Hot Mix Asphalt Construction Research Articles

A review of environmental emissions from asphalt plants and paving

Asphalt is a black, thermoplastic, hydrocarbon material extracted from crude oil and widely used in road construction all over the world. In order to meet the requirements of construction technology, asphalt always needs to be heated to flow state in the process of mixing and paving, during which a large amount of asphalt fume is released. Asphalt fume is a complex mixture of inorganic compound gases, volatile organic compounds and particulate matter, which poses a serious threat to the natural environment and the health of practitioners. This review presents HMA and WMA constituents and the potential health effects of criteria and Hazardous pollutants generated from asphalt pavement construction. Hot mix asphalt (HMA) and warm mix asphalt (WMA)are a major construction materials used for highway roads, building roads, airport runways, parking, and other pavement repairs in the worldwide. During HMA construction, a considerable number of volatile organic compounds (VOCs) are generated during asphalt pavement construction, and present negative effects on workers health. Accurate identification, quantification and measurement of emissions during HMA and WMA paving operations were used to identify and quantify VOCs, SVOCs, hazardous air pollutants (HAPs) and polycyclic aromatic hydrocarbons (PAHs) in asphalt fumes during production and paving activities.

Mechanical and environmental performance comparisons of improved asphalt pavement wearing courses with high quality aggregates, steel slags, and polymeric compound

The use of waste materials in the construction of hot mix asphalt (HMA) pavements is an important opportunity for environmental sustainability. When properly designed, the alternative mixtures may also guarantee excellent mechanical performance.In this study, the results of an experimental analysis carried out on dense-graded HMAs are presented. In particular, the performance of a “traditional” surface mixture with limestone aggregate (designed with neat bitumen or a polymer-modified bitumen within the typical acceptance requirements for intended use in wearing courses) was compared with two alternative mixtures. The research investigated a surface mixture including coarse basaltic aggregates (a high-quality non-renewable resource) and one in which the coarse aggregate is substituted by a waste material, i.e. steel slags, in a high percentage. Both the improved mixtures included neat bitumen and a polymeric compound too, for advanced performance. Finally, for a more comprehensive comparison, a Life Cycle Assessment - LCA (cradle-to-gate approach) was carried out on the different mixtures, to compare the environmental impacts related to their production in asphalt plants, considering the features of the materials and fuels involved. The laboratory results showed comparable structural performance for the two mixtures with basalt aggregates and steel slag. In addition, other positive aspects concerned the higher crushing resistance of metal slag compared to basalt aggregates and the lower percentage of bitumen required by the proposed mixture with slags, with evident practical benefits. Furthermore, the LCA provided useful information about the environmental sustainability of the different mixtures, so that the feasibility of use of these recycled materials may be evaluated considering not only the technical and cost perspectives but the environmental ones too. The numerical results evidenced remarkable benefits for several impact categories for the mixtures with recovered waste materials, with promising advantages with their growing wide adoption.

A synthesis on utilization of waste glass and fly ash in cold bitumen emulsion mixtures

The generation of waste materials is a global concern and attempts are being made to utilize these wastes in the construction industry. The development of road infrastructure everywhere is going at a fast pace which increases the environmental degradation, fossil fuel consumption, global warming, and depletion of natural materials because of hot mix asphalt (HMA) usage. The detrimental effects of generation of waste in large quantities at a global scale and virgin material/energy consumption in HMA construction are of prime concern and need to be addressed. The construction/maintenance of pavement must be environmentally, economically, and socially sustainable. Use of cold bitumen emulsion mixtures (CBEMs), a type of cold mix asphalt (CMA), is a way forward for development of sustainable road infrastructure. The incorporation of wastes in CMA can be a sustainable solution to problems linked to waste generation and development of flexible pavements with HMA. This work summarizes the staging evaluation of CBEMs incorporated with waste glass (WG) and fly ash (FA) utilizing mechanical characteristics, water sensitivity and environmental impact, critical gaps in the literature, and recommendations to address those gaps. A detailed analysis on CBEMs using WG as a replacement of fine aggregate showed comparable stability/stiffness and multifold resistance to rutting than HMA. Fly ash filler in CBEMs reported extraordinary increase in stability, stiffness, rutting resistance, and water sensitivity than reference CBEM/HMA. The focus of the research area should continue on the exploration of waste materials for use in CBEMs to achieve a better environment for society and to promote sustainability in the pavement industry.

