The underlying purpose of any pavement is to provide a safe, smooth and reliable surface for the intended users. In the case of hot mix asphalt (HMA) pavements, this includes producing a surface that is resistant to the principal HMA distress types: permanent deformation (or rutting) and fatigue damage (or cracking). To protect better against these distress types, there have recently been changes in HMA mixture design practice. These changes have had the positive effect of producing more damage resistant mixtures but have also had the effect of producing mixtures that require more compaction effort to obtain required densities. It is important to understand what properties of an HMA mixture contribute to their compactability. This study presents analysis of the correlation between HMA mixture properties and laboratory compaction parameters for the purpose of predicting compactability. Mixture property data were measured for a variety of mixtures; these mixtures were compacted in the laboratory and compaction parameters were collected. A statistical analysis was implemented to correlate the mixture data to the compaction data for the purpose of predicting compactability. The resulting model performs well at predicting compactability for mixtures that are similar to the ones used to make the model, and it reveals some mixture properties that influence compaction. The analysis showed that the binder content in an HMA mixture and the slope of the aggregate gradation curve are important in determining the compactability of a mixture.

The effects of using alkali-silica reaction (ASR) affected recycled concrete aggregate (ASR-RCA) in hot mix asphalt (HMA) were investigated in this study. Dilatometer and modified beam tests were performed to determine the possibility of new ASR occurring in reactive aggregates within the HMA or re-expansion of existing gel. The Lottman test and micro-calorimeter were used to determine the moisture susceptibility of HMA made with ASR-RCA. A differential scanning calorimeter (DSC) with thermogravimetric analysis (TGA) was used to evaluate the drying of an artificial gel and x-ray diffraction (XRD) was used to check for the potential presence of gel in the filler fraction of the ASR-RCAs. Micro-deval and freeze-thaw tests were evaluated for their potential to indicate the presence of excess micro-cracks or ASR gel. Expansion testing indicated that both ASR-RCAs were still reactive with 0.5 N NaOH solution saturated with calcium hydroxide (CH) at 60 degrees C. Dilatometer testing of HMA specimens in NaOH CH solution at 60 degrees C indicated a reaction between the asphalt binder and the solution, but little, if any, ASR. The lack of expansion in the modified beam test supports the binder-solution interaction. However, dilatometer testing in deicer solution at the same temperature indicated that some ASR may have occurred along with the primary binder-solution interaction. The volume change characteristics associated with the binder-solution interaction with and without ASR was supported by the change in pH and alkali concentration of the test solution. DSC/TGA testing indicated that the artificial gel dehydrated at approximately 100 degrees C. XRD analysis of the filler indicated that some gel may have accumulated in this fraction. Moisture damage testing indicated good resistance to moisture damage by HMA mixtures made with ASR-RCA especially compared to a virgin siliceous aggregate. Micro-deval and freeze-thaw tests can detect the presence of micro-cracks due to ASR in ASR-RCAs as higher mass loss than the virgin aggregate. The potential distress mechanisms that may occur when using ASR-RCA in an HMA pavement were identified. Results obtained using accelerated laboratory conditions were extrapolated based on anticipated field conditions. Guidelines for the mitigation of potential distresses in HMA made with ASR-RCA are presented.

The permeability of hot mix asphalt (HMA) is of special interest to engineers and researchers due to the effects that water has on asphalt pavement performance. Significant research has been done to study HMA permeability. However, most of the studies primarily focused on relating permeability to the average percent air voids in the mix. Such relationships cannot predict permeability accurately due to the different distributions of air void structures at a given average percent of air voids. Air void distribution is a function of many factors such as mix design, compaction method, and aggregate properties. Recent advances in X-ray computed tomography and image analysis techniques offer a unique opportunity to better quantify the air void structure and, consequently, predict HMA permeability. This study is focused on portraying permeability as a function of air void size distribution by using a probabilistic approach that was previously developed by Garcia Bengochea for soils. This approach expresses permeability as a function of the probability density function (pdf) of the air void size distribution. Equations are derived in this thesis to describe this relationship for laboratory specimens compacted using the linear kneading compactor (LKC) and Superave^TM gyratory compactor (SGC) as well as for field cores (labeled as MS). A good correlation exists between permeability and the pdf of the air voids that formed the flow paths (i.e. connected voids). The relationship between moisture damage, air void structure, and cohesive and adhesive bond energy is also investigated in this study. Moisture damage is evaluated by monitoring changes in mechanical properties due to moisture conditioning. The influence of air void structure on pore pressure is studied using a recently developed program at Texas A&M University that simulates fluid flow and pore pressure in a porous medium. The surface free energy of the aggregates and asphalt are calculated from laboratory measurements using the Universal Sorption Device (USD) and the Wilhelmy Plate method, respectively, in order to test the compatibility of the aggregates with the asphalt in the presence of water.

