Tack Coat Application Rate Research Articles

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.

Investigation of interlayer bonding performance between asphalt concrete overlay and Portland cement concrete using inclined shear fatigue test

The interlayer bonding between the asphalt concrete (AC) overlay and the Portland cement concrete (PCC) layer has an essential influence on the composite asphalt pavement performance. However, there is still little work on the interlayer bonding performance of composite pavement by inclined shear fatigue test. The purpose of this study is to investigate the interlayer bonding performance with four tack coat types and three PCC surfaces under the effect of repeated loading and water erosion. The optimal tack coat application rates were first determined by shear strength and applied in the following study. The shear fatigue performance of interlayer bonding with different tack coats and PCC surfaces was analyzed based on the conventional S-N fatigue model. Then, the effect of freeze–thaw cycles on the interlayer bonding was investigated according to fatigue lives and fatigue life ratios. Furthermore, the axle load conversion factor was calculated based on the shear fatigue life used for the composite pavement design. The analysis results indicate that the interlayer applied modified asphalt as the tack coat realizes higher strength and more extended shear fatigue life, which means better loading and moisture resistance. The calculated conversion factor shows a higher value compared to the specification stipulation. This research contributes to the interlayer design and construction of composite pavement, including tack coat selection, PCC surface treatment, interlayer fatigue life prediction, and axle load conversion.

Evaluation of the Interlayer Bond Strength of Micro-Surfacing Mixes

This paper presents the results of the first study to evaluate the effects of the tack coat and micro-surfacing mix properties on the interlayer bond strength between the micro-surfacing layer(s) and existing pavement surface. Several factors were investigated, which included the type of tack coat material, tack coat application rate, and the residual binder content of the micro-surfacing mix. To this end, a total of 14 field micro-surfacing test sections were installed on Ohio State Route 03 in Wayne County, Ohio. While the first seven sections were constructed with a single micro-surfacing layer, the other seven sections had double micro-surfacing layers. Five tack coat application rates and two residual binder contents were evaluated. The testing plan involved obtaining core samples from the constructed sections 1 week, 4 months, and 12 months after construction. The obtained field cores were tested in the laboratory using two types of pull-off tests and a torque bond strength test. The results of bond strength tests on obtained field cores and the statistical analysis performed on these results indicated that sections with no tack coat had significantly lower bond strength than those with tack coat with at least 0.05 gallons per square yard (gsy) total application (0.0083 gsy residual application rate). Furthermore, results indicated that the use of 0.75% lower residual asphalt binder content in micro-surfacing mixes resulted in significantly lower bond strength between the micro-surfacing and existing pavement. The tack coat material properties had some effect on the interlayer bond strength; however, this effect was statistically insignificant.

Laboratory investigation of the bonding performance between open-graded friction course and underlying layer

Open-graded friction course (OGFC) is attracting great concerns due to the benefit in safety. This study investigated the fracture performance between OGFC and different underlying layers (A and B). The stress intensity factor (KIC) and the critical strain energy release rate (J-integral) were obtained at 0 and 25℃ to characterize the fracture behaviors. Several parameters of the interface were obtained. Correlations between the interface parameters and the fracture behaviors were built. Results indicated that the optimum tack coat rate of the specimens combined by OGFC and underlying layer A (OGFC-A) was larger than that of OGFC-B. The difference in optimal tack coat application rates can be traced back to the difference in the interface parameters. The fracture resistance of OGFC-A was superior to OGFC-B, which was also caused by the interface difference. With the increasing of texture depth, the average roughness, or fractal dimension, KIC and J-integral increased gradually.

A comprehensive laboratory evaluation of the factors affecting the Micro-Surfacing interlayer bond strength

This paper presents the results of a comprehensive laboratory study to evaluate the effects of the tack coat and micro-surfacing mix properties on the interlayer bond strength between the micro-surfacing layer(s) and asphalt pavement surface. Several factors were investigated, which included: the type of tack coat material, the tack coat application rate, and the residual asphalt binder content of the micro-surfacing mix, the number of micro-surfacing layers, and the existing pavement surface texture. Two types of pull-off tests and a torque shear test were used to evaluate the interlayer bond strength of laboratory prepared samples. Statistical analysis was conducted on the results of the conducted bond strength tests. The results indicated that samples with no tack coat had significantly lower bond strength than those with tack coat with at least 0.05 gallons per square yard (gsy) total application (0.0068 gsy residual application rate). Furthermore, results indicated that the use of 0.75% lower residual asphalt binder content in micro-surfacing mixes resulted in significantly lower bond strength between the micro-surfacing and existing pavement. The tack coat material properties had some effect on the interlayer bond strength; however, this effect was statistically insignificant. The use of double layers of micro-surfacing generally resulted in lower bond strength compared to the use of a single layer for micro-surfacing application. In general, the bond strength was not significantly affected by the existing pavement surface texture.