Mechanical performance of sustainable asphalt mixtures manufactured with copper slag and high percentages of reclaimed asphalt pavement

The use of reclaimed asphalt pavement (RAP) in the construction of hot mix asphalt (HMA) pavements is a widely used alternative in the development of sustainable road infrastructure. For this reason, the use of higher RAP contents continues to be a topic of interest. This study evaluated the performance of semi-dense asphalt mixtures incorporating 50% to 70% RAP and 7.5% and 15% copper slag (CS) as partial replacement of aggregate, to determine the influence of CS on the effective increase of RAP in the design of sustainable asphalt mixtures. The mixtures were evaluated using macrotexture, fatigue strengths, water sensitivity, and the Hamburg wheel tracking test. The results show that the use of RAP improves the permanent deformation resistance (RD) and fatigue life of the mixtures, while the mean texture depth (MTD) and indirect tensile strength ratio (ITSR) decrease. The incorporation of CS in the mixtures with RAP improved MTD and ITSR compared to the mixtures including only RAP and allowed higher RAP contents in fatigue and Hamburg wheel tests without showing a negative influence.

Model Development for the Prediction of the Resilient Modulus of Warm Mix Asphalt

Increasing material prices coupled with the emission of hazardous gases through the production and construction of Hot Mix Asphalt (HMA) has driven a strong movement toward the adoption of sustainable construction technology. Warm Mix Asphalt (WMA) is considered relatively a new technology, which enables the production and compaction of asphalt concrete mixtures at temperatures 15-40 °C lower than that of traditional hot mix asphalt. The Resilient modulus (Mr) which can be defined as the ratio of axial pulsating stress to the corresponding recoverable strain, is used to evaluate the relative quality of materials as well as to generate input for pavement design or pavement evaluation and analysis. Based on the aforementioned preface, it is possible to conclude that there is a real need to develop a predictive model for the resilient modulus of the pavement layer constructed using WMA. Within the experimental part of this study, 162 cylindrical specimens of WMA were prepared with dimensions of 101.6 mm in diameter and 63.5 mm in thickness. The specimens were subjected to the indirect tension test by pneumatic repeated loading system (PRLS) to characterize the resilient modulus. The test conditions (temperature and load duration) as well as mix parameters (asphalt content, filler content and type, and air voids) are considered as variables during the specimen’s preparation. Following experimental part, the statistical part of the study includes a model development to predict the Mr using Minitab vs 17 software. The coefficient of determination (R2) is 0.964 for the predicted model which is referred to a very good relation obtained. The Mr value for the WMA is highly affected by the temperature and moderately by the load duration, whereas the mix parameters have a lower influence on the Mr.

Deformation and Resilient Behavior of Hot and Warm Mix Asphalt Concrete

Development of hazardous gases emissions through the production and construction of Hot Mix Asphalt (HMA) have encouraged the transition to Warm Mix Asphalt (WMA) which is considered as one of the best choices of sustainable materials in asphalt pavement. The temperature reduction in the mixing, handling, and compaction of the mix gets in saving energy, cutting emissions and significant cuts in construction costs. In this investigation, two WMA mixtures have been prepared in the laboratory using medium curing cutback (MC-30) and cationic emulsion asphalt. HMA mixture was also prepared for comparison. Marshall size Specimens of (101.6 mm) in diameter and (63.5 mm) in height were constructed from these mixtures and subjected to repeated Indirect Tensile Strength test (ITS) to determine the effect of asphalt type and content on deformation and resilient behavior of asphalt mixture. Another group of cylindrical specimens of (101.6 mm) diameter and (101.6 mm) in height have been constructed from these mixtures and subjected to repeated compressive stresses test to determine the rutting resistance of asphalt mixture. Test results were analyzed and compared. It was concluded that, the permanent deformations for cutback and emulsion treated WMA was higher than that of HMA by (50 and 35) % respectively. The Resilient Modulus (Mr) at 25 ⁰C under repeated (ITS) for cutback and emulsion treated WMA was lower than that of HMA by (39.95 and 27.94) % respectively. On the other hand, the (Mr) for cutback and emulsion treated WMA was higher than that of HMA by (43.75 and 5.47) % respectively under repeated compression load at stress level 0.138 (MPa).

