Tack Coat Type Research Articles

Predictive model for the interface bond strength of geosynthetic-reinforced asphalt layers

Innovation in the use of geosynthetics in roadway applications has resulted in the development of several different products, such as asphalt reinforcement geogrids and paving mats to minimize reflective cracks and limit moisture infiltration. For a proper performance of the reinforced asphalt systems, an adequate interface bond strength has proven to be crucial. However, the influence of the different paving interlayer characteristics, combined with tack coat types, and tack coat rates on the interface bond strength remains unclear. In this study, a comprehensive program of interface shear tests was conducted using Leutner shear device and laboratory-prepared reinforced asphalt specimens. The program involved eight geosynthetic types, two tack coat types, and three application rates. Results revealed that the geosynthetic type, tack coat type and rate, as well as the interactions among the parameters significantly affect interface bond strength. Multiple linear regression analysis indicated that geogrid aperture area, geosynthetic thickness, geotextile backing thickness, and the presence of bitumen coating are the most affecting parameters on bond strength. A predictive model for the bond strength based on geosynthetic parameters is presented. Based on literature results for specimens extracted from the field, the proposed predictive models were found to adequately predict interface bond strength.

Installation of geosynthetic interlayers during overlay construction: Case study of Texas State Highway 21

Geosynthetic interlayers in the form of geotextiles, geogrids, and geocomposites have been used to minimize reflective cracks and enhance overlay performance through functions such as stress relief, reinforcement and moisture barrier. However, proper geosynthetic installation and asphalt overlay construction practices are essential to the adequate performance of geosynthetic-reinforced asphalt overlays. In this study, various factors determining the successful construction of a geosynthetic-reinforced asphalt overlay are discussed in light of experiences during the construction of experimental test sections constructed in Texas State Highway 21. The project included nine different types of geosynthetic interlayers including four polymeric geogrid composites, three fiberglass geogrid composites, one fiberglass grid, and a fiberglass paving mat. The experimental test section included both sensor- and non-instrumented sections. The constructability evaluation of such experimental sections revealed that the primary factors influencing tack coat type and application rates include the pre-existing surface condition, geosynthetic type and their asphalt retention capacities. The geosynthetic installation procedures adopted in the experimental sections were proficient and comprised a specialized installation equipment that is capable of pre-tensioning the geosynthetics during the installation to minimize wrinkles and irregularities. Additionally, particularly high temperature of the pre-existing asphalt surface resulted in blistering of geotextile backing and subsequently leading into an excessive bleeding of tack coat through the geosynthetic apertures that resulted in tracking of construction equipment wheels. Recommendations on efficient geosynthetic installation and overlay construction techniques include adopting the tack coat type and application rates based on project-specific conditions, and using such tack coat to determine the asphalt retention capacity of the geosynthetic interlayer to be used in the project. Additional recommendations include minimizing the movement of construction vehicles on top of the geosynthetic interlayer, and adopting asphalt sanding technique to restore the friction between the paver and surface to minimize possible damage to the geosynthetic interlayer.

Optimisation and field assessment of poroelastic wearing course bond quality

Compared to typical asphalt mixtures, poroelastic mixtures are characterised by high porosity and high flexibility, which are desirable for traffic noise reduction. However, the same properties increase the risk of debonding from the lower layer, which is a significant source of premature damage. The study investigates which of the factors – tack coat agent, type and texture of the lower layer – have the greatest impact on interlayer bonding quality. From 27 variants of interface bond techniques investigated in laboratory, 8 were selected and constructed on two full-scale test sections. Monotonic direct shear loading and cyclic direct shear loading tests with normal force were used for this purpose. The tests indicated that softer bitumen used for the tack coat and the milled texture of the lower layer improves bond quality. However the appropriate laying compaction has the major influence. Poroelastic mixtures are much more sensitive to technological imperfections than standard asphalt mixtures.

