Performance Evaluation of Crumb Rubber Modified Bitumen on Binder Course of Stone Mastic Asphalt Mix

Performance Evaluation of Crumb Rubber Modified Bitumen on Binder Course of Stone Mastic Asphalt Mix

Anusha T M 1, Jagadeesh H S 2

1Research Scholar, Dept of Civil Engineering, BMS College of Engineering, Bangalore, Karnataka- 560019, India.

2Professor, Dept of Civil Engineering, BMS College of Engineering, Bangalore-19, Karnataka- 560019, India.

Abstract:- Utilization of crumb rubber modified bitumen for wearing course in stone mastic asphalt mix pavement has been widely researched by many researchers due to its enormous benefits. This present paper focuses on the performance of binder course in stone mastic asphalt mixes using Crumb Rubber Modified Bitumen (CRMB) as a binder at five different levels, namely 5.7%, 6%, 6.3%, 6.6% and 6.9% respectively by weight of bituminous mixes. The optimal of crumb rubber modified bitumen was identified by carrying out Marshall stability test, Indirect tensile strength, fatigue and Rutting test. Based on the results obtained, it was observed 6.3% of crumb rubber modified bitumen improves the performance of binder course in stone mastic asphalt mix.

Key words : Crumb rubber, Stone mastic asphalt mix, Indirect tensile strength, Fatigue, Rutting, binder course.

1. INTRODUCTION

   Bituminous concrete mix is a combination of aggregates and binder. The aggregates acts as the structural skeleton of the pavement and bitumen acts as the glue of the mix. The properties of the aggregates have direct and significant effect on the performance of the pavement Patel et al. (2016) and Sun et al. (2018). The utilization of commercial by-products and recycled materials in construction as secondary and alternative materials has gained widespread acceptance and is becoming more important. The demands for industrial by-products and recycled materials are increasing per annum Joni et al. (2019). Using industrial by- products in pavement engineering not only provides construction materials with possible savings over new materials, but it also reduces demands on natural construction materials. It also protects the environment and save money through reducing the amount of waste materials requiring disposal. An asphalt pavement, which is designed and constructed properly will eventually undergo various types of failures due to various reasons such as number of years pavement served, type of paving materials used and due to other environmental factors etc Tran et al. (2015) Irfan et al. (2018) and Wang et al. (2019). Among various types of pavement failures rutting or grooving on the top layer is the major type of failure reduces the life of the flexible pavements. This may be due to the insufficient compaction of base/sub-base layer or bituminous layers during construction. The type of mix used in pavement construction plays an important role for minimizing the rut depth. Stone Mastic Asphalt or Stone Matrix Asphalt (SMA), is one such mix that provides tough and a durable asphalt mix. It is highly used as a rut-resistant mix for wearing and intermediate courses.

   SMA is a gap graded asphalt mix that has a stone-on-stone contact to provide strength and has a rich mortar binder to provide durability. Generally, SMA is more expensive than conventional bituminous mixes because SMA requires high asphalt content, more durable aggregates and fibers as a stabilizer. The cost of stone matrix asphalt is found to be 20-25 % higher than the typical dense graded mixes. Thus, there is a need for the study of alternate materials which can reduce the cost of SMA mix. Reclaimed Asphalt Pavement (RAP) is the scarified pavement material containing aggregates and asphalt. Large quantities of RAP materials are generated during construction and maintenance of the highway Hanumantharao et al. (2019) and Joni et al.(2019).. The use of reclaimed asphalt pavement materials can substitute the high consumption of coarse aggregates and asphalt for SMA mix. On the other hand recycling of RAP also reduces the use of depleting natural aggregates and solves the disposal issues of reclaimed asphalt material generated from pavement rehabilitation.

   Problem statement and aim of the study: Virgin Bitumen (VG 30) is commonly used in most part of India, and moreover, Indian roads subjected to higher traffic loading and hot weather conditions. The weather conditions in India leads to variation of temperature of about 60°C at surface to 30°C at subgrade during summer. The main objective of this study was to evaluate the effect of crumb rubber modified bitumen in binder course of stone mastic mix. Which involves the study of volumetric properties and mechanical properties of SMA mix in the binder course.

2. MATERIALS AND METHOD

   The experimental program in this research studies aim to evaluate the effect of CRMB for binder course by evaluating the mechanical properties of crumb rubber modified stone mastic asphalt mixes.

