There are different places in India where natural stone aggregates are not available for constructional work. Plastic coated OBBA can solve the problem of shortage of stone aggregate to some extent. The engineers are always encouraged to use locally available materials. The present investigation is carried out to evaluate the plastic coated OBBA as an alternative material for bituminous road construction. Shredded waste plastics are mixed with OBBA in different percentages as 0.38, 0.42, 0.46, 0.50, 0.54, and 0.60 of the weight of brick aggregates. Marshall Method of mix design is carried out to find the optimum bitumen content of such bituminous concrete mix prepared by plastic coated OBBA. Bulk density, Marshall Stability, flow, Marshall Quotient, ITS, TSR, stripping, fatigue life, and deformations have been determined accordingly. Marshall Stability value of 0.54 percent of plastic mix is comparatively higher than the other mixes except 0.60 percent of plastic mix. Test results are within the prescribed limit for 0.54 percent of plastic mix. There is a significant reduction in rutting characteristics of the same plastic mix. The fatigue life of the mix is also significantly higher. Thus plastic coated OBBA is found suitable in construction of bituminous concrete road.
There are different states in India where rocks are not locally available. The stone aggregates need to be transported from other places for constructional work. Modified overburnt brick aggregate (OBBA) can solve the problem of shortage of stone aggregate to some extent. Bricks are produced from the locally available soil by burning the molded earth to desired forms. Approximately 5–10% of bricks manufactured in modern kilns are rejected because of their nonconformity with relevant specifications [
The properties of plain OBBA are weaker compared to natural stone aggregate. It has lower specific gravity, high pore rate and thus high water absorption, and lower impact and crushing resistance. The mechanical properties of bituminous concrete with plain OBBA are usually inferior to those of bituminous concrete with natural stone aggregate. In a recent study it is found that the bituminous concrete mix with 4% cement coated OBBA shows considerable improvement in various mechanical properties of bituminous concrete mix compared to the plain OBBA concrete mix [
Use of brick aggregate in concrete preparation is not new to the engineers. In Germany during the post-Second World War period, it was necessary to satisfy an enormous demand for the supply of constructional materials along with the removal of debris of war for rebuilding the country. By using these rubbles and demolished aggregates, it was possible not only to reduce site clearing costs but also to meet the need for building materials [
If the thin plastic comes in contact with hot aggregate it fills up the pores in the aggregate and forms a thin film of plastic coating on the surface of the aggregate. Plastic coated OBBA becomes less porous and thus reduces water absorption to a great extent.
In this study plastic coated OBBAs are used to prepare the bituminous concrete mix. OBBAs are heated to a temperature of 190°C and shredded plastic bags are spread over the hot aggregates. In this temperature, the thin plastic pieces get softened and form a coating over the aggregate of about 90–95% of the surface area. Shredded waste plastic bags are mixed with OBBA in different percentages as 0.38, 0.42, 0.46, 0.50, 0.54, and 0.60 of the weight of brick aggregates to improve the properties. The bituminous concrete mix with plastic coated OBBA shows considerable improvement in various mechanical properties of the mix compared to the plain OBBA. The basic objective of the study is to utilize the waste overburnt brick as well as waste plastic in an ecofriendly way. The main objective of the present study is to evaluate the plastic coated OBBA as an alternative material for bituminous road construction.
Bitumen is commonly known as asphalt cement or asphalt. It is mainly used as binder mixed with aggregate particles to form bituminous concrete. In this study, VG-30 grade bitumen has been used as binder to prepare the bituminous concrete mix. The penetration test of bitumen is carried out at a temperature of 25°C. The properties of bitumen used in this study are presented in Table
Properties of bitumen.
Sl. number | Test performed | Test result | Acceptable values |
---|---|---|---|
1 | Specific gravity | 0.99 | 0.99 (minimum) |
2 | Penetration (mm) | 83 | 80–100 |
3 | Softening point (°C) | 47 | 35–50 |
4 | Ductility (cm) | 92 | 75 (minimum) |
Aggregates normally constitute 90–95 percent of the weight of the total mix. The function of aggregate in a bituminous concrete mix is to provide a rigid skeleton and to reduce the space occupied by the bitumen content and fines. Aggregates have certain physical properties which judge the suitability of aggregate for specific uses. The physical properties of aggregates generally refer to the structure of the particles that form the aggregate. Though it is difficult to model directly the performance of bituminous mixture using aggregate properties, the properties like gradation, hardness, toughness, and porosity have major effects on the performance of bituminous mixture. Aggregate impact, Los Angeles abrasion, water absorption, and soundness test are carried out as per AASHTO T 96-02 (2015) and ASTM codes [
Properties of aggregate.
