Shih-Hsien Yang

Effect of Mineral Filler Characteristics on Asphalt Mastic and Mixture Rutting Potential

This study, part of the NCHRP 9–45 Project, analyzed the effect of mineral filler properties on asphalt mastic and the rutting potential of asphaltic mixture. The mineral filler properties were characterized by four tests: Rigden voids (RV), fineness modulus (FM), calcium oxide (CaO) content, and methylene blue value. The rheological properties of asphalt binder and mastic were characterized with the use of apparent viscosity and multiple stress creep recovery tests. Dynamic modulus and flow number tests were conducted to examine the asphaltic mixture rutting potential. The tested mixtures included several variables: four asphalt binder types, including virgin and polymer modified; two aggregate gradations; and a selected group of fillers. The study concluded that asphalt mastic performance was significantly affected by the fractional voids in the filler and possibly by the CaO content and FM. This effect, however, depended on binder type. On the one hand, the styrene–butadiene–styrene modified binder showed the strongest effect as a result of the mineral filler inclusion when tested as mastic. On the other hand, RV and CaO content showed relatively greater correlation with the mixture rutting potential, as compared with other filler properties. Addition of RV improved the prediction models for dynamic modulus and flow number. The effect of RV on the mixture rutting potential was more pronounced for the coarse mixture than for the fine mixture.

Validity of Asphalt Binder Film Thickness Concept in Hot-Mix Asphalt

Despite the possible benefits of implementing asphalt binder film thickness into current specifications to address durability problems, most of the related research has been theoretical and only a few attempts have been made to measure this property experimentally. The objective of this study was to investigate the concept of asphalt binder film thickness experimentally on the basis of measurements obtained by image analysis techniques, reflective light microscopy, and scanning electron microscopy. The results of the experimental program were used to gain insight into the concept of asphalt binder film thickness and its validity. Experimental results indicated that asphalt binder films coating large aggregates do not actually exist in hot-mix asphalt. Instead, what are referred to as asphalt binder films surrounding large aggregates are actually asphalt mastic films. These films are highly irregular in shape and have a thickness greater than 100 μm in the mixture considered in this study. The asphalt binder films in the mastic were observed at a thickness of 2 μm in the mixtures considered. However, these entities do not represent asphalt binder coatings around aggregates; they are only part of a blend with fine aggregates and mineral fillers. Microscopic analysis showed that air voids usually appear near the boundary between large aggregates and asphalt mastic.

Threshold Identification and Field Validation of Performance-Based Guidelines to Select Hot-Poured Crack Sealants

Hot-poured bituminous crack sealing has been widely accepted as a routine preventative maintenance practice. With proper installation, the sealing is expected to extend pavement service life by 3 to 5 years. However, current specifications for selection of crack sealants correlate poorly with field performance; hence, a set of new testing methods, based on sealant rheological and mechanical properties, was developed recently. Measurements of the mechanical properties of crack sealant at low temperatures are among the criteria introduced as part of the developed performance-based guidelines. The main purpose of this study was to identify and validate the low-temperature selection thresholds for the newly developed performance-based guidelines for selecting hot-poured bituminous crack sealants. In this study, selection criteria for crack sealant bending beam rheometer (CSBBR) and crack sealant direct tension tester (CSDTT) tests were identified. Two performance parameters for CSBBR test were used for the selection criteria: stiffness at 240 s and average creep rate (ACR). Both parameters were identified by comparing laboratory testing results with known sealant field performance, obtained from a long-term study in Canada. The selection criterion for the CSDTT test was extendibility, on the basis of field values reported in the literature. The recommended selection criteria were used to predict the field performance of 12 sealants evaluated by the National Transportation Product Evaluation Program (NTPEP). Results showed good correlation between the proposed selection thresholds and NTPEP field sealant performance.

Low-temperature characterization of hot-poured crack sealant by crack sealant direct tensile tester

The current specifications for selecting crack sealants correlate poorly with actual field performance. To address this issue and assist in predicting the low-temperature properties of hot-poured bituminous crack sealants, a modified direct tensile tester method has been developed. Sample geometry is modified to accommodate testing sealants. A sensitivity analysis considering various loading rates, sample lengths, and cross-section areas was conducted to define both optimized specimen geometry and testing protocol. Two types of sealants, having a wide range of rheological behaviors (one polymer-modified and one having crumb rubber), were tested at low temperature. Results showed that the rich polymer–modified sealant has a high resistance to failure compared with the sealant with crumb rubber–modified. Each sealant was tested at the lowest corresponding expected service temperature. A performance parameter, strain energy density, was proposed to differentiate crack sealant material in the laboratory.

Linear Viscoelastic Modeling for Hot-Poured Crack Sealants at Low Temperature

To understand the behavior of hot-poured bituminous-based crack sealants at low service temperatures and to predict their field performance, a constitutive stress-strain relationship must be described. This would allow predicting in situ crack sealant response to both thermal and traffic loading. This paper verifies the linear viscoelastic behavior of crack sealants. Ten sealants having high polymer contents were tested at −4 to −40°C using a Crack Sealant Bending Beam Rheometer (CSBBR). The convolution integral principle was used to obtain relaxation moduli from measured creep compliance data. A Prony series viscoelastic model was used to characterize mechanical behavior of crack sealant at low temperatures. The sealant’s linear response was checked by implementing two conditions of linearity described by Marasteanu and Anderson. Simulation for the sealant linear viscoelastic deflection response during the loading and unloading was conducted using a three-dimensional finite-element model. This study conc...

Preliminary Evaluation of Field Aging Characteristic of Warm Mix Asphalt

This study is aimed at evaluating the rate of long-term aging of WMA compared to conventional hot-mix-asphalt (HMA). A test section with recorded traffic and weather information was designated in this study. Field cores of two WMAs and one conventional HMA were taken from the field periodically. Both mix and binder properties of retrieved were measured in the laboratory. The resilient modulus and indirect tensile test were performed to characterize mixture properties. The rheological properties of extracted binder were measured by the dynamic shear rheometer (DSR) in order to obtain the complex shear modulus (G*) as well as the phase angle (δ) of binder with and without the WMA additives.