ENVIRONMENTAL IMPACT OF VOLATILE ORGANIC COMPOUNDS EMITTED FROM ASPHALT PAVEMENT

Hot mix asphalt (HMA) is a major construction material used for building roads, airport runways, and parking lots (ASCE 2014). During HMA construction, a massive amount of volatile organic compounds (VOC'Ss) is emitted from the hot asphalt mixtures, creating a potential health risk to on-site workers. Few studies have quantitatively investigated (Chong et al., 2013). The constituents and the potential health effects of the VOC's generated from HMA pavement construction were studied. This paper presents the results of a study in which air samples were collected at multiple locations and time points of several projects during HMA pavement construction and were their chemical compositions and concentrations subsequently characterized by using gas chromatography/mass selective detector (GC/MSD). Although the individual concentrations of the identified chemicals were found to be below various exposure limits, their collective effect on human health remains unknown and may not be ignored (Chong et al., 2013).

Pavement Manager at Risk in Construction of Hot Mix Asphalt

Pavement management is part science, part management, and part experience. After several decades of promoting pavement management, many road owners are still reluctant to use it as they lack the knowledge, the experience, or the confidence. The problem is further complicated by the emergence of a large list of new products and techniques that are self-proclaimed to achieve miracles but fall short. The outcome of this arrangement is that thousands of miles of roads still cost more to maintain than if effective pavement preservation techniques were used. This paper attempts to resolve this dilemma by introducing the role of Pavement Manager at Risk (PMAR), allowing a Pavement Manager to offer a long-term pavement preservation service to a client in return for a fixed per-mile premium. This allows the knowledgeable Pavement Manager, who would typically be a Pavement Engineer or a practitioner with extensive knowledge and experience, to implement effective pavement preservation techniques and share the economic benefit with the owner. In this study, the responsibilities of the Pavement Manager at Risk (PMAR) will be introduced. The type of analysis it needs to run will be demonstrated in a case study. In this paper, a sample analysis is presented to present the financial aspects of managing a network of local roads. Pavement treatment cost, pavement condition, and treatment life extension in addition to the admin, mobilization, striping, and occasional patches expenses are presented. The benefits and risks of this approach are described.

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%.

Effects of Short-Term Aging on Asphalt Binders and Hot Mix Asphalt at Elevated Temperatures and Extended Aging Time

The production process of Hot Mix Asphalt (HMA) causes a short term aging (STA) to asphalt binder due to the heating of both asphalt binder and aggregates before mixing together. Laboratory protocols are followed to simulate the STA conditions for both asphalt binders and asphalt mixtures. STA protocols expose asphalt binders or asphalt mixtures to specific aging temperature for a specific period of time to produce stiffening that is similar to that of actual production conditions. Successful construction of HMA in cold season/regions may require elevating the production temperature of HAM to achieve proper compaction of HMA layers. Producing HMA mixtures at elevated temperatures may cause further increase in the binder stiffness and negatively affect the future field performance of asphalt pavements. This negative affect can be even worse especially if it is coupled with extended exposer time increase. This study aims to investigate effect of elevated production (mixing and STA) temperatures and exposure time on the stiffening of binders and asphalt mixtures. The binder experiment involved aging of two Performance Graded (PG) binders (PG 76-16 and PG 64-22) at two different temperatures and aging durations. The asphalt mixture experiment involved the STA of asphalt mixtures produced in the laboratory at mixing and STA temperatures 25°F above standard practice and aging time 2 and 4 hours longer than standard practices. The effect of different aging times and temperatures was investigated by running viscosity tests on binders and dynamic modulus |E*| and Indirect Diametrical Strength (IDT) tests on asphalt mixtures. The results showed that increasing the mixing and STA temperatures by 25°F seems to have no significant effect on the asphalt mixture properties while doubling the standard STA time seems to have a significant effect on binder and asphalt mixture properties.

