STRESS CREEP RECOVERY ANALYSIS FOR IRAQI MODIFIED ASPHALT BINDER

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 11, November 2018, pp , Article ID: IJCIET_09_ Available online at aeme.com/ijciet/issues.asp?jtype=ijciet&vtype= =9&IType=11 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed MULTIPLE STRESS CREEP RECOVERY ANALYSIS FOR IRAQI MODIFIED ASPHALT BINDER Alaa H Abed Assistant Professor (PhD) in Civil Engineering Department, Al-Nahrain University, Baghdad, Iraq Hasan Al-Mosawe Lecturer (PhD) in Civil Engineering Department, Al-Nahrain University, Baghdad, Iraq ABSTRACT Asphalt binder properties is one of the key factors affecting the performance of asphalt mixtures. Agencies try to improve the behavior of asphalt binder by adding some modifiers to increase specific characteristics. The use of binder in Iraq is commonly the neat binder that is produced from the different refineries in the country. It is valuable to test the neat binder by advanced testing techniques (multiple stress creep recovery test, MSCR) and modify the local binder with different types of modifiers and different percentages to overcome the rutting problems in the field. In this research, Daura neat binder was selected to be characterized and improved by adding some modifiers. Four types of modifiers were used with different percentages, which are: the styrene-butadiene-styrene (SBS) by 2% and 4%, styrene-butadiene- styrene with cross-linkerr by 2%, and polyphosphoric acid (PPA) by 1%, and functionalized polyethylene (PE) by 3.5%. It is found that the MSCR test well recognizes the improvement of the binder. Moreover, the addition of SBS to the neat binder, sufficiently improve the recoverable creep compliance and percent of recovery of the binder. The resultss showed that the addition of 4% SBS to the neat binder improved the percent of recovery by 17 and 70 times and the non-recoverable compliance by 4.2 and 4 times compared with the neat binder at 100 and 3200 Pa respectively. This is attributed to encourage highway agencies to use the modified binder and the MSCR testt in constructing roadways and testing their materials. The aim of this research is to improve and analyze the Iraqi asphalt binder properties by adding some modifiers and using advance evaluation techniques editor@iaeme.com

2 Alaa H Abed and Hasan Al-Mosawe Cite this Article: Alaa H Abed and Hasan Al-Mosawe, Multiple Stress Creep Recovery Analysis For Iraqi Modified Asphalt Binder, International Journal of Civil Engineering and Technology (IJCIET), 9(11), 2018, pp INTRODUCTION The increase in traffic volume and loads on the roads causes large damages in the pavement. This would oblige researchers to develop more advanced methods to improve the asphalt pavement to resist such high loads and also to improve the method of evaluating that materials. The main aim of such improvement is to achieve asphalt pavement material with higher durability and last longer which result in cost effective material. One of the popular methods to achieve such improvement is to add some polymer modifiers to the asphalt binder to reduce rutting and cracking. When an asphalt binder is suggested to be used in road materials, it should be processed in series of tests to assess its strength and ability to resist rutting and cracking. The elastic recovery test is the main test used to evaluate the presence of elastomers in modified binder. The higher the elastomers the better the resistance to rutting. However, the state department of transportation (DOT) experts were dissatisfied with this test because the test takes long time to complete (4-5 hours) and most agencies do not follow the American Association of State Highway and Transpiration Officials (AASHTO) standard guidelines to perform the test, D'Angelo, et. al. (2007). In general, the nonrecoverable deformation in asphalt cement (binder) has great impact on the rutting performance of the resulting asphalt mixture. NCHRP 9-10 research program developed the multiple stress creep recovery (MSCR) test. The MSCR test is based on the properties of creep phase and recovery phase of the asphalt binder (Bhaia et. al., 2001); the test is then modified by Dongré et al (2003). The test is validated by several researchers to study the behavior of the asphalt binder at high temperatures, and it was found that the test resulted better characterization of binder than the routine superpave parameters G*/sinδ, (D'angelo et al, 2006; Tabatabaee and Tabatabaee, 2010; Wasage et al, 2011; Gibson et al, 2012; Subhy, 2017; Zoorob et al, 2012). The creep recovery compliance (Jnr) is sensitive to stress level and temperature. The stress dependency can be easily captured by using the modified asphalt binder with polymer. In binders that are modified with high percent of modifiers, the normal recovery duration is not enough to allow a full recovery of the binder to occur. In such case, the delayed elastic residue strain will be gathered with the viscous component which produce a decrease in the highest value of the resulted strain and the irrecoverable strain value in the next cycle (Shenoy 2001). 2. MULTIPLE STRESS CREEP AND RECOVERY (MSCR) The test composed of applying a shear stress in the form of repeated creep recovery on the asphalt binder for a short period of time (1 second). The stress is then removed for 9 seconds to allow recovery to occur in the material (as shown in Figure 1). The full test consists of repeated this process 10 times using different stress levels. The different stress levels usually increase gradually starting from 25 Pa and then doubled each time until it ends at Pa. It is usually performed for samples aged by RTFO to emulate the field aging in the stages of mixing and that of paving. It, as described in ASTM D or AASHTO TP standards, allows a disc of asphalt binder conducted between two parallel plates each of thickness 25 mm and using the dynamic shear rheometer (DSR) test. The new test procedure allows two stress levels of 100 and 3200 Pa to be applied for 1 second and allow recovery for editor@iaeme.com

