In-place Air Voids Research Articles

Development of mechanical properties predictive model of extracted asphalt binder based on long-term field asphalt pavements

This paper was to develop a prediction framework for obtaining the rheological properties of extracted and recovered asphalt binders utilizing mixture performance and other factors such as in-place air voids, pavement structure, traffic level, and aging duration. A total of 21 field projects consisting of 66 pavement sections were included in the analysis, which were located in different climatic zones with various RAP contents, traffic levels, pavement structures, pavement age, and material properties. Results indicate that the neural network can be successfully adopted to predict cracking-related binder properties consisting of effective asphalt binder, G*sin(δ) and binder fracture energy, and rutting-related binder properties including high temperature performance grade (PG), MSCR Jnr3.2, and R3.2. Both prediction and validation models worked well for pavement sections with varied contents of RAP when new data was introduced.

Impact of warming temperature on asphalt pavement overlay performance and cost: case study in New Jersey

This study aimed to quantify the impact of warming temperatures on flexible pavement overlay performance with the effects of various in-place air voids. The performance models in Mechanistic-Empirical (ME) Pavement Design were locally calibrated and used to predict pavement distresses. The findings indicated transverse cracking due to low temperatures would become less problematic with milder winters, while more extreme high temperatures in summers contributed to faster pavement deterioration especially in the fatigue cracking. The analysis results showed that using the historic climate inputs in pavement design would overestimate the service lives for asphalt pavement overlays. As the in-place air void increases from 5% to 7% under the climate change scenario, the predicted pavement life decreases by 3–4 years. Further analysis showed that, with the effects of warming temperatures, agency costs could be reduced by controlling in-place air void through pay adjustment in quality assurance of the pavement construction.

Rutting performance of flexible pavements using new energy-based potentials

A new energy-based approach is presented for the prediction of rutting performance in flexible pavement systems. The underlying modeling approach is developed based on the thermodynamics of irreversible processes with new state variables introduced to account for the meso-structural changes in the internal structure arrangement due to grain boundary sliding. The model is simplified and implemented in a pavement analysis framework for the evaluation of the model performance in the rutting prediction using a series of well-documented data of well quality controlled WesTrack pavement sections. Densification behavior is observed in measured rutting data during the initial age of each pavement section. A simplified densification model is introduced based on its correlation with in-place air void content. The energy-based plastic model associated with the densification model effectively captured the rutting behavior of all three gradation groups used in the WesTrack project. The result of the analysis shows that the model accurately captures the rutting tendencies observed in flexible pavement sections with decreasing rate of accumulation of plastic deformation over the pavement life due to the aging effects. The mechanism of rutting development can be effectively explained by the present models supported by precise predictions of all the details of initial densification behaviors and seasonal variations during the test period in the WesTrack project.

Field Performance of Foaming Warm Mix Asphalt Pavement

Water-containing and water-based foaming warm mix asphalt (WMA) technologies have been widely used in recent years but their long-term field performance is scarcely documented. This paper summarizes the field performances of six water-containing foaming and 10 water-based foaming WMA pavements across the United States and compares them with corresponding hot mix asphalt (HMA) pavements. Two series of field distress surveys were conducted to measure wheel-path longitudinal cracking, transverse cracking, and rut depth. Field cores were extracted to measure the in-place air void content, aggregate gradation, and asphalt content. The volumetric properties and field performance of foaming WMA and HMA control pavements were evaluated. The foaming WMA pavements showed slightly higher in-place air void (i.e., lower in-place density) than the HMA pavements. It was also found that the foaming WMA pavements in general had comparable or more wheel-path longitudinal cracking than the HMA pavements. The long-term field performance of foaming WMA pavements for transverse cracking and rutting were found to be similar to control HMA pavements. The study also reinforced the importance of in-place air void and asphalt content, finding that slightly higher asphalt content and lower in-place air void content may be beneficial for long-term resistance to cracking of asphalt pavements. As a result of the findings, the optimal pavement maintenance time was estimated to be four to five years since paving for full-depth pavement projects.

