Laboratory evaluation of antioxidants for asphalt binders

https://doi.org/10.1016/j.conbuildmat.2010.06.058Get rights and content

Abstract

A laboratory study was carried to investigate whether certain antioxidants could be used to reduce age-hardening in asphalt binders. Several additives including: Vitamin E, Irganox 1010, Irgafos P-EPQ, carbon black, hydrated lime, and DLTDP/furfural, were evaluated. The modified asphalt binders were subjected to two accelerated oxidative aging regimes in the laboratory. Short-term oxidative aging of the binders was simulated using a rolling thin film oven while long-term aging was performed using a pressure aging vessel. The effects of aging on the binders were evaluated based on changes in rheological properties of asphalt binders undergoing oxidative aging. Binders modified with a combination of furfural and DLTDP was found to posses the lowest aging index. The antioxidant-treated binders exhibited improved performance at both high and low pavement temperatures.

Introduction

Asphalt binders get stiffer and more brittle with age. This phenomenon is commonly called aging or age-hardening. Several factors have been cited to explain the phenomenon of age-hardening in asphalt. The major causes of age-hardening commonly cited include oxidation, volatilization, polymerization, thixotropy, syneresis, and separation [1], [2], [3], [4]. Among these factors, oxidation and volatilization are generally considered as the most important factors affecting aging in asphalt paving mixtures.

Oxidation is the irreversible chemical reaction of atmospheric oxygen with asphalt. Oxidation of asphalt can occur throughout the life of an asphalt pavement such as during mixing, field placement, and during service. The rate and amount of oxidation depends on factors such as chemical composition of the asphalt, environmental conditioning, and length of exposure to weathering.

Age-hardening of paving grade asphalts is a major factor affecting durability bituminous pavement. Many highway and airfield pavements fail in service prematurely due in part to excessive hardening of the asphalt binder as a result of oxidation. Excessive hardening and brittleness caused by oxidation during hot-mix asphalt (HMA) production and also during service increase the susceptibility of asphalt pavements to cracking. Cracked pavements allow water to percolate into the pavement structure to weaken the pavement base and hasten pavement deterioration. Reduction of oxidative hardening using antioxidants could lead to longer lasting pavement and substantial savings in life cycle cost.

Several antioxidants have been used in the past to control oxidative hardening in asphalt pavements [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Initial laboratory investigations of these antioxidants showed some promise. However, most of these antioxidant systems for retarding oxidative hardening have not performed satisfactorily in the field due to problems such as degradation, volatility, and loss of the antioxidant from the asphalt system. Another problem associated with some of the currently used antioxidants is that their use results in tender mixes since the antioxidants often soften the binder excessively. Therefore the need still exists for developing more effective antioxidants treatments for controlling oxidative hardening in paving asphalts.

The usefulness of asphalt binders as paving materials is dependent on the resistance to change of their physical properties across the range of temperatures encountered in a typical pavement. Aging significantly changes both the chemical and physical properties of asphalts. Physical properties such as penetration, ductility, viscosity, and stiffness are all affected to some extent by aging. Since aging per se is not a measurable property, the net changes in the chemical and physical properties due to aging have been used to measure the extent of aging by many investigators. Methods for measuring asphalt aging can be grouped into two: chemical analysis and physical measurements. Four classes of asphalt physical property measurements namely single-point measurements, temperature susceptibility parameters, shear susceptibility parameters, and linear viscoelastic have all been used in the past to evaluate the extent of asphalt aging [26]. Of these, single-point measurements are the most common. Evaluation of aging in this study was limited to analysis of physical measurements for simplicity and also to be in conformity with previous studies on asphalt aging.

Aging index computations based on the single-point measurements are one of the most common procedures used to estimate aging and provide ranking among different asphalt binders. Aging index is defined as the ratio of a given binder property after a given level of aging to that before aging as shown in Eq. (1). The most common parameter for computing aging index of asphalt binders has historically been based on viscosity measured at 60 °C. Kandhal et al. [27] reported that aging indices computed using apparent viscosity at 25 °C and 0.05 s−1 shear rate correlated best with age-hardening and asphalt pavement durability in Pennsylvania. It was reported that ravelling appeared only on pavements with aging index values of 12 or higher after long-term aging.

As previously noted, aging index can be computed based on any asphalt physical property that changes with aging. Shown in Fig. 1 is a comparison of aging index using viscosity and SUPERPAVE rutting parameter G*/sin δ for 37 different asphalt binders form the Materials Reference Lab [28]. The results suggest relationship between viscosity and G*/sin δ is quite good. Screening of antioxidant evaluated in this study was therefore based on G*/sin δ aging index instead of viscosity-based aging index.Aging index=Physical property of aged asphaltPhysical property of original asphalt

Section snippets

Purpose and scope

The primary objective of this study was to determine if asphalt age-hardening could be controlled using antioxidants. Effective antioxidants for asphalt stabilization cannot be predicted a priori; all new potential antioxidants will have to be tested to determine their effectiveness in controlling asphalt aging. The effectiveness of antioxidants are not linearly related to concentration, therefore several antioxidants at various concentrations were tested and screened during the study.