Characterizing the fatigue cracking behaviors of OGFC pavements using the overlay tester

The objective of this study was to evaluate the fatigue performance of the composite specimens combined by OGFC and the underlying dense-graded layer (OGFC-AC) by conducting overlay tester (OT) tests. Other two types of specimens, including single layer OGFC13 and single layer AC20, were fabricated to make comparable analysis with OGFC-AC composites. For OGFC-AC specimens, the effects of tack coat application rate and contaminations (soil and oil) were quantificationally explored. Peak tensile stress, cracking rate index (CRI), and dissipated energy were obtained and analyzed. Meanwhile, the damage propagation during the fatigue tests were analyzed using a damage factor. Results indicated that the peak tensile stresses of OGFC-AC composites were somewhere between OGFC13 and AC20. Contaminations would attenuate the peak tensile stress. There existed a power exponential relation between dissipated energy and the load cycle. CRI and damage factor presented the same development law in demonstrating that the fatigue cracking resistance of OGFC13 was superior, followed by AC20, and the performance of OGFC-AC was inferior. The results of CRI and damage factor showed that an optimum tack coat application rate (0.4 kg/m2) existed at which the OGFC-AC composites presented the least cracking potential. The contamination of soil partially increased the cracking resistance, which was probably due to the fact that some sand particles in soil increased the friction and interlock effect between OGFC and the AC layer.

Development of an Interface Shear Strength Tester and a Model Predicting the Optimal Application Rate of Tack Coat

Tack coat application rates and testing conditions differ among nations and construction conditions because various tack coat materials are available. In this study, newer materials are optimized for addition to porous asphalt pavements exposed to torrential rainfall, which is common in South Korea. Interface shear strength (ISS) tests are used to define the optimum application rates (OARs) of tack coat materials generally used in South Korea, by reference to the Korean Design Standard (KDS), the Korean Construction Standard (KCS), and features of pavement construction and bonding. We performed ISS tests using asphalt mixtures with porosities of 3, 5, and 7% to explore the effect of porosity on shear strength. The ISSs associated with varying tack coat proportions were earlier determined by creating polynomial regression equations. Here, we develop a predictive model using a non-linear function to estimate the OAR of tack coat and compare our approach with the earlier polynomial regression analysis. Based on the ISSs, the golden section search method was applied to define the OARs afforded by the predictive polynomial function. We used the generalized reduced gradient algorithm to construct a nonlinear predictive function using data from the ISS tests. Finally, our comparative analysis showed that the predictive model using the non-linear function was superior to the polynomial model in terms of both error rate and predictive tendency.

Effects of design parameters and moisture conditions on interface bond strength between thin friction course (TFC) and underlying asphalt pavements

As a new pavement surface treatment, thin friction course (TFC) is mixed with asphalt emulsion, SBR modifier, single particle size basalt aggregate, and cement. In this study, a test apparatus derived from the pure direct shear test was proposed to investigate the effects of design parameters and moisture conditions on the interface strength. Specifically, the design parameters include the tack coat application rates, the material compositions of TFC, and the texture depths of the underlying pavement. Finally, the analysis of variance (ANOVA) was conducted. According to the results, the increased application rate of tack coat and texture depth of underlying pavement could improve the interface bonding performance. The existence of moisture degraded the bond strength between TFC and the underlying pavement. The increased tack coat application rate could mitigate the detrimental effects of moisture conditions on the interface bond strength. In addition, the optimized material compositions of TFC can only strengthen the interface bond strength slightly. To sum up, the tack coat application rate shows the most significant effect on the interface bond strength, followed by the texture depths of the underlying pavement surface and moisture conditions. Furthermore, the interaction of texture depth and tack coat application rate also has a significant influence on interface bonding performance between TFC and the underlying pavement surface.

Effect of 3D roughness characteristics on bonding behaviors between concrete substrate and asphalt overlay

Asphalt overlay on cement concrete pavement is a common strategy in pavement maintenance. On the other hand, an asphalt layer is generally paved on a concrete bridge deck to provide competitive performance. In this study, the bonding performance between concrete substrate and asphalt overlay was explored from a perspective of interface roughness. Concrete slabs with a strength grade of C50 were fabricated first. Asphalt concretes were paved with an air void content of 4%. The roughness parameters, including surface roughness, root mean square of roughness, and fractal dimension, were obtained from image technique and surface reconstruction. Relationships between surface roughness parameters and direct shear strength were quantitatively studied. The correlation between roughness parameters and optimal tack coat application rate was also built. Results show that the surface roughness linearly increased with the fractal dimension. Larger surface parameters, which was demonstrated as the surface roughness, root mean square of roughness and fractal dimension, contributed to a superior shear performance. Optimal tack coat application rates existed for all specimens. With the increase of surface roughness parameters, the optimal tack coat application rates increased as well. On the other hand, the cohesion strength and internal friction derived from Mohr–Coulomb theory are affected by the roughness parameters of substrates.

