Advancements in Materials, Vol. 3, Issue 2, Oct  2019, Pages 17-29; DOI: 10.31058/j.am.2019.32001 10.31058/j.am.2019.32001

Influence of Microcrack Healing on Deformation of Recycled Asphalt Concrete Binder

, Vol. 3, Issue 2, Oct  2019, Pages 17-29.

DOI: 10.31058/j.am.2019.32001

Saad Issa Sarsam 1* , Rana Khalid Hamdan 1

1 Department of Civil Engineering, University of Baghdad, Baghdad, Iraq

Received: 13 July 2019; Accepted: 30 August 2019; Published: 11 October 2019

Abstract

Recycling of aged and distressed asphalt concrete pavement could be considered as an acceptable sustainable issue to reserve the pavement properties and extend its service life. In the present investigation, asphalt cement was subjected to aging in the laboratory, then recycled with polyethylene and crumb rubber. Asphalt concrete specimens were prepared using the recycled binder. Specimens were subjected to repeated indirect tensile stresses and repeated punching shear stresses using the pneumatic repeated load system PRLS at 25°C. After 1200 load repetitions, the loading was terminated, and the specimens have practiced microcrack healing by external heating for two hours at 60°C. Specimens were subjected to another loading cycle of 1200 load repetitions under tensile or shear stresses. The deformation of the specimens was monitored through a continuous video capture. It was concluded that the permanent deformation value under repeated punching shear stresses and repeated indirect tensile stresses decreased after healing by (9.5, 42.5 and 78.3) % and (51, 50, and 46.2) % at asphalt content of (4.8, 5.3 and 5.8) % respectively as compared to the case before healing. Permanent deformation decreases by (40.6, 44, and 16.6) % and (14.1, 10.5, and 30) % for (0.5, 1.0, and 1.5) % of crumb rubber content at optimum asphalt content under repeated punching shear and ITS respectively, while the permanent deformation decreases by (42.4, 42.5, and 32.8) % and (2.6, 11.5, and 6.7) % for (0.5, 1.0, and 1.5) % of Polyethylene content at optimum asphalt content under repeated punching shear and ITS respectively.

Keywords

Recycled binder; Healing; Deformation; Shear; Tensile stress; Repeated loading

1. Introduction

Totally recycled HMAs have been prepared and their performance specifications (resistance to water damage, rutting resistance, stiffness of the mixture, durability, and binder aging) have been assessed. It was stated that totally recycled HMAs could be considered as a suitable alternative for pavement work, especially if recycling agents are used to decline their production and spreading temperatures and to enhance their performance. The used engine oil could be considered suitable from economic and environmental points of view, [1]. Silva et al., [2] addressed that, using rejuvenator can improves the performance of the totally recycled HMA mixtures (i.e., longer life cycle), and reduces the mixing temperature (i.e., lower energy consumption), also it is necessary to have an adequate workability. Pradyumna and Jain, [3] compares the properties of mixture with rejuvenator agents, which was prepared in laboratory on the recycled asphalt pavement material, while their performance was compared with virgin mixes. The recycled mixtures had practiced Various performance tests such as index of Retained Stability, Indirect Tensile Strength (ITS) and Tensile Strength Ratio (TSR), and Resilient Modulus test. Sarsam, [4] studied the recycling of laboratory aged asphalt concrete and concluded that the aging process had increased Hveem cohesion value, while it exhibits negative influence on Marshall properties, tensile, and flexural strength properties. It was concluded that recycling exhibits positive impact on the Asphalt concrete overall properties, while it changed the deflection mode from cracking to bending. The aim of the present investigation is to recycle the laboratory aged binder with polyethylene and crumb rubber, then the influence of microcrack healing and moisture damage on the resilient modulus of the prepared asphalt concrete will be verified.

2. Materials and Methods

2.1. Asphalt Cement

Asphalt cement of 40-50 penetration grade was obtained from Dora refinery; Table 1 shows the physical properties of the binder.

Table 1. Physical Properties of Asphalt Cement.

