The focus in recent years has been to make asphalt mixes more affordable, and this has led to the increased use of recycled materials and binder modifications. Consequently, one often-heard complaint is that the recent mixes are more susceptible to cracking. There is an urgent need for a practical cracking test for routine use in the process of mix design, quality control, and quality assurance testing. This paper develops an indirect tensile asphalt cracking test (IDEAL-CT). The IDEAL-CT is typically run at room temperature with 150-mm diameter and 62-mm high cylindrical specimens with a loading rate of 50 mm/min. The IDEAL-CT is a simple (no instrumentation, cutting, gluing, drilling, or notching of specimens), practical (minimum training needed for routine operation), and efficient test (test completion less than one minute). The test can be performed with regular indirect tensile strength test equipment. As described in this paper, the IDEAL-CT is sensitive to key asphalt mix components and volumetric properties including reclaimed asphalt pavement and recycled asphalt shingles content, asphalt binder type, binder content, aging conditions, and air voids. The proposed test also has a much lower coefficient of variation than traditional repeated load cracking tests. Furthermore, the IDEAL-CT results were compared with field cracking data collected from the Federal Highway Administration’s accelerated load facility, Texas SH15 and SH62, and MnROAD. The IDEAL-CT characterization correlated well with field performance in terms of fatigue, reflective, and thermal cracking. Last but not the least, the ruggedness test performed in this study indicated that the IDEAL-CT, after combining both statistical and practical views, could be considered as rugged with all four variables: specimen thickness, loading rate, test temperature, and air voids.
Several highway agencies have either implemented or considered implementing performance tests to predict the cracking potential of asphalt concrete (AC) mixes in the laboratory setting. One such test, the overlay tester (OT), simulates the opening and closing of cracks induced by daily temperature variations and tensile strain generated by traffic loads. The variability of the OT results is expressed as a major concern in reliably characterizing cracking potential of AC mixes. A more fundamental analysis process and more mechanistic performance indicators were implemented that consider the two stages of the cracking mechanism (i.e., crack initiation and crack propagation). The repeatability of the proposed performance indices, critical fracture energy and crack progression rate, seems to be better than the current criterion based on the number of cycles to dissipate 93% of the initial maximum peak load. The proposed cracking methodology and associated preliminary failure limits seem to characterize and satisfactorily discriminate the cracking resistance of AC mixes. Given its promise in this study, the proposed OT test method is recommended as a routine test during the mix design process of AC mixes to predict and screen their cracking susceptibility.
The existing design method for RAP mixtures assumes virgin and RAP binders fully blend. However, full blending may not occur and the impact of partial blending on mixture cracking performance is still unclear. A previous study revealed that RAP gradation, which is not currently considered from the standpoint of binder blending, controls the distribution of RAP binder within a mixture and consequently affects cracking performance. The objective of this study was to develop a methodology that overcomes the uncertainty of blending and effectively predicts fracture properties of RAP mixtures. This methodology is based on the evaluation of the interstitial component (IC) of a mixture (i.e., the fine portion that governs cracking performance) by means of a direct tension test named ICDT test. Two RAP sources and four RAP contents were considered. ICDT specimens were produced by blending the fine portion of RAP and virgin aggregate with virgin binder in the same way and corresponding proportions as in RAP mixtures. Binder and mixture fracture properties from the previous study were used for comparison. Mixture and IC exhibited almost similar reduction in fracture energy density (FED) with increasing RAP content, whereas fully blended binder exhibited a less pronounced reduction. This indicated that IC better simulated the actual blending that occurred in mixtures. Mixtures with coarsely graded RAP (less RAP content in the IC) exhibited better fracture properties; thus, the key to satisfactory cracking performance appears to be minimizing the amount of RAP in IC. Consequently, the stiffening effect of RAP on the fine portion that controls cracking performance should be directly evaluated, instead of placing focus on the fully blended binder or the whole mixture. The ICDT test was proven to be a valuable tool to predict fracture properties of RAP mixtures.
