Abstract
This dissertation specifically focused on assessing the variation in asphalt mix properties at non-standard test temperatures using standard and modified bitumen’s. How asphalt concrete pavement performs in adverse climates has been cause for concern for decades. Polymer modified bitumen’s are being used to improve asphalt performance in warmer and colder climates.
This research project will assess the direct effect of temperature on asphalt and its likelihood to cause permanent deformation. This will be achieved through research and laboratory testing. By carrying out ITSM testing on samples of asphalt using modified and unmodified bitumen’s, testing them at non-standard test temperatures, I hope to determine how extremely temperature effects asphalt.
Contents
1.4 Research questions, aim and objectives.
2.5 Effects of Climate Change on Asphalt Pavement
4.2.3 Modified Samples Combined
5.2 Effects on asphalt of an adverse climate
5.3 How base course and wearing course react to varying climates
5.4 How Density affects stiffness
5.6 How does modifying the bitumen affect its properties?
Chapter 7: Recommendations for further works
Acknowledgements
I would like to thank firstly my supervisor, Dr David Woodward for his positive input and influence throughout the lab testing and research, David thought of different ideas to discuss which had a positive contribution in regards to the testing method and dissertation writing.
I would also like to thank the laboratory technician Ian Martin in the Highways Lab for his influence in relation to the testing. Ian’s expert knowledge in using machines like the gyratory compactor and ITSM testing apparatus was key in successful completion of the research.
In addition, I would like to thank Lagan Bitumen for providing modified samples for testing, allowing me to further the research.
List of Abbreviations
Chapter 1:
Introduction
This dissertation considers the variation in asphalt mix properties at non-standard test temperatures using standard and modified bitumen’s. Throughout this research project, I will investigate the need to use modified bitumen’s in areas of the world where climates can be excessively warm and cold. I will determine what type of bitumen is best suited for certain climates.
In this chapter, I will discuss the need for modified bitumen’s along with examples and determine what type of asphalt is best suited to this research project.
Current bitumen’s are tested for use at standard room temperature of around 20°C. While this is perfectly acceptable when the bitumen is only going to be used in countries like the UK and Ireland, where excessively warm or cold temperatures are extremely rare and surface temperature of asphalt roads would rarely exceed 40°C even in summer months. This is not so suitable however in countries like Oman, United Arab Emirates or other Middle East countries. The air temperature in these countries can average well above 50°C for up to six months a year; this can lead to the surface temperature of asphalt roads reaching above 80°C. I believe it is clear that the same bitumen used in asphalt for cooler climates is clearly not suitable for extremely hot climates; different types of modified bitumen’s are evidently needed to extend the life span of road pavements in these more extreme climates.
While rutting in asphalt caused by high temperatures is one type of failure, another major type of failure is cracking due to freezing temperatures. Modified bitumen will also be required in extreme cold climates to prevent cracking due to freezing. Countries such as Sweden and the Canada have a need for modified asphalt as during winter months the average temperature is around -3°C, for which if standard asphalt was used cracking would be a consistent problem for asphalt pavement. However, failure is not the only problem with asphalt in cold temperatures, in icy conditions the skid resistance properties of asphalt are considerably reduced and wear of the asphalt surface can be increased due to use of studded tyres and/or chains.
There several different types of asphalt that are used in pavement construction throughout the world today. British standards list specifications for seven different types, these are Asphalt concrete (AC), soft asphalt, hot rolled asphalt (HRA), stone mastic asphalt (SMA), mastic asphalt, porous asphalt and reclaimed asphalt. Out of these the four most common are AC, HRA, SMA and porous asphalt. In the UK and Ireland HRA would be the most commonly used followed by SMA. British standards BS EN 13108-1 to BS EN 13108-8 refers material specifications for asphalt. Hot rolled asphalt is very popular in the UK due the large quantities of high stability sand available from local sources. However, throughout the rest of the world Asphalt concrete is the most popular type of asphalt used in pavement construction. AC is applied at generally the same thickness as HRA but does have a lower bitumen content, which, as it is the bitumen that softens in warm temperatures; this would also be more suitable for warmer climates. This along with the reason that it is the most common type used throughout the world is why I have decided to carry out my experiments using asphalt concrete.