   1. Materials: asphalt binder with penetration grade 40/60 and average softening point of 56°C was utilized. Table 3 and 4 illustrate the physical and chemical properties of crumb rubber modified bitumen respectively. In the present studies crumb rubber with grade 55 is selected based on the climate condition in southern part of India I S 15462 (2004) and

      density of CRMB was found to be 1.11 (gm/cm3). CRMB 55 was procured from Mangalore Refineries and Petrochemicals Limited, Mangalore , Karnataka , India.

      The composite aggregate consists of the coarse, medium, and fine aggregate with a maximum 19 mm thickness. Fine aggregate consists of the manufactured sand resulting from crushing operations going through a sieve of 2,36 mm and held on a sieve of 0,075 mm. Aggregates of for this study are collected from KMS crusher, Bagalur, Tamilnadu. The properties of aggregates are summarised in table 1.

      Table 1: Physical Properties of aggregates

      Property	Test	Natural Aggregates	RAP aggregates	IRC-SP: 79 (2008) Specifications
      Particle shape	Combined EI & FI	10.51%	22.68%	Max 30%
      Strength	Aggregate crushing	23%	19.56%	Max 30%
      Toughness	Aggregate Impact value	17.51%	9.73%	Max 18%
      Water absorption	Water absorption	0.4%	0.55%	Max 2%
      Specific gravity	Specific gravity	2.734	2.66	2.5-2.8

      The gradation for 19mm SMA is carried out as per Indian Road Congress SP: 79: 2008 as illustrated in table 2.

      Table 2: Aggregate gradation adopted for SMA (Binder course) as per MORT&H

      IS Sieve Size (mm)	Percentage passing					Desired Gradation		Obtained gradation
      	20mm down	12mm down	6.3mm down	Baghouse dust	dust	upper limit	lower limit
      26.5	100	100	100	100	100	100	100	100
      19	89.4	100	100	100	100	100	90	95.44
      13.2	11.7	100	100	100	100	70	45	62.0
      9.5	0	69.5	100	100	100	60	25	51.20
      4.75	0	0	30	100	99.6	28	20	23.96
      2.36	0	0	6	100	81.2	24	16	17.32
      1.18	0	0	0	100	67.8	21	13	14.78
      0.6	0	0	0	100	60.4	18	12	14.04
      0.3	0	0	0	100	53	20	10	13.3
      0.075	0	0	0	96	42.6	12	8	11.94

      100

      100

      80

      80

      20

      20

      0

      0.01

      0.1

      1

      Sieve Size, mm

      10

      100

      0

      0.01

      0.1

      1

      Sieve Size, mm

      10

      100

      60

      60

      40

      40

      % Passing

      % Passing

      Fig. 1: Gradation of 19mm SMA mix

      Table 3: Physical Properties of CRMB-55

      Bitumen test	Bitumen grade CRMB-55	Standard test
      Penetration @ 25 °C	57	ASTM D5
      Softening point @ °C	56	ASTM D36
      Flash Point @ °C	280	ASTM D92
      Elastic Recovery @15 °C	35	ASTM D6084
      Separation @ 3°C	2.9	ASTM D7173
      Viscosity @ 135°C (mPas)	301.5	ASTM D4402
      Ductility @ 25°C	>100	ASTM D113
      Specific Gravity	1.03	ASTM D972

      Table 4: Chemical Properties of CRMB-55 Mahrez (1999)

      Chemical Components	Test result
      Acetone extract (%)	23.1
      Rubber hydrocarbon (%)	46.6
      Carbon black content (%)	25.08
      Ash Content (%)	5.2
      Natural rubber content (%)	43.85
      Particle size	425

   2. Sample Preparations and test Method: In the design of bituminous mixes, the Marshall method of mix design is generally being practiced in India. It is a former design method developed by Bruce Marshall. In this method, the plastic deformation resistance of the cylindrical sample of the bituminous mix is measured when the mix is loaded at 5 cm/minute on its lateral surface. Marshall Stability is defined as the load carrying capacity of the specimen in kg or kN at the standard temperature of 60 °C. In the Present studies CRMB is added to SMA mix at different percentages of 5.3%, 5.7%, 6%, 6.3% and 6.6.% by the weight of total mix and filler of 10% is added to preparing SMA mixes, approximately 1200gm of aggregates are weighed and heated to a temperature of 175°C to 190°C and required a quantity of bitumen is heated to a temperature of 120°C to 165° C. Heated bitumen is added to the heated aggregates and mixed thoroughly at the specified mixing temperature by hand mixing or using a mechanical mixer. The prepared mix is placed in a pre-heated mould of 95°C to 165°C and compacted using a hammer by applying 50 blows on either side. Compacted moulds are kept for one day without disturbance, then samples are extracted from moulds and the dimensions and weight of samples are noted down. After that samples are kept in water bath maintained at 60°C for half an hour. Then the specimens are tested in Marshall testing machine and stability, flow are noted. Then the specimen properties are calculated and illustrated.