The objective of this study was to evaluate the effects of incorporating recycled materials, i.e., reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS), and the use of warm-mix technologies on fatigue performance of asphalt mixtures and pavement structures using the viscoelastic continuum damage (VECD) approach. For this purpose, ten mixtures from the full-scale test lanes constructed at the Federal Highway Administration (FHWA) Accelerated Loading Facility (ALF) were acquired and characterized in the laboratory. The dynamic modulus test and direct tension cyclic fatigue test were employed to assess the linear viscoelastic property and fatigue characteristics, respectively. Within the VECD framework, two parameters, namely material fatigue sensitivity (MFS) and structure fatigue sensitivity (SFS) were developed to represent the fatigue resistance of asphalt mixtures and their performance in pavement structures, respectively. Both parameters can be easily obtained via the strain-based fatigue simulation using the experimental data without extra requirements on the specimen failure location and the number of cycles to failure in the cyclic fatigue test. The validity of MFS was verified by the critical strain energy release rate obtained from semi-circular bend (SCB) testing at intermediate temperature. Based on the obtained dynamic modulus and MFS data, an increase in the content of recycled materials was able to enhance the stiffness of hot-mix asphalt (HMA) mixtures while compromising the fatigue resistance. Implementation of warm-mix technologies benefited materials’ fatigue performance but the improvement was not substantial. Use of soft binder yielded pronounced fatigue benefits for HMA mixtures with high RAP content. The proposed SFS parameter resulted in the same performance ranking of the ALF lanes as the measured fatigue lives. Moreover, quantitatively a power-law function was found to adequately correlate SFS with the field measurements.
Warm mix asphalt (WMA) technology and reclaimed asphalt pavement (RAP) materials have been increasingly used in asphalt paving mixtures due to environmental and cost benefits. Combining WMA and RAP offers more economic and environmental benefits compared to using either alone. To evaluate the combined effect of WMA and RAP, two WMA mixtures with 20% and 30% RAP were produced using water-injection plant foaming, and they were compared with two comparable HMA mixtures with 20% and 30% RAP. The four mixtures were paved on I-70 near Eagle, Colorado, in May 2013. Laboratory performance properties of plant-produced mixes and field performance of the four test sections after 13, 25, 38 months were evaluated. The research results showed that the effect of water foaming WMA and RAP was not significant on the laboratory performance properties, construction quality and field performance. Thus, water-injection plant foaming WMA could be used to produce WMA mixtures with 20% and 30% RAP at a lower production temperature. These sections will continue to be monitored to evaluate their long-term performance and compare with the laboratory test results.
Illinois has many years of experience using various reclaimed materials in highway construction, and in recent years, recycled asphalt shingles (RAS) have been adopted for use in hot-mix asphalt (HMA), along with much higher amounts of reclaimed asphalt pavement (RAP). These reclaimed asphalt materials usually contain aged asphalt binders, which may increase the mix brittleness and hence, pose a challenge for maintaining a flexible pavement and ensuring good performance. To counter these hard asphalt binders, softer asphalts are incorporated into the HMA. The goal is for the final mix to provide acceptable mix properties for the life of the pavement. To determine the impact of recycled materials on pavement performance, this study monitored nine field projects in terms of the testing, construction, and performance of surface mixes that have a variety of asphalt binder replacement (ABR) levels from RAP and RAS which used different virgin asphalt binder grades. Simple performance tests (Hamburg wheel tracking test and the Illinois flexibility index test (I-FIT)) were used to evaluate the mix designs. Flexibility index (FI) from the I-FIT showed good correlation with field crack development, especially after first year performance of the mix. Early-age field performance showed that placing the HMA overlay directly over existing bare concrete pavement or milling off all the HMA and placing the new overlay on concrete pavement results in higher extents of cracking in early age than the sections that left an HMA layer in place. Regardless of which mix type is designed and what material sources are used, the performance of the mix should be evaluated to ensure it has sufficient flexibility to resist cracking before the mix is used in road construction. This allows owners and contractors to use low-cost reclaimed and recycled materials to the extent possible without negatively impacting pavement performance.