In countries, all around the world deformations like rutting and cracking in asphalt pavement is a continuous problem. This problem obviously increases in countries with more adverse climates. Standard unmodified asphalt will begin to soften once the surface temperature begins to reach around 50°C, which can occur even when the air temperature is as low as about 20°C. The need for asphalt mix that has a higher resistance to deformations in adverse climates is definitely needed to improve driving conditions and increase the working life of the asphalt pavement. Even in England in 2013 part of the M25 around London had to be closed due to the road surface beginning to soften, as this is one of the busiest motorways in the UK, it caused major traffic delays. If this can happen in the UK when the air temperature was only 25°C, then countries closer to the equator could be suffering a problem like this year round. Modified bitumen for use in the road construction seems to be the best solution to this problem and could solve the problem of softening asphalt.
The aim of this research project is simply to assess the variation in asphalt mix properties at non-standard test temperatures, using standard and modified bitumen’s. We should be able to achieve this through the use of an ITSM (Indirect Tensile Stiffness Modulus) test, which is a non-destructive test that will let us test the sample at different temperatures and recording any variations, which occur.
The main objectives of this research project will be carrying out the necessary laboratory experiments to answer my research questions. This will include:
Chapter 2:
Literature Review
This chapter shall introduce the work defined in this dissertation. A background to the dissertation is given by way of justification for work.
Asphalt is a commonly recognised road covering material. The main material used in asphalt consists of an aggregate, sand and bitumen. The bitumen, which is used as a binder in asphalt, is the main focus of my report as it has the largest effect on the performance of asphalt in relation to adverse temperatures. There are several varieties of asphalts; the most common of these are Asphalt Concrete (AC), Hot Rolled Asphalt (HRA), Stone Mastic Asphalt (SMA) and porous asphalt. These all have their advantages, which is why certain regions tend to choose one type over the others. This may include climate, availability of aggregate or even the type and volume of traffic. Asphalt surfaces must perform to a high standard, to ensure this they are laid and compacted in layers according to British Standards BS EN 13108. These layers differ depending on the type of asphalt being used and the application of the surface e.g. road pavement, footpath.
Hot Rolled asphalt (HRA) is a very fine-grained material, most commonly used on public highways in the UK and Ireland, and relies on the presence of embedding chippings of a hard stone to improve durability and to add traction. HRA is a dense mixture of mineral aggregate, sand, filler and bitumen that complies with EN 13108. There is a high proportion of sand in the mix resulting in a low percentage of air voids when it is compacted. The mortar of bitumen, sand and filler fines gives HRA its strength. HRA is peculiar to the UK and Ireland, and came into use because of the large quantities of high stability sand available which eked out localised sources of aggregates. The main advantages of HRA are:
Stone Mastic Asphalt or SMA is a dense wearing course material, which was originally developed on the continent to overcome the issue of rutting due to the action of studded tyres on road surfaces. The mineral aggregate skeleton of SMA is gap-graded and the voids are filled with a mastic of fine aggregate, filler and binder that complies with BS EN 13108. Due to the high stone content and open nature of the aggregate matrix, traffic loads are transmitted through the interlocking stone skeleton rather than through the mortar. SMA has found use in Europe, Australia, the United States, and Canada as a durable asphalt surfacing option for residential streets and highways. The main advantages of SMA are:
Porous asphalt is a permeable asphalt, which allows water to pass freely through to the underlying structure. Porous asphalt is produced and placed using the same methods as conventional asphalt concrete; it differs in that fine aggregates are omitted from the asphalt mixture. The remaining large, single-sized aggregate particles leave open voids that give the material its porosity and permeability. To ensure pavement strength, fibre may be added to the mix or a polymer-modified asphalt binder may be used. Advantages to porous asphalt are:
Asphalt concrete is a composite material commonly used to surface roads, parking lots, and airports. It consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. The components of asphalt concrete include asphalt aggregate and asphalt binder (bitumen). Mineral filler is sometimes added to hot mix asphalt concrete. Aggregates used in asphalt concrete comprise approximately 95 percent of the mix by mass. Proper aggregate grading, strength, toughness, and shape are needed for mixture stability. The advantages to asphalt concrete are:
.. (2015). ADVANTAGES OF ASPHALT. Available: http://www.eapa.org/promo.php?c=171. Last accessed 4th Dec 2016.