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.

Application of time-temperature superposition principle to pull-off tensile strength of asphalt tack coats

Flexible pavements are multilayered structures that are designed to withstand vehicular traffic and thermal loading. Tack coat provides the bonding between these multilayers, which is a critical mechanism to provide a pavement with the monolithic action of asphalt layers to resist traffic and thermal loading, thereby dictating the pavement’s service life. Asphalt binder bond strength (BBS) is an indicator that can be used to evaluate the interlayer bonding ability of tack coat and changes as a function of temperature and loading rate. The focus of this paper is to prove that the time-temperature superposition principle is applicable to the BBS of various tack coat materials. In order to achieve this goal, BBS and dynamic shear rheometer (DSR) tests were conducted on four different tack coats, CRS-2, CRS-1h, NTCRS-1hM, and Ultrafuse. The Pneumatic Adhesion Tensile Testing Instrument (PATTI) was used to determine the BBS at 13 different temperatures ranging from 5 °C to 53 °C. The BBS data showed that adhesive failures between the binder and pull stub of PATTI caused the drop of BBS below 5 °C to 15 °C for hard (CRS-1h) and Non-tracking (NTCRS-1hM, Ultrafuse) tack coat. In addition to the BBS test, DSR tests were performed on the emulsion residue to measure the time-temperature shift factors at the reference temperature of 20 °C. It was found that the time-temperature shift factors determined from the DSR tests could be successfully used to shift the BBS vs. stress rate curves to construct the mastercurve for all four tack coat materials at a residual application rate of 0.14 L/m2 (0.03 Gal/yd2) as long as the BBS test exhibited cohesive failure between the binder and pull-off stubs. A simple method based on the BBS values at two temperatures is proposed to predict the mastercurve for routine characterization of the BBS mastercurve. No definite trend in the BBS mastercurve emerged among the different tack coat application rates for the different tack coats.

Laboratory investigation of modified bitumen for interlayer in rigid–flexible composite pavement

Adhesion of composite pavement plays a significant role in the durability and maintenance of this type of pavement. The present research aims to assess the bonding and fatigue performance of rigid–flexible composite pavements through laboratory testing at different tack coat application rates. Three types of modified bitumen, crumb rubber-modified bitumen containing hydrated lime (CR/HL), crumb rubber-modified bitumen containing natural zeolite (CR/NZ), and crumb rubber-modified bitumen (CRMB), were selected as the tack coat. Shear fatigue and direct shear tests were utilized to assess the bonding properties of tack coats. The study also examines the behavior of modified bitumen by examining its viscosity, rheological properties, and performance grade. The results show that CR/NZ exhibits better performance in rheological behavior and at various temperatures compared to CR/HL and CRMB. Also, depending on the type of tack coat, shear strength tests show a range of 0.6–0.9 l m−2 as the optimal tack coat dosage. Finally, based on the optimal tack coat, shear strength ratings for various bitumen types may be classified as CRMB < CR/HL < CR/NZ.

Developing Technologies and Procedures to Reduce Tracking and Achieve Uniform and Accurate Tack Coat Application

The tack coat bond is known to affect the longevity of asphalt pavements. Proper interlayer bonding prevents successive pavement layers from acting independently of one another and creating non-uniform stress and strain profiles in the pavement structure. Poor bonding between pavement layers can result in various pavement failures such as slippage cracking, debonding, and early fatigue cracking, all of which contribute to a reduced pavement fatigue life. Tack coat application rate and uniformity (that can be achieved by uniform tack coat application and by avoiding/minimizing tracking) are two major factors that control the performance of the tack coat bonding and longevity of the pavement structure. In this study, a wireless scale system (OreTackRate) that can be controlled from a tablet computer was developed to measure tack coat application rate accuracy and uniformity. The developed wireless scale system was recommended to be implemented during construction to validate application rate accuracy and uniformity. In addition, a distributor truck certification process was developed and presented in this study. The developed scale system can also be used to determine whether the applied tack coat is cured at any time point during construction. Residual tack coat application rate can also be measured using OreTackRate during construction. Implementation of all these tests, procedures, and technologies is expected to improve the tack coat uniformity during construction and improve the overall longevity of the pavement structure.

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.