In the present study, rutting performance, cracking resistance, and durability of five plant-produced asphalt mixes containing 12% reclaimed asphalt pavement (RAP) and 3% recycled asphalt shingles (RAS) and produced with different warm mix asphalt (WMA) technologies were evaluated through characterization of extracted asphalt binder and performance tests conducted on asphalt mix specimens. For all of the extracted and recovered asphalt binders, continuous grades and the difference between critical low temperatures, Tcr parameter, were determined from the performance grading and a Glover-Rowe (G-R) damage zone was evaluated at 45°C and 10 rad/s. It was revealed that application of a rejuvenating agent (RA) significantly reduced the high PG grade of the overall asphalt binder. The binder test results also indicated that the chemical-additive-based WMA technology had an advantage over the foaming-based technology in terms of asphalt binder durability. Furthermore, application of RA improved the asphalt binder durability. Comparison of G-R parameters of the recovered asphalt binders showed that using RA and lowering the virgin binder high PG true grade improves the overall binder ductility and damage resistance. Asphalt mix performance tests included dynamic modulus, flow number, and semi-circular bend. The dynamic modulus test data indicated that application of RA and lowering the virgin binder high PG grade lowered the mix stiffness at low frequencies. Comparison of the methods to compensate the effects of highly aged RAP and RAS binders indicated that the mix prepared with RA and one level high PG grade drop performed better than the mix prepared by dropping the PG grade by two levels in terms of cracking resistance and rutting performance. The findings give credence to utilization of rejuvenating agents and softer virgin binders in balanced RAP/RAS mix design approaches.
Although the use of high reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) contents in asphalt mixtures is desirable for environmental and economic reasons, these mixtures are prone to cracking, raveling, and other durability-related pavement distresses mainly due to the heavily aged recycled binders. Highway agencies and the asphalt paving industry have been exploring the use of recycling agents (RA) in order to produce these mixtures with desirable performance. This study focused on characterizing the long-term rejuvenating effectiveness of RA on asphalt blends and mixtures with high RAP and RAS contents. Materials from two field projects were used to prepare a number of asphalt blends and mixtures with various combinations of base binder, recycled material, and RA. These blends and mixtures were subject to various aging protocols prior to being characterized for their oxidation kinetics, rheological properties, and cracking resistance. The test results indicated that the RA evaluated in this study were effective in partially restoring the properties of recycled materials, but their rejuvenating effectiveness diminished with aging. Nevertheless, the recycled blends and mixtures with RA achieved equivalent or even better rheological properties and cracking resistance than those with an allowable amount of recycled materials per agency specifications but without RA. In addition, adding RA had no significant effect on the oxidation kinetics of the recycled blends, but increased their susceptibility to physical hardening in response to oxidation. Finally, the correlation between laboratory aging protocols for asphalt blends and mixtures were determined; the laboratory long-term oven aging protocols of five days at 85°C on compacted specimens and one day at 135°C on loose mix yielded binders with equivalent rheological properties to those subjected to rolling thin film oven (RTFO) plus approximately ten and 40 hours of pressure aging vessel (PAV), respectively.
The use of porous friction course (PFC) provides numerous safety benefits and improves the noise quality of surrounding areas. Many agencies once used PFC for these reasons, but have since stopped using PFC due to performance issues. PFC pavements have reportedly been prone to raveling and cracking which leads to reduced service life. In addition, PFC is also typically more expensive than a dense-graded mix due to its use of high quality aggregates, modified asphalt binder and higher asphalt binder contents. Research is needed to extend the service life of PFC pavements in order to encourage agencies to start, or continue, use of PFC for its safety benefits. The objective of this research is to address the raveling and cracking distresses commonly seen by adjusting the asphalt and dust content of PFC mixes to improve durability. This was accomplished by using an array of performance tests to evaluate the effect of additional fine aggregate passing the 0.075 mm (P-0.075) sieve on two PFC mixtures: one that had good field performance (up to 18 years) and one that had poor field performance (less than eight years). It was found that the Cantabro test was a good indicator of mix performance and a maximum loss of 20% is recommended. The study revealed the importance of increased percent passing the 0.075 mm sieve to provide more durable PFC mix designs. An increased P-0.075 content had a positive effect on almost all of the results; thus, it is recommended that the current P-0.075 gradation band be expanded.