SCRB Specification, [6]

Unit

Result

Test procedure as per ASTM, [5]

40-50

1/10mm

40

Penetration (25ᵒC, 100g, 5sec) ASTM D 5

≥ 100

Cm

167

Ductility (25ᵒC, 5cm/min). ASTM D 113

50-60

ᵒC

54

Softening point (ring & ball). ASTM D 36

-

-

1.04

Specific gravity at 25° C, ASTM D 70 – 03

After Thin-Film Oven Test ASTM D-1754

> 55

1/10mm

87

Retained penetration of original, % ASTM D 946

> 25

Cm

147

Ductility at 25 ° C, 5cm/min, (cm) ASTM D-113

-

%

0.32

Loss in weight (163ᵒC, 50g,5h) % ASTM D-1754

2.2. Crumb Rubber

It was produced by mechanical shredding of used tires and was obtained from tires factory at AL-Najaf governorate, the rubber type is (recycled) from used tires. Table 2 exhibit the grain size distribution of crumb rubber.

Table 2. Gradation of crumb rubber.

Sieve No.

Sieve Size(mm)

Passing by weight%

No.16

1.18

100

No.30

0.9

78

No.50

0.3

25

No.200

0.075

0

2.3. Polyethylene

It was a Low-Density Polymers, found to be suitable for blending with asphalt. It has a melting temperature of 160°C. Table 3 present the mechanical and thermal Properties of Polyethylene.

Table 3. Mechanical and thermal properties of low-density Polyethylene.

Properties

Unit

Value

Tensile strength

MPa

10

Tensile Elongation

%

> 350

Flexural Modulus

MPa

8

Hardness (Shore D)

..........

50

Vicat Softening point

°C

88

Brittleness Temperature

°C

< -175

2.4. Coarse and Fine Aggregate

The aggregate used in this work was obtained from the Nahrawan quarry. Crushed Sand was used as fine aggregate (particle size distribution between sieve No.4 and sieve No.200). The sizes of coarse aggregate range between (12.5 mm) to (4.75 mm) according to SCRB specification, [6]. Table 4 shows the physical properties of aggregate.

Table 4. Physical Properties of Coarse and Fine Aggregate.

Property

Value

ASTM, [5] Designation No.

Coarse Aggregate

Bulk specific gravity

2.339

C127-01

Apparent specific gravity

2.414

C127-01

Water absorption %

1.323

C127-01

Wear % (los Angeles abrasion)

13.05

C131-03

Fine aggregate

Bulk specific gravity

2.727

C128-01

Apparent specific gravity

3

C128-01

Water absorption %

3.333

C128-01

2.5. Selection of Aggregate Gradation

In this study, the selected gradation was Wearing Course with 12.5 (mm) nominal maximum size, according to specification of SCRB, [6]. Table 5 show selected aggregate gradation

Table 5. Specification Limits and Selected Gradation of HMA Mixtures.

Sieve Opening(mm)

Sieve Size

% passing by weight of total aggregate

Selected gradation

SCRB, [6] specifications Limit (Type IIIB)

12.5

1/2"

100

100

9.5

3/8"

95

90-100

4.75

No.4

70

55-85

2.36

No.8

49.5

32-67

0.3

No.50

15

7-23

0.075

No.200

7

4-10

2.6. Mineral Filler

In this investigation, Limestone dust has been used, which is obtained from Al- Nahrawan factory. It is thoroughly dry and free from lumps or aggregations of fine particles; the physical properties are presented in Table 6.

Table 6. Physical properties of Limestone Dust.

Property

Limestone Dust

% passing sieve 200

96

Specific gravity

2.68

2.7. Aging of Asphalt Cement

To simulate the aging process of asphalt cement during its service life in the field, Asphalt cement was subjected to aging process using the thin film oven test apparatus, asphalt cement practices 163°C of heating for five hours in the rotating shelf of the oven. Asphalt cement was collected after the heating and cooled to room temperature. It was denoted as aged asphalt cement.