DETERMINATION OF MAXIMUM IN-PLACE AIR VOID FOR IMPERMEABLE HOT MIX ASPHALT PAVEMENTS

Obtaining adequate density is a major requirement in the construction of hot mix asphalt (HMA) pavements. Density is very much related to the air voids. As air voids increase, the density decreases. This study determined the maximum in-place air void for impermeable HMA pavements. A total of 497 core samples were obtained from 57 different ongoing HMA construction projects immediately after rolling. Nine different mix types utilised in this study were fine dense-graded 9.5 mm, 12.5 mm, 19.0 mm and 25.0 mm nominal maximum aggregate size (NMAS) mixes, coarse dense-graded 9.5 mm, 12.5 mm and 19.0 mm NMAS mixes, and Stone Matrix Asphalt (SMA) 9.5 mm and 25.0 mm NMAS mixes. Bulk specific gravity of each core sample was determined using both American Association of State Highways and Transportation Officials (AASHTO) T 166 and vacuum sealing methods, and permeability was determined using American Society for Testing and Materials (ASTM) PS129-01. This study found that in-place air void content was the most significant factor affecting permeability. The in-place air voids for dense-graded HMA pavements should not exceed 7%.

Reflective cracking relief interlayer for asphalt pavement rehabilitation: from development to demonstration

Reflective cracking is one of the major type of distresses associated with the use of asphalt concrete (AC) overlay for rehabilitating deteriorated asphalt pavements. This paper briefly describes the research efforts completed in Nevada to identify the best promising techniques to mitigate reflective cracking in AC overlays under Nevada’s climatic and materials’ conditions. The main outcome of the study was the development of a preliminary performance-based mix design specification for an experimental stress relief course (referred to as ESRC) to be placed between the AC overlay and the milled AC surface. Consequently, in summer of 2015, the Nevada Department of Transportation (NDOT) implemented the developed specification on a demonstration project on US 95 in southern Nevada. The project included test sections with three different strategies: (1) AC overlay on top of the ESRC mixture, (2) AC overlay on top of the NDOT fine-graded Type 3 mixture (SRC-T3), and (3) AC overlay without any stress relief layer. An extensive laboratory evaluation was conducted on all three mixtures using both laboratory-mixed laboratory-compacted and field-mixed laboratory-compacted mixtures. Core samples were also collected after construction and were evaluated for in-place thickness and air voids as well as resistance to reflective cracking. The data showed promising results for the ESRC mixture in terms of its resistance to fatigue and reflective cracking while maintaining an acceptable level of stability and resistance to rutting. A windshield survey conducted approximately 13 months after construction showed no distresses in any of the surveyed sections. In summary, the study showed a very good performance for the ESRC mixture thus far, making it a promising technique for reflective cracking mitigation in Nevada.

Long-Term Field Aging of Warm-Mix and Hot-Mix Asphalt Binders

Limited field studies have considered the aging of warm-mix asphalt (WMA) binders, especially from the perspective of long-term aging. This paper quantifies the long-term (10 to 82 months) field aging properties of WMA binders and the control hot-mix asphalt (HMA) binders and identifies the key factors associated with long-term field aging of asphalt. Asphalt binders from 23 field projects consisting of 65 HMA and WMA pavements were recovered, and high-temperature performance grade (PG) was tested. The effects of climate, month of aging, WMA technologies, and original binder high-temperature PG on field asphalt aging were analyzed. A prediction model that included multiple parameters was developed and validated. Results indicated that Evotherm WMA binder had a lower high-temperature PG than HMA binder shortly after construction, but this difference reduced with time. No statistical difference of field aging between HMA and WMA binders was observed. The climate effect on asphalt field aging was apparent within dry areas or freeze areas, whereas the aging difference between dry and freeze areas was inconclusive and requires further research. Other conclusions were that ( a) the field asphalt aging affects more of top-down longitudinal wheelpath crack than transverse crack, ( b) foaming WMA binder ages slowest of all binders considered, ( c) PG 64-XX and PG 70-XX binders aged more than PG 58-XX and PG 76-XX binders, and ( d) the prediction model had good agreement with test results and was well validated. The identified factors that affected field asphalt aging were overlay thickness, in-place air voids, effective binder content, complex shear modulus, and solar radiation.

Derivation of pay adjustment for in-place air void of asphalt pavement from life-cycle cost analysis

The objective of this study is to develop performance-related pay adjustment (PA) for in-place air void of asphalt pavements using pavement management data and life-cycle cost analysis (LCCA). In-place air void data were collected from quality assurance (QA) records for a large number of projects constructed in New Jersey from 1995 to 2005. Pavement condition index data were extracted from pavement management database for the pavement sections where air void data were available. Empirical pavement performance models were developed with sigmoidal functions and used to predict pavement service life. An exponential model form was used to relate the expected pavement service life to the quality measures of in-place air voids. After the rationality of the model was checked, LCCA was performed to derive the PA using different analysis periods and maintenance strategies. Monte Carlo simulations were conducted to capture the variation of PA due to the uncertainty of overlay service life. The PA could be significantly affected by the maintenance strategy if it is estimated using the short analysis period with single overlay, while the PA calculated using the infinite analysis period provides a conservative boundary that is not sensitive to the maintenance strategy. The developed LCCA framework provides the flexibility of determining the PA based on state agencies’ practice on QA and pavement maintenance.