Mechanical Properties of Thin Surface Treatment for Pavement Maintenance

Specification tests for thin surface treatment are mainly simulated or empirical; without considering fundamental mechanical or rheological properties of the material. Thus, it is difficult to incorporate the test results into mechanical-based pavement design analysis. A series of test methods, which quantify performance-related mechanical properties of thin surface treatment employed in pavement maintenance and pavement preservation is thus needed. The objective of this study is to investigate the performance-related mechanical properties of thin surface treatment materials for pavement maintenance and preservation. The Micro-Surfacing Mat and Precast Rubber Asphalt Mat were used in this study. The Finite Element Model result indicated that the Modified Leutner Shear Test adequate to evaluate the direct shear strength of the thin surface treatment. The results show that the sensitivity loading frequency and the temperature susceptibility of the Precast Rubber Asphalt Mat were reduced by Rubber Modified Asphalt content. The Precast Rubber Asphalt Mat has greater interfacial shear strength as well as shear stiffness compared to those of Micro-Surfacing Mat. The tack coat application rate is crucial for the interfacial shear strength of Precast Rubber Asphalt Mat. This research found that shear stress and the displacement rate are positively related to the interfacial shear strength and shear stiffness. The interfacial shear strength and shear stiffness are negatively related to testing temperature. The Micro-Surfacing Mat had higher dynamic direct shear modulus, lower loading frequency sensitivity, and better rutting resistance than Precast Rubber Asphalt Mat.

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.

Assessing the Bond Strength of Hot Mix Asphalt Pavement for Wearing and Binder Courses

This study investigated the use of a shear box device to measure the bond condition between two layers of hot mix asphalt pavement: the wearing course and the binder course. The wearing course analysed was a Malaysian dense-graded asphaltic concrete mixture of nominal maximum aggregate 10 mm in size (AC10), which was applied over the binder course of another dense-graded asphaltic concrete mixture, AC28. A range of bond conditions was investigated by selecting various asphalt emulsions, application rates, and wearing course thicknesses based on the Malaysian standards of specification. Test results showed that interface shear strength increased as tack coat application rates and wearing course thicknesses increased. Among the tested asphalt emulsion types, a modified asphalt emulsion called RS2KL provided the highest shear resistance. Findings also show that a binder's complex shear modulus elastic portion (G*/sinδ) can affect interface shear strength for thin mixes at low rates of tack coat application.

Development and Validation of a Model to Predict Interface Bonding Between Pavement Layers

During the planning of overlay construction activities, a contractor and/or state agency may be interested in selecting a tack coat material and application rate that would provide adequate interface bonding at the site. The objective of this study was to develop an interface shear strength (ISS) predictive model to estimate interface bonding between the hot-mix asphalt (HMA) overlay and the underlying pavement layer. To achieve this objective, 10 field rehabilitation projects were selected in six states that included 33 in-service test sections representing different traffic and climatic conditions. The overlay construction used different types of tack coat at various residual application rates. Field cores were obtained to measure ISS using a direct shear test device, referred to as the Louisiana Interlayer Shear Strength Tester (LISST). Influencing factors to be included in the model were pavement surface type and mean texture depth, residual application rate, and characteristics of tack coat residues. The experimental data were complemented with test results from a recently completed study for model development and validation. Two types of statistical regression models (linear and nonlinear) were evaluated. Results of the analysis showed that the predicted ISS obtained from the proposed models were in good agreement with the measurements. Further, the developed nonlinear model showed better prediction accuracy than the linear model. The nonlinear model can be used effectively for optimum selections of tack coats given the project conditions. The results presented herein were part of NCHRP Project 9-40A, Field Implementation of the Louisiana Interface Shear Strength Test.

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.

Evaluation of the effective parameters on shear resistance of interface in a geocomposite-reinforced pavement

Application of geosynthetics is known as an important way to reduce and delay emergence of reflective cracks. However, reliance on these materials can have some disadvantages, including reduction of shear resistance in the interface between two HMA layers, along with emergence of some defects in areas on which vehicles brake, accelerate or turn. A large number of parameters affect the interlayer shear resistance. In this research activity, a double-shear device has been developed and evaluated in order to measure shear resistance between layers in the interface zone. The device is equipped by a system for application and control of normal compressive and tensile loading. In this research, using the L16 (2 × 2–4 × 4) orthogonal array, the factors that are most influential on the shear resistance of the interlayer zone reinforced by geocomposite are evaluated. Temperature, with effectiveness 2.4 times greater than that of the other parameters, the effect of which is relatively uniform, is found to be the most relevant parameter, followed by the tack-coat application rate. The findings indicate that the shear loading rate and geocomposite grid size have the next most significant contribution to the maximum shear resistance, both with and without application of normal load.