2.8. Recycling of Aged Asphalt Cement

2.8.1. Preparation of Recycled Asphalt Cement (Asphalt Cement Blended With Low-Density Polyethylene)

The aged asphalt cement was recycled by digestion with polyethylene, asphalt cement was heated to 150 °C and then blended with Low-Density Polyethylene with different percentages of (0.5 , 1 and 1.5) % by weig0000000000000000ht of asphalt cement using mechanical mixer, a blending speed of 200 rpm and elevated temperatures (160°C) for 60 minutes was implemented to promote the possible physical and chemical bonding of the components.

2.8.2. Preparation of Recycled Asphalt Cement (Asphalt Cement Blended With Crumb Rubber)

The aged asphalt cement was recycled by digestion with crumb rubber using the wet process. The asphalt cement was heated to 160 °C and then blended with crumb rubber with different percentages of (0.5, 1 and 1.5) % by weight of asphalt cement at a blending speed of 1500 rpm for 60 minutes in the laboratory using mechanical mixer to promote the physical and chemical bonding of the components. During the blending process, the crumb rubber dispersed and reacts with the asphalt. Swelling and formation of bubbles could be observed after the blending process.

2.8.3. Preparation of Asphalt Concrete Specimens

The aggregates were dried to a constant weight at 110ºC, then sieved to different sizes, and stored. Coarse and fine aggregates were combined with mineral filler to meet the specified gradation shown in Table 5. The combined aggregate mixture was heated to a temperature of (150ºC) before mixing with asphalt cement. The recycled asphalt cement with polyethylene or crumb rubber was heated to the same temperature of (150ºC), then it was added to the heated aggregate to achieve the desired amount and mixed thoroughly using mechanical mixer for two minutes until all aggregate particles were coated with thin film of asphalt cement. Marshall Size specimens were prepared in accordance with ASTM, [5] D1559 using 75 blows of Marshall hammer on each face of the specimen. The optimum asphalt content for each recycled asphalt cement type was determined as per the procedure above. The prepared Marshall Size Specimens were divided into two sets, the first set was subjected to the repeated indirect tensile strength test at 25 ºC, while the second set was subjected to double punching shear strength determination at 25 ºC. Additional asphalt concrete specimens have been prepared using asphalt cement of 0.5% above and below the optimum asphalt content. Specimens have been tested in duplicate using the pneumatic repeated load system PRLS, and the average value was considered for analysis. Figure 1 shows part of the prepared specimens and the PRLS.

Figure 1. Part of the Prepared Specimens and the PRLS.

2.8.4. Repeated Indirect Tensile Stress (ITS) Test

The test was conducted according to Sarsam and AL-Zubaidi, [7] and Sarsam and AL-Shujairy, [8]. The Pneumatic repeated load system (PRLS) was implemented. Asphalt concrete specimens were subjected to repeated indirect tensile stress at 25 ˚C to allow the initiation of micro cracks. Such timing and test conditions was suggested by Sarsam and Saleem, [9]; Sarsam and Husain, [10]; and Sarsam and Jasim, [11]. Compressive repeated loading was applied on the specimen which was centered on the vertical diametrical plane through two parallel loading strips (12.7 mm) wide. Such load assembly applies indirect tensile stress of 0.138 MPa on the specimen in the form of rectangular wave with constant loading frequency of (60) cycles per minutes. A heavier sine pulse of (0.1) sec load duration and (0.9) sec rest period is applied over test duration. Before the test, Specimens were stored in the chamber of the testing machine at room temperature (25±1 ˚C), dial gage of the deformation reading was set to zero before test start and the pressure actuator was adjusted to the specific stress level. The test was continued for 1200 load repetitions, then it was terminated. the Specimens were withdrawn from the testing chamber and stored in an oven for 120 minutes at 60 ° C to allow for crack healing initiation. Specimens were returned to the testing chamber, conditioned for 120 minutes at 25 ° C, and then subjected to another cycle of repeated indirect tension at 25 ° C for 20 minutes. The deformation of the specimens under repeated indirect tensile stress and the number of load repetitions were captured using digital video camera fixed on the top surface of the (PRLS) throughout the test. The impact of healing on the accumulated permanent deformation was assessed. The average of two specimens of each mixture type was calculated and considered for analysis as recommended by Sarsam and Mahdi, [12]. Figure 2. Exhibit the repeated ITS test setup.