3 Multiple Stress Creep Recovery Analysis For Iraqi Modified Asphalt Binder 9 seconds for 10 cycles and no time lag between cycles are applied. The parameters that are obtained from MSCR test are: % = 100 Eq. 1!" #$ %#& 1 ( ' ) = * (+) - Eq. 2.!" #$./ %#& 1 ( ' ) = * (+) - Eq. 3./ where: 0 (") : recoverable shear strain; 0 ($) : instantaneous shear strain; 0 (!") : permanent shear strain; and!": non-recoverable compliance. () () Figure 1 A typical one cycle of creep-recovery for Daura binder modified by 4% SBS It is recommended to use the non-recoverable creep compliance as performance indicator instead of the current SHRP parameter G*/sinδ (D'Angelo, 2007). The Jnr can estimate the percent of perfection that happens to the modified binder performance compare to neat binder (D'Angelo, 2009). The Jnr estimation at high magnitudes of applied stresses and at non-linear material properties has is more precise because the strain in binder film on aggregate surfaces is much higher than the strain occurs in the asphalt mixture (Subhy, 2017). 3. RESULTS AND DISCUSSION This section deals with the more reliable testing properties of the different types of binder which differs from G* and δ that represent the linear viscoelastic behavior of the material. The MSCR, therefore, was established to study the behavior of the material at higher stresses which represent regions outside the linear viscoelastic range. The test was performed on the different types of binders at their performance grade temperature and at two stress levels, 100 and 3200 Pa. It can be seen from Figure 2 and Figure 3that the addition of the modifiers editor@iaeme.com

4 Alaa H Abed and Hasan Al-Mosawe showed a very good reduction in strain values, which is an improvement to the performance. In both stress levels, 100 and 3200 Pa, it can be seen that the reduction of the accumulated strain is more than half of the base binder for both modifiers, PPA and 2% of SBS. The other modifiers showed better strain reduction which reaches to more than 7 times in case of 3.5% P.E at 100 Pa and to more than 4.5 times in case of the addition of 4% SBS at 3200 Pa. The increase in stress level from 100 to 3200 Pa made a slight change in the order of the best modifier effect on the binder, however the higher stress level is more sensitive in evaluating this issue because it more simulative to the high traffic loads. The addition of 4% SBS to binder showed the best performance improvement which is expected because of the elastic property of it which allow a range of recovery occur in the modified binder unlike the plastomers. Figure 2 Accumulated Strain for base and modified binders at 100 Pa Figure 3 Accumulated Strain for base and modified binders at 3200 Pa editor@iaeme.com

5 Multiple Stress Creep Recovery Analysis For Iraqi Modified Asphalt Binder 3.1. Non-recoverable compliance (Jnr) The improvement of the modified binder can be estimated by the non-recoverable compliance (Jnr); it is measured by 1/Paor 1/kPa and it is sensitive to the applied stress. In this research, Jnr was calculated for the base and modified binders and is shown in Figure 4. It can be seen that increasing the stress from 100 to 3200 Pa did not make significant performance change in most of the binders especially those modified with elastomers. However, binders that are modified with plastomers(functionalized polyethylene (PE) and polyphosphoric acid (PPA)) showed a clear increase in the Jnr which represents the effect of the modifier on the binder. The other plastomer modifier used also showed an increase in the Jnr but in less manner. The Jnr results conform the findings that the binder modification by 4% SBS resulted in lowest value of Jnr which means that it has the best performance among the other modified binders in this research. Figure 4 Jnr of the base and modified binders at two stress levels 3.2. Percent of Recovery Elastic recovery of the binder is represented by the percentage recovery results in addition to the creep compliance Jnr. The mean percent of recovery values of 10 cycles at each level of stress are calculated and presented in Figure 5. In general, it is obvious that the unmodified binder would suffer lower percentage of recovery than those modified with modifiers. Interestingly, the figure shows that at 100 Pa the addition of %3.5 PE to the base binder recorded a high percent of recovery. However, it demolished when the stress increased t On the other hand, the addition of %4 SBS to the base binder increase the recovery by 17 and 70 times compared to the base binder at 100 and 300 Pa respectively. The %4 SBS also showed less reduction in recovery results when the applied stress increased from 100 to 3200 unlike the other modified binders editor@iaeme.com