The scope

Identification of suitable antioxidants

Several additives were reviewed for inclusion in the study. The major criteria used in selecting these antioxidants were that the selected antioxidants posses both lower volatility as well as higher resistance to extraction during hot-mix production and under service conditions. Some of the selected antioxidants have never been used for controlling oxidative aging of asphalt mixes.

Preliminary screening tests results

Table 1 shows the summarized results of DSR testing performed at 64 °C for modified binders. Testing was conducted at multiple percentages of additives for some antioxidants. At least three replicate specimens of each modified binder were tested. Variability in DSR testing data (evaluated using coefficient of variation, COV) averaged about 3.0% for the binders considered in this paper. This level of variability in DSR testing data are consistent with the maximum COV of 3.9% recommended under

Summary and conclusions

The effects of the antioxidants on age-hardening were evaluated by measuring the rheological properties of asphalt binders before and after selected levels of aging. Short-term and long-term aging were simulated using the rolling thin film oven at 163 °C and the pressure aging vessel at 100 °C respectively for the asphalt binders. The rheological response of the modified asphalt binders was evaluated using the dynamic shear rheometer and the bending beam rheometer. The effectiveness of the

Acknowledgments

Results presented in this paper were obtained during the author’s affiliation with the University of Illinois at Urbana-Champaign. Support provided by Professor William Buttlar and Professor Barry Dempsey are greatly appreciated.

References (29)

  • Vallerga BA, Monismith CL, Granthem K. A study of some factors influencing the weathering of waving asphalts. In:...
  • Traxler RN. Durability of asphalt cements. In: Proceedings of the association of asphalt paving technologists, vol. 32....
  • Finn FN. Factors involved in asphalt pavement surfaces. NCHRP 39. National cooperative highway research program....
  • Roberts FL, Kandhal PS, Brown RR, Lee D, Kennedy TW. Hot mix asphalt materials, mixture design, and construction. NAPA...
  • B.D. Beitchman

    Effects of antioxidants on asphalt durability

    J Res Natl Bureau Standards – C. Eng Instrum

    (1960)
  • Wurstner RG, Higgins WA, Craig WG. Laboratory evaluation of factors influencing the performance of paving asphalts –...
  • Martin KG. Preliminary micro-viscometer studies of carbon black/rubber/bitumen dispersions. In: Proceedings of the...
  • K.G. Martin

    Influence of stabilizers on bitumen durability

    J Appl Chem

    (1966)
  • Martin KG. Laboratory evaluation of antioxidants for bitumen. In: Proceedings of the Australian Road Research Board –...
  • Traxler RN. Effect of small amounts of DC-200 silicone fluid on viscosity and resistance to hardening of asphalt...
  • R.M. Januszke

    Paving asphalt additives in durability determination

    Indust Eng Chem Prod Res Develop

    (1971)
  • Plancher H, Green EL, Petersen JC. Reduction of oxidative hardening of asphalts by treatment with hydrated lime – a...
  • Haxo HE, White RM. Reducing the hardening of paving asphalts through the use of lead antioxidants. In: Proceedings of...
  • Haas RCG, Thompson E, Meyer F, Tessier RG. The role of additives in asphalt paving technology. In: Proceedings of the...
  • Cited by (152)

    • Dilauryl thiodipropionate as a regeneration agent for reclaimed asphalts

      2023, Construction and Building Materials
      Citation Excerpt :

      In general, regenerated binders showed significative lower values of NCI when compared to non-regenerated ones, indicating that DLTDP may improve the aging resistance of the regenerated binders. A possible explanation for this finding may be attributed to the fact that DLTDP can inhibit peroxide formation, thus, preventing the further oxidation of the binders [101,164]. SARA fractionation provides helpful information about the chemical composition and polarity of molecules constituting the asphalt binders, even when RAP binders are considered [165].

    • Dispersion, compatibility, and rheological properties of graphene-modified asphalt binders

      2022, Construction and Building Materials
      Citation Excerpt :

      The three major distresses that occur in asphalt pavements are firmly associated with the performance of asphalt binders [4,5]. To mitigate the distresses and extend the lifespan of asphalt pavements, researchers and practitioners have been attempting to enhance the performance of asphalt binders utilizing various modifiers and additives including polymers, fillers, fibers, extenders, antioxidants, anti-stripping agents, crumb rubber, and plastics [6–13]. Polymers such as styrene–butadienestyrene (SBS) are the most prevalent among these modifiers and additives [14].

    View all citing articles on Scopus
    View full text