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Stone matrix asphalt : theory and practice
\"A comprehensive introduction, this book presents the history, materials, requirements, properties, and applications of Stone Matrix Asphalt (SMA). Detailing the requirements and materials for the mix, including asphalt cement, aggregates, and stabilizers, the author discusses design processes and implementation, alternative design methods, and best practices and production processes both in the U.S. and abroad. It covers issues specific to the mix, such as permanent deformation and fatigue resistance, as well as special applications of SMA, including bridge deck surfacing, airfields, and runways. Written in an easy-to-read style, it draws on the author's notable expertise and provides over 400 references\"-- Provided by publisher.
Book
The Challenges of Using Reclaimed Asphalt Pavement for New Asphalt Mixtures: A Review
Reclaimed Asphalt Pavement (RAP) material mainly consists of removed asphalt concretes from existing infrastructures and, to a minor extent, of wasted or rejected mixes during the production processes. Being composed of two valuable non-renewable resources, i.e., aggregates and bituminous binder, its conscious use can ensure the sustainability of asphalt pavement construction. Thanks to the use of RAP material in new asphalt products, the USA saved 4.1 million tons of virgin binder and 78 million tons of virgin aggregates in 2018. Therefore, the use of RAP for the production of new asphalt formulations at the top of the recycling hierarchy is preferable instead of being down-cycled in low-value applications. The RAP material represents one of the most re-used construction products worldwide; in 2018, approximately 88% wt. and 72% wt. of RAP were used in USA and Europe, respectively, as aggregates for Hot, Warm and Cold Asphalt Mixtures and for unbound layers. Several studies have revealed positive responses of the recycled asphalt mixtures with high or very high content of RAP. However, the common practices of many countries still limit the RAP content to a 15–20% wt., on average, in the recycled asphalt mixes. The amount of RAP in asphalt concretes can be significantly increased by applying good management practices of the RAP, either processed or not, as well as novel production technologies and advanced mix design approaches. This manuscript aims to summarize the state-of-the-art of use of RAP aggregates in new asphalt mixtures. The economic and environmental benefits are also discussed.
Journal Article
A Comprehensive Review of Biochar Utilization for Low-Carbon Flexible Asphalt Pavements
A large amount of biomass waste is produced globally, and its production and improper management are major environmental issues. Pavement industries consume large amounts of natural resources and adversely impact the environment. Thus, the utilization of waste materials, such as biochar from biomass, has been prioritized as an innovative and sustainable strategy. However, there is currently a paucity of knowledge regarding the utilization and performance of biochar in flexible asphalt pavements. Thus, the purpose of this study was to provide a comprehensive literature review of studies conducted between 2010 and 2022 on the advancement and application of biochar in flexible asphalt pavement production. This review also highlights biochar production materials (feedstocks) and processes. This review further evaluates the viability of biochar as a carbon-neutral material utilized in producing asphalt pavements. Owing to its exceptional and variable physicochemical properties, biochar has demonstrated improved performance for a variety of applications in flexible asphalt pavements. According to the review, for optimum performance, a particle size < 75 µm is recommended as a modifier for asphalt binders and mixtures with a content range of 5–10 wt.% of the binder, while a particle size of 1–5 mm is recommended as a filter layer. In addition, the review concluded that as a carbon-neutral material, biochar has many possibilities that can aid in reducing CO2 emissions. The challenges and future perspectives, underlying study niches, and future research suggestions for biochar application in the flexible asphalt pavement industry are also highlighted. As a result, this review will contribute to the increased sustainability and eco-friendliness of flexible asphalt pavements by encouraging the transition to carbon-negative and emission-reducing pavements. The current review will assist researchers in identifying research gaps that will encourage the high-potential, sustainable, and multifaceted application of biochar in the pavement industry for greater environmental benefits.
Journal Article
Life Cycle Assessment of Greenhouse Gas Emissions from Recycled Asphalt Pavement Production
With the growing impact of climate change, there is an increasing need and obligation to reduce the responsible greenhouse gases (GHG) in road construction as well. Using life cycle assessment (LCA) methods, several studies have already separately analysed individual parameters of the asphalt production process and illustrated potential improvements in terms of GHG reduction. However, the data of most assessments originate from single sources and databases, and as such can offer little validation against unreliable assumptions. For this reason, in addition to conducting separate assessments at quarries, batch asphalt mixing plants, and construction sites in order to collect energy and material consumption data with which to calculate GHG emissions, this work relies on the results of multiple sources found in the literature. Using the structure for environmental product declarations (EPDs) in EN 15804, our results are divided into the different stages of a life cycle and the corresponding modules. This allows for systematic comparison of different products and eliminates previous uncertainties regarding the inclusion of benefits beyond the system boundary. The results show the dominance of asphalt binder in the material footprint and the corresponding advantage of substituting virgin material with recycled material, as well as the influence of material moisture on GHG emissions in the production process. In addition to the evaluating the material itself, two road sections with increasing traffic volume (and increasing share of electric mobility) were examined and compared with the traffic-related GHG emissions over a 30-year lifetime. We can confirm that traffic has a substantially higher share of the total GHG emissions (>95%); however, as its regulation is the responsibility of governments, the construction industry can only bring about improvements in its own sphere in seeking to further climate protection.
