The total road network in India had increase more than two folds since 1990. The demand for transportation is ever growing. The main drawback in the conventional mix is its temperature susceptibility. In order to cater the current day needs of the road transportation sector the quality of the materials needs to be improved, especially bitumen, superior quality which would sustain in heavier load condition and perform well under higher stress levels irrespective of the temperature and climatic conditions has to be used. VIATOP plus FEP Das Pellet is a commercially available bitumen modifier, which can be used to modify binder in both wet and dry condition. This product is a unique pelletized blend of 20% Arbocel ZZ 8/1 and 80% functional additive. The advantages of using this product are excellent resistance towards deformation, improved ageing properties, reduced cracking, improved workability and long storage life.

The objectives of the present study, include

• To arrive at the optimum dosage and assess the effectiveness of the elastomeric modifier in modifying VG-10 and VG-30 grade binder.
• To study and compare the following properties for the conventional VG-10 and VG-30 binder with the elastomeric modified VG-10 and VG-30 binder for BC Grade-II and DBM Grade-II bituminous mixes.
• Mechanical and Volumetric properties of the mix.
• Tensile Strength.
• Moisture Susceptibility of the mix.
• Fatigue Behaviour.

Neil C. Kurtz and Stroup (1992) discuss the conventional Asphalt AC-5 and AC-20 grade asphalt binders were modified with rubber and the following modified asphalts were prepared, AC-5+17% rubber (AC5R), AC-20+Rubber (AC20R) and AC-5+16% Rubber + extender oil (AC5RE). The laboratory research on both static and repeated load were tested at warm temperature, the temperature were maintained at 77 ^oF and 104 ^oF. The research was conducted in four phases, first phase dealt with arriving at OBC, second phase dealt with permanent deformation characteristics of asphalt rubber and unmodified bitumen, phase three was about low temperature cracking comparison between asphalt rubber and unmodified bitumen, fourth phase dealt with fatigue characteristics for asphalt rubber and unmodified mixture. The addition of GTR to asphalt mixes exhibited less permanent deformation at higher temperature when compared to unmodified bitumen, this was confirmed with both static and repeated load test.

Gupta and Veeraragavan (2009) compared the fatigue behavior of SBS modified bitumen to that of neat bitumen. 60/70 grade bitumen was used as the neat bitumen and PMB-70 as modified bitumen. A mixing temperature of 180 ^oC and a compaction temperature of 165 ^oC were selected for SBS modified mixes. DBM Grade-II is the OBC obtained at 4.5% for neat bitumen and 4.8% for SBS modified. Stability of 18.55 kN was obtained for neat bitumen and 23.50 kN was obtained for SBS modified bitumen. The Retained Marshall Stability, TSR were 71% and 86% for neat bitumen and 89% and 96% for modified, respectively. An increase of 2 to 2.5 times in resilient modulus of polymer-modified mixes was observed as compared to conventional bituminous mix.

Mutiu Akinpelu et al. (2013) decribe polyethylene was considered as polymer additive for the modification of bitumen. Optimum bitumen content was found to be 7%. Polyethylene by weight of optimum bitumen content was added in the five proportions (2.5, 5.0, 7.5, 10, 12.5, and 15%) and tested. 12.5% of polyethylene by weight of conventional bitumen was found to improve stability, air voids and voids of mineral aggregates and reduction in the density compared to other mixes of polyethylene doses.

Nabin Rana Magar (2014) mainly dealt with the use of CRMB manufactured from the waste tyre scrap. The crumb rubber was added at 15% to the weight of bitumen. The research is done on the varying sizes of crumb rubber and the four different sizes of crumb rubber used are coarse (1 mm -600 μm); medium size (600 μm - 300 μm); fine (300 μm-150 μm); and superfine (150 μm - 75 μm). The mixing temperature of bitumen and crumb rubber was maintained at 160 ^oC and the initial hand mixing time was 3-4 minutes, to achieve the complete blend the mix is mechanically stirred for about 50 minutes while o maintaining the constant temperature of 160 ^oC. It was observed that the sample prepared using crumb rubber size (0.3-0.15 mm) gave the highest stability value of 1597.64 kg, minimum flow, maximum unit weight, maximum air voids and minimum VMA and VFB % values when compared to other crumb rubber particle sizes.

3.1 Aggregates

In the research, crushed stone aggregates were obtained from R.N.S. Stone Crusher Plant Jigani in Bangalore, which was used to prepare the BC-II & DBM-II mix specimens and physical properties of aggregate, fulfil the requirements as per MoRT&H 5^th revision. The properties of aggregates are presented in Table 1.

