The continuous rise in waste rubber generated at an alarming proportion from motor car tyres used has become a dilemma. It is estimated that around the world, about a billion tires are dumped up in landfills each year. The recycle of waste tires economically is almost not possible. When burnt, they are harmful to the environment and could also create serious health hazards.
The study of these waste materials has been widely carried out for the last twenty years. Waste tire rubber has been associated with several applications such as being used as a replacement for coarse aggregates in asphalt pavements. The disposal of these tires as waste material has been a major environmental concern. As such, researchers and engineers alike thought of finding a way of putting the material to good use in civil engineering field. Then the idea of using scrap tire as coarse aggregate by shredding tyres into required sizes of coarse aggregates in line with mix design specifications.
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Asphalts which have tire rubber incorporated in them are known to be durable, as their resistance to cracking increases. Permanent deformation resistance also increases with susceptibility to temperature reduction.
C:\Users\professorre\Documents\My Received Files\scrap tyre. ( www. csiro.au.com).jpg
Fig 1.1 Scrap tire deposited in landfills. (www.csiro.au.com)
The number of scrap tires added to our landfills can only be reduced by recycling them, which is the only feasible choice left and it's a promising prospect.
Scrap tires can be used in two different processes, wet and dry process. Dry process requires scrap tyre to serve as aggregates and then coated with asphalt binder, while in the wet process, it serves as the modifier to the binder and then used to coat the aggregate particles.
1.2 Problem statement.
Most countries fail to control the disposal of their waste materials properly, especially the solid waste. Tire rubber has been a significant trouble for countries as millions of them are added to our landfills all the time. Waste tire is known to serve as a breeder for mosquitoes and other insects and also a waste of valuable land. (Scrap tire management council, 1999) recognises that this is not a good technique for disposing waste tyre.
So, the question is what do u really do with a tire that has been used and completely worn out so much that it cannot be used in a car anymore. The researchers then said why not we shred this tire, use it as an aggregate in asphalt pavement and let it be driven on by more cars. This method will most certainly reduce the number of scrap tires out there and also addresses the environmental problem caused by scrap tire disposal. (Rubber pavement association, 2006) studies also shows that rubber tire asphalt concrete reduces noise by around 50 %.
Objectives of study.
The objectives of this study are:
To investigate the effects of scrap tire rubber on the properties asphaltic concrete.
To determine by Marshall Test the optimum conditions for asphalt concrete with scrap rubber tire as coarse aggregates.
To investigate the feasibility and utilization of recycled products in civil engineering with regards to asphalt pavements.
Scope of study.
The scope of this study concentrates on preparing asphalt concrete mix based on the Malaysian mix design specified by JKR.
Asphalt concrete mixture that will be used in this study is (ACW 14) asphalt concrete for wearing course, with scrap rubber tire as part of coarse aggregate.
This study will focus on finding two Marshall Parameters. The Marshall Stability and flow.
All laboratory works will be conducted at highway laboratory in Lagenda Kolej.
2.1 Types of Pavements
A highway pavement is when processed materials are used to prepare superimposed layers and are placed on the natural soil sub-grade to form a structure, and charged with the function of distributing vehicle applied loads to the sub-grade.(Mathew, 2009) Pavements are of two categories in general, namely:
Flexible Pavement and
Flexible pavements and Component Layers.
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Bituminous flexible pavement surfacing are the most widely used around the world. The seasonal and daily significant temperature variations, the significant intensity of traffic due to over loading of trucks and commercial vehicles has been known to be responsible for the development of failure symptoms in the early life of pavements such as deformation, cracking and pot holes on surfaces.
Multiple layers of granular natural materials are used to construct a pavement that is said to be flexible; it is then covered by a bitumen surfaced layer. The load transmitted from the tyre bends (flex) the pavement. The aim in the design of this pavement structure is to ensure that excess load on a layer transmitted from the tyre is avoided. When a particular layer is overstressed as a result of excessive flexing, the pavement will ultimately fail. In flexible pavements, the characteristics strength of each layer varies, therefore, distribution pattern of load varies from layer to layer. The lower layers of the structure are considered to have the weaker materials (most flexible) and the top layer having the stronger material (least flexible).
High stress levels occur at the surface of the pavement, since only a small portion of area is in contact with the wheel load. In contrast, the use of weaker materials in the lower part of the pavement structure is enabled by lower stress level occurrence as a result of the wheel load being applied to a larger area.
22.214.171.124 Surface Course.
Surface course is the uppermost layer which is made of bituminous materials and mineral aggregate mixtures, usually constructed of dense graded asphalt concrete (AC). The surface course of a flexible pavement is the primary concern of this research study.
The functions and requirements of this layer are:
Serves as waterproof material to underlying bases, and provides characteristics such as friction, smoothness and drainage.
Surface should provide a smooth and skid-resistant riding surface.