6 Alaa H Abed and Hasan Al-Mosawe Figure 5 % Recovery of the base and modified binders at two stress levels It can be noticed that the addition of the elastomers to the binder increased its properties and it resistance to deformation better than that of the elastomers. 4. CONCLUSIONS Asphalt binder characterization is a very important factor tin the performance of asphalt mixtures. A local Iraqi asphalt binder was selected and modified by different types of modifiers and tested for MSCR test. Several conclusions can be drawn from this research and are listed below: Although the current standard asphalt binder tests (penetration and softening point) are carried out and shows agreement with the standards, the performance of the mixture in the field is not as required. The MSCR showed the poor behavior of the neat binder that cause the improper pavement performance in the field because of its simulative stress application. The modification of the binder showed a steep improvement in in the performance in terms of Jnr and % recovery. The % recovery recorded the highest when 3.5 P.E was added to the binder at 100 Pa. The best modified binder performance was achieved by adding 4% of SBS to the modified binder, especially the performance sustained when stress increased to The modified binder was improved by 17 times compared to the neat binder. The addition of 4% SBS reduced the non-recoverable compliance Jnr by approximately 4 times the Jnr for the neat binder at the two levels of stress. The 2% SBS with crosslinker modified binder achieved good behavior and approximately sustained that behavior with the increase of the applied stress. Therefore, it could be mentioned that the SBS modification is a good option for the local Daura neat binder editor@iaeme.com

7 Multiple Stress Creep Recovery Analysis For Iraqi Modified Asphalt Binder REFERENCES [1] D'Angelo, John A., and Raj N. Dongre. "Creep and recovery." Public roads 70, no. 5 (2007). [2] Bahia, Hussain U., D. I. Hanson, M. Zeng, H. Zhai, M. A. Khatri, and R. M. Anderson. Characterization of modified asphalt binders in superpave mix design. No. Project 9-10 FY' [3] Dongré, Raj, John D Angelo, Gaylon Baumgardner, and Gerry Reinke. "New developments in refinement of the superpave high temperature specification parameter." In 40th annual meeting of the Petersen asphalt research conference, Laramie, WY [4] D'ANGELO, J., R. Dongre, and G. Reinke. "Evaluation of repeated creep and recovery test method as an alternative to SHRP+ requirements for polymer modified asphalt binders." In Proceedings Of The Fifty-First Annual Conference Of The Canadian Technical Asphalt Association (Ctaa): Charlottetown, Prince Edward Island, November [5] Tabatabaee, Nader, and Hassan Tabatabaee. "Multiple stress creep and recovery and time sweep fatigue tests: Crumb rubber modified binder and mixture performance." Transportation Research Record: Journal of the Transportation Research Board 2180 (2010): [6] Wasage, T. L. J., Jiri Stastna, and Ludo Zanzotto. "Rheological analysis of multi-stress creep recovery (MSCR) test." International Journal of Pavement Engineering 12, no. 6 (2011): [7] Gibson, Nelson, Xicheng Qi, Aroon Shenoy, Ghazi Al-Khateeb, M. EminKutay, Adrian Andriescu, Kevin Stuart, Jack Youtcheff, and Thomas Harman. Performance testing for Superpave and structural validation. No. FHWA-HRT [8] Subhy, Ayad Tareq. "Characterisation and development of rubberised bitumen and asphalt mixture based on performance-related requirements." PhD diss., University of Nottingham, [9] D'Angelo, John, Robert Kluttz, Raj N. Dongre, Keith Stephens, and Ludo Zanzotto. "Revision of the superpave high temperature binder specification: the multiple stress creep recovery test (with discussion)." Journal of the Association of Asphalt Paving Technologists 76 (2007). [10] D'Angelo, John A. "The relationship of the MSCR test to rutting." Road Materials and Pavement Design 10, no. sup1 (2009): [11] Shenoy, Aroon. "Refinement of the Superpave specification parameter for performance grading of asphalt." Journal of transportation engineering 127, no. 5 (2001): [12] Zoorob, S. E., J. P. Castro-Gomes, LA Pereira Oliveira, and J. O connell. "Investigating the multiple stress creep recovery bitumen characterisation test." Construction and Building Materials 30 (2012): editor@iaeme.com