Figure 2. Repeated ITS Setup.

2.8.5. Repeated Double Punch Shear Stress (PSS) Test

The second group of asphalt concrete specimens were subjected to repeated double punch shear stresses (PSS) for at 25 ˚C to allow the initiation of micro cracks. Compressive repeated loading was applied on the specimen which was centered between the two plungers of 25.4mm diameter as per the procedure described by Sarsam and AL-Shujairy, [8]. Such load assembly applies compressive load which was resisted by the specimen through shear resistance. The stress on the specimen is in the form of rectangular wave with constant loading frequency of (60) cycles per minutes. A heavier sine pulse of (0.1) sec load duration and (0.9) sec rest period is applied over test duration. Before the test, Specimens were stored in the chamber of the testing machine at room temperature (25±1 ˚C), dial gage of the deformation reading was set to zero before test start and the pressure actuator was adjusted to the specific stress level of 0.138 MPa. The test was continued for 1200 load repetitions, then it was terminated. The Specimens were withdrawn from the testing chamber and stored in an oven for 120 minutes at 60 ° C to allow for crack healing initiation. Specimens were returned to the testing chamber, conditioned for 120 minutes at 25 ° C, and then subjected to another cycle of repeated shear stresses at 25 ° C for 20 minutes. The deformation of the specimens under repeated punching shear stress and the number of load repetitions were captured using video camera for both conditions. The impact of healing on the accumulated permanent deformation was assessed. The average of two sample of each asphalt cement percentage was calculated and considered for analysis as recommended by Sarsam and Mahdi, [12]. Figure 3. Exhibit the repeated double punching shear test setup.

Figure 3. Repeated Double Punch Shear Setup.

2.8.6. Microcrack Healing Process

The repeated tensile or shear stresses was continued for 1200 load repetitions, upon completion of test, the recording was terminated. Specimens were withdrawn from the PRLS and stored in an oven for 120 minutes at 60ºC to allow the crack healing process by external heating. Specimens were returned to the PRLS chamber, conditioned for 60 minutes at 40±1˚C and subjected to another 1200 load repetitions, the deformation was monitored by digital camera throughout the test. The average of three specimens was calculated and considered for analysis.

3. Results and Discussion

In flexible pavement design, Permanent deformation is an important factor. This occurs due to increase in traffic load and tire pressure; the permanent deformation occurs in upper layers rather than in the subgrade. By using the dynamic indirect tensile test, the permanent vertical strain is measured at a stress level 0.138 MPa and a temperature (25°C). The classical power model is used in this study to express the relationship between permanent microstrain and logarithm of load repetitions. At N=1, the intercept (a) represents the permanent strain. The larger strain value refers to higher potential for permanent deformation, while slope (b) represents the rate of deformation. High slope value for a mixture indicate an increase in the material deformation rate. Low slope value for mix is Prefer to prevent the rutting in the asphalt pavement. Permanent deformation is analyzed based on slope, intercept, and permanent deformation at 1200 load cycles.

3.1. Effect of Microcrack Healing on Intercept Parameter Under Repeated ITS and Punching Shear

Figure 4 demonstrates the impact of microcrack healing on permanent deformation parameters (intercept and slope) of control mixture. It can be noted that in general, the intercept decreases after healing for both testing techniques, while the slope increases in case of shear stress and decreases in case of tensile stress.

Figure 4. Effect of Microcrack Healing on Intercept Under Repeated ITS and Punching Shear.

The intercept decreases by (36.3, 18, and 83) % and (59.4, 70.8, and 74.2) % for (4.8, 5.3, and 5.8) % asphalt content under punching shear and ITS respectively indicating stiffer mixture formation after healing. On the other hand, the slope increases by (16, 16, and 3.4) % and decreased by (6.6, 28, and 47.8) % for (4.8, 5.3, and 5.8) % asphalt content under punching shear and ITS respectively. Such variation in the slope behavior could be attributed to the variation in the testing technique and the specimen assembly. It also indicates that the control mixtures tested in punching shear are more susceptible to increased rate of permanent deformation than those tested under tensile stress. Similar findings were reported by Copeland, [13] and Zaumanis et al, [14].

