Development of a Design Catalog for Bonded Concrete Overlay Pavements Considering the Regional Characteristics of Korea

The design of overlay pavement in Korea, using the American empirical method, does not consider the unique Korean climate, pavement material, and traffic conditions. Therefore, in this study, a mechanistic–empirical design catalog for bonded concrete overlays (BCO) that are appropriate for Korean pavement conditions was developed. First, the thickness of the new pavement slab was determined through the Korean pavement design method, which uses a mechanistic–empirical design program according to the traffic volume of the region with the worst climatic conditions in Korea. Then, finite element analysis models of new jointed concrete and BCO pavements were developed to determine the BCO thickness by adjusting it until the stress–strength ratio of an existing slab of BCO pavement was equal to that of a new concrete pavement slab. By repeating this procedure, a design catalog was developed for the sustainable management of concrete pavement according to the traffic volume, elastic modulus, and thickness of the existing slab after milling. The appropriateness of the BCO thickness predicted by the design catalog was verified by comparing it with that predicted by other design methods.

Brillouin scattering spectrum-based crack measurement using distributed fiber optic sensing

Brillouin scattering-based distributed fiber optic sensing (Brillouin-DFOS) technology is widely used in health monitoring of large-scale structures with the aim to provide early warning of structural degradation and timely maintenance and renewal. Material cracking is one of the key mechanisms that contribute to structural failure. However, the conventional strain measurement using the Brillouin-DFOS system has a decimeter-order spatial resolution, and therefore it is difficult to measure the highly localized strain generated by a sub-millimeter crack. In this study, a new crack analysis method based on Brillouin scattering spectrum (BSS) data is proposed to overcome this spatial resolution-induced measurement limitation. By taking the derivative of the BSS data and tracking their local minimums, the method can extract the maximum strain within the spatial resolution around the measurement points. By comparing the variation of the maximum strain within the spatial resolution around different measurement points along the fiber, cracks can be located. The performance of the method is demonstrated and verified by locating and quantifying a small gap created between two wood boards when one of the wood boards is pushed away from the other. The test result verifies the accuracy of the crack strain quantification of the method and proves its capability to measure a sub-millimeter crack. The method is also applied to a thin bonded concrete overlay of asphalt pavement field experiment, in which the growth of a transverse joint penetrating through the concrete–asphalt interface was monitored. The method successfully locates the position, traces the strain variation, and estimates the width of a crack less than [Formula: see text] wide using a Brillouin-DFOS system with [Formula: see text] spatial resolution.

Evaluation of Bonded Concrete Overlay of Asphalt under Accelerated Loading

Bonded concrete overlay of asphalt (BCOA), previously known as ultra-thin whitetopping (UTW), has been widely used to repair aged asphalt concrete (AC) pavements with moderate distresses. Because of the increasing costs of roadway maintenance, Louisiana has a great interest in determining whether thin BCOA (usually 2–6 in.) is a suitable and cost-effective alternative to the current practice of roadway maintenance. The objective of the study was to evaluate the performance of BCOA pavement and to identify the influence of in-situ interface bond strength on the performance of BCOA pavements. Three full-scale BCOA test sections with thicknesses of 6 in., 4 in., and 2 in. of Portland cement concrete (PCC) over an aged asphalt pavement were tested under accelerated pavement test (APT) loading under typical pavement conditions in southern Louisiana. Each section was trafficking-loaded to a failure (i.e., all the slabs in the loading path were cracked) under alternating load magnitudes of 9 kips and 16 kips of the ATLaS dual-tire wheel load. A falling weight deflectometer (FWD) backcalculated the effective thickness, a trench-cutting investigation was undertaken, and in-situ pull-off test revealed that a good bond was established initially between the PCC and AC layer. Several non-destructive test (NDT) methods indicated that the distresses of a BCOA slab could be coupled with a possible debonding at the PCC-asphalt interface. This paper mainly focuses on the APT results and the performance of BCOA test sections with different overlay thickness.

Full-Scale Evaluation of Concrete-Asphalt Interphase in Thin Bonded Concrete Overlay on Asphalt Pavements

Thin bonded concrete overlay on asphalt (BCOA) pavements rely on concrete-asphalt bonding to resist traffic loading. To investigate variables affecting bonding, experimental data were used from 15 instrumented thin BCOA sections, with 11 tested with heavy vehicle simulators (HVS). Sections included three slab sizes, four rapid-strength concrete mixes, new and old asphalt bases, and three asphalt surface texturing techniques. Analysis of strain data from HVS testing served to determine the concrete-asphalt bonding condition. Laboratory testing and forensic data from the sections were also evaluated. Overall, the performance of concrete-asphalt bonding in the sections with 1.8 × 1.8 m (6 × 6 ft) slabs was excellent. In these sections, concrete-asphalt bonding remained intact throughout the HVS testing despite the unfavorable testing conditions, which included flooding of the section, channelized traffic at the slab edge, and HVS wheel (half axle) loading of up to 100 kN (22.5 kips). The sections with 3.6 × 3.6 m (12 × 12 ft) slabs presented a delamination band between the asphalt and concrete along the perimeter of the slabs. This delamination was a tensile break occurring in the asphalt around 5–10 mm (0.2–0.4 in.) below the concrete-asphalt interphase caused by the large vertical hygrothermal deformations in the slabs. Because of this asphalt failure, the concrete and asphalt worked as two independent layers near the transverse joints. Based on laboratory procedures, it was observed that cement paste penetration into the asphalt layer caused a reinforcing effect in the concrete-asphalt interphase. It was also observed that milling and micromilling did not improve the concrete-asphalt bonding.

Accelerated Testing of Full-Scale Thin Bonded Concrete Overlay of Asphalt

A research study was conducted with the goal of determining the expected performance life of thin bonded concrete overlay of asphalt (BCOA) in California. Eleven thin BCOA sections were built and tested with the Heavy Vehicle Simulators (HVS) in Davis, California. The performance of the sections in the HVS testing provided insight into the mechanics of the thin BCOA structures and the effects the different rapid-strength concrete materials, traffic, jointing, and base factors on their performance, including testing in both very wet and very dry conditions. Overall, the performance of the thin BCOA sections in the HVS testing was excellent. The eleven sections resisted the predefined HVS loading without cracking. In five of the sections, that loading was equivalent to 6 million single-axle loads and included load levels more than twice the legal limit in California, channelized traffic at the shoulder edge of the slabs, and a continuous water supply that simulated flooded conditions. The main conclusion from this research study is that a well-designed, well-built thin bonded concrete overlay with half-lane width slabs placed on top of an asphalt base that is in fair to good condition can provide 20 years of good serviceability on most of California’s non-interstate roadways.

Performance of Concrete Overlays on Illinois Interstates, 1967 through 2016

The Illinois Department of Transportation (IDOT) has been constructing concrete overlays of existing concrete pavements on the Interstate system for nearly 50 years. The construction of two bonded concrete overlays and eight unbonded concrete overlays have been documented to date. IDOT has also constructed one thin unbonded concrete overlay. An evaluation of performance history of the eleven pavement sections was undertaken. The following conclusions can be drawn from the evaluation of the concrete overlays in Illinois: 1) bonded concrete overlay performance on the Interstate system varied widely, and should only be used in the future judiciously, with engineering judgment; 2) unbonded concrete overlays performed consistently well, with all observed pavements exceeding or expected to exceed their design lives and design traffic factors; and 3) the thin unbonded overlay was too new to conduct a meaningful analysis of performance.