The characterization of asphalt binder at low temperature is of fundamental importance for selecting and designing asphalt materials with good and durable performance in regions experiencing severely cold climates. The current specification addresses this issue based on the Performance Grading (PG) system, developed during the Strategic Highway Research Program, and on low temperature creep tests performed on asphalt binder with the Bending Beam Rheometer (BBR). Recently, an alternative experimental method was proposed to relate the complex modulus, obtained with the Dynamic Shear Rheometer (DSR) at low temperature, to the BBR creep stiffness. However, while DSR tests are performed in air, the BBR relies on an ethanol bath for conditioning the binder specimens, making the relation between complex modulus and creep stiffness dependent on the specific cooling medium. In this paper, the effect of cooling medium on the low PG and on the rheological properties obtained from DSR and BBR tests is experimentally investigated and modeled. First, DSR and BBR tests, in ethanol and air, are performed on a set of different asphalt binders. Then, a relationship between the complex modulus in the time domain and the creep stiffness obtained both in ethanol and air is derived and the low PG for both cooling media is estimated. Finally, 2 Springs 2 Parabolic Elements 1 Dashpot (2S2P1D) and the Huet models are used to compare the effects of ethanol and air on the rheological properties of the asphalt binders. It is found that air results in higher creep stiffness and smaller m-values compared to ethanol. The two rheological models indicate that complex modulus and creep stiffness present the same kernel model parameters only in the case of air. This suggests that the low performance grade, obtained from BBR tests in ethanol, is strongly affected by the cooling medium, as well as the recently proposed procedure based on DSR tests. Based on the finding of the present research, the use of air for BBR creep tests is recommended.
Cracking is one of the most prevalent types of distresses in asphalt pavements. There are different cracking index parameters that are determined from tests conducted on binders and mixtures to assess cracking potential. The objective of this study is to compare binder and mixture parameters and evaluate the similarities and differences between the rankings and values obtained. This study includes binder- and mixture testing on 14 plant produced mixtures including three different binder grades, three binder sources, three aggregate gradations, and mixtures containing a range of RAP and/or RAS contents. Testing included PG grading and 4-mm DSR testing on the extracted and recovered binders that were long-term aged. Mixture testing included complex modulus, SVECD fatigue, and DCT testing on short-term aged mixtures. Parameters evaluated included high and low PG temperatures, Tcr, Glover-Rowe parameter (binder- and mix-based), R value, dynamic modulus, phase angle, number of cycles to failure from SVECD and LVECD analysis, and fracture energy. The results show that generally the binder parameters correlate well with each other but the mixture parameters do not. Good correlation was observed between binder and mixture stiffness-based parameters, but there was generally low correlation observed between binder and mixture cracking parameters for the mixtures evaluated in this study, possibly a result of differences in aging level. Recommended future work includes non-linear statistical analysis, incorporation of field performance, and testing on long-term aged mixtures
The AASHTO M 320 specification for thermal cracking—meant to limit damaging temperatures to only a 1 in 50 risk in any given winter—stipulates that asphalt cement chemically (irreversibly) aged in the rolling thin film oven (RTFO) and pressure aging vessel (PAV) be tested after minimal cold conditioning. Creep stiffness and creep rate (m-value) are determined with specimens rapidly cooled to 10°C above the pavement design temperature and then conditioned for only an hour prior to testing. As a result, materials are often tested in a non-equilibrium state and pavements end up under-designed for thermal cracking; adjacent sections can show from best-case to worst-case performance. Several Ontario user agencies have recently implemented a specification to effectively limit cracking due to reversible aging: “Determination of Performance Grade of Physically Aged Asphalt Binder Using Extended Bending Beam Rheometer (EBBR) Method” (Ministry of Transportation of Ontario designation LS-308 and recently adopted by AASHTO under designation TP 122-16). This empirical protocol tests beams after 72 hours of cold conditioning to determine a low temperature grade as well as a grade loss from the 1 hr results specified in AASHTO M 320. Grade losses are sensitive to the presence of deleterious additives (waxes, air blown residues, recycled engine oil bottoms (REOB)). Further, by testing recovered material from paving mixtures, the protocol also provides a secure way to account for the presence of recycled pavement (RAP), and to monitor for overheating during production. The extended BBR method has several limitations: (1) it requires a relatively large quantity of 150 grams of aged material; (2) it takes a relatively long 72 hours to complete; and (3) it quenches the binder from room temperature to two cold temperatures, namely 10°C and 20°C above the pavement design limit (Td+10 and Td+20), and therefore, because of its empirical nature, it is unclear if the results obtained are relevant for other thermal histories. Since these drawbacks have slowed implementation, current research is focused on the following improvements: (1) modeling the aging/hardening processes within the Ozawa theoretical framework; (2) reducing sample requirement to less than 12 grams; (3) shortening testing time to less than 24 hours; (4) conditioning at more temperatures between ambient and the pavement design limit; and (5) automating the procedure. Modeling efforts are based on an analysis of non-isothermal phase transformation kinetics. This paper presents results obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) three-point bending tests on a number of Ontario asphalt cements under varying cooling rates. The application of the Ozawa theory provides an improved understanding of how thermal history and variable aging tendencies can explain vast performance differences between pavement sections of identical AASHTO M 320 grades. It is suggested that by adding an upper limit on the Ozawa exponent to the low temperature asphalt cement specification, in order to reduce the rate of reversible aging, user agencies will be able to better control this type of cracking.