Table 1. Physical Properties of Aggregates

3.2 Bitumen

The VG-10 bitumen was obtained from Mathura refinery and VG-30 bitumen from Mangalore refinery. Both the bitumen was tested for their basic properties: penetration value, softening point, ductility and specific gravity, fulfil the requirements as per IS 73:2013. The results are presented in Tables 2 and 3.

Table 2. Physical Properties of VG-10 Neat Bitumen

Table 3. Physical Properties of VG-30 Neat Bitumen

3.3 Bitumen Modifier

Bitumen (VG-10 & VG-30) is modified by using elastomeric pellets as modifiers at different modification levels (5%, 10%, 12.5%, 15%, and 17.5%). The elastomeric pellets used in the study for binder modification is shown in Figure 1. The wet process is carried out which is recommended to add the VIATOP plus FEP to bitumen, which has previously been heated up to approximately. 180 ^oC, portion-wise under stirring with a suitable stirrer within 5 minutes to the hot paving grade bitumen at 180 ^oC. The bitumen is mixed intensively with the stirrer at 200 rpm for a further 4 hours. The bitumen temperature of at least 180 ^oC for the specified time period must be complied with and checked. The optimum dosage of the elastomeric pellets is determined by comparing the modified bitumen results with the properties of IS 15462:2004 modified bitumen. The results are presented in Tables 4 and 5.

Figure 1. VIATOP Plus FEP Pellets

Table 4. VG 10 Bitumen was Modified with VIATOP Plus FEP Fibers

Table 5. VG 30 Bitumen was Modified with VIATOP Plus FEP Fibers

3.4 Ageing Characteristics of Modified Binders

Thin Film Oven Test (TFOT) conducted as per ASTM-D 1754- 97 on different binders to evaluate the effect of ageing on Elastomeric Pellets modified binders developed in the present investigation. The results are presented in Tables 6 and 7.

Table 6. Thin Film Test Results of Modified Binder

Table 7. Thin Film Test Results of Modified Binder

4.1 Gradation

As per the specification of MoRT&H 5^th revision the gradation of aggregate for DBM-II and BC-II mix is obtained by Rothfutch's method. The results are presented in Tables 8 and 9. The gradation curves are shown in Figures 2 and 3, respectively.

Table 8. Gradation of Aggregates for DBM Grade-II

Table 9. Gradation of Aggregates for BC Grade-II

Figure 2. Gradation Curve of Aggregates For DBM-II Mix

Figure 3. Gradation Curve of Aggregates For BC-II Mix

4.2 Marshall Mix

As per the specification of ASTM D-1559-96, Marshall Mix designs of DBM-II and BC-II with neat and modified binders are obtained. The results of marshall properties, such as stability, bulk density, air voids, flow, VMA and VFB, respectively for DBM-II and BC-II neat and modified bituminous mixes by varying the percentage of binder (VG- 10 & VG-30) are presented in graphs as shown in Figures 4- 15. The Marshall properties at OBC for DBM-II and BC-II neat and modified bituminous mixes satisfy the requirements as per MoRTH 5^th revision and IRC: SP: 53-2010 and are presented in Tables 10 and 11.

Figure 4. Comparison of Stability v/s Bitumen Content for DBM-II Mixes

Figure 5. Comparison of Bulk Density v/s Bitumen Content for DBM-II Mixes

Figure 6. Comparison of Air Voids v/s Bitumen Content for DBM-II Mixes

Figure 7. Comparison of Flow v/s Bitumen Content for DBM-II Mixes

Figure 8. Comparison of VMA v/s Bitumen Content for DBM-II Mixes

Figure 9. Comparison of VFB v/s Bitumen Content for DBM-II Mixes

Figure 10. Comparison of Stability v/s Bitumen Content for BC-II Mixes

Figure 11. Comparison of Bulk Density v/s Bitumen Content for BC-II Mixes

Figure 12. Comparison of Air Voids v/s Bitumen Content for BC-II Mixes

Figure 13. Comparison of Flow v/s Bitumen Content for BC-II Mixes

Figure 14. Comparison of VMA v/s Bitumen Content for BC-II Mixes

Figure 15. Comparison of VFB v/s Bitumen Content for BC-II Mixes

Table 10. Summary of Marshall Properties at OBC for DBM-II using Pellets Dosage (with 12.5% & 15%) by Weight of Binder (VG-10 and VG-30)

Table 11. Summary of Marshall Properties at OBC for BC-II using Pellets Dosage (with 12.5% & 15%) by Weight of Binder (VG-10 and VG-30)

Performance tests, such as ITS, TSR, and repeated load fatigue test were conducted on the different mixes of DBMII and BC-II at OBC.