Moisture induced damage of hot mix asphalt pavements has a significant economic impact in terms of excessive maintenance and rehabilitation costs. The moisture sensitivity of an asphalt mix depends on the combined effects of material properties, mixture design parameters, loading conditions and environmental factors. Traditional methods to assess moisture sensitivity of asphalt mixes rely on mechanical tests that evaluate the mix as a whole. These methods do not measure material properties and their role in moisture sensitivity of the mix independently. This information is very important to select materials resistant to moisture induced damage, or to modify locally available materials to improve their resistance to moisture damage for economic reasons. The objective of this research is to develop experimental and analytical tools to characterize important material properties that influence the moisture sensitivity of asphalt mixes. Quality of adhesion between the aggregate and bitumen binder in wet and dry conditions plays an important role on the moisture sensitivity of the asphalt mix. A part of this research work was to develop the Wilhelmy plate method and the Universal Sorption Device to measure the surface free energy components of the bitumen and aggregate with adequate precision and accuracy, respectively. Surface energy of these materials was used to identify parameters based on thermodynamics that can quantify their interfacial adhesion and propensity to debond in the presence of water. The thermodynamic parameters were shown to correlate well with the moisture sensitivity of asphalt mixes determined from laboratory tests. Specific surface areas of the aggregates were also used to account for the influence of mechanical interlocking at the micro scale. In some mixes, chemical bonding also contributes to the adhesion between bitumen and aggregate. The use of a micro calorimeter was introduced in this research as a versatile and fast tool to quantify the combined effects of physical and chemical adhesion between these materials.

Today, a large quantity of waste is generated from the replacement of residential and commercial roofs. Many of the roofs being upgraded with previously constructed from asphalt shingles. Recycled Asphalt Shingles (RAS) contain nearly 30% of asphalt cement by mass, which can be a useful additive to asphalt pavements. In addition, shingles can offer significant potential savings through recycling and recovery as a construction material in flexible pavement. Currently, one and a half million tons of roofing shingle waste is generated each year in Canada related to the replacement of residential and commercial roofs and 90% of this valuable material is sent to landfills. If engineered properly, the addition of RAS into Hot Mix Asphalt (HMA) can provide significant benefits. The University of Waterloo’s Centre for Pavement and Transportation Technology (CPATT) is committed to working with public and private sector partners to develop sustainable technologies for the pavement industry. Using RAS in HMA can lead to economical, environmental and social benefits. Examples of which are reduced waste going to landfills and a reduction in the quantity of virgin material required. This research has involved the Ontario Centres of Excellence (OCE) and Miller Paving Limited. It was conducted to evaluate the performance of HMA containing RAS in both field and laboratory tests. A varying percentage of RAS was added to six common Ontario surface and binder layer of asphalt mixes. The intent was to determine if RAS could be added to improve performance and provide longer term cost savings. Laboratory testing was performed to evaluate the mix behavior. The elastic properties, fatigue life and resistance to thermal cracking were all evaluated at the CPATT laboratory. The characteristics of the mixes were evaluated by carrying out Dynamic Modulus, Resilient Modulus, Flexural Fatigue and Thermal Stress Restrained Specimen Test (TSRST) tests following American Association of State Highway and Transportation Officials (AASHTO) and American Society for Testing and Materials (ASTM) standards. Field test sections were constructed from HMA containing RAS to monitor the pavement behavior under natural environmental and traffic loading conditions. Evaluation of the field sites was performed using a Portable Falling Weight Deflectometer (PFWD) and carrying out distress surveys following the Ministry of Transportation Ontario (MTO) guidelines. The results to date show the sections performing very well with minimal to no distress developing. The results of the laboratory testing and field performance evaluations have shown encouraging results for the future use of RAS in HMA. If RAS can properly be engineered into HMA it can be a useful additive in both the surface and binder layers of the flexible pavement structure. Ultimately, the use of RAS in HMA can provide both an environmentally friendly and cost effective solution to the Ontario paving industry.