Test performed | Stone aggregate | OBBA | Plastic coated OBBA | |||||
---|---|---|---|---|---|---|---|---|
0.38% | 0.42% | 0.46% | 0.50% | 0.54% | 0.60% | |||
Aggregate impact value | 22.4% | 29.6% | 28.6 | 27.3% | 26.2% | 24.6% | 23.9% | 23.8 |
Los Angeles abrasion value | 15.1% | 32% | 31.3 | 31.0% | 30.1% | 27.6% | 25.2% | 25.2 |
Water absorption value | 0.96% | 6.6% | 5.9 | 5.3% | 4.9% | 3.5% | 2.9% | 2.5 |
Specific gravity | 2.64 | 1.89 | 1.99 | 2.04 | 2.16 | 2.24 | 2.45 | 2.46 |
The mineral fillers in a bituminous concrete mix consist of finely divided mineral matters such as rock dust, slag dust, hydrated lime, hydraulic cement, fly ash, loess, and other suitable mineral matters. Mineral fillers should have 100 percent of the particles passing 0.60 mm, 95 to 100 percent passing 0.30 mm, and 70 percent passing 0.075 mm. In this study, stone dust has been used as mineral filler. The standard test method mentioned in ASTM code is followed [
Properties of stone dust.
Sl. number | Test performed | Test result |
---|---|---|
1 | Specific gravity | 2.7 |
2 | Bulk density (kN/m3) | 18.1 |
Plastic is an essential component of numerous consumer products. All kinds of plastic are not the same. They are usually synthetic and derived from petrochemicals, but few of them are partially natural too. Society of the Plastics Industry (SPI) classifies the different types of plastic as SPI Code numbers 1 to 7. Plastic with SPI code 1 is made of Polyethylene Terephthalate (PET) commonly used to make beverage bottles, medicine jars, combs, and so forth. Plastic with SPI code 2 is made of High-Density Polyethylene (HDPE) commonly used to make containers for milk, motor oil, and so forth. Plastic with SPI code 3 is made of polyvinyl chloride (PVC) commonly used to make PVC pipes. Plastic with SPI code 4 is made of Low-Density Polyethylene (LDPE) commonly used to make plastic cling wrap, sandwich bags, squeezable bottles, plastic grocery bags, and so forth. Plastic with SPI code 5 is made of polypropylene (PP) commonly used to make syrup bottles, stadium cups, and so forth. Plastic with SPI code 6 is made of polystyrene (PS) commonly used to make disposable coffee cups, packing foam, and so forth. Plastic with SPI code 7 is made of Polycarbonate (PC) and polylactide commonly used to make compact discs, medical storage containers, and so forth [
Waste plastic carry bags are used in this study. Plastic carry bags are a type of shopping bags made from various kinds of plastic materials. Most of the carry bags are made up of Polyethylene (PE), Polypropylene (PP), and so forth. PE is the most popular and most widely used plastic all over the world. This material has wide range of properties with excellent fatigue and wear resistance. It has excellent impact resistance, low moisture absorption, and high tensile strength. The material is characterized by its thickness and softening temperature. The test results of plastic used in the study are tabulated in Table
Properties of plastic.
Type of material | Thickness ( |
Softening point |
---|---|---|
Cup | 150 | 100–120°C |
Parcel cover | 50 | 100–120°C |
Carry bags | 10 | 100–120°C |
Film | 50 | 100–120°C |
Bituminous concrete is a composite material commonly used to surface roads in flexible pavement. It consists of mineral aggregate bound together with bitumen and compacted. Bituminous concrete is prepared by heating the bitumen in order to decrease its viscosity and to dry the aggregate in order to remove the moisture from it prior to mixing. In this study, the oven dried OBBAs are heated to 190°C temperature and then plastic shreds of size less than 2.36 mm are mixed on the aggregate. When the plastic shreds come in contact with the hot aggregate they melt and form a thin film on the surface of the aggregate. The coated aggregate is kept in room temperature for 24 hrs. The coated aggregate, mixed with hot bitumen in 150°C temperature, prepares the bituminous concrete mix. The bituminous concrete is characterized through different laboratory experiments [
Bituminous concrete mix is commonly designed by Marshall Method. In this method, the resistance to plastic deformation of cylindrical specimen of bituminous mixture is measured. The test procedure is used in the design and evaluation of bituminous paving mixes. In this present study, Marshall Test is performed with stone aggregate as well as with overburnt brick aggregate. The standard gradation of aggregate to prepare the test specimen, followed in this study as per MoRT&H [
Gradation of aggregate for bituminous concrete.