Bitumen is a specialist fuel grade, typically only produced in about 65% of refineries around the world. It is perhaps best described as a complex mixture of components with various chemical structures. A majority of these structures consist of carbon and hydrogen and are therefore termed hydrocarbons. A number of other structures are also contained in bitumen, which are heteroatoms, which are atoms other than hydrogen and carbon like oxygen, sulphur and nitrogen. It is the complex arrangement of hydrocarbon and heteroatom molecules, which give bitumen its unique balance of properties.
Dr Ian Lancaster (2000). Asphalts in Road Construction. London: Thomas Telford. P50-60.
The primary use of bitumen is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete and accounts for approximately 85% of the bitumen consumed in the United States and about 70% worldwide. Asphalt concrete pavement mixes are typically composed of 5% bitumen cement and 95% aggregates (stone, sand, and gravel). Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.
Bitumen is defined as “A viscous liquid, or a solid which is substantially non-volatile and softens gradually when heated”. There are six main properties of bitumen, these are:
It is not strictly correct however to describe bitumen as a solid at low temperature as there will always be an element of viscous flow. Rather like glass, bitumen at low temperatures is best described as a super cooled liquid.
Dr Ian Lancaster (2000). Asphalts in Road Construction. London: Thomas Telford. P50-60.
Although there are a vast number of crude oils currently available, only a small percentage of these are directly suitable for the manufacture of bitumen. It has been estimated that the total number of crude oils available at present exceeds 1500, with less than 100 of these being suitable for bitumen production. The main reason for this is the varying bitumen content of these crudes. In the UK and Ireland, most bitumen manufacture is from Middle Eastern, Venezuelan or Mexican crudes with a small percentage coming from North Sea crude. Bitumen is produced from crude oil through a fractional distillation process. It is heated to approximately 300˚c and fractionally distilled under atmospheric pressure.
From a performance point of view, bitumen is one of the most important constituents of an asphalt mixture. For areas with hot temperatures the most important performance requirements for asphalt mixtures and asphalt layers are resistance to permanent deformation (rutting) and resistance to surface cracking induced by ageing. The bitumen has a great influence on these performance requirements. Bitumen’s are generally modified with atactic polypropylene (APP), styrene butadiene styrene (SBS), synthetic rubber or other agents that create a uniform matrix that enhances the physical properties of the asphalt. SBS and APP are the most common bitumen modifiers. SBS (Styrene-Butadiene-Styrene) modifies the asphalt by forming a polymer network within the bitumen. SBS gives the bitumen rubber-like characteristics and improved resistance to aging and weathering. APP (Atactic Polypropylene) is a thermoplastic polymer, which forms a uniform matrix within the asphalt. This enhances the bitumen’s performance by increasing its UV resistance, increasing its flexibility at low temperatures and improving its flow resistance at high temperatures.
Anil Srivastava and Ronald van Rooijen. (2000). Bitumen performance in hot and arid climates.
As SBS polymers are not particularly increasing the stiffness of bitumen binders, they are sometimes perceived not to be the optimum modifiers in hot climates. It is demonstrated that SBS-modified binders can be formulated over a wide temperature range. Mix stiffness obviously has to be considered at the prevailing temperatures, this implies that harder binders and often somewhat leaner mixes are used in hot climates. There is irony in these decisions. Amplified by a more rapid ageing in hotter climates, the limits of flexibility are reached before high permanent deformation takes place. As a result, for instance, in Saudi Arabia pavement cracking is a more prominent issue than rutting. The relation between the softening point and the SBS content is clearly shown in figure 2.1, which displays how the softening point of asphalt is dramatically increased when SBS content reaches 4%.
