Ultrathin Whitetopping Pavements Research Articles

Interface horizontal shear strength requirement in Ultra-thin whitetopping (UTW) pavement.

Ultra-thin whitetopping (UTW) is a thin (5-10 cm) layer of concrete overlaying over an existing asphalt pavement. This concrete layer is bonded on the asphalt surface. Although UTW has been successful in strengthening asphalt pavement, in some cases, the composite pavement may debond at the interface under the concrete slab due to high shear stress. This paper aims to determine the interface shear strength required for UTW pavement systems using theoretical methods and calibrated numerical models (FEMs). The study analysed 432 pavement scenarios with different slab sizes, thicknesses, and material properties. The results show that higher shear stress occurs when the asphalt modulus is stiffer. The size of the slab, the modulus of the supporting layer, and the asphalt thickness have only a minor effect on the shear stress value. However, the thickness of the concrete slab significantly affects the maximum shear stress in the UTW, with an increase of up to 36.6% when reducing the slab thickness from 100mm to 50 mm. The FEM calculations can be used to determine the required interface horizontal shear strength for UTW.

Experimental investigation of interface treatment technique on interface shear bond fatigue behavior of Ultra-Thin Whitetopping

The bonded concrete overlays on existing asphalt pavements are classified into three subcategories namely whitetopping, thin-whitetopping and Ultra-Thin Whitetopping (UTW). The design service life of UTW overlays depends on several factors such as interface bond strength, slab thickness, slab size, material strength and underlying material condition. The quality of the interface bond depends on both surface preparation and the UTW placement procedure. The interface bond between two layers helps in the monolithic action of the pavement section by shifting the neutral axis from the middle of the UTW slab to the bottom of UTW slab. The composite action had a direct impact on the long-term performance of the UTW overlays. To assure good bonding, milling method is usually applied at the interfaces during UTW overlay construction. The interface bond strength due to milling technique can be measured with the help of several devices arranged by different laboratories. This paper investigates the interface shear bond strength and shear fatigue behavior of UTW pavement for different interface treatment techniques. For this experimental purpose, a laboratory direct shear testing method and procedure was used. Two interface treatment technique like groove and piercing method have been analyzed. Interface treatment with piercing technique had shown highest shear bond strength and k-modulus values. Incorporating groove interface technique with an inclination of 0–45 degrees and piercing interface treatment has been proposed. The interface shear bond fatigue behavior of piercing treatment technique with different debonding conditions are discussed. As expected the increase in debonding leads to decrease in interface shear stress and fatigue performance.

Ultra-thinwhite topping concrete mix with sustainable concrete materials – a literature review

ABSTRACTIndia is an agriculture-based country in which preserving the life of existing bituminous pavements connecting rural areas is very much important along with development of National highways and Expressways. Ultra-thin white topping is a thin concrete overlay of 50 mm–100 mm which can be constructed on bituminous pavement with surface failures, which provides long life and low life cycle cost. Incorporation of sustainable concrete materials in these pavements will improve flexural strength, abrasion resistance and solar reflectance and reduces carbon footprint. This paper discusses the key factors affecting the performance of ultra-thin white topping pavement, UTW Concrete mix blended with binary, ternary supplementary cementitious materials from the projects executed and recent research. The importance of research on quaternary blended SCM concrete in UTW overlays for bituminous roads makes pavement economic, enhances long-term performance and durability and increased sustainability were discussed. Further finite element modelling of ultra-thin white topping was done using the ANSYS software with the results obtained from the laboratory and it is observed that for concrete mix C3 UTW pavement with thickness 100 mm and 1000 mm, joint spacing as modulus of rupture is higher than critical Corner stress.

Feasibility of whitetopping pavements for resurfacing thin asphalt pavements

Many asphalt pavements have experienced rutting (wheel path deformation) while many others have experienced cracking. One of the possible solutions to this problem is the use of whitetopping, which is a composite section with a concrete layer over an existing asphalt pavement. Whitetopping has an advantage over an asphalt overlay in that the concrete surface is stronger and thus is more resistant to rutting and surface-initiated cracking. This research attempts to study the feasibility of whitetopping for resurfacing of thin asphalt pavements (less than 100 mm) in tropical and sub-tropical countries. Whitetopping pavement test track constructed at the acceleration testing facility in a tropical climate, at the Florida Department of Transportation (FDOT), was used for the study. A three-dimensional (3-D) finite element model (FEM) was developed to simulate the field conditions using SAP2000 structural analysis software. The developed model was verified with field measured strain data. The verified analytical model was used to perform a parametric study in order to find the sensitivity and effects of loading conditions, joint spacing, joint conditions, whitetopping thickness, asphalt thickness, interface bond between asphalt and whitetopping, elastic modulus of concrete and asphalt, base and subgrade layers and temperature differentials in concrete. This study found that the developed model can be used to estimate the maximum anticipated stresses in whitetopping pavements. The research revealed that ultra thin whitetopping pavement (less than 50 mm thick) is not suitable for resurfacing of thin asphalt pavements. A minimum concrete thickness of 60 mm and 80 mm is required for a 80 mm asphalt thickness with a joint spacing of 0.9 m for axle load controlled at 80 KN (18 kips) and 98 KN (22 kips), respectively. The parametric study revealed that the minimum thickness needs to be adjusted with other design parameters. Doi: http://dx.doi.org/10.4038/jnsfsr.v40i4.5043 J.Natn.Sci.Foundation Sri Lanka 2012 40 (4): 293-302