3. RESULTS AND DISCUSSIONS

   1. Marshall test results

      1. Marshall stability. The results obtained for different percentage CRMB 55 is tabulated in table 6 and illustrated in figures 2, 3, 4 and 5. Pavement may subjected to number of repeated stresses, deformation and also fatigue cracks due to the movement of heavy traffic loads on the pavement so, it is necessary that the mix design used for the pavement construction should be done properly in order to withstand stresses coming from the vehicles. Mix design should possess resistance to low temperature cracking, moisture damages and also permanent deformation. In the design of SMA mix, several properties are considered such as percentage of air voids, voids in mineral aggregates binder content, voids in aggregates are should be within the permissible limit [23].

         Table 5 SMA mix requirements as per IRC: SP: 79-2008

         Mix Design Parameters (%)	Requirements
         Air void content	4
         Bitumen content	5.8 min
         Cellulous fibres	0.3% minimum by weight of0total mix
         Voids In mineral Aggregates (VMA)	17 min
         Tensile Strength Ratio (TSR)	85 min

         Table 6 Marshall stability test results for different content of CRMB

         Bitumen Content	Air voids AV (%)	Voids in the mineral aggregates VMA (%)	Flow value (mm)	Stability (kN)
         5.7	5.79	17.97	2.07	8.85
         6	4.95	17.80	2.50	9.88
         6.3	4.12	17.64	3.18	11.10
         6.6	3.88	17.98	4.23	9.33
         6.9	3.64	18.33	5.06	8.38

         12.00

         11.00

         10.00

         9.00

         8.00

         7.00

         5.4

         5.9

         6.4

         6.9

         7.4

         12.00

         11.00

         10.00

         9.00

         8.00

         7.00

         5.4

         5.9

         6.4

         6.9

         7.4

         CRMB 55 (%)

         CRMB 55 (%)

         MARSHAL STABILITY (kN)

         MARSHAL STABILITY (kN)

         Figure 2 Stability values versus CRMB Content

         6

         FLOW (mm)

         FLOW (mm)

         5

         4

         3

         2

         1

         5.4 5.7 6 6.3 6.6 6.9 7.2

         CRMB 55 (%)

         AIR VOIDS (%)

         AIR VOIDS (%)

         Figure 3 Flow results versus CRMB Content

         7.00

         6.00

         5.00

         4.00

         3.00

         2.00

         1.00

         0.00

         7.00

         6.00

         5.00

         4.00

         3.00

         2.00

         1.00

         0.00

         5.4

         5.6

         5.8

         6

         6.2

         CRMB 55 (%)

         6.6

         6.8

         7

         5.4

         5.6

         5.8

         6

         6.2

         CRMB 55 (%)

         6.6

         6.8

         7

         6.4

         6.4

         Figure 4 Air void results versus CRMB Content

         18.40

         18.30

         18.20

         18.10

         18.00

         17.90

         17.80

         17.70

         17.60

         18.40

         18.30

         18.20

         18.10

         18.00

         17.90

         17.80

         17.70

         17.60

         5

         5.5

         6

         CRMB 55 (%)

         6.5

         7

         5

         5.5

         6

         CRMB 55 (%)

         6.5

         7

         VMA (%)

         VMA (%)

         Figure 5 VMS results versus CRMB Content

         As per table 5, which explains the mix design parameters for typical SMA mix [23]. The Marshall stability test results satisfies all the volumetric properties such stability, flow, VMA and air voids which is tabulated in tableand illustrated in figure 2, 3, 4 and 5. Among all the percentages of CRMB 55 , the stability value obtained for 6.3% of CRMB55 was higher compare to other percentages of CRMB 55 and further increase in CRMB 55 content the stability value started decreasing.

         In the case of Marshall flow value and CRMB 55 content, 6.3% of CRMB 55 achieved the desired flow value further increase in binder content leads to increase in flow value which in turn leads to increase in voids. With respect to voids filled in mineral aggregates (VMA) and Air voids (Av) i.e. VMA should be min 17% and AV should be 4% respectively , both the mix design parameter was satisfied by 6.3% of CRMB 55. Further SMA mixes samples with 6.3% CRMB 55 is prepared using Marshall mix design method which is designed and developed by Bruce Marshall and Indirect tensile strength , fatigue and rutting test is carried out.