Figure 2.1
W. Vonk and R. Hartemink. (2004). the softening point and the SBS content.
British standards for Polymer Modified Bitumen’s (PMBs) is BS EN 14023: 2010. Pavements designed and constructed for heavy-duty traffic and extreme weather conditions require specially designed engineered bitumen grades. By changing the characteristics of normal bitumen with the addition of a polymer, we can create bitumen with much more strength and significant higher resistance to parameters like fatigue and permanent deformations for road pavements. Polymer modified bitumen’s will result in:
Greater durabilityFig2.2
From previous experiments and testing, it has been determined that one of the main factors for resistance to rutting is the bitumen content and the type of bitumen used. Modified bitumen has better results of resistance to permanent deformation compared to standard bitumen. Also increasing the binder content decreases the resistance to permanent deformation. However, with the increase of binder content, cracking has been proven to become less likely. In general, it is widely accepted that in terms of being effected by temperature, the higher percent of bitumen content the more likely rutting is to occur at higher temperatures.
A flexible pavement consists of several different layers, which consist of a sub-grade, sub-base course, base course and surface course. If any of these layers become weak or unstable, then it will result in the failure of the flexible pavement. It is due to this reason that is very important to design and construct each layer with the utmost care.
When it comes to a flexible pavement there are many ways in which it can fail, the most common of these are:
S.K. Khanna & C.E.G. Justo. (2015). TYPES OF FAILURES OF FLEXIBLE PAVEMENT
Rutting is one of the main distresses in the asphalt pavements, especially in higher summer temperatures and/or under heavy loads. It is the load-induced permanent deformation of asphalt pavements and may occur in any layer of a pavement structure. It is one of the main distresses occurring in asphalt pavements and badly affects the comfort-ability, ride-ability, motorist safety, and general performance
Due to the joint function of heavy traffic loading and continuous peculiar high temperature, serious rutting failure appeared after the south section of Jing-Zhu Expressway was opened to traffic for two years. The total average rut depth (RD) reached 10mm and the maximum RD was about 30mm. The RD distribution shown in Fig2.2, 90% is larger than 5mm and 5% is more than 20mm. So rutting is a very serious problem in this expressway and a cause for concern.
Fig 2.3
Zhang Qi-sen , Chen Yu-liang , Li Xue-lian. (2009). Rutting in Asphalt Pavement under Heavy Load and High Temperature
Low temperature cracking is the most prevalent distress found in asphalt pavements built in cold weather climates. As the temperature drops, the restrained pavement tries to shrink. The tensile stresses build up to a critical point at which a crack is formed. Thermal cracks can be initiated by a single low temperature event or by multiple warming and cooling cycles and then propagated by further low temperatures or traffic loadings. This type of deformation is manifested as a series of transverse cracks that extend across the pavement surface in response to cold ambient temperatures. Much research has been devoted to the problem of thermal cracking. Specifically, a number of thermal cracking models have been developed to predict the onset or amount of cracking that is to be expected for a given set of conditions.
Fig 2.4
Dave VanDeusen. (2015). Low Temperature Cracking in Asphalt Pavements.
Climate change having a significant impact on the UKs highway network, for example drier summers are causing more incidences of subsidence and wetter winters are causing greater frequency of flooding. This is also having a less obvious effect on the asphalt pavement of the UKs highways, due to increased average temperatures and changes in rainfall patterns.
Knowledge of the “stiffness” of bituminous mixtures is obviously a key element for the analysis and “rational” structural design of flexible pavements. Performance tests are used to relate laboratory mix design to actual field performance. The key parameters that are focused on during testing are:
The testing method I will be using for this research project will be the Indirect Tensile Stiffness Modulus and Fatigue Measurement (ITSM) test. This is a non-destructive test which will allow me to test the same sample several times allowing for accurate results. I will carry out this test at a minimum of three different test temperatures, which will be 5°C, 20°C and 60°C. It may be necessary to carry out more tests at smaller intervals depending on the results achieved. To achieve more data, I will soak the test sample in water, freeze it and then thaw it. Simply to see how this also affects the sample stiffness.