Interface shear strength and shear fatigue resistance of fibreglass grid-reinforced asphalt concrete test specimens

ABSTRACT This research was undertaken to study the effects of grid opening size and tack coat type on both the shear strength and shear fatigue resistance at the interface of fibreglass grid-reinforced asphalt concrete specimens and, more importantly, to correlate these effects with the interfacial fatigue performance under four-point bending beam fatigue loading. The specimens were fabricated using a 12.5-mm nominal maximum aggregate size surface mixture. Two types of fibreglass grid, differing only in the grid opening size, and two tack coats, a PG 64-22 asphalt binder and a slow-setting anionic asphalt emulsion with low viscosity, were used to reinforce the specimen interfaces. The digital image correlation technique was utilised to measure displacements, strains, and crack lengths. The test results indicate that a strong tack coat and a grid with large openings can potentially improve the shear resistance of a grid-reinforced interface but the effects of these two parameters might differ under monotonic and cyclic loading conditions. The cyclic shear, beam fatigue, and monotonic displacement-controlled shear test results suggest that the grid opening size plays a key role in the interface shear fatigue performance, however tack coat quality plays a more important role on the interface shear strength of the specimens.

Effect of binder rates and geogrid characteristics on the shear bond strength of reinforced asphalt interfaces

Practical applications and theoretical studies have demonstrated that the presence of the geosynthetic configures a fragile point in the contact between asphalt layers, which can cause problems such as slips and detachments. Geosynthetic characteristics combined with tack coat type and rate can lead to different interface shear bond results. A field-laboratory coupled testing program was conducted to investigate the effect of binder rates combined with geogrid properties on the interface shear bond performance. Increase in application rate on geogrid-reinforced samples showed a great effect on interface shear bond. The stiffer geogrid provided lower interface shear strength and interface shear stiffness, while presented highest geogrid coverage area. Geogrid physical characteristics had more significant influence than geogrid tensile properties. Results suggested that a combination of geogrid characteristics and other factors (binder type, asphalt mix, test temperature and test equipment) can also significant influence geogrid-reinforced asphalt interface mechanism. Findings encourage new investigations to understand the complex behavior of geogrid-interface shear bond and to establish guidelines to determine geogrid properties required for asphalt reinforcements, stablishing correlations between shear equipments and testing procedures.

Effect of tack coat emulsion type, application rate, and surface type and texture on early-age interlayer shear strength of pavements in cold regions

ABSTRACT Tack coat binder is much softer shortly after construction compared to that after aging during in-service life which raises the likelihood of early-age interlayer shear failure. This study was undertaken to evaluate the effects of tack coat type (CRS-2P, CSS-1h, and SS-h), application rate (0, 0.140, 0.281, and 0.702 L/m2), surface texture (grooved Portland Cement Concrete (PCC), new, aged and worn, and milled Hot-Mix Asphalt (HMA)), and freeze–thaw (F-T) cycles on early-age Interlayer Shear Strength (ISS) of laboratory-compacted samples. It was found that, tack coats with a hard binder grade applied at a low residual rate resulted in higher early-age ISS values compared to those prepared using a polymer-modified tack coat. F-T cycles were not found to have a significant effect on the early-age ISS values of specimens with HMA bottom layer. However, all tested tack coats were found to be significantly effective in improving the ISS values of samples with grooved PCC surface texture. For samples compacted on grooved PCC without tack coat, freeze–thaw cycles were found to considerably reduce the ISS values. Application of tested tack coats on grooved PCC was found to mitigate the adverse effect of F-T cycles on ISS values.

Influence of Ageing on Flexible Pavement Interface Bond under Repeated Shear Stresses