Aging of asphalt binders has a significant impact on the rheological properties of asphalt binders and thus affects the performance of asphalt pavements. The rate of binder aging is accelerated at high temperatures. This study presented a case study on the effect of aging of the asphalt binder properties in the State of Qatar where asphalt mixtures experience harsh environmental conditions of elevated temperatures. The researchers collected field cores from five-year old trial pavement sections in Qatar, recovered the binder and tested to evaluate the change in the rheological properties of the binders. Test results indicated that there is a significant effect of aging on the rheological properties of asphalt binder in Qatar. This effect was more prominent in the wearing course of pavements, diminishing with an increase in pavement depth. Binders along the wheel path experienced less aging compared to the shoulder. Aggregate type and mix design methods were also found to be affecting the extent of aging of asphalt binder in the field. Furthermore, the researchers found that the current practice of aging asphalt binders in the PAV to simulate aging in the field is not sufficient for Qatar’s conditions. It is recommended to extend the PAV aging period from the standard 20 hours for a hot climate like Qatar and it might go up to about 70 hours based on the results of this study.
The asphalt foaming process, as one of the major warm mix asphalt (WMA) technologies, can significantly increase the volume of asphalt binder with large surface area in the unit volume and thus generate a strong coating with high shear strength of the mix and improved workability. It allows lower production and construction temperatures and less greenhouse gas and other emissions. Foaming asphalt has generally been achieved by introducing water as a foaming agent into hot asphalt flow before mixing with aggregate at a certain temperature. The water will evaporate and expand the asphalt volume and reduce its viscosity. However, both the formation and decay of the foamed asphalt binder is a highly thermodynamic process, which makes the characterization of the foamed asphalt binder extremely difficult. A high fidelity model to simulate the foaming process will provide a powerful tool to conduct virtual experiments of WMA production and optimize the asphalt foaming process and WMA design. To this end, a numerical model using smooth particle hydrodynamics (SPH) is developed to simulate the asphalt foaming process. A self-developed nozzle-based foamer was used to generate foamed asphalt binder at different water contents. Three primary parameters, i.e., expansion ratio, half-life and foam index, that have been widely applied to evaluate the foaming characteristics of foamed asphalt, have been studied. It was found that the simulation results agree well with the experiments. Parametric studies were further conducted by using the numerical model to evaluate the effects of environmental controlling parameters on the foaming characteristics of the foamed asphalt binder.
The Hamburg Wheel Tracking (HWT) laboratory test uses loaded wheel(s) to apply a moving load on asphalt mixture specimens to simulate traffic loading on asphalt pavements. Given that different machines with various degrees of compliance with the current American Association of State Highway and Transportation Officials (AASHTO) T 324 requirements are used by highway agencies, this study aimed to assess the capabilities of commercially available and representative HWT equipment, and to evaluate different analysis and reporting methods for rutting and stripping performance assessment. After performing a comprehensive evaluation of devices from different vendors, considerable discrepancies on equipment capabilities and configurations were identified. The machines did not meet all the requirements set forth in AASHTO T 324 including those for the wheel position waveform, the temperature range, and the reporting parameters. Evaluation of existing analysis methods revealed significant inconsistencies among different methods and deficiencies in the specification. Recommended modifications to the machines and test method were provided.
