J.-F. Masson

Bitumen morphologies by phase-detection atomic force microscopy.

Bitumen is a complex mixture of hydrocarbons for which microstructural knowledge is incomplete. In an effort to detail this microstructure, 13 bitumens were analysed by phase‐detection atomic force microscopy. Based on morphology, the bitumens could be classified into three distinct groups. One group showed fine domains down to 0.1 µm, another showed domains of about 1 µm, and a third group showed up to four different domains or phases of different sizes and shapes. No correlation was found between the atomic force microscopy morphology and the composition based on asphaltenes, polar aromatics, naphthene aromatics and saturates. A high correlation was found between the area of the ‘bee‐like’ structures and the vanadium and nickel content in bitumen, and between the atomic force microscopy groups and the average size of molecular planes made of fused aromatics. The morphology and the molecular arrangements in bitumen thus appear to be partly governed by the molecular planes and the polarity defined by metallic cations.

Rapid FTIR method for quantification of styrene‐butadiene type copolymers in bitumen

The mid-IR molar absorptivity for polystyrene (PS) and polybutadiene (PB) blocks were obtained for five styrene-butadiene-styrene (SBS) and SB copolymers, including linear, branched, and star copolymers, and their blends with bitumen. The average absorptivity for PS and PB blocks was 277 and 69 L mol−1 cm−1 and it was little affected by the S/B ratio or the copolymer architecture. In the presence of bitumen, Beers law was obeyed but the respective PS and PB absorptivity was 242 and 68 L mol−1 cm−1, possibly because of weak interactions between the copolymer and bitumen. The absorptivity values were used to calculate the concentration of SB-type copolymers in blends with bitumen with an accuracy of 10% or better. The method can be used to probe the stability of bitumen–copolymer blends in storage at 165°C, to determine the copolymer concentration in commercial polymer modified bitumen (PMB), and to assess the resistance of PMB to weathering.

Low‐temperature bitumen stiffness and viscous paraffinic nano‐ and micro‐domains by cryogenic AFM and PDM

In an effort to better understand the structure and behaviour of bitumen in low temperature, we describe the first use of cryogenic atomic force microscopy and phase detection microscopy to characterize bitumen nano‐ and micro‐structures. The results were interpreted in light of glass transition temperatures (Tgs) for bitumen fractions. The domains visible by microscopy, the catana, peri and para phases, were attributed to domains rich in asphaltenes, naphthene and polar aromatics, and saturates, respectively. Between −10°C and −30°C, atomic force microscopy images revealed topographic features not visible in atomic force microscopy images acquired at room temperature. According to phase detection microscopy and Tgs, the features were assigned to viscous unfrozen saturates. Upon cooling to −72°C, unfrozen domains of 20–400 nm were observed. These domains were found in the paraphase rich in saturates and in the periphase rich in naphthene aromatics and polar aromatics. The findings indicate that new viscous domains form upon cooling to low temperatures owing to phase segregation, and that some bitumens are never entirely rigid in low temperatures.

Analysis of Bituminous Crack Sealants by Physicochemical Methods: Relationship to Field Performance

Bituminous crack sealants were analyzed by viscometry, fluorescence microscopy, infrared spectroscopy, thermogravimetry, modulated differential scanning calorimetry, and low-temperature tensile testing. The results indicate that sealants are blends of bitumen, oil, copolymer, and filler. Upon blending, these components produce a three-phase system that consists of a polymer-modified bitumen (PMB) matrix, a filler, and a filler-PMB interface. Spectroscopy and microscopy indicate that the PMB phase is rich in styrene-butadiene copolymer, that the filler is recycled rubber, sometimes mixed with calcium carbonate, and that the interface depends on the filler and the oil content in the sealant. The physicochemical methods were used to predict the short- and medium-term performance of sealant mixtures. The short-term performance predicted from viscometry and microscopy correlated well with the 1-year field performance of the sealants. Sealants showed two glass transition temperatures (Tg’s), and a reasonable correlation was also found between low Tg and medium-term performance in a wet-freeze climate. However, because Tg measurements do not account for stress relaxation and aging effects, correlation was not perfect.

