Characteristics of Sulfur Asphalt Concrete in Pavement Construction

1. Introduction
Asphalt have been widely used in highways, roads, and streets in the world. However, the current oil reserves will be insufficient in coming decades, causing an increase in price of bitumen and thus in the price of asphalt pavement construction as well. In addition, conventional bitumen is a viscoelastic binder which performs satisfactory in most of the flexible pavement. But the conventional binder is not able to sustain the performance criteria in rutting deformation and cracking due to increase in heavy traffic loads and adverse climatic conditions [1]. The conventional asphalt binder is generally characterized by poor adhesion, low temperature and plastic properties, leading to poor strength of pavement structure. In order to solve this problem, the asphalt binder needs to be modified with some additives whose tendency is to empower the bitumen performance. Modified asphalt binder is characterized by improved flexibility and longer service life, it also has a lower brittleness temperature and higher softening temperature.  Therefore, a lot of research efforts have been made to develop new materials to substitute for asphalt binder or to improve binder characteristics like bio-binder, Toner, crumb-rubber, SBS [2,3,4,5,6].   
   Moreover, some studies have pointed the use of sulfur as a possible alternative [7,8,9,10].  In the early 1970s, sulfur was used to replace asphalt as a binder extender. FHWA Demonstration Project No. 54 (DP54) [7] was conducted to compare the performance of the Sulfur Extended Asphalt (SEA) pavement and the conventional asphalt concrete (AC) pavement control sections. The test results showed that there was no significant difference in overall performance between the SEA and AC pavement sections and thus the sulfur could potentially be used as a binder extender with no significant deleterious effect on the pavement’s susceptibility and performance.  Zhang et al. [8] used thermal analysis and dynamic viscosity tests to evaluate the effects of thermal oxidative ageing on dynamic viscosity for sulfur-modified asphalt. It was found from the study that the sulfur-modified asphalt structure had a great effect on the properties of binders before and after ageing. Also, Gedik et al. [9] investigated the optimum sulfur content as alternative binder additive in asphalt pavements using superpave binder test methods. The promising results demonstrated that the optimum sulfur content increases the performance of the binder.  Moreover, Elkholy et al. [10] partially substituted the asphalt binder with different percentages of modified sulfur, the modified sulfur substituted asphalt binder had higher resistance against cracking of the pavement at low temperatures, and least permanent deformation at high temperatures. These studies only focused on the properties of the sulfur as extend binder additive, there were no studies conducted investigating the performance of the sulfur modified binder in asphalt mixtures.
The main objective of this study is to investigate the performance of sulfur modified asphalt mixtures. To accomplish this objective, various laboratory tests for asphalt binder and asphalt mixtures were conducted. First, the engineering properties and morphologies of the sulfur modified asphalt binder were investigated using the Scanning Electron Microscopy (SEM). Second, marshall stability (MS) test, wheel tracking (WT) test, indirect tensile (IDT) test, and indirect tensile fatigue (IDTF) tests were conducted to evaluate the performance resistance of sulfur modified asphalt mixtures. Finally, the performance of sulfur modified asphalt mixtures was simulated and evaluated using the mechanistic empirical pavement design guide (MEPDG) program.
2.    Testing Results

• Based on SEM tests, it was found that addition of 30% and 40 % sulfur in asphalt binder, the voids seem to be completely filled. This would increase the adhesion between the asphalt particles in sulfur modified asphalt mixture.

• An optimum sulfur content of 40% can be used as replacement for asphalt binder since it improves the toughness, rut resistance (significantly under high temperature conditions) and fatigue cracking initiation and resistance of asphalt mixtures.

• Using the MEPDG program to evaluate the performance of sulfur modified asphalt mixtures, the results validated that the addition of sulfur content in asphalt mixtures can enhance its performances significantly in terms of rutting, bottom up cracking, and TD cracking under field conditions.

• Further studies are recommended to investigate the effect of the sulfur modified mixtures on rutting and cracking performance asphalt mixtures under actual field conditions.

References

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3.  Kök, B. V., & Çolak, H. Laboratory comparison of the crumb-rubber and SBS modified bitumen and hot mix asphalt. Construction and Building Materials, 25(8), 3204-3212, 2011.

4.  Notani, M. A., Moghadas Nejad, F., Khodaii, A., & Hajikarimi, P. Evaluating fatigue resistance of toner-modified asphalt binders using the linear amplitude sweep test. Road Materials and Pavement Design, 1-14, 2018.

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7. G.L. Crawford and W.F. Boles, Sulfur-Extended Asphalt – Close-out Summary of Project Activities. FHWA-DP-54-9, Demonstration Project No. 54,1986.

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9. A. Gedik, A.H. Lav, Determining Optimum Sulfur Content as Alternative Binder Additive in Asphaltic Concrete Pavements, Journal of Materials in Civil Engineering. 28(2016) 1-12.

10. S.A. Elkholy, A.M.M. Abd El-Rahman, M. El-Shafie, Z.L. Abo-Shanab, Physical and rheological properties of modified sulfur asphalt binder, International Journal of Pavement Research and Technology 11 (2018) 838-845.

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