Kamilla L. Vasconcelos

A Framework to Quantify the Effect of Healing in Bituminous Materials using Material Properties

ABSTRACT Significant evidence exists in the literature that healing has a substantial effect on the performance of asphalt mixtures and therefore asphalt pavements. The incorporation of the healing mechanism in tandem with the crack growth mechanism is necessary for comprehensive modeling of the fatigue or fracture processes in asphalt mixtures. This paper presents a new framework that combines material and mechanical properties of the bitumen to predict the effect of healing on mechanical properties and performance of the asphalt mixture. This framework is based on an analytical approach that will allow it to be incorporated with future analytical models of crack growth and damage. The paper also presents a new test method using the dynamic shear rheometer to obtain some of the material properties related to the healing mechanism that are required in the proposed framework. Results from preliminary tests conducted on selected materials support the hypothesis used in the development of the framework and the DSR based test method.

Surface Free Energy to Identify Moisture Sensitivity of Materials for Asphalt Mixes

Conventional methods to quantify the moisture sensitivity of asphalt mixtures are based on the comparison of mechanical properties of the mix before and after a moisture-conditioning process. Although this approach consolidates the effect of material and mixture properties on moisture sensitivity, it does not identify the causes responsible for the poor or good performance of the mixture. In this study, surface free energy of asphalt binders and aggregates was used to derive energy parameters that quantify the moisture sensitivity of various combinations of materials. The moisture sensitivity of 12 asphalt mixtures carefully designed to represent a wide range of asphalt-aggregate interactions was measured in the laboratory under controlled conditions. Test results indicate that the moisture sensitivity of these mixtures correlates well with the energy parameters, which are based on the surface energy properties of the constituent materials. Incorporating the specific surface area of the aggregate into the energy parameters improved this correlation. The proposed energy parameters have the potential to serve as an effective tool by which to select material combinations that result in asphalt mixtures that are more resistant to moisture-induced damage.

Experimental Measurement of Water Diffusion through Fine Aggregate Mixtures

The water diffusion attributable to concentration gradients is among the main mechanisms of water transport into the asphalt mixture. The transport of small molecules through polymeric materials is a very complex process, and no single model provides a complete explanation because of the small molecule’s complex internal structure. The objective of this study was to experimentally determine the diffusion of water in different fine aggregate mixtures (FAM) using simple gravimetric sorption measurements. For the purposes of measuring the diffusivity of water, FAMs were regarded as a representative homogenous volume of the hot-mix asphalt (HMA). Fick’s second law is generally used to model diffusion driven by concentration gradients in different materials. The concept of the dual mode diffusion was investigated for FAM cylindrical samples. Although FAM samples have three components (asphalt binder, aggregates, and air voids), the dual mode was an attempt to represent the diffusion process by only two stages ...

History dependence of water diffusion in asphalt binders

Despite the importance of hysteresis of water diffusion in polymeric materials, only limited literature is available on this subject. The FT-IR-ATR spectroscopy technique was used to investigate the effect of cycling moisture boundary conditions on the diffusivity of moisture of three asphalt binders. Each sample passed through three hydration cycles and two dehydration cycles. The existence of hysteresis of moisture diffusivity in asphalt binders is validated. The increase in moisture diffusivity is primarily attributed to the change in microstructure of the asphalt binder after being exposed to moisture. This is supported by atomic force microscope images of asphalt binder before and after exposure to water. Evidence to an increase of water trapped in the form of vapour even after dehydration was observed, and this may also contribute to the increase in diffusivity. This topic is still under investigation by this research group.

Influence of Reduced Production Temperatures on the Adhesive Properties of Aggregates and Laboratory Performance of Fine Aggregate-Asphalt Mixtures

ABSTRACT Several new technologies have made production of hot mix asphalt (HMA) possible at lower temperatures by reducing binder viscosity and increasing mixture workability. The asphalt mixture produced using this technology is referred to as warm mix asphalt (WMA). In this study, three aggregates and two asphalt binders were used with a synthetic zeolite to produce six different types of Fine Aggregate Matrix (FAM), that were prepared at three different mixing and compaction temperatures. The first objective of this study was to evaluate the impact of reducing mixing and compaction temperatures on the mechanical behavior of these mixtures using the Dynamic Mechanical Analyzer (DMA). Secondly, the micro calorimeter was used to measure the total energy of adhesion (TEA) between the asphalt binder and aggregates treated at different temperatures. Results from the DMA indicate that shear modulus and fatigue cracking resistance of the FAM typically decreased when the mixing and compaction temperatures were reduced. TEA results indicate that residual moisture on aggregate surfaces at reduced mixing temperatures does not contribute significantly to the observed reduction in the mechanical results at lower mixing temperatures.