Quantitative analysis of functional polymer in recycled tyre rubber used in modified asphalt binders

Ground tyre rubber (GTR) has been employed to modify asphalt binders used in hot-mix asphalt construction since the early 1960s. Proper formulation of GTR-modified asphalt binders provides for substantial improvement in performance over conventional asphalt binders, while providing an outlet for disposal of waste tyres. Physical characteristics of GTR are considered to be vital to the final performance of the asphalt paving mixture, with some state agencies specifying chemical composition requirements for GTR used in binder modification. Adequate analysis and understanding of the functional polymer content, polymer available in GTR to improve asphalt binder properties, and other chemical characteristics of GTR remain lacking. Thermogravimetric analysis (TGA) is a method used to measure the change in mass of a material measured as a function of temperature or time facilitating acquisition of information on properties of the material and its composition. This paper introduces an instrumental TGA method to analyse recycled tyre rubber, also known as ground tyre rubber or GTR, for better understanding and quantification of the functional polymer content, as well as general chemical characteristics, of GTR used to modify asphalt binders.

Volatile Organic Compounds Generated in Asphalt Pavement Construction and Their Health Effects on Workers

Hot mix asphalt (HMA) is a major construction material used for building roads, airport runways, and parking lots. During HMA construction, a massive amount of volatile organic compounds (VOCs) is emitted from the hot asphalt mixtures, creating a potential health risk to on-site workers. Few studies have quantitatively investigated the constituents and potential health effects of the VOCs generated in HMA pavement construction. This paper presents the results of a study in which air samples were collected at multiple locations and time points of several projects during HMA pavement construction and were subsequently characterized for their chemical compositions and concentrations by using gas chromatography/mass selective detector (GC/MSD). The analysis results are compared with occupational exposure limits mandated or recommended by various agencies. Although the individual concentrations of the identified chemicals were found to be below various exposure limits, their collective effect on human health remains unknown and may not be ignored. This paper contributes to the knowledge of the types and concentrations of VOCs generated in asphalt pavement construction, their potential health risks to workers, and possible mitigation measures.

Using MEPDG to Develop Rational Pay Factor for Hot Mix Asphalt Construction

Most highway agencies are using subjective measures to rate the quality of construction projects. The main purposes of rating the contractor performance are for qualification, bidding, or payment schedules. The pay factor (PF) can be defined as a multiplication factor that is often used to determine the contractor pay for the unit of work. The objective of this paper is to propose a rational methodology for defining PF based on basic understanding of the effect of different hot mix asphalt parameters on pavement life. Mechanistic- Empirical Pavement Design Guide (MEPDG) software is used to find the effect of different variables on pavement life. Three main factors considered in pay factor equation for their effect on pavement life:air voids, asphalt content, and percent passing sieve # 200 (P200). The pavement lifebased on the fatigue and rutting failure criteriaare used in the PF model to reflect actual contractor performance.The developed PF model was implemented on a case study.