• ITS test procedure was followed as per the specification of ASTM: D-6931-07.
• TSR is defined as the ratio of average tensile strength of conditioned specimen to the average tensile strength of unconditioned specimen.
• Stress levels of 15% and 20% are selected for DBM-II and BC-II mixes with the loading period of 0.5 s and rest period of 0.5 s.

Tables 12 and 13 describe the results of the performance tests.

Table 12. Performance Properties at OBC for DBM-II using Pellets Dosage (with 12.5% & 15%) by Weight of Binder (VG-10 and VG-30)

Table 13. Performance Properties at OBC for BC-II using Pellets Dosage (with 12.5% & 15%) by Weight of Binder (VG-10 and VG-30)

6.1 Discussions

6.1.1 Material Properties

6.1.1.1 Physical Properties of Aggregates and Binder

• Physical properties of coarse aggregates and fine aggregates used in this research are determined and found out to be acceptable as per the requirements of the specification of MoRT&H 5^th Revision.
• Physical properties of (VG-10 & VG-30) binder are determined and the results satisfy the requirements as per the specification of IS 73-2013.
• Physical properties of the modified bitumen are determined. The results obtained fulfill the requirements as per the specification of IS 15462:2004 for CRMB 50, CRMB 55, and CRMB 60.

6.1.1.2 Physical Properties of Neat and Modified Binder

• Reduction in penetration value of 28% and 62% for modified asphalt (12.5% & 15% pellets) is obtained, compared to its VG-10 neat binder. Also, there is reduction in penetration value by 42% and 48% for modified asphalt (12.5% & 15% pellets) compared to its VG-30 neat binder. This shows that there is increase in hardness of the binder with the incremental addition of modifier pellets to the neat binders.
• Increase in softening value of 25% and 34% for modified asphalt (12.5% & 15% pellets) compared to its VG-10 neat binder. Also, there is increase in softening value of 21% and 23% for modified asphalt (12.5% & 15% pellets) compared to its VG-30 neat binder. The increase in softening point obtained due to modification of binder shows the reduction in susceptibility of bituminous mixtures to temperature variations.
• The Separation value of 0.15 ^oC & 0.6 ^oC were observed for VG-10 12.5% & 15% modified binder, respectively. Also, 0.85 ^oC & 0.63 ^oC seperation value were observed for VG-30 12.5% & 15% modified binder, respectively. These are well within the limits which indicates that the binder is modified completely without any suspended particles.

6.1.1.3 Thin Film Oven Test on Modified Binder

• The loss in the mass did not occur in any mix after ageing.
• The reduction in penetration value at 25 °C were 6%, 6%, 7%, & 5% for (VG-10 12.5%) modified, (VG-10 15%) modified, (VG-30 12.5%) modified, and (VG-30 15%) modified binder respectively.
• The increase in softening point was found to be 2 ^oC, 2 ^oC, 1.03 ^oC, & 1 ^oC for (VG-10 12.5%) modified, (VG-10 15%) modified, (VG-30 12.5%) modified, and (VG-30 15%) modified binder, respectively.
• The elastic recovery at 25 ^oC was 25%, 51%, 36%, & 44% for (VG-10 12.5%) modified, (VG-10 15%) modified, (VG-30 12.5%) modified, and (VG-30 15%) modified bitumen, respectively.

The ageing properties on the modified binder indicates that the binder is very less affected by ageing which proves that the modified bituminous mixtures will yield higher shelf life.

6.1.2 Marshall Properties

The Marshall properties of VG-10 & VG-30 bituminous mix in unmodified and modified condition were tested. The results obtained for these mixes adhere to the specification of MoRT&H 5^th revision.

6.1.2.1 Stability

The stability of the modified binder shows immense improvement over neat binder. This is due to the increase in stiffness of binder with the addition of modifier to the binder.

6.1.2.2 Density

BC Grade–II

• The density of the mix for VG-10 remains same for all the three mixes as 2.4 g/cc.
• The density of the mix for VG-30 has found to be 2.34 g/cc, this increased to 2.42 g/cc for 12.5% modification and 2.49 g/cc for 15% modification.

DBM Grade-II

• Increase in the density of 5% and 5.23% for modified asphalt (12.5% & 15%) compared with the neat binder VG-10.
• Increase in the density 0.2% for modified asphalt (12.5% & 15%) compared with the neat binder VG-30.