   2. Indirect Tensile Strength: The bituminous mixes are tested for long term stripping susceptibility through the indirect tensile strength test. The specimens are tested for the change in diametrical tensile strength due to the effects of water saturation and accelerated stripping phenomenon observed due to freezing and thawing. The test is carried out for 6 sets of compacted asphalt mix. 3 mixes are tested for ITS in a dry condition and the other 3 are tested after subjecting to a freeze-thaw cycle. Test is carried out as per ASTM D 6931 (2012). ITS test is conducted for the marshall specimens having air voids of 7+/- 0.5%. The required percentage of air voids can be obtained by adjusting the number of blows for the marshall specimens. Six specimens having air void content of 7% are casted. Three of them are tested for dry. The other 3 are subjected to vacuum pressure of 13-67 kPa then wrapped through plastic film and placed in a freezer for 16 hrs at 18+/-3°C. After freezing of the specimens, they are subjected to thawing by keeping them in a water bath maintained at 60+/-1°C for 24 hours. Both dry and wet specimens are placed in a water bath at 25+/-0.5°C for 2hour then tested for indirect tensile strength. Table explains ITS results. Referring to table 7 illustrates 6.3% CRMB 55 content showed higher tensile strength and tensile strength ratio compare to remaining percentage of CRMB 55 i.e. 5.7%, 6%, 6.6% and 6.9%.

      Table 7 ITS test results for conventional SMA mix (CRMB 55)

      Samples	Average height of the sample (mm)	Average diameter of the sample (mm)	Maximum load (N)	Tensile strength (kPa)	Average tensile strength (kPa)
      Unconditioned
      S1	73.90	101.05	4470	381.01	349.87
      S2	73.37	102.57	3050	257.97
      S3	73.54	101.17	4800	410.65
      Conditioned
      S1	71.96	101.37	3582	312.56	308.39
      S2	71.44	101.42	2945	258.73
      S3	69.86	102.42	3978	353.88
      Tensile Strength Ratio (TSR)					88.14%

      rut depth mm

      rut depth mm

      Immersion Wheel Tracking Test / Rutting test. For rutting test the aggregates and bitumen are preheated for specified temperature and mix is prepared in the pan. The prepared mix is poured into the rutting mould having dimensions of 600mm × 100 mm × 200 mm. The specimens are compacted using UTM for the required thickness. Then the prepared mould is fixed in the testing equipment and tested for the tyre pressure of 5.6 kg/cm2 with speed of the wheel as 25 passes/minute. The rut depth is taken for every 500 passes until 10000 passes or the rut depth is equal to 12mm (whichever is encountered first). The rut depth readings are taken on either side of the specimen at a distance of 15 cm from the edges and average rut depth is calculated. Figure 6 and Figure 7 shows 6.3% content of CRMB 55 played a key role in reducing the rut depth compared to 5.7%, 6%, 6.6%, 6.9% of CRMB 55 content of in SMA mix

      6.00

      5.00

      4.00

      3.00

      2.00

      conventional SMA mix

      6.00

      5.00

      4.00

      3.00

      2.00

      conventional SMA mix

      1.00

      0.00

      1.00

      0.00

      0

      2000 4000 6000 8000 10000 12000

      0

      2000 4000 6000 8000 10000 12000

      Number Of Passes

      Number Of Passes

      Figure 6 Rut Depth Values for 45 mm thickness specimen

      6.00

      5.00

      Rut depth in mm

      Rut depth in mm

      4.00

      3.00

      2.00

      1.00

      CONVENTIONAL SMA

      0.00

      0 2000 4000 Num 6000 passes 8000 10000 12000

      ber of

      Figure 7 Rut Depth Values for 45 mm thickness specimen

   3. Indirect Tensile Fatigue Test / Fatigue Test

   The fatigue test is conducted on the conventional SMA mix with 6.3% of CRMB 55 ITFT apparatus. In the indirect repeated load testing, the fatigue value is determined using recoverable horizontal and vertical deformation that occurred by applying dynamic loading on the specimen. The specimen is tested at three different temperature (25oC, 35oC and 45oC) and four stress levels (10%, 20%, 30% and 40% of failure stress). The specimen of 6.3% CRMB 55 content is deemed to be failed when it undergoes vertical deformation of 5 mm due to fatigue loading. The Figs 8 10 shows the log-log plot of fatigue cycles vs Micro strain (horizontal tensile strains) for three types of sample mixes at three temperature. The figures also provides the respective regression equation of the form logNf = logk1 + k2log. It can be observed from the above figures and summarized data, the y – intercept (logk1) of regression equation represents the number of fatigue cycle at failure for unit strain. At lower room temperatures (i.e., 25oC and 35oC), the intercept is highest for SMA mix with 6.3% CRMB 55 yielded good results compare to SMA mix @ 45 oC.

