalt pavement, which had experienced severe rutting problems. Layer thicknesses for the UTW were 80 mm and 100 mm. The joint spacings for the UTW panels were 1.2 m and 1.6 m. High early strength concrete was used in this project. Polypropylene fibers were included in the concrete for the sections on the west side of the weight platform and plain concrete was used on the east sections. The joints on the east section were sealed with silicone sealant and the joints on the west section were left unsealed. Falling weight deflectometer tests and frequent condition surveys were performed on the projects. After 1 year of service and 1.1 million equivalent single-axle loads, the UTW shows good performance. Success and long-term performance of the UTW is highly dependent on the degree of bonding between the UTW and the asphalt base. During the study period, panels 1.2 m2 and 1.6 m2, concrete with and without fibers, sealed and unsealed joints, showed similar performance. It is predicted that the 1-year performance of the UTW at the weigh station is equivalent to 4.5 years of service at a medium traffic intersection.

Ultrathin Whitetopping: State-of-the-Practice for Thin Concrete Overlays of Asphalt

Ultrathin whitetopping (UTW) is a concrete overlay of a distressed asphalt pavement, 50 to 100 mm thick, with close joint spacing. The overlay is specifically bonded to the existing asphalt pavement. It may or may not contain fibers. By bonding the UTW to the existing asphalt surface, the UTW forms a composite pavement section with the underlying asphalt, which reduces the stresses in the concrete layer. This composite pavement section delivers the longer life and durable performance characteristics of concrete pavement and is cost competitive with ordinary asphalt. Many areas are discussed, but not all questions about UTW are answered. A snapshot of the current state of the practice as it now stands is presented.

BASIC STUDY ON ULTRA-THIN WHITETOPPING

This paper covers the basic study on ultra-thin white topping that is also been developed in European countries and U. S. A. The aims are to find out its applicability through making mini model experiments, research on the interface shear stress under various temperature and traffic loads by FEM program. As the results, the characteristics of slab temperature and underlying existing asphalt pavement, the effects of the pavement temperature on the interface shear stress and bending stress, and fatigue damage are revealed.

Ultra-Thin, Fiber-Reinforced Concrete Overlays for Urban Intersections

An industry partnership involving state and local highway officials; ready mix concrete producers; and fiber, admixture, and cement suppliers paved the way for extensive testing of a new concrete technology in Tennessee. Known as ultra-thin whitetopping (UTW), this experimental repair procedure involves placing a layer 50 to 75 mm (2 to 3 in.) thick of high-strength concrete over milled asphalt. Crucial to a long life for the thin concrete is a high synthetic fiber content, normally 1.4 kg/m3 (3 lbs/yd3) with joints spaced at a minimum of 0.92 to 1.22 m (3 to 4 ft) on center. From 1992 to 1995, seven cities in Tennessee participated in UTW demonstrations. The field tests were so successful that synthetic fiber-reinforced UTW is now being bid on many state and local projects. Presently, the primary use of UTW is to rehabilitate high average daily traffic intersections. Other potential uses include overlays of residential streets, parking lots, and airport aprons.

Ultra-Thin, Fiber-Reinforced Concrete Overlays for Urban Intersections

An industry partnership involving state and local highway officials; ready mix concrete producers; and fiber, admixture, and cement suppliers paved the way for extensive testing of a new concrete technology in Tennessee. Known as ultra-thin whitetopping (UTW), this experimental repair procedure involves placing a layer 50 to 75 mm (2 to 3 in.) thick of high-strength concrete over milled asphalt. Crucial to a long life for the thin concrete is a high synthetic fiber content, normally 1.4 kg/m3 (3 lbs/yd3) with joints spaced at a minimum of 0.92 to 1.22 m (3 to 4 ft) on center. From 1992 to 1995, seven cities in Tennessee participated in UTW demonstrations. The field tests were so successful that synthetic fiber-reinforced UTW is now being bid on many state and local projects. Presently, the primary use of UTW is to rehabilitate high average daily traffic intersections. Other potential uses include overlays of residential streets, parking lots, and airport aprons.