Surface should be tough enough to resist distortion under traffic.
126.96.36.199 Base Course.
The base course underlies the surface course and consists of sand and crushed stone of gravel. This layer also contributes to the sub-surface drainage and the distribution of additional load.
Under the base course is the sub-base, this may be omitted only if the subgrade is of a very high quality soil. The sub-base also provides structural support and improves drainage.
Deep under is the subgrade layer, this is the layer that carries the applied wheel load. The layer should be strong enough to support wheel loads, else, the result will be failure as their will be excessive flexing. It is important that the subgrade never gets overstressed; the compaction of the subgrade should be at a desirable density, close to the optimum moisture content. (Mathew, 2009)
Fig 2.1 Flexible pavement. (www.nra.co.za)
Rigid Pavement and Component Layer.
A rigid pavement is also known as a Portland Cement Concrete (PCC). As the name implies, a rigid pavement is substantially stiffer than a flexible pavement. This stiffness is as a result of the high modulus of elasticity of PCC which in turn results in low deflection under loading. (Thomas, 2006). Rigid pavements can have steel reinforcement, this is used to control thermal stresses to lower or eliminate joints and maintain tight crack widths. Rigid pavements can serve for as long as 20-40 years without maintenance or rehabilitation. Rigid pavements require around two weeks for curing and hardening before it can be used.
188.8.131.52 Surface Course.
This is the uppermost layer which serves as the waterproof layer to the underlying ones and also the layer that comes in contact with traffic loads. This layer is made of Portland Cement Concrete. Some of the functions of the layer is to provide smoothness, friction, drainage and noise control. This surface usually varies in thickness, but not outside the range of 6 inches for light traffic and 12 inches for heavy traffic.
184.108.40.206 Base Course.
This layer underlies the surface course. This layer helps in preventing possible soil movement of the subgrade due to slab pumping.(ACPA, 2001) The layer provides:
Distribution of additional load.
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Contributes to drainage and resistance to frost.
This is the layer between the base course and the subgrade. The layers primary function is to serve as a structural support, usually performs same characteristics as the base course, such as:
Working platform for construction
This layer is sometimes omitted if the subgrade is of high quality.
This is the existing soil layer, and should be sufficiently strong enough to withstand all stresses caused by compaction traffic at a time when the upper layers such as the sub-base and surface course layers are being constructed. A very good subgrade allows for the omission of the sub-base.
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Fig 2.2 Rigid pavement. (www.nra.co.za)
2.2 Asphaltic Concrete Bituminous Mix (AC)
This is a mixture of coarse and fine aggregates, filler and bituminous mixture which is mainly used for road pavements.
One of the primary materials used in the construction and maintenance of roads around the world is Asphalt concrete. The relative cheapness and abundance of asphalts and aggregate materials which exhibit properties such as durability, stability, moisture resistance when combined effectively and resistance to permanent deformation has qualified the materials as the best for road construction. It has become more important, that year after year, these materials perform at their utmost levels to fight off environmental effects, and the effects of increased traffic. ( Lytton et al, 2005)
The continuous increase in traffic volume around the world has prompted the desire for proper pavement performance. If the subgrade can carry all loads induced by traffic under all conditions of service appropriately through pavement layers, then bituminous pavement is assured of adequate performance.
There are variety of reasons that can be responsible for the degradation of Asphalt pavement when the best materials are used, traffic loading is usually a typical distress cause. Asphalt concrete pavement performance can be significantly affected by water, environmental conditions such as temperature. The quality of asphalt concrete deteriorates with moisture. (Kollipara, 2003).
Common Defects in Flexible Pavement
The common defects in asphalt pavements are of two major types, namely:
2.3.1 Fatigue Cracking in Asphalt Concrete.
Fatigue cracking is an important distress in Asphalt concrete pavement that must be avoided. This distress is caused as a result of repeated bending caused by the passage of heavy loaded trucks over the pavement surface. Some researchers have identified the "alligator" or "chicken wire" crack pattern as the classical type of failure which appears on the pavement surface. When a car moves on the pavement surface, and depression is caused, it allows cracks to be initiated longitudinally at the edge of the depressed zone moving in the same direction as the car in parallel. As wheel loading increases repeatedly, the evidence of alligator pattern shows. Fatigue models determined experimentally can be used to predict the approximate asphalt pavement performance. (Frocht, M.M, 1948)
Fig 2.3 Fatigue crack (www.tehamacountypublicworks.ca.gov)
Fatigue crack severity levels are classified as follows according to FHWA.
Low. This is when an area of cracks has little or no connecting cracks; when the cracks are not sealed or spalled. No evident pumping.
Moderate. This is when an area of interconnected cracks tend to form a complete pattern. Here, there may be spalled or sealed cracks; but still no evident pumping.
High. This is when a complete pattern is formed by an area of severely spalled interconnected cracks. There may be evident pumping here.