N. Baldo, M. Dal Ben, M. Pasetto. (2010). Indirect Tensile Test for the Determination of the Stiffness and the Resilient Modulus of Asphalt Concretes
Although this dissertations focus is on how temperature effects asphalt concrete, I also intend to test samples at several different densities to observe how this also will effect ITSM results. Density is achieved by compaction of the paver-laid asphalt-aggregate mixture. The squeezing together of the aggregates increases their surface-to-surface contact and inter-particle friction, resulting in higher stability and pavement strength. If a pavement has low density (usually defined as less than 92 percent of Gmm), the air voids are interconnected and premature pavement distresses can result. These may be in the form of premature oxidation aging, increased cracking, rutting, structure weakening and stripping. Optimally, a pavement is compacted as much as possible during construction. It is usually not possible for one to achieve the design density of 96 percent by rolling due to lack of mixture confinement, so we compact the mat as much as possible, which many have found to be 92 to 93 percent of Gmm. Further compaction of the pavement is usually achieved over several summers by traffic until a pavement reaches its design density of 96 percent.
Phillip Blankenship (2015) How much does density matter?
Chapter 3:
Methodology
The objective of this research project is to assess variation in asphalt mix properties at non-standard test temperatures using standard and polymer modified bitumen’s. I will achieve this by carrying out several tests at varying temperatures on both modified and unmodified bitumen’s, to determine what bitumen is best for use in certain climates.
The test I will use to determine this will be an Indirect Tensile Stiffness Modulus (ITSM) test. This is a non-destructive test, which will allow me to carry out several tests on the same sample, leading to the most accurate results.
To begin with, I determined what type of asphalt is best suited to carrying out these experiments. As the objective of this research is to determine the asphalt performance in abnormal climates, which is most common in Middle Eastern countries, I have decided to use the type of asphalt most popular in that area. Asphalt concrete is used extensively throughout the world, for this reason I have decided it is best suited for carrying out this investigation.
To begin I prepared five separate test samples made of asphalt concrete. These all consisted of the same material but where compacted to different densities, ranging from densities between 2324.65 kg/m³ and 2114.65 kg/m³. They were compacted using a gyratory compactor, which allowed me to input a certain amount of gyrations to produce samples of varying densities. Once the samples where compacted the gyratory compactor allowed me to see the sample density, as well as the sample thickness which is also needed for ITSM testing.
Before testing could be carried out the samples needed to be conditioned to the testing temperature. This involved placing all samples into the refrigerated incubator for a minimum for 4 hours before testing could be carried out. An ITSM test, which is also housed in the refrigerated incubator, was then carried out on all of these samples to obtain stiffness data at a standard room temperature of 20°C. As the ITSM test is non-destructive, I will then carry out the test again on the same samples at 30°C, 40°C, 10°C and 15°C. From the data collected, I was able to see clearly how the stiffness (MPa) of the samples was affected by temperature. This trend continued clearly over the range of densities proving how dramatic the effect that temperature has on stiffness.
After completion of the original samples I created, modified samples provided by lagan bitumen where used for testing. Eight samples in total where provided, four of which were of an MD62 base course, and the other four were an MD57 wearing course. These samples where tested at the same temperatures of the original samples and there stiffness recorded.
Fig 3.1 The ITSM machine inside the refrigerated incubator along with the samples
From the data that I collected, I was able to determine how the asphalt tested would have performed in varying temperatures had it been on a road surface.
N. Baldo, M. Dal Ben, M. Pasetto. (2010). Indirect Tensile Test for the Determination of the Stiffness and the Resilient Modulus of Asphalt Concretes
Fig 3.2 ITSM testing apparatus set up with a sample ready for testing.
Chapter 4:
Results
The five samples of asphalt concrete that I prepared where compacted to varying densities to also collect data on how density effects stiffness. I decided to compact the samples using varying amounts of gyrations, which were 400, 100, 80, 60, and 20 gyrations. As density increases with compaction, this resulted in densities of 2324.65 kg/m³ for sample 1, 2235.18 kg/m³ for sample 2, 2198 kg/m³ for sample 3, 2142.09 kg/m³ for sample 4 and 2114.65 kg/m³ for sample 5. I believed that this range of densities was enough to display the effects that density will have on stiffness as well as temperature. The lowest tests being carried out at 10°C were due to that being the lower limit of the ITSM machine, and higher limit of 40°C was decided because at that temperature the stiffness values of the samples where becoming very low.