3.2. Effect of Recycling Agent (Low Density Polyethylene) and Healing on Intercept Parameter

As demonstrated in Figure 5, When Polyethylene (low density) is introduced as a recycling agent, the intercept decreased by (67.8, 78.3, and 68) % and (5.5, 9.4, and 14.8) % for (0.5, 1.0, and 1.5) % of polyethylene content at optimum asphalt content under punching shear and ITS respectively. However, the intercept decreased by (74.4, 70.9 and 40.1) % at (0.5, 1 and 1.5) % Polyethylene after healing as compared to control mixture under punching shear test. When the specimens were tested under repeated ITS, the intercept decreased by (29.2, 69, and 79.8) % at (0.5, 1 and 1.5) % Polyethylene after healing as compared to control mixture. On the other hand, the slope increases by (23.3, 59.2, and 48.1) % and decreased by (3.2, zero, and 3.2) % for (0.5, 1.0, and 1.5) % polyethylene content under punching shear and ITS respectively. It can be noted that both testing techniques exhibit lower intercept values after implication of polyethylene recycling agent as compared to the case of control mixture.

Figure 5. Influence of Polyethylene on Crack Healing.

3.3. Effect of Recycling Agent (Crumb rubber) and Healing on Intercept Parameter

Figure 6 exhibit that when Crumb Rubber is added as a recycling agent by (0.5, 1.0, and 1.5) %, the intercept value decreased by (37.4 , 19.1 and 2.2) % under repeated ITS before healing, while after healing process, the intercept value decreased by (74.3, 49.2 and 36) % for (0.5, 1 and 1.5) % rubber respectively as compared to control mixture. The intercept decreased by (66.4, 48.5, and 46.3) % and (35, 51.5, and 23.8)% for (0.5, 1.0, and 1.5) % of crumb rubber content at optimum asphalt content under punching shear and ITS respectively. On the other hand, the slope increases by (27.5, 12.5 and 25.8) % and decreased by (5.8, 2.8, and 3.2) % for (0.5, 1.0, and 1.5) % crumb rubber content under punching shear and ITS respectively. such behavior agrees well with the work reported by Buttlar et al., [15]; Shuler, [16] and Akisetty et al., [17].

Figure 6. Influence of Crumb Rubber on Crack Healing .

3.4. Effect of Recycling Agent on Permanent Deformation

Permanent deformation (micro strain) for each asphalt mixture under both testing techniques for control mixture is presented in Figure 7. For control mixture, the permanent deformation decreases with increasing percentage of asphalt, and when applying healing process. The permanent deformation value under repeated punching shear stresses and repeated indirect tensile stresses decreased after healing by (9.5, 42.5 and 78.3) % and (51, 50, and 46.2) % at asphalt content of (4.8, 5.3 and 5.8) % respectively as compared to the case before healing.

Figure 7. Influence of Healing on Variation of Permanent Deformation.

When recycled binder with various percentages of crumb rubber was implemented at optimum asphalt content, it can be observed at Figure 8 that the permanent deformation increases as the crumb rubber content increase regardless of the testing technique or the microcrack healing process. This may indicate that the suitable rubber content is 0.5 % of optimum asphalt content to exhibit the minimum deformation. After the crack healing process, it can be noted that the permanent deformation in microstrain decreases by (40.6, 44, and 16.6) % and (14.1, 10.5, and 30) % for (0.5, 1.0, and 1.5) % of crumb rubber content at optimum asphalt content under repeated punching shear and ITS respectively. such finding complies with Xu et al., [18].

Figure 8. Influence of Crumb Rubber and Healing on Variation of Permanent Deformation.