Sieve in mm | % passing by weight of specimen | Cumulative % passing | Cumulative % retained | % of aggregate and mineral filler |
---|---|---|---|---|
19 | 100 | 100 | 00 | Coarse aggregate 38% |
13.2 | 90–100 | 89.5 | 10.50 | |
9.5 | 70–88 | 79.0 | 21.0 | |
4.75 | 53–71 | 62.0 | 38.0 | |
|
||||
2.36 | 42–58 | 50.0 | 50.0 | Fine aggregate 55% |
1.18 | 34–48 | 41.0 | 59.0 | |
0.60 | 26–38 | 32.0 | 68.0 | |
0.30 | 18–28 | 23.0 | 77.0 | |
0.15 | 12–20 | 16.0 | 84.0 | |
0.075 | 4–10 | 7.00 | 93.0 |
Mineral filler 7%.
Design criteria as per MoRT&H.
Test performed | Minimum stability |
Flow (mm) | Compaction level (both sides) | Air void | VMA (minimum) | VFB | Marshall Quotient (kN/mm) | Tensile strength ratio (minimum) |
---|---|---|---|---|---|---|---|---|
Results | 9 kN | 2–4 | 75 | 3–5% | 10% | 65–75% | 2–5 | 80% |
Marshall Test results on different aggregate.
Properties | Stone | OBBA | Plastic coated OBBA | |||||
---|---|---|---|---|---|---|---|---|
0.38% | 0.42% | 0.46% | 0.50% | 0.54% | 0.60 | |||
OBC (%) | 05.10 | 9.4 | 9.0 | 8.8 | 8.3 | 8.0 | 8.0 | 8.0 |
Unit weight (kN/m3) | 24.1 | 23.0 | 23.1 | 23.2 | 23.3 | 23.7 | 23.9 | 24.0 |
Marshall Stability (kN) | 17.50 | 8.5 | 9.8 | 10.6 | 11.8 | 12.4 | 13.3 | 13.4 |
Flow (mm) | 3.90 | 3.1 | 3.29 | 3.5 | 3.75 | 3.82 | 3.9 | 4.2 |
% of VA | 4.12 | 4.88 | 4.90 | 4.91 | 4.95 | 5.0 | 5.0 | 5.2 |
% of VMA | 14.27 | 21.9 | 21.7 | 21.6 | 20.4 | 20.1 | 19.9 | 18.6 |
% of VFB | 68.00 | 83 | 80.1 | 79 | 78.1 | 74.4 | 74.2 | 74.1 |
Marshall Quotient (kN/mm) | 4.49 | 2.74 | 2.98 | 3.02 | 3.15 | 3.24 | 3.41 | 3.27 |
Stripping value test is the determination of binding strength of the aggregate and bitumen. Standard guideline as specified by IS: 6241-1971 is followed to complete the test. 200 gm of clean, oven dried aggregates passing 20 mm sieve and retained on 12.5 mm sieve is heated to 150°C and mixed with 5% bitumen by weight of aggregate which is preheated to 160°C before the preparation of mix [
Stripping value test results.
Sl. number | Plastic for coating aggregate used in the mix | Stripping (%) |
---|---|---|
1 | 0.38% | 9 |
2 | 0.42% | 5 |
3 | 0.46% | 2.5 |
4 | 0.5% | 0 |
5 | 0.54% | 0 |
6 | 0.60% | 0 |
The indirect tensile strength (ITS) test is used to measure the tensile strength of the bituminous concrete which can be used to assess the fatigue behavior. The standard procedure as per ASTM D 6931 is followed to prepare the sample for the test as well as to measure the failure loads [
Indirect tensile strength test results.