C:\Users\professorre\Documents\My Received Files\low fat.jpg C:\Users\professorre\Documents\My Received Files\moderate fat.jpg
Fig 2.4Low severity fatigue fig 2.5 moderate severity fatigue
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Fig 2.6 High severity fatigue. www.tfhrc.gov
2.3.2 Permanent deformation in Asphalt Concrete.
Permanent deformation (rutting) is another distress that occurs in Asphalt pavements. This distress occurs particularly in hot and humid climates. Asphalt is known to soften at high temperatures. Permanent deformation is something that should be carefully considered in the design of Hot mix Asphalts. The viscosity of asphalt binder falls to a low point during hot weather months, thereby making resistance to rutting critical. Quality aggregate and proper gradation can be used to control permanent deformation. (Freddy L, Roberts et al, 1996)
Out of all distress types that affect the performance of hot mix asphalts, permanent deformation is the one most likely to be a sudden failure due to unsatisfactory mix. Other distresses are typically long-term failures. Sometimes permanent deformation is more evident after a rain when depressed areas are rain-filled with water. This is a danger to vehicles as it tends to pull the vehicle, with this, the driver could lose control and possibly leading to accidents.
Fig 2.7: Rutting. (www.halifax.ca)
According to the Jabatan Kerja Raya (JKR) Malaysia's specifications, severity of rutting is classified into three levels.
Low severity level: This is where rut depth is less than 12mm.
Moderate severity level: This is where rut depth is between 12mm and 25 mm.
High severity level: This where we have depths greater than 25mm.
2.4 Components of Asphalt concrete.
The key to having an effective and long lasting asphalt concrete is by having an economical blend of the best material constituents which make asphalt concrete. These materials are : coarse aggregate, fine aggregate, bituminous binder and filler.
2.4.1 Fine Aggregate.
This mainly is an aggregate that passes a sieve test of 2.0mm and contains no more coarse material than allowed in BS EN 13043
2.4.2 Filler Aggregate.
This is mainly aggregate that passes a sieve test of 0.063mm as approved by BS EN 13043. Examples are the Portland cement, hydrated lime and fly ash. Filler serves an important function as material tends to fill voids so as to produce a durable, dense mix and also stiffen the mix.
2.4.3 Bituminous Binder.
Bitumen binder is the black, viscous and oily material obtained by refinery process from crude oil. For the purpose of asphalt concrete, bitumen type should be of penetration grade 60-70 or 80-100. The quality of bitumen binder used is important as it holds the key to binding other materials together as a coherent mass. Under normal temperature, bitumen usually is fairly hard. Bitumen becomes soft when heated and flows. It is its ability to solidify when cooled, and mixed with aggregate to form a pavement surface that makes it a good material for asphalt concrete.
Bitumen property is dependent on the original binder property and on ageing of the binder which occurred during production, storage, transport and laying. Bitumen also serves as a water proof material at a quite reasonable and low cost. (Potgieter, 2004)
2.4.4 Coarse aggregate.
This is aggregate predominantly retained on No. 4 (4.75mm) sieve size. Examples of coarse aggregates are crushed rock and blast furnace slag. The stability of a mixture is dependent on the shape of coarse aggregate.(Maupin and Mokarem, 2006). Coarse aggregate could be angular in shape and free from dust, clay, vegetable and other organic material. (JKR)
2.5 Aggregate gradation.
Gradation is considered the most important property of aggregate that influences the performance of asphalt pavement. Some properties of hot mix asphalt such as stiffness, stability, durability, fatigue resistance and resistance to permanent deformation can be largely affected by aggregate gradation. Gradation of aggregate normally is expressed as a total percentage passing various sieve sizes.
There are three types of standard design aggregate gradation, namely; Asphalt concrete wearing course 10 (ACW 10), Asphalt concrete wearing course 14 (ACW 14) and the Asphalt concrete binder course 28 (ACB 28). The ACW 14 is selected for the purpose of this study as both control and modified specimen. The standard gradation is referred from the standard specification for road works, Malaysia, JKR/SPJ/2008-S4.
Gradation is determined by sieve analysis. Sieves are stacked from the largest openings on top to the smallest opening at the bottom and a pan is placed at the bottom of the stack. By passing materials through series of sieves and weighing the material retained on each sieve, gradation is determined.
Table 2.1 below shows the gradation limits for ACW 14.(JKR/SPJ/2008-S4).
BS Sieve Size
% Passing By Weight
2.6 Rubber Modified Asphalt.
The use of scrap tire in asphalt pavements by highway engineers started in the 1950's (Hanson, 1984). The engineers hoped to utilize the flexible rubber nature in a more durable asphalt pavement. Early trials did not yield favourable results as modified asphalt would cost more and with a service life shorter than that of conventional asphalt.