Use of Mechanistic Models to Investigate Fatigue Performance of Asphalt Mixtures

Effects of design air void contents, design voids in mineral aggregate (VMA), and in-place air voids on the fatigue performance of asphalt mixtures were investigated with mechanistic analyses based on the viscoelastic continuum damage (VECD) analyses and the mechanistic–empirical pavement analysis using the AASHTOWare Pavement ME Design program. The VECD analyses included the simplified viscoelastic continuum damage model at the material level and two structural models: ( a) layered viscoelastic analysis and ( b) layered viscoelastic pavement analysis for critical distresses. The mix design of a 2013 accelerated loading facility test lane was selected to develop the volumetric mix designs with the design air voids of 3%, 4%, and 5%, design VMAs of 13%, 14%, and 15%, and in-place air void contents of 5%, 7%, and 9% with the Bailey method. Dynamic modulus and direct tension cyclic fatigue tests were performed in accordance with the AASHTO TP 107 procedure. The test results showed that the linear viscoelastic property was affected by the design VMA, design air void content, and in-place air void content in order of sensitivity. Also, the damage states at failure determined from the damage characteristic curves and the mechanistic fatigue predictions had consistent trends as observed for the design VMA, in-place air void, and design air void content in rank of sensitivity. Finally, the design VMA, in-place air void, and design air void parameters were found to be sensitive in the mechanistic analyses, whereas the parameter that was most sensitive in the pavement mechanistic–empirical analysis was the in-place air void content.

Estimating the hotmix asphalt air voids from ground penetrating radar

Traditionally, in-place air voids are obtained based on field cores. Coring is a destructive and time-consuming process. This study presents a high speed Non-Destructive Testing (NDT) technique with Ground Penetrating Radar (GPR) to characterize the in-place air voids. A total of 92 cores were retrieved from three field projects to establish relationship between the air voids and the measured dielectric by GPR. A statistical model was developed to express the air void value as a function of dielectric and other variables. Contour air void maps could also be produced for the entire pavement sections. The results from the underlying studies have been used as the basis for the repair strategy selections.

Stochastic Estimation of the In-Place Dynamic Modulus for Asphalt Concrete Pavements

AbstractThe dynamic modulus of asphalt concrete mixtures is a key property in assessing asphalt pavement performance based on its role in the mechanistic-empirical design method. The dynamic modulus is also considered to be used as one of the major characteristics in performance-related specifications for quality assurance. However, no feasible method to estimate the mean and variance of the in-place dynamic modulus for the as-built asphalt pavement has been suggested. This paper presents a methodology of stochastically evaluating the in-place dynamic modulus of the as-built asphalt pavement using a relationship of in-place air voids and a set of single dynamic modulus values measured in the laboratory. The methodology was validated with asphalt mix collected from a construction site. The comparison plot between the estimated in-place dynamic modulus and as-designed asphalt mix demonstrated a simple way to evaluate the as-built mix quality. This methodology provides several practical advantages to determi...

Estimation of Lives of Deficient Superpave Pavements

Nonconforming Superpave® mixtures are often encountered during construction of asphalt-surfaced pavements in Kansas. There is no rational method available to find the potential reduction in life of these pavements. Results are presented for a study in which a methodology has been developed to estimate the lives of Superpave pavements that are out of specifications for simulated in-place density and air voids. Five fine-graded, 12.5-mm nominal maximum aggregate size Superpave mixtures, sampled from five different projects, were used in this study. Replicate test specimens were prepared at three different target air void levels at Ndesign gyrations and four air void levels of the molded gyratory specimens. Hamburg wheel tests were conducted on replicate samples up to a rut depth of 20 mm or 20,000 wheel passes, whichever came first. The results were also analyzed to compute three parameters: creep slope, stripping slope, and stripping inflection point. Analysis of the results shows that, in general, higher simulated in-place density up to a certain limit results in a higher number of wheel passes up to a 20-mm rut depth in the Hamburg wheel tester. Superpave mixtures with very low air voids at Ndesign level performed very poorly in the Hamburg wheel tester. Statistical analysis of the Hamburg wheel tester results using the analysis of variance approach indicated that, for most mixtures, air voids at Ndesign and simulated in-place density have a significant effect on the average number of wheel passes to the failure condition. Good prediction of potential loss of pavement life can be made from the results of Hamburg wheel tests on the deficient mixtures. Thus Hamburg wheel test results can be used for estimation of life of defective Superpave pavements.