Journal Article
A Review on the Durability of Recycled Asphalt Mixtures Embraced with Rejuvenators
Reclaimed asphalt pavement (RAP) has received much attention recently due to its increased use in hot mix asphalt (HMA) pavements to enhance pavement sustainability. The use of aged asphalt in RAP, which is highly oxidised and has lost its properties due to exposure to traffic loads and climatic conditions throughout its lifespan, can cause asphalt mixtures to stiffen and embrittle, thus negatively affecting the behaviour of asphalt mixtures. This issue may be resolved by including rejuvenating agents that can restore both physical and rheological properties of aged asphalt by increasing maltene fractions and decreasing asphaltene. However, the high restoration capacity of any kind of rejuvenating agent does not assure the durability of restored aged asphalt. This study explored the performance and durability of rejuvenated asphalt mixtures embedded with several types of rejuvenators identified from the extensive literature review. The study serves as a significant reference to predict future challenges in rejuvenating aged asphalt.
Journal Article
Sensor-Based Structural Health Monitoring of Asphalt Pavements with Semi-Rigid Bases Combining Accelerated Pavement Testing and a Falling Weight Deflectometer Test
The Structural Health Monitoring (SHM) of pavement infrastructures holds paramount significance in the assessment and prognostication of the remaining service life of roadways. In response to this imperative, a methodology for surveilling the surface and internal mechanical responses of pavements was devised through the amalgamation of Accelerated Pavement Testing (APT) and Falling Weight Deflectometer (FWD) examinations. An experimental road segment, characterized by a conventional asphalt pavement structure with semi-rigid bases, was meticulously established in Jiangsu, China. Considering nine distinct influencing factors, including loading speed, loading weight, and temperature, innovative buried and layout configurations for Resistive Sensors and Fiber-optic Bragg Grating (FBG) sensors were devised. These configurations facilitated the comprehensive assessment of stress and strain within the road structure across diverse APT conditions. The methodology encompassed the formulation of response baselines, the conversion of electrical signals to stress and strain signals, and the proposition of a signal processing approach involving partial filtering and noise reduction. In experimental findings, the asphalt bottom layer was observed to undergo alternate tensile strains under dynamic loads (the peak strain was ten με). Simultaneously, the horizontal transverse sensor exhibited compressive strains peaking at 66.5 με. The horizontal longitudinal strain within the base and subbase ranged between 3 and 5 με, with the base registering a higher strain value than the subbase. When subjected to FWD, the sensor indicated a diminishing peak pulse signal, with the most pronounced peak response occurring when the load plate was situated atop the sensor. In summary, a comprehensive suite of monitoring schemes for road structures has been formulated, delineating guidelines for the deployment of road sensors and facilitating sustained performance observation over extended durations.
Journal Article
Combined effects of basalt fiber geometrical characteristics on pavement performance of asphalt mixtures
Fibers have been widely adopted in asphalt mixture to improve its pavement performance. Lignin fiber and polyester fiber are the most popular two choices. Lignin fiber is derived from wood, which is not aligned with the principles of sustainable development. The production process for polyester fiber is more complex and costly, presenting both environmental and economic challenges in engineering applications. In contrast, basalt fiber is cost-effective, exhibit excellent wear resistance and impact toughness, and possess high mechanical strength. It is an ideal choice to improve pavement performance of asphalt mixtures. However, most of the existing studies focused on analyzing a single characteristic index of basalt fiber. They neglected the composite effects of geometric characteristics of basalt fiber, such as fiber diameter and length, on the pavement performance of asphalt mixtures at varying fiber contents. Therefore, taking the SMA-13 as an example, the combined effect of basalt fiber geometrical characteristics (fiber diameter, fiber length, and fiber content) on pavement performance are elucidated. Additionally, a random forest algorithm is adopted to perform a weight analysis of fiber characteristics and their correlation with pavement performance.