Measurement of Water Diffusion in Asphalt Binders Using Fourier Transform Infrared-Attenuated Total Reflectance

The presence of moisture in asphalt mixtures deteriorates their structural integrity. Moisture also acts as a catalyst to promote other forms of pavement distresses. Two critical factors influence the rate and intensity of moisture-induced damage: (a) the speed of moisture transport within the asphalt mixture and binder and (b) the influence of moisture on the cohesive and adhesive properties of the constituent materials. Quantifying these factors is essential to understand, model, and mitigate moisture-induced damage in asphalt mixtures. The experimental and analytical procedures used to measure diffusivity of the asphalt binder are presented. Fourier transform infrared–attenuated total reflectance spectroscopy was used to monitor the diffusion of water into thin films of asphalt binder. The diffusion process was characterized by changes in the portions of the spectra that correspond to the presence of water. Two models were used to fit the data obtained: a diffusion model that followed Ficks second law and a dual mode diffusion model with two diffusion coefficients (D1 and D2) and weighting factor X1. Four asphalt binders were evaluated (AAB, AAD, AAF, and ABD), and all presented better fitting under the dual mode diffusion. Diffusivities of asphalt binders AAB, AAD, and AAF were statistically similar, but diffusivity of asphalt binder ABD was different from that of the others.

Laboratory and field evaluation of cold recycling mixture with foamed asphalt

Cold recycling with foamed asphalt stabilisation has been gaining acceptance and growing steadily. This study evaluates the performance of cold recycled mixes stabilised with foamed asphalt, with respect to the effects of confining stresses, and material moisture content. An experimental test section with a foamed stabilised recycled material used as the base course was monitored through quality control and quality assurance and falling weight deflectometer (FWD) tests. In laboratory, indirect tensile strength, triaxial resilient modulus, and permanent deformation tests were performed. Based on the results obtained, one can conclude that the curing is a critical consideration in terms of timing and its influence on pavement performance. Triaxial tests showed the stress dependency of this bitumen-stabilised material, while permanent deformation results indicated some potential for damage in early stages after construction. On the field evaluation, FWD data indicated the decrease in deflection with time, as a result of the increase in the layers stiffness.

Field Aging Evaluation of Asphalt Binders by Chemical and Rheological Characterization

Two field aged asphalt binders were evaluated in the study. The binders were extracted and recovered from samples that were collected from two 4 cm HMAs in the field at different times. Chemical and rheological tests were performed to quantify the aging. The binder’s chemical properties were evaluated by SARA fractions (saturates, asphaltenes, resins and aromatics), gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The rheological tests were carried out in a dynamic shear rheometer (DSR). Dynamic shear modulus (|G*|) and multiple stress creep and recovery (MSCR) tests were performed to evaluate the change in the binders rheological properties. Both chemical and rheological results confirm the continuous aging of the asphalt binder in the field, mostly up to 24 months after construction, although the greatest aging occurs during mixing. Rheological results indicated that after 36 months of field aging, the two binders were performed similarly even though they aged differently.

Aging Characterization of Biobinder Produced from Renewable Sources

This study aims to investigate the effect of the temperature in the aging of a biobinder obtained from vegetal source. In this sense, the Rolling Thin Film Oven Test test was performed according to the ASTM D2872 (2012), considering the standard test temperature (163 °C) and two others test temperatures (150 °C and 180 °C). The unaged and aged binders (Neat Asphalt Binder, AC 30/45, and the biobinder) had their rheological and chemical properties analyzed. Under the same aging conditions, it was found that the biobinder was more susceptible to aging than the neat asphalt binder (AC 30/45). Regarding the biobinder aged under different conditions, the incremental RTFOT temperature presented some beneficial aspects to high-temperature performance; however, it might compromise the performance at intermediate temperature which can be inferred from fatigue tests. Chemical results indicated that the carbonyl and sulphoxide indexes were not adequate for the analysis of the oxidation and aging of the biobinder.

Highly Modified Asphalt Binder for Asphalt Crack Relief Mix

Reflective cracking is a common issue with respect to rehabilitated asphalt pavements, especially when the rehabilitation is done by applying a hot-mix asphalt overlay on the existing damaged pavement. Several approaches can be adopted to delay reflective cracking. They include an increase of the overlay thickness and the use of a stress relief asphalt mixture (SRAM), which is a fine-graded, flexible, and thin asphalt interlayer. Because the efficiency of a SRAM is highly related to the properties of the asphalt binder used in the mixture, it is of interest to use a highly modified asphalt (HiMA) binder. This paper describes a field test comprising three sections at BR-116 (a heavily trafficked highway in Brazil). One of the rehabilitation strategies used for a cracked asphalt pavement was a 2.5-cm SRAM (produced with a HiMA binder) and 5-cm styrene–butadiene–styrene (SBS) hot-mix asphalt (HMA). The other two strategies were to apply SBS HMA overlays of different thicknesses (7.5 cm and 10.5 cm). The aim was to evaluate and compare the capability of these solutions to control reflective cracking. Rheological properties and multiple stress creep and recovery tests were performed on the asphalt binders, and the semicircular bending test was performed on the asphalt mixtures. The surface conditions were monitored, and the results for each section were compared. After a 29-month period, the section that received the interlayer had the lowest cracked area and showed better resistance than the overlays did to reflective cracking and better maintenance of the original thickness of the pavement.