The durability of interface bond was not sufficiently taken into consideration, and the research work in this field is scares and scattered. The interface bond usually practices dynamic shear stresses throughout its service life while ageing due to volatilization provide stiffness at the interface. In this investigation, an attempt has been made to assess the durability of the interface bond in terms of resistance to ageing under repeated shear stresses. Two types of tack coat (Rapid Curing cutback RC-70 and Cationic Medium setting emulsion CMS) and three application rates have been implemented in the preparation of two layers slab samples (base overlaid by binder, and binder overlaid by wearing) courses using roller compactor. Asphalt concrete core specimens were obtained from the roller compacted slab samples and subjected to long term ageing, then the specimens were subjected to 1200 repeated shear stress cycles. The accumulation of permanent deformation was monitored. Afterwards, the specimens were tested for interface shear strength at 20 °C. Control specimens were also tested for comparison. It was concluded that ageing reduces the total microstrain for RC-70 tack coat by (43.6, 25.6, and 29.5) % and (50, 51.3, and 30.2) % for (binder-base) and (wearing-binder) interfaces for the application rate of (0.15, 0.33, 0.5) l/m2 respectively. However, ageing reduces the total microstrain for CMS tack coat by (37, 35.5, and 40.3) % and (45.2 , 49, and 46.8) % for (binder-base) and (wearing-binder) interfaces for the application rate of (0.1, 0.23, 0.35) l/m2 respectively. Ageing increases the interface bond shear strength by a range of (8-27)% for various interfaces, tack coat type and application rates.

Investigation of Tack Coat Bond Damage Mechanism in Asphalt Surfaced Pavements under Dynamic Truck Loads

Bonding created by the tack coat allows the pavement system to carry heavy truck loads as a monolithic structure and improves the structural integrity. In Oregon and throughout the U.S.A., CSS-1H is the most commonly used tack coat type. However, field observations have revealed that new engineered tack coats, although more expensive, outperform the conventional types in relation to shear resistance. In this study, the impact of these new engineered emulsions on in-situ bond performance was quantified by laboratory testing and numerical modeling. Bonding damage performance of all tack coats was experimentally determined by using direct shear tests. Full-scale moving truck load models were developed and calibrated using the load-displacement parameters obtained from the laboratory shear tests. The impact of adverse construction conditions, such as dust, rain, and tack coat coverage, on tack coat bond damage under heavy truck loads was determined. It was concluded that the presence of dust had relatively the lowest contribution to shear damage. Rain during construction had the highest impact on the damage behavior and tack coat application on a wet surface increases the potential for damage by 20.1%. A 50% coverage of tack coat during construction resulted in 12.8% higher damage levels compared with 100% tack coat coverage of the surface area. Moving load models for heavy trucks caused 2.44 times more bonding damage at the bonded interface compared with the damage created by smaller trucks (F450).

Laboratory investigation of OGFC-5 porous asphalt ultra-thin wearing course

Porous asphalt ultra-thin wearing course is an efficient preventive maintenance treatment to improve road performance and prolong its life. Due to the high porosity of porous asphalt mixture, it provides high drainage capacity and reduces noise, hydroplaning, water splash and spray. However, the high porosity of this mixture also leads to a decreased strength and raveling resistance in comparison to dense-graded wearing course. Hence, in this study, the durability, void characteristic, shear resistance, and interlayer shear strength of OGFC-5 porous asphalt ultra-thin wearing course (OGFC-5) were investigated through laboratory test. Durability test results show that OGFC-5 can achieve good water stability and raveling resistance when the thickness of asphalt film increases to 14 μm and the viscosity of asphalt increases to 35,000 Pa.s. Void characteristic test indicates that finer OGFC (OGFC-5) has a smaller void size, a less proportion of large voids than coarser ones (OGFC-10 and OGFC-13), which results in a lower water permeability of OGFC-5 asphalt mixture. Shear resistance test shows that finer OGFC (OGFC-5) has a slightly larger cohesion strength and a smaller internal friction angle than coarser ones. Additionally, the interlayer shear strength of OGFC-5 was obviously affected by test temperature, tack coat type, and application rate. The interlayer shear strength of OGFC-5 is at the maximum when the application amount of tack coat is 0.8 kg/m2. The experimental results in the study provide a technical support for the application and promotion of porous asphalt ultra-thin wearing course.