Fig 4.1
Although the main aim of this research project was to determine the effect of temperature on the stiffness of asphalt samples, the data I have collected also clearly defines the effect of density or compaction. As the stiffness of sample 1 is reaching over 18000 MPa, this sample would be very susceptible to cracking at this low temperature.
Fig 4.2
I decided to carry out a test at 15°C due to the large gap between 20°C and the 10°C results. The trend of stiffness increasing with density also continues although sample 3 shows an anomaly, as this does not follow the general trend. However, stiffness has decreased significantly from 10°C, which already shows an emerging trend with temperature.
Fig 4.3
20°C is the standard testing temperature for ITSM testing. The trend of density to stiffness continues at 20°C however, sample 3s deviation does increase as we can see from the R² value decreasing to 0.673. The stiffness does also decrease considerably from 15˚C, showing how only a 5˚C change can have significant effect on asphalt pavement.
Fig 4.4
Another 10˚C increase in temperature shows a noticeable decrease in stiffness, continuing the trend. The deviation of sample 3 has begun to decrease here also, becoming closer to what was predicted.
Fig 4.5
At 40°C, the trend for temperature continues with the stiffness values becoming very low. With stiffness values this low rutting would begin to become a significant problem and would most likely lead to permanent deformation occurring. This is also the only temperature at which the density to stiffness relationship is almost perfectly represented. The R² value of 0.997 shows how there is very little deviation, showing direct correlation.
| Samples | Density (kg/m³) | Stiffness (Mpa) at 40°c | Stiffness (Mpa) at 30°c | Stiffness (Mpa) at 20°c | Stiffness (Mpa) at 15°c | Stiffness (Mpa) at 10˚c |
| 1 | 2324.65 | 1099.5 | 3156.5 | 8204.5 | 12701.5 | 18024.6 |
| 2 | 2235.18 | 897.5 | 2559.5 | 6494 | 11910.5 | 14658.5 |
| 3 | 2198 | 806 | 2780 | 7773 | 12303 | 14412.5 |
| 4 | 2142.09 | 651 | 2127 | 6026 | 10056.5 | 13018 |
| 5 | 2114.65 | 575 | 1637.5 | 5832 | 10154 | 12886.5 |
Fig 4.6
When all the data is displayed together, it becomes very clear how susceptible to temperature these samples really are. I believe the decision to carry out an extra test at 15˚C proved very useful as it slots into the existing data perfectly. Exactly as expected the stiffness decreases as the temperature increases. Over a small temperature range of only 30˚C, its effect on stiffness is dramatic. When the data is combined here it also
I was provided with eight samples of asphalt concrete from Lagan bitumen in Dublin. These consisted of four MD62 base course samples, and four MD57 wearing course samples. The four samples for each material were made to the same density, weight and a similar thickness. This was to eliminate any anomalies like sample 3 in the previous experiments. The eight samples were tested at the same temperature and in the same way as the previous samples as well. The temperatures tested did show a wide range of results so the hope was that the modified samples would not be as noticeably effected.
Fig 4.7
The four MD57 samples that where provided from Lagan bitumen were tested at the same five temperatures as the previous samples. They showed a similar pattern when tested at the different temperatures. MD57 is a wearing course so the aggregates used where finer in texture to allow for a smoother finish. This would lead to a higher bitumen content in the sample, which would lead to the sample becoming more susceptible to temperature. I believe this is the reason that at higher temperatures the ITSM test did return lower stiffness values. However, at colder temperatures, the samples were not affected to the same extent as the unmodified samples. This would lead me to the conclusion that this sample material would perform well in colder climates. This is due to how low the stiffness values were at higher temperatures, which would make the samples very prone to rutting or other high temperature deformations.
Fig 4.8
This group of samples are of an MD62 base course. They again followed the same trend as the previous test samples in relation to temperature. However, the samples themselves had a larger deviation at each individual temperature. The most likely cause of this would be that the samples where compacted to slightly different densities, but as I did not make the samples I cannot guarantee this. This material did seem to behave well at higher temperatures, as it maintained an adequate stiffness with only sample dipping below 200MPa. As this is a base course, the aggregate used is larger and therefore the bitumen content is lower, which should lead to temperature having less of an effect. In cold temperatures the ITSM results did rise quite considerably although still not reaching the same stiffness as the unmodified samples, which were also a base course. The results of this sample are actually quite promising as the sample behaved reasonably well in both high and low temperatures, so it would be suitable for any climate.