Laboratory evaluation of the effects of short-term oven aging on asphalt binders in asphalt mixtures using HP-GPC

Both the RTFO (rolling-thin film oven) aging of asphalt binders and the STOA (short-term oven aging) of asphalt mixtures are designed to simulate aging during the construction of hot mix asphalt (HMA) pavements. Many studies have been conducted evaluating the aging effects on asphalt binders since their properties can be easily measured using many conventional tests, such as rotational viscometer, DSR (dynamic shear rheometer), and BBR (bending beam rheometer). However, studies on asphalt mixture aging have been limited to mechanical properties such as strength and fatigue characteristics because considerable effort is required to identify the aging of the asphalt binder in a mixture. This study evaluated the effects of short-term oven aging on asphalt mixtures using the GPC (gel-permeation chromatography) procedure. Nine asphalt mixtures, using three different binder sources, were prepared and five short-term aging methods were used to evaluate these mixes. For comparison, the RTFO aging was also conducted for nine asphalt binders. The aging of a binder within asphalt mixtures, including polymer-modified mixtures, could be identified under various short-term aging conditions. Statistical analysis of the GPC test results indicated that two commonly used short-term aging methods in the laboratory, a 154 °C oven aging for 2 h and a 135 °C oven aging for 4 h, are not significantly different, based on the increase in the large molecular size (LMS) ratios. The RTFO aging method was found to have less effect on binder aging than the short-term oven aging methods of asphalt mixtures.

Thermal Imaging of Hot-Mix Asphalt Paving Projects in Connecticut

Results of a study on thermal segregation of hot-mix asphalt (HMA) during pavement construction are presented. The significance of thermal segregation to pavement performance should not be overvalued, because it is not only possible but probable that other factors play more significant roles. For example, the idea is presented that density achieved is more dependent on HMA temperature (T) than temperature differentials (ΔT). It is surmised that thermal segregation has a negligible effect until cold-area temperatures drop below certain threshold values. This reasoning is based on results of a 5-year pavement condition survey that demonstrated little, if any, relationship between temperature differentials located with an infrared camera during HMA construction and subsequent damage to a pavement's surface. Although 5 years may be too short a period for some distresses to develop, extensive reflective cracking was observed at some locations; this demonstrates reflective cracking played a more prominent role than ΔT. Comparisons of asphalt contents and grain-size distributions between cold areas and their surrounding normal-temperature pavements demonstrated no significant differences, suggesting that temperature differentials in HMA during construction are not necessarily indicative of particle segregation. Finally, definitions for the terminology associated with HMA construction and infrared thermography are presented.

Selection of Optimum Gravel Aggregate Size to Resist Permanent Deformation in Hot-Mix Asphalt

Siliceous river gravels form a significant fraction of the different types of aggregates used in the construction of hot-mix asphalt (HMA) pavements. Even after gravel particles are crushed into smaller-size fractions, a significant proportion of the larger-size fractions retain their original shape and surface texture. As a result, HMA with a larger nominal maximum aggregate size (NMAS) has a higher percentage of rounded and low-angularity particles, which might make it more susceptible to rutting. Using a smaller NMAS may decrease the percentage of rounded and angular aggregates in the mix, but potentially at the expense of loss in shear strength of the mix. This study evaluated the effect of increasing aggregate angularity by decreasing NMAS on the rutting potential of HMA mixes containing siliceous gravels. Nine mix designs composed of three different NMASs and siliceous aggregates from three different sources were included in this study. The percentage of rounded and angular aggregates in each mix was quantified using image analysis and crushed-face count. The rutting potential of HMA mixes was assessed on the basis of Hamburg, dynamic modulus, flow time, and flow number tests. Results verify that a decrease in NMAS results in a decrease in the percentage of rounded and angular aggregates. However, rutting performance improves initially with a decrease in NMAS but then decreases; this indicates an optimum size that maximizes the rut resistance of HMA with siliceous aggregates. Results from this study are especially useful in selecting an optimum aggregate size for HMA mixes in locations where river gravels are the main source of locally available aggregates.