Accurate determination of asphalt content and aggregate gradation is critical for controlling quality of asphalt mixtures during construction. Most state specifications require quantitative evaluation of the asphalt content of mixes as a criterion for acceptance. The ignition oven test procedure specified in American Association of State Highway and Transportation Officials (AASHTO) T 308 (Standard method of test for determining the asphalt binder content of Hot Mix Asphalt [HMA] by the ignition method) is required or allowed by most state departments of transportation (DOTs) for determining the asphalt content and aggregate gradation of asphalt mixtures. The ignition oven test specified in AASHTO T 308 procedure requires the determination of asphalt content correction factors for each asphalt mix and for each ignition oven used. However, in some instances when numerous asphalt mix designs and several ignition ovens are available, correction factors (CFs) are shared between ignition units, even when that practice is not allowed by the standard. There is a need to identify the consequences of sharing correction factors between units/mixes and also to identify testing parameters that affect the measured CFs. By identifying possible causes of variation, the test procedure could be adjusted to make the CFs more consistent between ignition ovens. Also, it should be possible to reduce the amount of difference in CFs between all types of equipment. A study was conducted to assess the variability of ignition oven CFs for different ignition oven unit brands and mixes to better understand the implications of sharing CFs. Twenty-three laboratories used various brands of ovens to test four mixes containing aggregates with varying CFs. The results indicated that CFs were significantly different for the different mixes even when the same unit brand was used. The within-lab and between-lab precision developed in this study suggests that different precision statements are necessary for aggregates with high breakdown potential and that the current precision included in AASHTO T 308 was likely developed for low weight loss aggregate making it unacceptable to use for aggregates with higher CFs. It was also found that the addition of lime caused no significant difference in the measured asphalt content when the CF was correctly measured. However, it was cautioned that a change in amount of lime during mixture production would affect the measured asphalt content. In addition, ways to minimise variability in asphalt CF were evaluated. It was determined that ignition tests conducted at lower temperature (427°C) proved to be effective in reducing the variability in measured asphalt content since the lower temperature reduced the asphalt correction factors for asphalt mixes.
Le présent code de bonne pratique décrit la mise en œuvre des enrobés bitumineux sur chantier, depuis la préparation des travaux jusqu'à l'ouverture de la route au trafic. Pour commencer, le premier chapitre décrit en détail le matériel utilisé. Les camions, les répandeuses de liant, les finisseurs, les alimentateurs et les compacteurs y sont traités, afin que le lecteur puisse entamer les chapitres suivants en connaissance de cause. La mise en place de l’enrobe doit être abordée comme il se doit : la préparation, tant administrative que logistique, est capitale pour la réussite du projet. L’organisation du transport est cruciale, car une alimentation uniforme et continue en enrobé est une condition fondamentale pour garantir un bon niveau de qualité. Le chapitre 3 traite de l’exécution du chantier. Il débute par une description succincte du fraisage et de la pose de la couche de collage. La pose des enrobés au finisseur est ensuite décrite en détail; le comment et le pourquoi des principaux réglages de la machine y sont expliqués. Arrive ensuite le compactage de l’enrobé, où l’on insiste sur l’importance d’un compactage suffisant des couches dans un intervalle de température correct. Le code de bonne pratique donne par la suite quelques spécificités sur la mise en œuvre des différents types d’enrobés. Le contrôle de la qualité pendant et après l’exécution des travaux est une étape importante du processus et est l’objet du chapitre 5. Le chapitre suivant aborde l’ouverture au trafic, et souligne l’importance du temps de refroidissement nécessaire avant que le trafic puisse circuler sur le revêtement neuf. Enfin, s’ensuivent quelques points d’attention importants liés aux conditions météorologiques lors de travaux, à la planéité, à l’homogénéité et à la ségrégation, ainsi qu’à la rugosité.