Fatigue performance of interface bonding between asphalt pavement layers using four-point shear test set-up

This paper aims to study the fatigue performance of interface bonding between asphalt pavement layers. To fulfill this objective, a four-point shear test (4PST) set-up was developed, and a series of fatigue tests were conducted on composite asphalt beam samples made up of stone mastic asphalt (SMA) and asphalt concrete (AC) mixtures. The combined effect of test temperature (3 levels), normal pressure (6 levels), loading frequency (5 levels), and shear stress (6 levels) with single tack coat type and application rate were considered for evaluation. Two interface failure criteria were successfully adopted in this study, and high correlation was relatively found between the fatigue test results and the corresponding fatigue life criteria. Findings of this study revealed that firstly, both the interface fatigue life and shear stiffness increased at all temperatures with increasing normal stress. Secondly, with increasing loading frequency, the interface fatigue life increased at each temperature. Thirdly, shear stiffness decreased with increasing shear stress for each temperature; the decrease was more pronounced at lower temperatures. Power laws were also proposed to characterize interface fatigue life at each temperature. Finally, the results of the analysis of variance (ANOVA) indicated that unlike the fatigue life, all factors had a significant effect on the shear stiffness. A multiple regression model was established successfully to predict the initial shear stiffness.

Asphalt mixture layers’ interface bonding properties under monotonic and cyclic loading

This paper focuses on investigating the interface shear bonding properties of asphalt pavement structures using both monotonic and cyclic direct shear tests. Several pavement structures were considered, differing in the asphalt mixture type and tack coat type, and laboratory preparation of the double-layered asphalt specimens. Based on the results on bond materials used in this research, it was found that the resulting shear strength from monotonic shear test can be used only as a rough indicator for long term interface bonding performance, because not all research and field experience could be reflected in the test results. The cyclic shear test employed in this study can be used for evaluating the interface fatigue performance. Additionally, differentiation between particular bond materials with respect to interface shear bonding properties is assured.

Strategies to reduce flexible pavement cracking in Florida

Cracking of flexible pavements, particularly top-down cracking, is the predominant distress in Florida. However, pavement failures due to cracking have reduced by ten per cent over the last ten years. This improvement in cracking resistance is primarily due to a focused and multifaceted research effort that includes laboratory studies, field test sections, and accelerated pavement testing. Most research efforts can be grouped into three main categories: asphalt binder modification, reflection cracking mitigation, and tack coat application rates and type. This paper presents the findings of these research studies and the strategies the Florida Department of Transportation has implemented to improve cracking resistance of flexible pavements.

Investigation of the interface bonding between concrete slab and asphalt overlay

Interface bonding between the cement slab and asphalt overlay is a significant point affecting mechanical behaviour and service life of the pavement. Many factors may influence the interfacial adhesive capacity, including asphalt mixture type, tack coat type and dosage, surface texture on layer below, temperature and moisture conditions. The aim of this study is to determine the most influential factors at the interlayer and evaluate their significant levels. An apparatus is designed to apply the direct shear test with normal load. Specimen is prepared by drilling cores from asphalt overlay over cement concrete pavement, which is constructed in laboratory. Six parameters with three values are examined by orthogonal test. Effects of these factors on interlayer performance are validated by boxplot. The test results conclude that surface texture on cement slab has the most significant influence on interlayer shear strength, and tack coat type, moisture and temperature come next. Rough surface texture like tining helps increase layers’ bonding. Cutback asphalt is not suitable as tack coat binder compared to emulsified asphalt. In addition, low temperature and dry condition can also improve interlayer shear performance.

Impact of tack coat application conditions on the interlayer bond strength

The intrinsic characteristics of tack coats play an important role in the adhesion between layers, but the conditions of application of these coats are equally crucial. In this context, the BRRC actively participates in a Belgian working group on tack coats and the objective is to carry out a “field” study about adhesion between layers while evaluating the influence of different parameters– such as type and rate of spread of tack coat, nature and preparation of the binder course, etc. With a view to this objective, a test site was constructed consisting of four test sections differing in type of tack coat, texture due to milling speed and cleaning operation of the binder course. The bond strengths were investigated by direct shear tests performed in the laboratory on specimens taken from the four test sections. This paper describes the conditions of application, the measurements made on site and the results of the interlayer adhesion test. The test sections were constructed in good conditions, leading to high shear strength values. Only the effect of tack coat type could be demonstrated, while for all milling speeds and cleaning operations considered in this study, the results were equally good and not significantly different.