When recycled binder with various percentages of Polyethylene was implemented at optimum asphalt content, it can be observed at Figure 9 that the permanent deformation increases as the Polyethylene content increase regardless of the testing technique or the microcrack healing process. This may indicate that the suitable polyethylene content is 0.5 % of optimum asphalt content to exhibit the minimum deformation. After the crack healing process, it can be noted that the permanent deformation in microstrain decreases by (42.4, 42.5, and 32.8) % and (2.6, 11.5, and 6.7) % for (0.5, 1.0, and 1.5) % of Polyethylene content at optimum asphalt content under repeated punching shear and ITS respectively. Similar finding could be detected in Shunyashree et al., [19] work.

Figure 9. Influence of Polyethylene and Healing on Variation of Permanent Deformation.

4. Conclusions

Based on the limitations of the testing program, the following conclusions may be drawn.

1. For control mixture, in general, the intercept decreases after healing for both testing techniques, while the slope increases in case of shear stress and decreases in case of tensile stress.

2. The intercept decreases by (36.3, 18, and 83) % and (59.4, 70.8, and 74.2) % for (4.8, 5.3, and 5.8) % asphalt content under punching shear and ITS respectively indicating stiffer mixture formation after healing.

3. The slope increases by (16, 16, and 3.4) % and decreased by (6.6, 28, and 47.8) % for (4.8, 5.3, and 5.8) % asphalt content under punching shear and ITS respectively.

4. When Polyethylene (low density) is introduced as a recycling agent, the intercept decreased by (67.8, 78.3, and 68) % and (5.5, 9.4, and 14.8) % for (0.5, 1.0, and 1.5) % of polyethylene content at optimum asphalt content under punching shear and ITS respectively.

5. The intercept decreased by (74.4, 70.9 and 40.1) % at (0.5, 1 and 1.5) % Polyethylene after healing as compared to control mixture under punching shear test. When the specimens were tested under repeated ITS, the intercept decreased by (29.2, 69, and 79.8) % % at (0.5, 1 and 1.5) % Polyethylene after healing as compared to control mixture.

6. When Crumb Rubber is added as a recycling agent by (0.5, 1.0, and 1.5) %, the intercept value decreased by (37.4, 19.1 and 2.2) % under repeated ITS before healing, while after healing process, the intercept value decreased by (74.3, 49.2 and 36) % for (0.5, 1 and 1.5) % rubber respectively as compared to control mixture.

7. Permanent deformation value under repeated punching shear stresses and repeated indirect tensile stresses decreased after healing by (9.5, 42.5 and 78.3) % and (51, 50, and 46.2) % at asphalt content of (4.8, 5.3 and 5.8) % respectively as compared to the case before healing.

8. Permanent deformation decreases by (40.6, 44, and 16.6) % and (14.1, 10.5, and 30) % for (0.5, 1.0, and 1.5) % of crumb rubber content at optimum asphalt content under repeated punching shear and ITS respectively, while the permanent deformation decreases by (42.4, 42.5, and 32.8) % and (2.6, 11.5, and 6.7) % for (0.5, 1.0, and 1.5) % of Polyethylene content at optimum asphalt content under repeated punching shear and ITS respectively.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this article.

Copyright

© 2017 by the authors. Licensee International Technology and Science Press Limited. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

References

[1] Sarsam S.; AL-Zubaidi I. Resistance to Deformation under Repeated Loading of Aged and Recycled Sustainable Pavement. American Journal of Civil and Structural Engineering, (AJCSE), 2014, 1(2), 34-39, April. Sciknow Publications Ltd. USA.

[2] Silva, H.M.R.D.; Oliveira J.R.M.; Jesus, C.M.G.Are totally recycled hot mix asphalts a sustainable alternative for road paving? Resources, Conservation and Recycling, 2012,60,38-48, DOI: 10.1016/j.resconrec.2011.11.013.

[3] Pradyumna, T. A.; Jain, P. K. Use of RAP Stabilized by Hot Mix Recycling Agents in Bituminous Road Construction. Transportation Research Procedia, 2016, 17, 460-467, DOI:10.1016/j. trpro.11.090.

