Walter S. Jordan

Haul Time Effects on Unmodified, Foamed, and Additive-Modified Binders Used in Hot-Mix Asphalt

In recent years, warm technologies have made enormous changes to the flexible pavement industry in a variety of ways. Warm-mix asphalt is the most recognizable warm technology product, although other advantages are associated with better compaction over a wide range of temperatures and have made long-haul distances appealing for some applications. This paper focuses on using warm-mix technology at traditional hot-mix production temperatures for the purpose of facilitating long haul distances. The primary objective of this study was to investigate how binder-related properties change with haul time when material was mixed at hot-mix temperatures. A secondary objective was to determine if any behavioral differences were present between asphalt binders with no additive, foamed asphalt binders, and asphalt binders with a chemical additive. Plant-mixed asphalt was used for the investigation. The overall conclusion of the research was that haul times of 1 to 8 h produced no major differences in aging for a given binder type or between binder types. Subtle differences were observed between binder types in some instances (e.g., low-temperature properties were slightly better for mixes using warm-mix technologies).

Correlation of Moisture Loss and Strength Gain in Chip Seals

One of the most subjective decisions made during chip seal construction concerns when to allow brooms and traffic on the newly placed surface. If traffic is allowed too early, damage to the surface and to vehicles may occur. If the chip seal is opened too late, traffic is disrupted and motorists are inconvenienced. The curing of asphalt emulsions in the field is related to many factors, all affecting how fast the asphalt emulsion cures. Three laboratory test methods that measure adhesive strength gain as a function of moisture loss are presented. Two of the methods were sweep tests, one performed according to ASTM D7000 and the other according to a modified method. The third test used frosted marbles to measure adhesive strength gain. Results of all tests were similar and indicated that strength in emulsion residues increased as the total moisture in the system was reduced. This finding is important because the moisture content is independent of the mechanism reducing it. Therefore, prediction of strength gain should be possible by measurement of the moisture loss of a given chip seal system. The time required to obtain that strength gain varies in seals because of differences in emulsion, aggregate, interaction factors, weather, ambient temperature, and other environmental factors. Test results indicated that as moisture loss approached 75% to 90%, strength gain was significantly enhanced.

Material selection and traffic opening guidance for chip or scrub seals

Chip and scrub seal material selection is a long-standing challenge to favourable pavement performance and, historically, is based on empirical methods. This paper’s primary objective is to provide guidance for a seal treatment system (i.e. emulsion and aggregates) at high and low temperatures in the context of rejuvenation and aggregate retention. In contrast, commonly used methodologies are less comprehensive, focusing, for example, on only one performance aspect (e.g. aggregate retention) or one material (e.g. emulsion). Temperature is a major consideration of this paper since commonly used specifications call for test temperatures opposite of what may be optimal (e.g. viscosity testing at 135°C is commonly used to characterise rejuvenation, though rejuvenation seeks to address distresses typically associated with lower temperatures, such as cracking). Recommendations, which better align test temperatures, are to use bending beam rheometer mixture beam testing to evaluate rejuvenation and sweep testing to evaluate aggregate retention and traffic opening.

Recommendations for Seal Treatment Rejuvenation Specifications Based on Bending Beam Rheometer Testing of Mixture Beams

Recently, use of pavement preservation technologies, such as bituminous seal treatments, has increased. Seal treatments are often used to rejuvenate aged asphalt pavements and can decrease permeability and retard oxidation, cracking, and raveling. Many factors affect rejuvenation, and current specifications governing how rejuvenation is characterized could be enhanced. Viscosity testing of asphalt binder extracted and recovered from a pavements near surface is the predominant means of characterizing rejuvenation (e.g., a product must reduce viscosity by 40% to be classified as a rejuvenator). This paper presents data that suggest other rejuvenation approaches are worth considering because (a) extraction and recovery can adversely affect viscosity results, (b) viscosity testing cannot be conducted without forced and unrealistic blending of aged binder and rejuvenator, (c) high test temperatures may not be the most informative for distresses of interest (e.g., cracking), and (d) viscosity could not detect rejuvenation behaviors of some proprietary products. Alternatively, this paper suggests rejuvenation specifications be developed with bending beam rheometer (BBR) testing of mixture beams sawn from laboratory-compacted asphalt surfaces (e.g., a product must increase the m-value by 0.040 to be classified as a rejuvenator). This approach has shown promise for viscosity testing, and many concerns about viscosity testing are alleviated with BBR testing. A specification approach that uses BBR testing of laboratory-compacted asphalt is described and recommended for rejuvenation characterization.

Comparing Pressure Aging Vessel Time to Field Aging of Binder as a Function of Pavement Depth and Time

The AASHTO R28 pressure aging vessel (PAV) binder conditioning protocol has been heavily used for over two decades as part of purchasing specifications. Many paving industry changes have occurred since PAV was implemented in the early 1990s. This paper provides discussion with respect to a controlled test section in which the exact binders from construction were subjected to multiple PAV times and compared with properties observed after 2 or 4 years of field aging. The data suggests that 2 and 4 years of field aging were best simulated by 21 h and 45 h of PAV time for binders extracted from the top 1.3 cm of the pavement surface. For binders extracted from 5.0 to 6.3 cm below the pavement surface (i.e., at depth), 2 and 4 years of field aging were best simulated by 3 and 14 h of PAV conditioning, respectively. These results indicate that a PAV rate of 11 h per year of simulation seemed adequate for binders aged on the pavement surface, and a PAV rate of 3 h per year of simulation seemed most reasonable for binders aged at depth. Considering these rates, the current 20-h protocol in R28 seems to simulate roughly 2 years of aging at the pavement surface and about 6.5 years at depth. The amount of field aging simulation at depth is within the range of 5 to 10 years of aging suggested by R28.

Conditioning and Testing Protocol Combinations to Detect Asphalt Mixture Damage

Asphalt mixes often have many ingredients that can interact with each other. When put into service, where there are multiple environmental effects, there are many interactions that need mixture testing. This paper’s objective was to evaluate laboratory conditioning protocols coupled with subsequent property measurements for their ability to detect damage of asphalt mixtures in the southeastern U.S. climate (or similar climates). The investigation’s focus is the property measurements themselves, and in particular how a given test can simultaneously assess multiple types of damage (i.e. oxidation, moisture damage, and freeze-thaw damage). While in service, mixtures can be damaged in multiple manners so laboratory conditioning protocols that expose specimens to multiple types of damage are needed as are test(s) that can detect these damages in a manner that can help assess performance during service. Four plant produced mixtures with all virgin ingredients were evaluated at intermediate temperatures with mixture and binder tests. The mixtures were well suited for such a comparison because they consisted of all virgin binder. Indirect tensile (IDT) strength did not relate to Cantabro Mass Loss (CML) or binder test results, which was concerning. Even more concerning was IDT’s inability to respond to laboratory conditioning protocols that considered multiple environmental effects (i.e., oxidation, moisture, and freeze-thaw). CML results related to binder properties and were able to reasonably detect multiple types of environmental effects. As such, Cantabro testing is recommended over tensile strength for intermediate temperature mixture property assessments related to non-load associated environmental effects.