Use of Superpave Gyratory Compaction Data for Rutting Prediction

This paper presents the estimation results of an improved nonlinear rutting progression model for asphalt concrete mixes. Rutting is modeled as a function of traffic, temperature, and mix characteristics, including voids filled with asphalt, asphalt content, in-place air voids, surface area, and the densification slope. Mixed effects, an advanced statistical technique that allows the consideration of several sources of randomness and autocorrelated disturbances, is used for the estimation of the model parameters. The estimation results with measurements from WesTrack indicate that the model is statistically significant. Further, the model correctly anticipates the dramatic failure of the WesTrack replacement sections (approximately 10–20 mm in a few days). Mixture rutting resistance is linked to the aggregate resistance to densification, as measured by the densification slope in the Superpave gyratory compactor. The model may provide a basis for identification of probable mix performance in the field with...

Comparative Analysis of Field Permeability Testing of Compacted Hot-Mix Asphalt Pavements: Using Air and Water Permeameters

The in-place permeability of asphalt pavements has been the focus of recent research as investigators try to establish links between pavement permeability and performance. Previous research concluded that pavements with in-place air voids exceeding 8% to 10% may be considered as excessively permeable, and it is generally accepted that excessively permeable pavements are more prone to oxidation and stripping of the asphalt binder, as well as more susceptible to freeze-thaw degradation. As the use of the Superpave® design procedures has increased, numerous questions have arisen regarding the effect of certain mix design parameters on the in-place density and permeability of compacted asphalt pavements. A recent investigation into this issue has generated the need for reliable test methods and equipment that can be used to assess the field permeability of in-place pavements. Results of field permeability tests conducted on newly constructed asphalt pavements by using both water and air permeameters are prese...

Comparative Analysis of Field Permeability Testing of Compacted Hot-Mix Asphalt Pavements

The in-place permeability of asphalt pavements has been the focus of recent research as investigators try to establish links between pavement permeability and performance. Previous research concluded that pavements with in-place air voids exceeding 8% to 10% may be considered as excessively permeable, and it is generally accepted that excessively permeable pavements are more prone to oxidation and stripping of the asphalt binder, as well as more susceptible to freeze–thaw degradation. As the use of the Superpave® design procedures has increased, numerous questions have arisen regarding the effect of certain mix design parameters on the in-place density and permeability of compacted asphalt pavements. A recent investigation into this issue has generated the need for reliable test methods and equipment that can be used to assess the field permeability of in-place pavements. Results of field permeability tests conducted on newly constructed asphalt pavements by using both water and air permeameters are presented. The data obtained indicate that currently accepted test methods based on the water permeameter may not produce repeatable results for all pavement types investigated. In contrast, test data obtained with the air permeameter indicate good repeatability for all included pavement types.

Evaluating Nonnuclear Measurement Devices to Determine In-Place Pavement Density

The air void content of both in-place and laboratory-compacted hot-mix asphalt may be the factor that most affects the performance of a properly designed mixture. A mediocre mix, well constructed with good in-place air voids, often will perform better than a good mix that has been poorly constructed. In-place density may be monitored by using three methods: cores, nuclear density gauge measurements, and nonnuclear density gauge measurements. A study was done to evaluate and compare two non-nuclear density devices, the pavement quality indicator (PQI) Model 301 and the PaveTracker, to in-place core densities. Testing and analyses of 20 projects showed that uncorrected gauge measurements (from each gauge) provided reasonable correlation (significant at a 5% level of significance) with core density measurements approximately 75% of the time. Average coefficients of determination for the relationships between uncorrected gauge measurements and core densities were approximately .5. Simulation analyses indicated that the error in measuring in-place air voids using calibrated PQI Model 301 gauge measurements based on the constant offset method can be 1% to 2.7% air voids for the average of 10 measurements. The numerical experiments also indicated that calibration of PQI Model 301 by simple offset or by slope and offset did not improve the correlation between the gauge and core densities.