Warm mix asphalt (WMA) technology has now been successfully used in Ontario for a few years. This shift in usage relates to extensions in construction season, reduced emissions, larger compaction windows, and potential fuel savings. This research between Miller Paving Ltd. and the Centre for Pavement and Transportation Technology attempts to better quantify the difference in hot mix asphalt (HMA) and WMA. The object of this study was three-fold. The first part of the research was to examine the strength characteristics of HMA and WMA as a function of storage time. The purpose of this evaluation was to quantify indirect tensile strength (ITS) and moisture susceptibility of HMA and WMA over time. The second objective involved evaluating the performance characteristics of HMA and WMA. Resilient modulus and dynamic modulus testing were completed on plant-produced HMA and WMA material, which was used to determine long-term performance properties of both mixes. The third and final objective of this study was an economic analysis performed to determine the difference in cost for construction and maintenance for the HMA and WMA pavements. This was completed to determine if the cost of the warm mix technology used in the production of the WMA was offset by fuel savings at the plant. The findings of the research included: • HMA and WMA had statistically equivalent air voids over a four-week storage period. • Dry and wet ITS results for the WMA increased over a four-week storage period while the HMA specimens did not show this same increase. • WMA material had slightly better workability than the HMA material although the values were statistically equivalent. • WMA mix had higher resilient modulus values than the HMA mix. • Dynamic modulus testing showed that at high temperatures, WMA showed to be slightly more susceptible to rutting than the HMA mix, and at lower temperatures, the HMA showed to be slightly more susceptible to fatigue cracking than the WMA mix. • The MEPDG showed that both the HMA and WMA pavements were deemed to be structurally adequate. • An economic analysis of the HMA and WMA pavements compared a life cycle cost analysis over a 20-year design life which included all costs associated with construction, maintenance, and rehabilitation of both the HMA and WMA and showed that the HMA was slightly more cost effective than the WMA. • A field trial was performed by Miller Paving Limited on Highway 62 in Madoc, Ontario showed that the WMA material was more effective at maintaining the temperature of the asphalt mixture during long hauling distances. • Overall the WMA exhibited the same performance properties as the HMA.

Due to the 15-20 year life span of roofing shingles, 1.5 million tonnes of asphalt roofing shingles are being demolished and replaced annually in Canada from both residential and commercial facilities. These roofing shingles are manufactured from very high quality materials which are considered a valuable by-product. Recycled Asphalt Shingles (RAS), a product containing approximately 30% asphalt cement by mass, is a valuable additive to Hot Mix Asphalt (HMA) pavements and a potential savings for the construction industry. Recycling of demolished asphalt shingles is a significant new step forward in abating the need to put the waste into landfills. This re-use creates a great opportunity in reducing materials being dumped at landfills while providing an additive to HMA mixtures for paving. Therefore, this leads to economic, environmental, and social benefits for all the stakeholders and road users such as reduced need for landfill space, conservation of virgin materials and environment, and financial saving. The research involved evaluating the use of demolished shingles in six typical Ontario Hot Mix Asphalt (HMA) mixtures; HL 3 (1.5% RAS, 13.5% RAP), binder layer mixes SP19 (6% RAS, and 3% RAS, 25% RAP), surface layer mixes SP12.5 FC 1(3% RAS, 17% RAP) and SP12.5 FC2 (6% RAS and 3% RAS, 12% RAP). The six HMA mixes were also designed to contain Recycled Asphalt Pavement (RAP). This further complicated the research as both RAP and RAS were added. All mixes were designed and tested at CPATT laboratory; in addition a test section was paved at the CPATT Test Track. This research involved both laboratory and field evaluations of mixes containing RAS to develop pavement performance modeling for all six mixes using the updated Mechanistic-Empirical Pavement Design Guide (MEPDG). A life-cycle assessment of the six HMA mixes was performed to quantify the environmental impacts using the Pavement Life-Cycle Assessment Tool for Environmental and Economic Effects (PaLATE) and rigorous economic costs/benefits were assessed using Life Cycle Cost Analysis (LCCA). Calibrations of models for Ontario conditions were completed. Test slabs were also constructed to simulate climatic changes by running freeze-thaw cycles based on weather data over the past ten years. Three field test sections located in the Town of Markham and one at the CPATT Test Track were monitored and assessed under as part of the research. Regular pavement condition assessments were carried out on all the test sections by performing non-destructive tests using a Portable Falling Weight Deflectometer (PFWD) and distress survey in accordance with the Ministry of Transportation (MTO) guidelines. The CPATT Test Track was evaluated with both the PFWD and surface distresses, whereas only distress surveys were performed on the three residential streets in the Town of Markham. The evaluations demonstrated that the pavements were in good conditions throughout the monitoring period of the research (four years for the three residential streets in the Town of Markham and two years for the CPATT Test Track). The structural analysis using the MEPDG indicated that Mix 3: SP19 3% RAS and 25% RAP had the best performance followed by Mix 2: SP19 6% RAS when considering all factors in the Life-Cycle Assessment. Mix 3 exhibited maximum savings on environmental emissions, energy and water usage, best adoptability to climatic change and skid resistance properties with minimal life cycle costs. The pavement performance and life-cycle assessment modeling demonstrated encouraging results for the use of RAS in HMA pavements from which guidelines were developed for its use. It is important to note that careful mix design should be carried out when RAS is added to HMA especially when RAP is also used. This includes measuring of all key properties especially at low and high temperatures. In short, RAS can be a valuable additive in both surface and binder layers of HMA pavements. It provides an environmentally friendly and cost-effective innovation for the Ontario paving industry and can be considered for usage elsewhere with appropriate engineering.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 114-117)

Dissertation (Ph.D.)--Auburn University, 2005. / Abstract. Includes bibliographic references (p.82-87).

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.183-191).