In the 1960's, a successful formula was formulated by Charles H, McDonald. (Winters,1989). Charles conducted an experiment adding tire rubber to hot liquid to repair pot holes. After mixing crumb rubber thoroughly with asphalt and allowing it to react for about 45-60 minutes, he realised a new material property. He called it Asphalt Rubber (A-R), (Huffman, 1980). By 1975, the formula of incorporating crumb rubber into hot mix asphalt was well researched and became popular. (Han Zhu, 1999).
There were about a billion landfilled tires in the United States in 1990. This number was subsequently reduced to 800 million in 1994, 500 million two years later, and a further 300 million in 2001. (Blumental, 2005).
2.6.2 The Issues.
Before asphalt rubber was generally accepted, there were several issues that needed to be addressed, such as recyclability, environmental concerns and high initial cost, etc. Thankfully, due to a number of reports and research projects and field trials, these issues have been subsequently addressed properly.
The recycling of hot mix asphalt mixes which had crumb rubber incorporated in them was an issue. The tire rubber used as a modifier could cause environmental air pollution problems during recycling. The question of how the recycled mix will be designed was hanging.
The Texas Transport Institute (TTI) undertook a study in 1995 on two of the earlier asphalt rubber recycle operation in the United States. (Crackford, 1995). The conclusion derived from the study approved of the recycling of the material and also stated that the material should have, if well-constructed after design an acceptable long term performance. The Texas Transport Institute report also said that the severity of air quality didn't look to be any more than that of conventional asphalt. Other studies at different locations confirmed these reports, otherwise the recycling of asphalt rubber would not have been possible, and the use of rubber in asphalt will be much worse than disposing used tires, since reclaimed asphalt pavement (RAP) would have to be disposed of.
220.127.116.11 Environmental Issues.
The National Institute for Occupational Safety and Health (NIOSH) limits for fume emissions study was carried out in 1993 on various numbers of asphalt rubber projects, and fume emissions were certified to be below recommended limits. (Gunkel, 1994).
During shredding and handling of tire shreds, the particles of shredded tire released into the atmosphere does not require any precautions for workers in ventilated area. (Ulfvarsson et al, 1998)
C:\Users\professorre\Documents\My Received Files\carlifornia tire fire, sep 1999 (littlegreenfascists.blogspot.com).jpg
Fig 2.8 Tire burning. (littlegreenfascists.blogspot.com)
This is a picture of over six-eight million tires burning after a lightning struck, leaving a stock pile of tires burning for twenty eight days in California, 1999. This is a danger to the environment.
18.104.22.168 Initial Cost Analysis.
Costs of asphalt rubber were higher per unit ton than that of conventional asphalt, until there were economies of scale in place. With the utilization of equivalency thickness ratio, the costs were higher initially. As a result of increased durability and strength in asphalt rubber, there was less material requirement. The ratio was 2:1 at times. (Douglas D, Carlson. Han Zhu, 1999). With the resistance to pavement cracking, there is also significant reduction in maintenance and its cost.
2.6.3 Methods of Incorporating Scrap Tire.
Generally, there are two ways of adding scrap tire rubber to asphalt mixtures. The first method is by incorporating crumb rubber into bitumen at high temperature, allowing them to mix thoroughly before bitumen comes in contact with aggregates. The second method is practised by replacing a percentage of coarse aggregate or filler with crumb rubber in the mixture before it is coated with bituminous binder. These processes are referred to as "Wet" and "Dry" processes respectively. The improvement of mix properties by addition of crumb rubber is dependent on many factors. These factors include process (wet or dry) by which rubber is incorporated, rubber nature, particle size of rubber and percentage by weight of rubber in the mix etc. (FHWA, 1997).
22.214.171.124 Wet process.
(0.15-0.6mm) Crumb rubber is blended for forty five minutes minimum with bitumen at an elevated temperature before being mixed with aggregates, usually 18-22 % bitumen weight range. (Hicks 2002).
During reaction, rubber tends to absorb light fractions from bitumen which causes rubber particles to swell, and crumb softening. The increment in binder viscosity allows for more bitumen to be used. The wet process requirement for the use of bitumen is at least 20% more than that of a Conventional hot- mix asphalt. This in turn improves mix durability. (Yue Huang et al, 2006).
It is believed by FHWA that in the wet process, resilient modulus will reduce with rubber particles in asphalt mixture, and therefore leading permanent deformation resistance. (FHWA, 1997). When designing asphalt rubber mixtures, the same design methods as adopted for conventional hot mix asphalt can be used, with the primary design factor being the stability of the mix. The standard paving machine also can be used for asphalt rubber mixture placement. However, a pneumatic tire roller cannot be used; roller tires carry with them the asphalt rubber. It gets stuck. (Epps, 1994).