Chip seals are among the most cost-effective surface treatments available for pavement preventive maintenance. However, frequent issues associated with asphalt emulsion early mechanical strength development, resulting in premature surface treatment failure, have led to the need to improve the characterisation of the chip seal curing process. As such, the use of an electrical resistance measurement has been studied to develop a sound construction methodology that prevents common failures that occur soon after construction. This paper presents a novel approach, based on electrical resistance measurements, to determine when a chip seal has developed enough binder adhesive strength to bond to the existing pavement while keeping the aggregate chips in place. The electrical resistance measurements provide a rapid, non-destructive indication of the amount of curing that has occurred. By implementing this methodology the user can determine when a chip seal has gained sufficient mechanical strength to allow for brooming or opening to unrestricted traffic without an undue loss of cover aggregate. Laboratory and full-scale field trials were conducted using a variety of materials. The electrical properties of the fresh seal coats were quantified by employing a handheld electrical device with a two-point probe resistance measurement. The experimental results suggest that chip seal systems have gained significant mechanical strength when the initial electrical resistance measurement increases by a factor of 10. As a result, this study establishes that electrical resistance measurements can be used to determine when a fresh chip seal has sufficiently cured to withstand the shear forces of brooms and uncontrolled traffic. The implementation of the technique could potentially impact chip seal construction quality, as well as service life performance.
Cracking is one of the most prevalent types of distresses in asphalt pavements. There are different cracking index parameters that are determined from tests conducted on binders and mixtures to assess cracking potential. The objective of this study is to compare binder and mixture parameters and evaluate the similarities and differences between the rankings and values obtained. This study includes binder and mixture testing on 14 plant-produced mixtures including 3 different binder grades, 3 binder sources, 3 aggregate gradations, and mixtures containing a range of reclaimed asphalt pavement and/or recycled asphalt shingles contents. Testing included PG grading and 4 mm dynamic shear rheometer testing on the extracted and recovered binders that were long-term aged. Mixture testing included complex modulus, simplified viscoelastic continuum damage (SVECD) fatigue, and disc-shaped compact tension testing on short-term-aged mixtures. Parameters evaluated included high and low performance grade (PG) temperatures, Tc , Glover–Rowe parameter (binder and mix-based), R value, dynamic modulus, phase angle, number of cycles to failure from SVECD and layered viscoelastic critical distresses analysis, and fracture energy. The results show that generally the binder parameters correlate well with each other but the mixture parameters do not. Good correlation was observed between binder and mixture stiffness-based parameters, but there was generally low correlation observed between binder and mixture cracking parameters for the mixtures evaluated in this study, possibly a result of differences in ageing level. Recommended future work includes non-linear statistical analysis, incorporation of field performance, and testing on long-term-aged mixtures.
During cold recycling, water is added to facilitate the dispersion of foamed asphalt in the mixture and to achieve uniform mixing and help compaction by providing sufficient lubrication. Too little water may cause difficulty in workability and compaction of the mixture, but too much water may extend the curing time and reduce density and strength. Therefore, the optimum water content (OWC) was considered as one of the most important factors in mix design procedures for cold recycling. Currently, mix design procedures for cold recycled foamed asphalt mixtures suggest adding water to the mixture at an optimum content to facilitate mixing and compaction. However, there is no standard method for determining the optimum total water content (OTWC) for cold recycling mixtures. Several empirical relationships were developed to determine the OTWC based on modified Proctor test results for Reclaimed Asphalt Pavement (RAP)/aggregate. However, the compaction effort in the modified Proctor test for RAP/aggregate may not match that for mixtures, which is compacted using the Superpave Gyratory Compactor (SGC) or Marshall hammer. A study is underway to improve the design method for cold recycled foamed asphalt mixtures with 100% reclaimed asphalt pavement (RAP). The purpose of this paper is to optimise the design procedure by developing a new method to determine OTWC. SGC was used to compact RAP instead of the modified Proctor test to match the compaction effort recommended for foamed asphalt mixtures. A regression model was developed to calculate the OTWC for a mixture based on the determined OWC of the RAP, foamed asphalt content, and binder type as factors. The method for determining OTWC for a mixture was validated using six different mixtures and was found to correlate well with the measured OTWC, even though two of six mixtures had underestimated OTWC due to different binder source. Further comparisons with other two OTWC determining methods showed the mixtures at the proposed OTWC had improvement in indirect tensile strength.