   3

   y = 0.7822x + 1.5693

   R² = 0.9371

   3

   y = 0.7822x + 1.5693

   R² = 0.9371

   1

   0.5

   0

   1

   0.5

   0

   0

   0.5

   1

   1.5

   Log(Microstrain),

   2

   2.5

   3

   0

   0.5

   1

   1.5

   Log(Microstrain),

   2

   2.5

   3

   4.5

   4.5

   y = 0.7101x + 2.1893

   R² = 0.9189

   y = 0.7101x + 2.1893

   R² = 0.9189

   4

   3.5

   4

   3.5

   y = 0.843x + 1.5261

   R² = 0.8713

   y = 0.843x + 1.5261

   R² = 0.8713

   2.5

   2

   2.5

   2

   y = 0.8032x + 1.1213

   R² = 0.8597

   y = 0.8032x + 1.1213

   R² = 0.8597

   1.5

   1.5

   40% Stress

   30% Stress

   20% Stress

   10% Stress

   40% Stress

   30% Stress

   20% Stress

   10% Stress

   4

   4

   y = 0.6366x + 1.9225

   R² = .8817

   y = 0.6366x + 1.9225

   R² = 0.8817

   3.5

   3.5

   y = 0.7388x + 1.4466

   R² = 0.8469

   y = 0.7388x + 1.4466

   R² = 0.8469

   3

   2.5

   3

   2.5

   y = 0.781x + 1.0876

   R² = 0.879

   y = 0.781x + 1.0876

   R² = 0.879

   10% Stress

   10% Stress

   2

   2

   20% Stress

   20% Stress

   Log(Fatigue Cycle)

   Log(Fatigue Cycle)

   Log(Fatigue Cycles)

   Log(Fatigue Cycles)

   Figure 8: Log Log plot of Fatigue Cycles vs Micro strain for conventional SMA mix at 25oC

   1

   0.5

   0

   1

   0.5

   0

   0

   0.5

   1

   1.5

   2

   2.5

   3

   3.5

   0

   0.5

   1

   1.5

   2

   2.5

   3

   3.5

   Log(Micro Strain),

   Log(Micro Strain),

   1.5

   1.5

   y = 0.7077x + 1.2146

   R² = 0.9052

   y = 0.7077x + 1.2146

   R² = 0.9052

   30% Stress

   40% Stress

   30% Stress

   40% Stress

   Figure 9: Log Log plot of Fatigue Cycles vs Micro strain for conventional SMA mix at 35°C

   4

   3.5

   y = 0.5031x + 2.2022

   R² = 0.7871

   4

   3.5

   y = 0.5031x + 2.2022

   R² = 0.7871

   3

   y = 0.6524x + 1.6409

   R² = 0.9228

   3

   y = 0.6524x + 1.6409

   R² = 0.9228

   1

   0.5

   0

   1

   0.5

   0

   0

   0.5

   1

   1.5

   2

   2.5

   3

   3.5

   0

   0.5

   1

   1.5

   2

   2.5

   3

   3.5

   Log(Microstrain),

   Log(Microstrain),

   2.5

   y = 0.6005x + 1.0977

   2 R² = 0.9274

   1.5

   2.5

   y = 0.6005x + 1.0977

   2 R² = 0.9274

   1.5

   10% Stress

   20% Stress

   30% Stress

   10% Stress

   20% Stress

   30% Stress

   Log(Fatigue Cycles)

   Log(Fatigue Cycles)

   Figure 10: Log Log plot of Fatigue Cycles vs Micro strain for conventional SMA mix at 45°C

4. CONCLUSIONS

   Based on the laboratory studies carried out, following conclusions can be derived.

   1. Stability / Strength of stone mastic asphalt mix is increased by adding 6.3% of CRMB 55.

   2. The volumetric properties of CRMB 55 in SMA mix for binder course, satisfies the standard requirements.

   3. Addition of 6.3% of CRMB55 increases the fatigue life of SMA mix at various temperature and stress levels, the mixture found to achieve higher fatigue life for 6.3% CRMB 55 compared to other percentage of CRMB 55.

   4. Addition of 6.3% of CRMB55 to SMA mix plays important role in improving the rutting resistance.

   5. Use of different modified binders, aggregate gradation and recycled materials are recommended for future studies.

   ORCID

   0000-0002-7549-7723

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