Asphalt Rubber helped reduce layer thickness of asphalt by 20-50% in dense-graded mixtures, and performance was not compromised, projects in the 1980's showed. (Kirk, 1991) The Oregon State University (OSU) carried out a leaching test more recently, and the report showed that asphalt rubber mixture leachate contaminants of about 50% was discharged into the surface and ground water system in the early days post laying. Three elements of harmful concentration were found. Mercury, benzothiazole and aluminium of 0.2 mg/L, 0.54 and 1.5 respectively. (Azizian et al, 2003). Rubber pavement association (RPA) found that noise can be reduced by at least 50% with the use of tire rubber mixture binder in open graded asphalt. (Rubber pavement association, 2006).
More researches have been made on the wet process around the world and enjoy more acceptance and usage than the dry process.
126.96.36.199 Dry process.
The dry process was originally developed in Sweden under the trade name Rubin and registered in the U.S.A as plusride.
In the dry process, this involves the replacement of part of the aggregate with scrap tire rubber. In the dry process, rutting resistance of the mixture is enhanced at intermediate temperature, but not cracking at low temperature. (S.R.Rebala, C.K.Estakhri, 1995) The dry process is usable for open, dense and gap graded hot mix asphalt mixtures. (Epps, 1994). Normally, the total aggregate weight in the dry process should not consist of more than 5% of rubber. ([Putman, Amirkhanian and Aune, 2002], FHWA) A special aggregate gradation is required for the dry process in avoidance of premature stripping as a result of interference between aggregate and crumb rubber, as a result of this, there is more demand of about 1.5-3% bitumen content than in conventional asphalt. (Hicks et al, 1988). A target air content of 2-4% is required for pavement premature ravelling to be prevented. (FHWA).
The careful control of reaction between bitumen and rubber particles is important, in times of temperature and time in order to possess the rigidity and physical shape requirement for a dry process. (Tortum et al, 2005)
2.7 Previous Works Using Recycled Tire Rubber
2.7.1 Research Study 1
A research study by (Cao Weidong 2007) on properties of recycled tire rubber modified asphalt mixtures' using "dry process" was conducted using crushed stones of diabase as coarse aggregate and limestone as fine aggregate. Hydrated lime from a commercial source was used as mineral filler, with tire rubber obtained from a tire industry in China. The rubber used was granulated at room temperature and freed of fabric and wire, with rubber particle size ranging from 1-3mm. In his study, a special designed gap graded aggregate similar to the gradation of stone mastic asphalt specified by China was used (13.2mm norminal maximum size), removing sieve of 2.36mm to provide enough room for rubber particles.
The specification of ASTM D1559 for Marshall Mix design was employed in the study. The study also used rubber contents of 1,2, and 3% by weight rubber content. Aggregate blending time was extended by 10-20s after adding rubber to disperse evenly, and then compacted with 75 blows per face with standard Marshall Hammer. 4% air void is considered when determining the Optimum Asphalt Content of mixture.
The results of the test showed that Optimum asphalt content of mixture, Marshall Stability and flow, and bulk specific gravity were all affected as a result of the addition of rubber. The absorption of rubber of Optimum asphalt content had slight increments. The values of Marshall Stability and flow both satisfied Marshall Criteria. His result also showed that the bulk specific gravity of a mixture of rubber modified asphalt decreases with increase in rubber content, this is because the specific gravity of aggregate is greater than that of rubber. (JTG F40-2004, Beijing 2004)
He concluded that special gap graded aggregates should be recommended for rubber modified asphalt using the dry process, and that stability and flow were satisfied with Marshall Criteria.
2.7.2 Research Study 2.
A research study was conducted by (Jocelyn Pao, 2008) on the performance of Hot-Mix Asphalt modified with crumb rubber tires on rut resistance. In the study, material bitumen of pen 80/100 for AC14 mix was used and coarse aggregate taken from a quarry at MRP Ulu Choh with requirement specifications complying the JKR standards for AC14. Hydrated lime (Calcium hydroxide) was used as filler. Crushed and granulated synthetic rubber from scrap tires was used at 0% (control sample), 5%, 10%, 15%, 20% and 25% rubber content. For the purpose of determining optimum bitumen content, each set of crumb rubber amount contained 4%, 4.5%, 5%, 5.5% and 6% bitumen content by total weight, and each specimen at a weight of 1200g.
The results of the test showed optimum bitumen content of control sample to be 5.3%, while that of rubber modified asphalt was 5.36%. Results also showed that rubber modified bitumen samples showed higher rut resistance compared to conventional asphalt. Marshall Parameters produced satisfactory results. However, it should be noted that the researcher cited some inaccuracies in the results obtained from the test as a result of malfunction in apparatus and also a variation in bitumen used, as there was shortage along the line and the replacement bitumen was not of the same quality.
In general, test produced satisfactory results.