Fatigue and fracture characterization of fiberglass grid-reinforced beam specimens using four-point bending notched beam fatigue test and digital image correlation technique

The purpose of this research is to develop an experimental and analytical framework for describing, modeling, and predicting the reflective cracking patterns and crack growth rates in GlasGrid®-reinforced asphalt pavements. In order to fulfill this objective, the effects of different interfacial conditions (mixture type, tack coat type, and grid opening size) on reflective cracking-related failure mechanisms and the fatigue and fracture characteristics of fiberglass grid-reinforced asphalt concrete beams were studied by means of four-point bending notched beam fatigue tests (NBFTs). Also, the digital image correlation technique was utilized to determine the lengths of the interfacial and vertical cracks during each test. The stress intensity factors (SIFs) at the crack tips were backcalculated using a finite element model and applying linear elastic fracture mechanic principles to the crack lengths. The local effect of the reinforcement on the stiffness of the system at a vertical crack-interface intersection or the resistance of the grid system to the deflection differential at the joint/crack (joint stiffness) for GlasGrid®-reinforced asphalt concrete beams was determined by implementing a joint stiffness parameter into the finite element code. The crack length and SIF test results were used to find the Paris’ law parameters for each interlayer condition. According to the NBFT results, GlasGrid® reinforcement retards reflective crack growth by stiffening the composite system and introducing joint stiffness. The results also show that the higher the bond strength and interlayer stiffness values, the greater the joint stiffness and retardation effects.

State of the art: interface shear resistance of asphalt surface layers

Interface shear resistance is a measure of the bonding between two layers under shear loading. Adequate interface shear resistance and long-term bonding of the surface to the underlying pavement are critical to the performance of pavement structures. Interface shear strength is a function of adhesion, friction and aggregate embedment or interlock and is commonly modelled as a Mohr–Coulomb type envelope. Measurement of interface shear resistance can be performed in the field on full-scale pavements, in the laboratory on cores recovered from the surface or in the laboratory using samples prepared in the laboratory. However, laboratory testing of cores recovered from the field is likely to be more reliable and repeatable than field testing. There is a large range of test methods and procedures for the measurement of interface bond. These test methods are generally grouped into three main loading mechanisms; axial tension, torsional shear and direct shear. Direct shear tests offer a more comprehensive assessment of the full interface strength. The interface’s resistance to shear can be characterised by its strength, modulus/stiffness or work/energy. The results are affected by the test protocol, tack coat type and application rate, test temperature, applied normal stress and rate of loading, interface condition and post-construction trafficking. Of these, the test temperature is the most influential factor. A number of studies have reported contradictory and conflicting conclusions with regard to the importance of various factors and conditions on the different measures of interface shear resistance. Such inconsistent findings likely stem from the complicated interaction between the various interface conditions and testing protocols. The fundamental factors affecting monotonic interface strength are now reasonably well understood. The focus of future research is expected to be on shear fatigue performance of interfaces.

Cracking resistance of thin-bonded overlays using fracture test, numerical simulations and early field performance

Thin-bonded bituminous overlays are becoming an increasingly popular pavement maintenance treatment, which can be used to restore smoothness, seal and renew the pavement surface and increase skid resistance. Thin-bonded overlays (TBOs) are constructed using a specialised type of paving equipment called a ‘spray paver’. A spray paver combines the operation of applying a tack coat and laying down asphalt concrete in a single pass. This allows for the application of a high rate of polymer-modified asphalt emulsion tack coat. Due to reduced thickness, cracking distress is more of a concern in this type of system. This paper describes a new approach for the evaluation of the cracking performance of TBO systems through fracture mechanics-based testing of laboratory and field specimens. Computer simulations and early field performance data are also used in the evaluation. This study is conducted in the context of three field projects which encompass seven different pavement test sections. The test sections allowed a number of variables to be studied, including type and application rate of tack coat emulsion and type of hot-mix asphalt gradation structure (gap graded vs. dense graded). Comparisons are also made between overlays constructed using spray paver and conventional paving process. All seven sections were computationally simulated to evaluate their performance in the context of thermal and reflective cracking potential. Fairly good agreement is observed between laboratory tests, computer simulations and field performance data. The results indicate that good thermal and reflective cracking resistance are expected from TBOs. Furthermore, it was observed that the cracking performance of TBOs depends on the type of gradation for the overlay mixture and the tack coat emulsion type and its application rate.