[4] Sarsam S. I. A study on aging and recycling of asphalt concrete pavement. University of SharjahJournal of Pure & Applied Sciences, 2007, 4(2), 79-93.

[5] ASTM. Road and Paving Materials, Annual Book of ASTM Standards, Volume 04.03, American Society for Testing and Materials, 2013, USA.

[6] SCRB. General Specification for Roads and Bridges. Section R/9, Hot-Mix Asphalt Concrete Pavement, Revised Edition. State Corporation of Roads and Bridges, Ministry of Housing and Construction, 2003, Republic of Iraq.

[7] Sarsam S.; AL-Zubaidi. Assessing Tensile and Shear Properties of Aged and Recycled Sustainable Pavement. IJSR Publication, 2014, 2(9), 2014-b, DOI: 10.12983/ijsrk-2014-p0444-0452.

[8] Sarsam S.; AL-Shujairy A. Assessing Tensile and Shear Properties of Recycled Sustainable Asphalt Pavement. Journal of Engineering, Volume 21 Number 6, June 2015.

[9] Sarsam S.; Saleem M. Influence of Micro Crack Healing on Flexibility of Recycled Asphalt Concrete. Journal of Advances in Civil Engineering and Construction Materials; 1(1): 2018, P. 26-39.

[10] Sarsam S.; Husain H. Monitoring the Deformation of Asphalt Concrete under Repeated Tensile and Shear Stresses through Micro Cracks Healing Cycles. Proceedings, International Conference on Highway Pavements and Airfield Technology 2017; ASCE T&D 08/2017.

[11] Sarsam S. I.; Jasim S. A. Assessing the Impact of Polymer Additives on Deformation and Crack Healing of Asphalt Concrete Subjected to Repeated Compressive Stress. Proceedings, 17th Annual International Conference on: Asphalt, Pavement Engineering and Infrastructure, 2018 LJMU, Wednesday 21st and Thursday 22nd February, Liverpool, UK.

[12] Sarsam S. I.; Mahdi M. S. Assessing the Rejuvenate Requirements for Asphalt Concrete Recycling. International Journal of Materials Chemistry and Physics. Public science framework, Vol. 5 No. 1. 2019. P 1-12.

[13] Copeland, A.Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice, Federal Highway Administration Report No. FHWA-HRT-11-021, 2011, FHWA, McLean, Virginia.

[14] Zaumanis M.; Mallick R.; Frank R. 100% hot mix asphalt recycling: challenges and benefits. 6th Transport Research Arena April 18-21, 2016. Transportation Research Procedia 14 P. 3493-3502, DOI: 10.1016/j.trpro.2016.05.315.

[15] Buttlar W.; Meister J.; Jahangiri B.; Majidifard H. Performance Characteristics of Modern Recycled Asphalt Mixes in Missouri, Including Ground Tire Rubber, Recycled Roofing Shingles, and Rejuvenators. Final report, Missouri Department of Transportation Project #TR-201712 MU Project #00056783 February 16, 2018.

[16] Shuler, S. Use of Waste Tires, Crumb Rubber, on Colorado Highways. Colorado Department of Transportation, DTD Applied Research and Innovation Branch, Technical report, 2011.

[17] Akisetty C. K.; Lee S. J.; Amirkhanian S. N. High temperature properties of rubberized binders containing warm asphalt additives. Construction and Building Materials,2007, 565-573, DOI: 10.1016/j.conbuildmat.2007.10.010.

[18] Xu O., L. Cong, F. Xiao, S.N. Amirkhanian. Rheology investigation of combined binders from various polymers with GTR under a short-term aging process, Construction and Building Materials, 2015, 93, 1012-1021, DOI: 10.1016/j.conbuildmat.2015.05.051.

[19] Shunyashree S.; Bhavimane T.; Archana M.; Amarnath M. Effect of use of recycled materials on indirect tensile strength of asphalt concrete mixes. IJRET: International Journal of Research in Engineering and Technology,2013, 226-232, DOI: 10.15623/ijret.2013.0213040.