2.7.3 Past Researches.
The FHWA believes that rubber particles in the wet process decreases the resilient modulus of asphalt mix, and therefore it permanent deformation resistance. (FHWA, 1997). Meanwhile in Brazil and India, the opposite was observed, where asphalt rubber mixture because of higher tensile strength and stiffness had a lower rutting potential at high temperatures. ([Bertollo et al., 2004] and Palit et al., 2004]). For low temperature performance, an 18-22% of rubber content was suggested by a study at Kansas State University (KSU), stated that in affecting the fracture and tensile performance of asphalt, a change within the range is less significant than varying the binder content within 6% and 9%. (Hussain et al, 1999). The Arizona State University (ASU) confirmed this, adding that a the result from a higher binder content in asphalt rubber mix, was the exhibition of a longer fatigue life. (Zborowski et al, 2004). (0.3-0.6 mm) rubber content at 10% of binder was approved by Liverpool University containing pen 50 or pen 100 bitumen, and as a result of this, fracture, fatigue and rutting resistance was increased. (Khalid and Artamendi, 2006).
A study at Arizona, U.S.A, on two stretches of road overlaid with 4 inches and 2 inches conventional and asphalt rubber respectively with sub-base and road-base were of the same construction in 1990. A picture of these two lanes was taken in 1998showing the difference of the road surfaces.
The picture shows the resistance to cracking of modified asphalt compared to that of conventional asphalt. This is proof that rubber modified asphalt performs better than the conventional asphalt and as such reducing cost of maintenance and repair.
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Fig 2.9 Shows two lanes of road in Arizona, (www.unixrubber.com)
A project in Brazil with Hot mix asphalt containing 15% of rubber in binder overlay discovered that cracking was 5-6 times faster in conventional asphalt, also with regards to interface strain, surface deflection and rut depth, asphalt rubber outperformed (Nunez et al, 2005). Also, when a similar binder of 15% rubber (0.2/0.4/0.6mm size) was used in Japan in dense graded asphalt, the mixture showed better performance in dynamic stability, flexural strain and strength value, and in 48h residual stability. The best lab results were showed with asphalt containing 0.2/0.4mm size rubber. (Suaza et al, 2005).
Asphalt rubber use in road surfaces, revealed some problems projects showed. In Virginia, a SAM (Stress absorbing membrane) trial section showed bleeding and loss of aggregate for asphalt rubber containing 20% crumb rubber content in the binder, and reflective cracking was not prevented as expected. (Maupin and Payne, 1997). The Nottingham centre for Pavement Engineering (NCPE) does not support the use of asphalt rubber in polymer modified bitumen (PMB), because the interaction of PMB-rubber is bound to compromise the rheological properties of the aged binder and as a result of this, the asphalt mixture durability. (Airey et al., 2002)
2.8 Advantages and Disadvantages of Scrap Tire in Asphalt.
Asphalt rubber has its advantages and disadvantages, here are some.
The numerous advantages of rubber modified bitumen (RMB) include its durability, quietness and also safety. (King county, 2006). It has been discovered that rubber modified bitumen is more resistant to rutting, thermal cracking, brittleness, reflective cracking and potholing compared to conventional asphalt mixture. These distresses are responsible for shortening pavement life and eventually increasing maintenance cost. (Nair, 2003). There is an improved skidding resistance when rubber modified mixtures are used and better visibility under rain which leads to a reduction in hydroplaning and ultimately reduces accidents. (Sikora, 2005). Researches also showed that noise caused as a result of contact between tire and pavement surface can be reduced by at least 50% when RMB is used. (Rubber pavement association, 2006)
The use of scrap tire in asphalt is environmentally friendly. Since millions of tires go to the landfills yearly, and causes environmental problems when ignored, its use in asphalt is a good outlet. The use of scrap tire rubber in asphalt enhances quality performance of road materials and at the same time preventing scrap tires from going to landfills.
Rubber modified asphalt's most important advantage may be its cost effectiveness. Initial cost of rubber modified asphalt may be up to 100% higher, but with the advantage of a longer service life and its resistance to most of pavement distresses, which in turn saves cost in terms of maintenance is a justification of its initial cost. (Summers, 2000). Again, while conventional asphalt may require up to 4 inch overlay, rubber modified asphalt needs 2, thus saving resources, cost of laying and time of construction. (Sikora, 2005)
The disadvantages are usually associated with preparation and storage. During preparation, careful control of temperature and mixing time is vital. There tends to be separation between asphalt and crumb rubber into phases, sometimes two or more leading to the decreased service life of rubber modified asphalt. This is as a result of rubber particle and asphalt interaction being weak. Storage time should be considered and not stored for a long period of time as deterioration could occur as a result of high temperature s used during mixing. (Summers, 2000)
2.9 Marshall Stability and Flow.
Stability is defined as the maximum load a well compacted specimen can withstand when tested at 60ÌŠ C (140ÌŠ F) before failure. This generally has to do with the mass viscosity measurement of aggregate-asphalt cement mixture. (Mukhtar Elsedigg, 2006).