Sl. number | Plastic % for coating of OBBA | The indirect tensile strength (N/mm2) | Tensile strength ratio (%) | |
---|---|---|---|---|
Unconditioned | Conditioned | |||
1 | 0.38% | 0.86 | 0.63 | 73.00 |
2 | 0.42% | 1.06 | 0.82 | 77.36 |
3 | 0.46% | 1.24 | 0.99 | 79.84 |
4 | 0.50% | 1.28 | 1.04 | 81.25 |
5 | 0.54% | 1.31 | 1.08 | 82.44 |
6 | 0.60% | 1.32 | 1.08 | 81.81 |
Resilient modulus (RM) of bituminous concrete mix is an important parameter for flexible pavement design and evaluation. It is defined as the ratio of the repeated stress to the corresponding resilient strain. The resilient modulus of a tested sample is calculated from the following equation:
Rutting is a longitudinal depression on groove in the wheel tracks. The ruts are formed according to the width of the wheel path. Pavement rutting not only decreases the service life of the roads but also creates perils for the road users. Rutting characteristics are studied using immersion wheel tracking device. Wheel tracking test is widely used for evaluating the rutting potential of pavements. In this method, a steel wheel with solid rubber tire is rolled to and fro over the specimen of bituminous surface of size 600 mm × 200 mm × 50 mm to test the rutting potential and then rutting depth is measured up to 8000 passes [
Repeated load test is conducted using fatigue testing machine developed by Geotran, New Delhi. An attempt is made to study the performance of bituminous concrete with plain and 0.54% plastic coated brick aggregate mix under the applied loads, 2 kN, 3 kN, and 4 kN, respectively, and frequency 5 Hz with sinusoidal type of waveform is applied at temperatures between 35°C and 37°C [
The results of Marshall Test show that the stability of the mix increases in equal proportion with the increase of the amount of plastic in the OBBA. At 0.60% plastic coating the value reaches up to 13.4 kN. But the flow value for such mix is 4.2 which is more than the highest permissible value 4.0 as mentioned in Table
Volumetric properties of bituminous concrete mix (using 0.54% plastic coated OBBA) at binder content versus stability, flow, air voids, bulk density, voids filled with bitumen, and void in mineral aggregate.
Stripping value reduces with the increase in the percentage of plastic coating. Stripping value is least when the percentage of plastic coating is 0.50 and 0.54%, respectively. It also satisfies the acceptable value (as per Table
Bituminous pavement surface can develop distress due to fatigue. It is caused by tensile strains generated in the pavement not only by traffic loading but also by temperature variation. If the tensile strength is higher and the tensile strength ratio is within the permissible limit, in another way, it can be said that bitumen concrete mix is safe against fatigue. From Table
The test is performed at different temperatures such as 5°C, 25°C, 35°C, and 45°C. The test results for resilient modulus test, obtained in the study, are shown in Figure
Resilient modulus values for the mix plain and modified aggregate (plastic coated).
In the present study, the stress that the wheel applies to the specimen is 0.70 MPa. Two LVDTs (Linear Variable Differential Transducers) are fitted to the axle of the rubber wheel to monitor the rut depth. The output of the LVDT is connected to a computer. Dedicated software monitors the rut depth and plots the graph for number of passes versus rut depth. The wheel tracking results are shown in Figure
Rut depth versus number of passes.
The test result shows that the fatigue life of bituminous concrete with plastic coated brick aggregate is much higher than that of bituminous concrete with plain brick aggregate mix with equal tensile strain. This is due to the hardness of aggregate mix with plastic coating. Figure
Tensile strain versus number of repetitions.
The results of the study reveal that the 0.54% waste plastic coated brick aggregate shows better performance as road aggregate. From this study, the following conclusions can be drawn: The stability of the bituminous concrete mix with 0.54% plastic coated brick aggregate is 56% higher than the mix with plain brick aggregate. Moisture susceptibility of the mix with modified aggregate is lesser than the plain mix. The TSR value for the mix with modified aggregate is 9.44% higher than mix with plain brick aggregate which indicates the improvement in the moisture sensitivity of the mix. Resilient modulus of the mix with 0.54% plastic coated brick aggregate at 35°C is 102% higher than the plain mix which indicates the higher stiffness of the mix. Rutting failure for the mix with 0.54% plastic coated brick aggregate is lesser than the plain mix and it points out that the failure for this mix may take place at later stage. Fatigue life of the mix with modified brick aggregate is also higher.
Thus, plastic coated overburnt brick aggregate can be used as an alternative material for bituminous road construction.
The authors declare that they have no competing interests.