Interface Layer Tack Coat Optimization

Interface bonding is a key factor affecting pavement performance life. This study focused on optimizing in situ tack coat application rate and field installation. The objective was to validate the laboratory-determined optimum residual application rate and evaluate the field performance of tack coat materials. The parameters analyzed included two cleaning methods (broom and air blast), two paving procedures (spray paver and conventional paving with use of a distributor and a regular paver), tack coat type (SS-1h, SS-1hp, and SS-1vh), and existing pavement surface. Projects were conducted on I-80 and Illinois Route 98. Cores were tested by using the interface shear test device. A life-cycle cost analysis that considered construction materials and paving methods was performed. Results showed similar bond strength for both cleaning methods; however, air-blast cleaning reduced the required optimum residual application rate. The resulting interface bond strength was similar when using either of the paving procedures considered. SS-1vh, a nontrack tack coat, performed better than any other material studied. Identification of the optimum tack coat application rate will help ensure cost-effective and efficient tack coat application in the field.

Development of fracture-energy based interface bond test for asphalt concrete

The behavior of the interface between adjacent pavement layers is one of the most important factors affecting pavement performance. Despite the importance of interface behavior between different pavement layers, there are few guidelines that can be used for construction, and the selection of tack coat type, application rate, and placement is usually based on empirical judgment. This paper presents a new fracture-energy based Interface Bond Test (IBT), which can be a practical method to evaluate the bond between pavement layers. The results of laboratory and field studies demonstrate the ability of the test to distinguish between samples produced with different tack coat application rates and modified versus unmodified tack coat material. Results from the IBT test were also compared with direct tension tests, and similar trends were found to exist.

Characterisation of interface bonding between hot-mix asphalt overlay and concrete pavements: modelling and in-situ response to accelerated loading

This study investigates the effects of pavement interface conditions on hot-mix asphalt (HMA) overlay response using the laboratory and field measurements accompanied by a numerical analysis. A laboratory and accelerated testing programme were conducted as part of a comprehensive study to determine the optimum tack coat application rate for HMA–Portland cement concrete (PCC) composite pavements by Leng et al. (2008, Transportation Research Record: Journal of the Transportation Research Board, 2057, 46–53; 2009, Transportation Research Record: Journal of the Transportation Research Board, 2127, 20–28). This study synthesises the accelerated and laboratory test results with a 3D finite element (FE) model to evaluate the effects of various bonding conditions on the overlay response as well as the interface behaviour. The model outcome was validated using the laboratory and field results. The FE model was utilised to extend the findings of this study to different temperatures, tyre configurations and loading conditions. Pavement interface was modelled using a hyperbolic Mohr–Coulomb friction model, whereas HMA overlay was modelled as a viscoelastic material. A moving load was applied and implicit dynamic analysis was carried out. Field and laboratory experiments along with the numerical analysis proved the importance of achieving good bonding at the pavement interface for HMA overlay. This study found that as pavement temperature increases, the interface bonding effects on the overlay response are amplified. This could be the main contributing factor to overlay rutting. The influence of interface condition on the HMA surface and bottom strains was evaluated using a numerical model supported by full-scale accelerated pavement testing results. The effects of varying interface properties such as stiffness and strength on the HMA overlay response were investigated. The numerical model provided a range of expected HMA critical strains under realistic interface conditions ranging from full bonded to debonded conditions. This study clearly shows the significance of tack coat type and application rate effects on pavement critical responses through laboratory, in-situ response and advanced modelling.