When an asphalt mixture is compacted with a standard Marshall hammer to a standard laboratory compactive effort, its strength is being measured by Marshall Stability. By increasing the asphalt cement viscosity grade to a higher level, stability of asphalt-aggregate mixture is increased. Out in the field, some of the factors that affect the stability of a mix includes, aggregate gradation, tire contact pressure, ambient temperature and types of loading, etc. The Marshall Stability helps in analysing the change in stability of a mix and therefore proper selection of optimum asphalt content. (Freddy Roberts et al, 1996) In order to satisfy the high traffic demands, there should be sufficient mix stability to avoid bleeding and rutting problems.
Flow is measure together with stability. Flow is the maximum deformation measured at the point of failure. When an asphalt mixture test indicates higher flow values, it tends to experience deformation under traffic, but when a lower flow value is shown, it means there is insufficient asphalt and normal void is lower than the per cent air voids. (Freddy Roberts et al, 2006) Marshall Stability's ratio to flow indicates the mix's deformation characteristics, and also shows materials permanent deformation resistance. (Mukhtar Elsedigg, 2006)
An in depth description of the test methods and procedures to be carried out in the laboratory for this research project is described in this chapter. The main purpose of this research project is to evaluate the effects of scrap tire rubber on the properties of asphaltic concrete. To achieve this objective, two test will be carried out in the highway and transportation laboratory in Lagenda Kolej, namely: Sieve analysis and the Marshall Stability and Flow test.
Samples to be tested are going to be prepared according to the JKR/SPJ/2008-S4 as a guide for all laboratory works and material fulfilment to comply with the Malaysian road works specifications. The asphaltic mixture to be used in this laboratory work is the asphaltic concrete for wearing course (ACW14). Table 3.1 below will show the new aggregate gradation by JKR, which will be adhered to in this project.
All samples used in this project will be done based on the Marshall Laboratory compaction method. Laboratory gradation mix design will have 3 specimens each prepared by bitumen content in accordance with the JKR standards range in Table 3.2 below with an increment of 0.5 in accordance with ASTM D1559. Coarse aggregate to be replaced will be in the standard range of 1-3% of shredded tire of 5mm,10mm and 14mm maximum size and then applying the standard 75 blows/face standard compaction for ACW14. Specimens will be tested for Marshall Stability and Flow after being compacted by the Marshall Hammer.
Table 3.1 Gradation limit for Asphaltic concrete (ACW14).
BS Sieve Size
% Passing By Weight
The bitumen to be used in this research is of pen 80/100 and the design bitumen content s used for the design process of all mixtures shall be as stated in JKR specification as in the Table below.
Table 3.2 Design Bitumen Content.
AC 10-Wearing course
AC 14-Wearing course
AC 28-Binder course
In addition, results obtained from laboratory work will be compared with the JKR/SPJ/2008-S4 requirements as shown in Table 3.3 below.
Table 3.3 Test and Analysis Parameters. (JKR/SPJ/2008-S4)
Air voids in mix (VIM)
Voids in aggregate filled with bitumen (VFB)
â€º 8000 N
3.2 Laboratory Test Procedure.
The Laboratory tests are divided into several stages, beginning with aggregate preparation. The aggregate gradation is used to design the Marshall mix sample. At first, sieve analysis is used to separate aggregates into sizes. Thereafter, the Marshall test is carried out to determine the optimum bitumen content for each mix type. The optimum bitumen content value is vital in designing the mixes to indicate other mix performance test.
Fig 3.1 below shows laboratory test flow.
Preparation of Specimen based on Tire and Bitumen Content
Marshall Mix design preparation based on Tire and Bitumen Content
Compaction of Specimen
Marshall Stability and Flow Test
Results and Analysis.
3.3 Aggregate preparation (Sieve analysis of coarse and fine aggregates, ASTM C136-84A)
The proposed aggregate gradation for the project shall be determined by this method. The results obtained from this method will be used to determine the compliance for the distribution of particle sizes with the necessary applicable specification requirements and to acquire data necessary to guide the production of different aggregate sizes and mixtures containing aggregate. ASTM C136 provides standard procedure for a dry sieve analysis which is faster and mostly used to estimate the actual gradation, while ASTM C117 caters for the washed sieve analysis procedure which is used to determine the amount of material passing the No 200 (0.075mm).
To ensure that aggregates are free of moisture and impurities, the materials to be used most be dried in an oven overnight for at least a day. Using the sieving machine, aggregates which remain will be separated into single sizes. After sieving, the retained aggregate on every sieve will then be collected and stored in containers; containers are labelled properly to avoid any mixing between aggregate sizes.
To determine the distribution particle size of coarse and fine aggregate, this test is performed.
Mechanical sieve shaker
For this purpose, aggregate must be dried to a constant weight in an oven at a temperature of 110Â± 5Ëšc before being used.