Selection of Optimum Gravel Aggregate Size to Resist Permanent Deformation in Hot-Mix Asphalt

Siliceous river gravels form a significant fraction of the different types of aggregates used in the construction of hot-mix asphalt (HMA) pavements. Even after gravel particles are crushed into smaller-size fractions, a significant proportion of the larger-size fractions retain their original shape and surface texture. As a result, HMA with a larger nominal maximum aggregate size (NMAS) has a higher percentage of rounded and low-angularity particles, which might make it more susceptible to rutting. Using a smaller NMAS may decrease the percentage of rounded and angular aggregates in the mix, but potentially at the expense of loss in shear strength of the mix. This study evaluated the effect of increasing aggregate angularity by decreasing NMAS on the rutting potential of HMA mixes containing siliceous gravels. Nine mix designs composed of three different NMASs and siliceous aggregates from three different sources were included in this study. The percentage of rounded and angular aggregates in each mix was quantified using image analysis and crushed-face count. The rutting potential of HMA mixes was assessed on the basis of Hamburg, dynamic modulus, flow time, and flow number tests. Results verify that a decrease in NMAS results in a decrease in the percentage of rounded and angular aggregates. However, rutting performance improves initially with a decrease in NMAS but then decreases; this indicates an optimum size that maximizes the rut resistance of HMA with siliceous aggregates. Results from this study are especially useful in selecting an optimum aggregate size for HMA mixes in locations where river gravels are the main source of locally available aggregates.

Thermal Imaging of Hot-Mix Asphalt Paving Projects in Connecticut

Results of a study on thermal segregation of hot-mix asphalt (HMA) during pavement construction are presented. The significance of thermal segregation to pavement performance should not be overvalued, because it is not only possible but probable that other factors play more significant roles. For example, the idea is presented that density achieved is more dependent on HMA temperature (T) than temperature differentials (ΔT). It is surmised that thermal segregation has a negligible effect until cold-area temperatures drop below certain threshold values. This reasoning is based on results of a 5-year pavement condition survey that demonstrated little, if any, relationship between temperature differentials located with an infrared camera during HMA construction and subsequent damage to a pavement's surface. Although 5 years may be too short a period for some distresses to develop, extensive reflective cracking was observed at some locations; this demonstrates reflective cracking played a more prominent role ...

Control of Superpave Gyratory Compactor's Internal Angle of Gyration: Experience of the Utah Department of Transportation

The State of Utah Department of Transportation started a program to use the dynamic angle validator (DAV) to measure the internal angle of all Superpave® gyratory compactors (SGCs) used in the construction of hot-mix asphalt in the state. Results show that differences in internal angle exist unless the compactors are calibrated regularly and technicians are trained in laboratory procedures. Once the program was in place, the internal angle of 36 of the 46 SGCs tested was within the limits of 1.16° ± 0.03°. However, seven SGCs, all of one model, had angles between 0.860° and 1.212°, with an average angle of 1.026° even after calibration. If the limits are narrowed to 1.16° ± 0.02°, then only 28 of 46 (60%) of the SGCs will be within the range. Results also show that it is possible to obtain acceptable density values on specimens compacted using machines that have internal angles outside the proposed range. It was concluded that the internal angle limits of 1.16° ± 0.03° were too restrictive for the machine...

Control of Superpave Gyratory Compactor's Internal Angle of Gyration

The State of Utah Department of Transportation started a program to use the dynamic angle validator (DAV) to measure the internal angle of all Superpave® gyratory compactors (SGCs) used in the construction of hot-mix asphalt in the state. Results show that differences in internal angle exist unless the compactors are calibrated regularly and technicians are trained in laboratory procedures. Once the program was in place, the internal angle of 36 of the 46 SGCs tested was within the limits of 1.16° ± 0.03°. However, seven SGCs, all of one model, had angles between 0.860° and 1.212°, with an average angle of 1.026° even after calibration. If the limits are narrowed to 1.16° ± 0.02°, then only 28 of 46 (60%) of the SGCs will be within the range. Results also show that it is possible to obtain acceptable density values on specimens compacted using machines that have internal angles outside the proposed range. It was concluded that the internal angle limits of 1.16° ± 0.03° were too restrictive for the machines and types of mixes used in the state of Utah. It was recommended that the equipment be calibrated often, that molds be checked for cleanliness and dents, and that temperature measuring devices be verified. When large differences in measured properties of compacted samples remain even after repeated calibration, the internal angle should be verified because it was noted that external calibration did not always correct the internal angle. That will help reduce conflict between state labs and consultants.