6.1.2.3 Flow Value

The flow value increases for the all the mixes as the bitumen content increase. The obtained flow value is in the range of 2-4 mm for the unmodified bitumen and 2.5-4 mm for modified bitumen as per the requirement of MoRT&H 5^th revision.

6.1.2.4 Air Voids

The air voids decreases as the bitumen content increases for all the mixes. The air voids that vary from 3-5%. 4% air voids is taken as reference value for the calculation of OBC.

6.1.3 Performance Characteristics

6.1.3.1 Indirect Tensile Strength

BC Grade-II

• The ITS value obtained for the mix with VG-10 neat bitumen is 126 kPa, for the mix with 12.5% and 15% modification are 371 kPa and 539 kPa, respectively.
• The ITS value obtained for the mix with VG-30 neat bitumen is 392 kPa, for the mix with 12.5% and 15% modification are 433 kPa and 909 kPa, respectively.

DBM Grade-II

• The ITS value for the mix with VG-10 neat bitumen is 147 kPa, for the mix with 12.5% and 15% modification are 269 kPa and 297 kPa, respectively.
• The ITS value for the mix with VG-30 neat bitumen is 299 kPa, for the mix with 12.5% and 15% modification are 471 kPa and 650 kPa, respectively.

The results revealed that the modified binder mix has more tensile strength when compared with conventional binder mix irrespective of the dosage.

6.1.3.2 Tensile Strength Ratio

The mix should have Tensile Strength Ratio of minimum 80% to satisfy the moisture susceptibility criteria.

BC Grade-II

• From moisture susceptibility results for the mix with VG 10 binder, it was found that TSR is 82% for conventional mix, 90% for mix with 12.5% modifier, 83% for mix with 15% modifier. All the three mix are satisfying the minimum criteria of moisture susceptibility. Mix with 12.5 % modifier is more resistant to moisture damage.
• The mix with VG 30 binder found that TSR is 88% for conventional mix, 92% for mix with 12.5% modifier, 100% for mix with 15% modifier. All the three mix are satisfying the minimum criteria of moisture susceptibility. Mix with 15% modifier is 100% resistant to moisture damage.

DBM Grade-II

• The mix with VG 10 binder found that TSR is 84% for conventional binder mix, 91% for mix with 12.5% modifier, 97% for mix with 15% modifier. All the three mix are satisfying the minimum criteria of moisture susceptibility. Mix with 15% modifier is more resistant to moisture damage.
• The mix with VG 30 binder found that TSR is 81% for conventional mix, 86% for mix with 12.5% modifier, 97% for mix with 15% modifier. All the three mix are satisfying the minimum criteria of moisture susceptibility. The mix with 15% modifier is more resistant to moisture damage.

6.1.3.3 Fatigue Characteristics

Flexure test is done in order to determine the number of repetitions of load the pavement can bear without failure. The study is conducted at 15% stress level.

BC Grade-II

• The number of cycles that the specimen can take was found to be 2267, 5000+, and 8000+ for the mixes with VG 10 neat bitumen, 12.5% and 15% modification, respectively.
• The number of cycles that the specimen can take was found to be 2500, 7000+, and 13000+ for the mixes with VG 30 neat bitumen, 12.5% and 15% modification, respectively.

DBM Grade-II

• The number of cycles that the specimen can take was found to be 1110, 3700+, and 4200+ for the mixes with VG 10 neat bitumen, 12.5% and 15% modification, respectively.
• The number of cycles that the specimen can take was found to be 1300, 4100+, and 13100+ for the mixes with VG 30 neat bitumen, 12.5% and 15% modification, respectively.

The modified binder samples took more repetitions of load compared to the neat binder samples and did not fail.

• The modified binder has higher softening point values and decrease in penetration value which is a sign of temperature resistance and superior quality binder.
• There is no increase in the mixing time and temperature with modified binder when compared to the neat binder.
• Increase in stability is noted in both BC grade-II and DBM grade-II mixes with the addition of modified binder which shows the improvement in adhesion of the mix.
• The moisture resistance has increased for both BC grade-II and DBM grade-II mixes with the modified binder (VG-10 and VG-30) at both 12.5% and 15% dosages.
• The fatigue characteristics have increased more than 1.5 times in case of modified binder used with BC grade-II mix. However, in case of DBM grade-II mix, significant increase can be seen only with the use of VG-30 modified binder.
• Through these limited lab studies, it was found that by adding VIATOP plus FEP to the binder at the dosage of 12.5% and 15% of the binder, a superior grade elastomeric modified binder is produced which can yield stable, moisture resistant bituminous mixes with longer fatigue life.