Backcalculation of Ultrathin Whitetopping Pavement Based on Saint-Venant’s Principle

AbstractWhitetopping (WT) or ultrathin whitetopping (UTW) overlay is defined as a portland cement concrete overlay on an existing deteriorated hot mix asphalt (HMA) pavement to improve both the structural and functional capability of HMA. During the past two decades, UTW overlays have gained great acceptance as an alternative to HMA overlay. However, there is a lack of a reliable method to evaluate the performance of in-service UTW pavements. Because of the small slab sizes of UTW pavements, backcalculation of pavement layer properties, based on the falling weight deflectometer, is challenging. This study developed a new approach, the Critical Distance Method, based on Saint-Venant’s principle, to backcalculate the portland cement concrete and equivalent substructure moduli of UTW pavement. It was proven to be an effective approach to determine the layer properties of UTW pavement, based on the finite element simulations. Traditional backcalculation methods, such as AREA theory and the MODCOMP6 software p...

Forensic Investigation of Ultrathin Whitetopping Pavements in Florida

Developed in the early 1990s, ultrathin whitetopping (UTW) is a relatively new technique for asphalt pavement rehabilitation. To evaluate the applicability of UTW pavement in Florida, in 1997, the Florida Department of Transportation (FDOT) constructed an experimental UTW pavement in a weigh station along I-10, located in north Florida. The performance of these test sections, however, was less than ideal, with the observation of some early cracking on the concrete surface, which developed into severe cracking with time. Therefore, a forensic investigation was conducted to determine the causes of the problems in these UTW sections, so that lessons could be learned from this experimental project, the use of UTW under Florida's conditions could be adequately assessed, and UTW technology could be properly applied in the future. The scope of work consisted of field evaluation, laboratory testing, and pavement design evaluation. Field evaluation included a pavement condition survey, pavement temperature measurement, nondestructive load testing using a falling weight deflectometer, and slab thickness determination. Laboratory tests were performed to determine concrete and asphalt material properties. Other design and traffic data were also acquired from FDOT. Data collected from the field evaluation and laboratory testing were used in conjunction with a mechanistic UTW pavement design/evaluation procedure to determine the possible causes for premature failure. From this comprehensive evaluation, the primary cause for the failure was found to be inadequate UTW pavement design. The inadequacy of the combination of thickness and slab dimensions contributed to the early cracking of the UTW pavement.

Mechanistic-Empirical Characterization of Bonding Between Ultra-Thin White-Topping and Asphalt Pavement

Abstract This paper presents a mechanistic-empirical methodology to evaluate the effect of partial bonding on ultra-thin white-topping (UTW) pavement structure. Based on the analytical work conducted for unbonded and fully-bonded interfaces, this paper displays the intrinsic relation between interface bonding and structural capacity, and provides a practical approach torelate interface bonding condition to UTW pavement structure. Information presented herein will help pavement engineers understand the composite behavior of the interface, and improve the current procedures for designing UTW pavement. Also, this paper provides fundamentals for pavement engineers to estimate UTW interface bonding using Falling Weight Deflectometer (FWD) testing. It is concluded that the asphalt layer's Poisson ratio has only a minor effect on the stresses in UTW pavement. Bonding affects the stresses under edge and center loading more significantly than under corner loading. The effect of bonding on the curling stress depends on UTW panel size. If the panel size is very large (3 m × 3 m) or very small (0.6 m × 0.6 m), the effect of bonding is negligible. The curling stress decreases significantly as the bonding condition improves if the panel size is 1.8 m × 1.8 m or 1.2 m × 1.2 m. It is also demonstrated by employing the FWD deflection measurements that as the UTW pavement age increases, its interface bonding may deteriorate.

Evaluation of Applicability of Ultrathin Whitetopping in Florida

A three-dimensional (3-D) finite element model for stress analysis of pavements with ultrathin whitetopping (UTW) under critical loading conditions was developed. The 3-D model developed was used to analyze the UTW test pavement sections at the Ellaville Weigh Station in Florida, which had less than satisfactory performance. The poorly performing UTW sections at the Ellaville Weigh Station were found to have relatively higher maximum computed stresses under critical loading conditions, which appeared to explain their poor performance and high percentages of cracked slabs. The 3-D model developed was also used to perform a parametric analysis to determine the effects of asphalt thickness, asphalt modulus, concrete thickness, concrete modulus, base stiffness, subgrade stiffness, slab dimension, temperature differential in the concrete, and applied load on the maximum stresses in UTW pavements under typical Florida conditions.

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.

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.