Sieve sizes are stacked and nested in order of decreasing size of opening from top to bottom.
Afterwards, samples are now placed on top of the sieves and then the shaking process is initiated by means of a mechanical sieve shaker. Agitation of the sieves should be done for a period of time, usually around three minutes.
In order to achieve the aim, sieving process should be continued until assured that there are no residues on individual sieve that will pass the sieve after a continuous hand sieving.
There are limitations on the amount of material on any given sieve, to allow all particles the chance to reach sieve opening during operation.
Fig 3.2 Mechanical Sieve Shaker.
3.4 Marshall Mix Design (ASTM D1559)
The purpose of this design process is to determine the optimum bitumen content of each asphaltic mixture. All mixtures will be compacted to a standard 75 blow/face in the laboratory for asphaltic concrete mixtures.
3.4.1 Preparation of Mix Design.
A).The following are the apparatus needed for the preparation of mix design.
Specimen mould assembly
Specimen mould holder
B). Test specimens should be:
Heated asphalt cement
Aggregate mix design which have been dried at a temperature of 105Ëšc to 110Ëšc.
C). Mixture Preparation.
Aggregates are weighed according to the percentage of amount of each size that is required for each mix design.
On a hot plate, the pan is heated to a temperature of 28Ëšc
The pan will then be charged with the heated aggregate and dry mixed thoroughly.
The required preheated bituminous material to the mixture is then weighted.
Careful handling of the mix is required, to prevent loss of mix, with temperature not falling out of the required range.
At this point, bitumen is then mixed thoroughly with aggregates, until all aggregates are well coated.
Finally, the mixture is then taken from the pan and is ready for compaction.
D). Compaction of Specimen.
All mixes have a desirable temperature for compaction, so the specimens are observed carefully until it has maintained this temperature. Then the process of compaction begins following the procedure listed below.
The mould assembly and compaction hammer face must be cleaned and heated in a boiling water at a temperature of 93-150Ëšc.
A filter paper is cut to fit the diameter of the mould and then placed at the bottom of the mould before placing the mix.
The prepared mixture will now be placed into the mould and spread by a spatula thoroughly.
The collar of the mould will be removed, and then the surface of the mixture smoothed with a trowel.
There is a re-recording of temperature once again, ensuring it is still in range.
The collar will then be assembled to the compaction pedestal in mould holder.
The 75 blow of a standard compaction hammer is now applied at a free fall distance of 500mm from mould base, with compaction hammer being assured to be perpendicular to the mould assembly base.
After this, the base plate is removed and another 75 blow is applied to the sample bottom which has been turned around.
After this, collar is lifted carefully from specimen.
The specimen will now be transferred to a smooth and flat surface for an overnight at room temperature.
Lastly, weight is recorded and sample is examined.
Fig 3.3 Prepared Marshall samples
3.4.2 Marshall Stability and Flow Test.
The purpose of this test is measuring the strength of a compacted asphalt mixture to a standard laboratory compactive effort. This test is used to measure the resistance to plastic flow of cylindrical specimens of asphalt mixture loaded on a lateral surface by means of Marshall Apparatus, and the method can be used for asphalt mix containing aggregate of up to 25.4mm maximum size. In addition, test serves as part of Marshall Mix Design procedure in selecting the design bitumen content.
Fig 3.4 Marshall testing machine.
Marshall Machine is a compression-testing machine, which is used to apply loads to specimens prepared for testing through a semi-circular testing head. The test specimen should be immersed in water for a period of at least 45 minutes at a controlled temperature of 60Â±1Ëšc. During hot summer months, maximum pavement temperature is approximately 60Ëšc, and so this provides the weakest condition of HMA mixtures.
Stability test is carried out simultaneously with flow test.
The test procedure is as follows.
The prepared specimens are immersed in a hot water bath for at least 45 minutes at a maintained temperature of 60Â±1Ëšc.
Fig 3.5 Samples immersed in water bath
Prior to carrying out the test, guide rods and test heads are cleaned thoroughly and well lubricated, to ensure free sliding of upper heads.
A temperature of 21-38Ëšc is recommended for the testing head.
Then the specimen is removed and placed from the water bath to lower segment of breaking head.
Then place upper segment of breaking head, and now place it in its position in the Marshall Machine.
Fig 3.6 breaking head is placed on a sample
Flow meter is placed in position over one of the guide rods.
Adjust flow meter to zero, holding sleeve firmly.
Fig 3.7 sample is placed in Marshall testing machine
Load is now applied to specimen, until it reaches its maximum. Notice that reading must be taken before loading specimen.
When the applied load starts decreasing, dial reading is taken and recorded as maximum load applied, that sample can sustain. (Stability force).
Record the last reading of flow meter. This is the flow value in mm.
The test should be done within 30 seconds of removing from hot water bath.