Journal Article
Sustainable use of reclaimed asphalt pavement (RAP) in pavement applications—a review
The purpose of this review is to examine the innovative usage of Reclaimed Asphalt Pavement (RAP) in flexible pavement applications. RAP is elucidated as isolated pavement earthly materials consisting of asphalt and aggregates. When the existing/old asphalt is removed for reconstruction, and resurfacing, these materials are generated. Now, it is highly required to classify the available RAP for further essential use in road construction. RAP addresses the issues regarding the diminishing of Virgin Aggregate (VA) sources, storage of material and disposal of RAP material nearby the site. The utilization of RAP includes social benefits like depletion of manufacturing waste, conservation of non-renewable natural stockpiles and low energy expenditure. The reviewed literature reveals that RAP has been utilized mainly for base and sub-base materials on the roads. To summarize, 100% replacement of VA by RAP possessed lesser strength and little resistance to creep and long-lasting deformations. Hence, RAP can be appended with natural aggregate or blended with cement or other admixtures like Fly ash (FA) or confined with geocell. It also accelerates the strength and stiffness of the base and sub-base of pavement as it degrades the failure like rutting and fatigue cracking of pavement due to dynamic loads.
Journal Article
An Interpretable Method for Asphalt Pavement Skid Resistance Performance Evaluation Under Sand-Accumulated Conditions Based on Multi-Scale Fractals
The skid resistance of asphalt pavement is vital for traffic safety and reducing accidents. Existing research using only wavelet transforms or fractal theory to study the pavement surface texture-skid resistance relationship has limitations. This paper integrates a wavelet transform and fractal theory to extract the multi-scale fractal features of pavement texture. It proposes an interpretable machine learning model for skid resistance assessments of sand-accumulated pavements. The three-dimensional (3D) texture of asphalt pavements is decomposed at multiple scales, and fractal and multifractal features are extracted to build a dataset. The performance of mainstream machine learning models is compared, and the eXtreme Gradient Boosting (XGBoost) model is optimized using the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) algorithm. The SHapley Additive exPlanations (SHAP) method is used to analyze the optimal model’s interpretability. The results show that asphalt concrete with a maximum nominal particle size of 13 mm (AC-13) has the most concentrated fractal dimension, followed by open-graded friction course with a maximum nominal particle size of 9.5 mm (OGFC-10), with stone matrix asphalt with a maximum nominal particle size of 16 mm (SMA-16) being the most dispersed. The singular intensity difference of the multifractal (Δα) changes oppositely to the fractal dimension (D), and the fractal dimension difference of the multifractal (Δf) decreases with the number of wavelet decomposition layers. The CMA-ES-XGBoost model improves R2 by 27.1%, 9%, and 3.4% over Linear Regression, Light Gradient Boosting Machine (LightGBM), and XGBoost, respectively. The 0.4–0.8 mm range fractal dimension most significantly impacts the model output, with complex interactions between features at different scales.
Journal Article
Reconstruction of Asphalt Pavements with Crumb Rubber Modified Asphalt Mixture in Cold Region: Material Characterization, Construction, and Performance
Dry-processed rubberized asphalt mixture has recently attracted a lot of attention as an alternative to conventional asphalt mixtures. Dry-processed rubberized asphalt pavement has improved the overall performance characteristics compared to the conventional asphalt road. The objective of this research is to demonstrate the reconstruction of rubberized asphalt pavement and evaluate the pavement performance of dry-processed rubberized asphalt mixture based on laboratory and field tests. The noise mitigation effect of dry-processed rubberized asphalt pavement was evaluated at the field construction sites. A prediction of pavement distresses and long-term performance was also conducted using mechanistic-empirical pavement design. In terms of experimental evaluation, the dynamic modulus was estimated using materials test system (MTS) equipment, the low-temperature crack resistance was characterized by the fracture energy from the indirect tensile strength test (IDT), and the asphalt aging was assessed with the rolling thin-film oven (RTFO) test and the pressure aging vessel (PAV) test. The rheology properties of asphalt were estimated by a dynamic shear rheometer (DSR). Based on the test results: (1) The dry-processed rubberized asphalt mixture presented better resistance to cracking, as the fracture energy was enhanced by 29–50% compared to that of conventional hot mix asphalt (HMA); and (2) the high-temperature anti-rutting performance of the rubberized pavement increased. The dynamic modulus increased up to 19%. The findings of the noise test showed that at different vehicle speeds, the rubberized asphalt pavement greatly reduced the noise level by 2–3 dB. The pavement M-E (mechanistic-empirical) design-predicted distress illustrated that the rubberized asphalt pavement could reduce the IRI, rutting, and bottom-up fatigue-cracking distress based on a comparison of prediction results. To sum up, the dry-processed rubber-modified asphalt pavement has better pavement performance compared to the conventional asphalt pavement.
Journal Article