Modification of bending beam rheometer specimen for low-temperature evaluation of bituminous crack sealants

It is difficult to evaluate effectively the low-temperature stiffness of bituminous hot-poured crack sealants with existing test methods. The standard bending beam rheometer (BBR) was found to be inappropriate for testing soft bituminous-based hot-poured crack sealant, even at a temperature of-40°C. To address this issue, the moment of inertia of the tested beam was increased by doubling its thickness (from 6.35 mm to 12.7 mm). For the new beam dimensions, only 4% of the beam center deflection is due to shear, a value deemed acceptable for sealant evaluation and comparison. On this basis, the BBR stiffness of hot-poured sealants was obtained at several discrete temperatures between-10°C and -40°C to assess the repeatability of the method for the evaluation of the low-temperature stiffness of bituminous sealants. Ten different sealants were tested at -40°C; three of these 10 were further tested at –35°C, –30°C, –28°C, –25°C, and –20°C; and the three “hard” sealants were tested at –10°C. A minimum of three replicates were used. The coefficient of variation on the measured stiffness after 60 s of loading was always lower than 18%, with almost 75% of the measurements having a coefficient of variation less than 10%. A pairwise comparison showed that the modified BBR could be used to classify sealant products according to their measured stiffness. As to the effect of temperature, it was found that the stiffness varies exponentially with temperature in the range of –40°C to –20°C. A statistical analysis of the results indicated that the modified BBR method could be used to classify sealants based on low-temperature stiffness.

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.

Deformation and tracking of bituminous sealants in summer temperatures: pseudo-field behaviour

The bituminous sealants used in the maintenance of roadways sometimes fail because of the excessive deformation or flow under the shearing action of tires in summer temperatures. This issue has yet to be studied and no data on sealant deformation and flow are available. To address this issue, a small-scale tracking test was developed and applied to 21 sealants held at temperatures between 46 and 82°C, typical pavement temperature maximums in North America. It was found that sealant shear deformation increased linearly or non-linearly with temperature, and that past a temperature threshold, sealants deformed excessively and tracked. The tracking failure temperature was readily identified. Some sealants showed a tracking failure at fairly low temperatures, 46–64°C, but most only failed at 76°C or beyond. The sealant flow characteristics, acquired under pseudo-field conditions, provide the basis for developing a performance-based method to assist in the selection of sealants with resistance to tracking.

Development of a viscosity specification for hot-poured bituminous sealants

Current crack sealant specifications focus on using simple empirical tests such as penetration, resilience, flow, and bonding to cement concrete briquettes (ASTM D 6690) [1] to measure the ability of the material to resist cohesive and adhesive failures. There is, however, no indication of the pertinence of these standard tests to predict the success of field installation and sealant performance. In an effort to bridge the gap between sealant fundamental properties and field performance, performance-based guidelines for the selection of hot-poured crack sealants are currently being developed. This paper proposes a new viscosity test procedure to help assess the propensity of sealants to wet the crack surface during installation. The proposed procedure calls for the use of a Brookfield rotational viscometer equipped with a modified spindle rod and an SC4-27 spindle at a speed of 60 r/min. Sealants are heated 20 min at the recommended installation temperature and the viscosity is measured after 30 s of spindle rotation in the hot sealant. These experimental conditions provide viscosities representative of sealant viscosity at shear rates during field application. The repeatability for within laboratory and between laboratories was found to be 5.4 and 17 %, respectively. This repeatability is comparable with the corresponding variability of the SuperPave viscosity test for asphalt binders.

Variations in Composition and Rheology of Bituminous Crack Sealants for Pavement Maintenance

Bituminous crack sealants are used for the preventive maintenance of asphalt concrete pavements. The selection of a durable sealant can be difficult, however, mainly because of the lack of correlation between standard sealant specifications and field performance. Hence, an approved list of materials based on past performance is sometimes used to select sealants. However, sealant durability and performance vary over time. To investigate the effect of sealant lot variation on sealant properties, six lots of two sealants from different suppliers were analyzed for filler and polymer contents and rheological response. It was found that the difference in composition and rheology between lots can be similar to that between sealants produced by different manufacturers. Hence, sealant lot-to-lot variation can partly explain the variation in the field performance of sealants. Therefore, lists of approved products drawn from the field performance of past years are ineffective in the selection of sealants for future maintenance. The application of segregated sealants was also investigated, including assessing the effect of melter stirring on sealant homogeneity and measuring the segregation of sealant upon cooling. It was found that sealants do not segregate after their application and subsequent cooling and that a rapid circumferential stirring of 25 revolutions per minute in the heating kettle allowed for the remixing of a segregated sealant.

Natural weathering of styrene–butadiene modified bitumen

Abstract: This chapter reports on the long-term weathering of 12 bituminous sealants that contain thermoplastic elastomers, namely block copolymers of polystyrene and polybutadiene. The goal of the work was to determine the rate and mechanisms of sealant weathering so that future accelerated aging tests could be developed. By means of physico-chemical analysis, much weathering was found to occur in the early years of service. Weathering pathways were found to be mass loss, oxidation, and copolymer degradation. Specific mechanisms include the loss of aromatics with time, the formation of sulphoxides, sulphones, and their acids, ketones, and carboxylic acids. Block copolymer degradation occurs mainly through a scission between polystyrene and polybutadiene blocks, and the crosslinking of polybutadiene fragments. The chapter ends with a brief discussion of the suitability of current accelerated aging tests to simulate the natural weathering of elastomeric sealants.