Field and Laboratory Investigation of Permeable Asphalt Mixes on Georgia Highways

The Georgia Department of Transportation (GDOT) investigated possible high permeability in asphalt mixes statewide in response to reports of prolonged wetness on pavements around the state after rainfall. In these locations, high permeability manifested itself as wet areas on pavement surfaces where wetness remained after natural conditions should have removed all moisture from the surfaces. Sixteen project sites were inspected for problem areas statewide, and core specimens were taken from six of the sites. Specimens were taken from areas considered representative of the problem areas in each project. The specimens were tested to determine the permeability, bulk specific gravity, maximum theoretical specific gravity, percentage of air voids, percentage of asphalt cement, and gradation of the mix. According to the findings of this investigation, some Superpaver; mixes that were designed in accordance with GDOT specifications exhibited undesirable permeability. The investigation determined that both mix design and construction contribute to permeable mixes; hence, permeability problems are to be corrected by a balanced adjustment to these processes, according to the following recommendations: ( a) for each Superpave mix type used in Georgia, develop mix-specific acceptance criteria for maximum in-place air voids; ( b) include evaluation of mix permeability in mix design; and ( c) provide continued quality control during construction operations to ensure the success of the mix-specific acceptance criteria.

Multicharacteristic Performance-Related Specification for Hot-Mix Asphalt Pavement: Complete Development Process

At a time when there is great interest in developing performance-related specifications incorporating multiple quality characteristics and several highly complex approaches are under development, it is questioned whether these procedures will be capable of providing the degree of practicality and ease of application sought by most practitioners. Alternatively, it is claimed that there is a simple, straightforward procedure that is suitable for most practical purposes. The components of this procedure have been successfully applied by the New Jersey Department of Transportation over a period of many years, and it is argued that additional complexity is rarely necessary or beneficial. An example is presented illustrating how readily obtainable data can be used, first to develop the performance model and then to develop the acceptance procedure for a specification for in-place air voids, thickness, and smoothness of hot-mix asphalt pavement. The example is presented in sufficient detail to demonstrate the ease with which this procedure can be learned and applied by individuals with only a basic background in engineering mathematics.

Developing Critical Field Permeability and Pavement Density Values for Coarse-Graded Superpave Pavements

Within the hot-mix asphalt (HMA) community, it is generally accepted that the proper compaction of HMA is vital for a stable and durable pavement. Low in-place air voids have been shown to lead to rutting and shoving, whereas high in-place air voids have been shown to reduce a pavement’s durability through moisture damage and excessive oxidation of the asphalt binder. Recent research has suggested that coarse-graded Superpave-designed mixes are more permeable than conventionally designed pavements at a given air void content. This higher permeability can lead to durability problems. The pavement density at which coarse-graded Superpave mixes become permeable was evaluated by using a field permeability device. On the basis of the data collected, 9.5- and 12.5-mm nominal maximum aggregate size (NMAS) mixtures become excessively permeable at approximately 7.7 percent in-place air voids, which corresponded to a field permeability value of 100 × 10−5 cm/s. Mixtures having a 19.0-mm NMAS became permeable at 5.5 percent in-place air voids, which provided a field permeability value of 120 × 10−5 cm/s. Coarse-graded mixes having an NMAS of 25.0 mm became permeable at 4.4 percent air voids, which corresponded to a field permeability value of 150 • 10−5 cm/s.

Statistical Model of Pavement Rutting in Asphalt Concrete Mixes

Pavement deterioration models are important inputs for the efficient management of pavement systems, the allocation of cost responsibilities to various vehicle classes for their use of the highway system, and the design of pavement structures. The development of an empirical rutting progression model with an experimental data set from WesTrack is described. The salient features of the model specification are as follows: ( a) three properties of the mix are sufficient to model the performance of the asphalt concrete pavement at WesTrack accurately; ( b) the model captures the effects of the high air temperatures at WesTrack; and ( c) the model predicts rut depths by adding predicted values of the increment of rut depth for each time period, which is particularly advantageous in a pavement management context. The three mix properties are a gradation index, which is obtained from the aggregate gradation; the voids filled with asphalt obtained for the construction mix in the Superpave gyratory compactor; and the initial in-place air voids. The specified model is nonlinear in the variables and the parameters and is estimated by using a random-effects specification to account for unobserved heterogeneity. The estimation results and prediction tests show that the model replicates the observed pavement behavior at WesTrack well.