Fig 4.9
When combined, both results show again the direct effect of temperature on the AC samples. There is also a clear difference on how base course and wearing course will react to temperature. I believe this would be due to the high binder or bitumen content in the wearing course compared to the base course. As the base course uses larger aggregate sizes, less surface area needs to be covered and therefore less binder is required. Where as in the wearing course, smaller aggregate along with sand sometimes, is used to achieve a smother finish, leading to a higher surface area and therefore larger binder content.
Chapter 5:
Discussion
The overall theme of this research detailed in this dissertation has been to develop an understanding of the variation in asphalt mix properties at non-standard test temperatures using standard and modified bitumen’s. This research was carried out by performing ITSM testing on several modified an unmodified test samples, at non-standard test temperatures. This chapter shall discuss the results presented in the results chapter. The structure of this chapter will be as follows;
Throughout the testing process of this research project, the effect of temperature on asphalt has been the key aim. It is well established that at colder temperatures the main effect would be thermal cracking, were as at warmer temperatures the most common problem would be rutting. Both of these failures can be blamed on excessive traffic but they are most likely caused by adverse temperatures, and then made worse by other factors.
I believe that carrying out the ITSM testing suited perfectly to displaying the effect temperature had on asphalt samples. As the graphs in the previous chapter display, temperature can have a dramatic effect on the way asphalt behaves in the real world and its susceptibility to failure.
Throughout every sample test on ISTM, all results have returned as predicted. Stiffness peaks at the coldest temperature (10˚C), and is at its lowest while testing at the warmest temperature (40˚C). Although this was generally expected, I was surprised by how defined the results were. There is a clear difference results even when only testing with a difference of 5˚C. When the unmodified samples are combined, it is shocking how well the 15˚C sample fits in between the 20 ˚C and 10 ˚C samples. This proves how temperature sensitive asphalt is. I believe it would be worthwhile to experiment further with temperature differences as small as 1 or 2˚C to see would this still have a noticeable effect.
The only samples to perform really well in warmer temperatures was the MD62 base course samples. Even during the 40˚C test, these samples still averaged 2256.375 MPa during the ISTM test. Shown in the graph below (Fig 5.1), the average MD62 results are compared to the unmodified sample 2. I chose sample 2 as it was compacted using 100 gyrations, which would be considered a very well compacted material, unlike sample 1 with 400 gyrations, which would not be realistic of a typical pavement. The MD62 samples maintain a continuous, steady curve whereas the unmodified has an irregular shape with no distinct pattern. The unmodified samples finish with a lower stiffness values at the warmer temperatures, and a higher stiffness value at the colder temperatures. Ideally, the MD62 samples have a lower maximum stiffness, and a higher minimum stiffness value. Proving that the modification was well suited to the requirements of the sample.
(Fig 5.1)
The difference in the wearing course results is most likely due to the higher bitumen content used for a wearing course compared to a base course. However if this statement was definitely the case the MD57 samples would have a much higher stiffness value when tested at the colder temperatures. This is proof that the bitumen used in the MD57 samples must be modified for use in colder temperatures, were, as 
the base course appears to be better suited to warmer climates.
Fig 5.2
As can be seen in the graph the MD57 samples do produce very poor results at the 40˚C test. Even when tests where being carried out the samples did begin to feel sticky, making evident how much the samples were being softened due to the high temperatures. These wearing course samples would deform very rapidly if used for highway surfacing in a warm climate. As the MD57 samples have an average stiffness value lower than 7000MPa during the 10˚C test even, it is a reasonable assumption to make that it has been specifically designed for use in colder climates. This sample would not be very susceptible to cracking and therefore would be suited to colder temperatures.
Although the main aim of this dissertation was to determine the effect of temperature on stiffness, through testing my unmodified samples I also collected data on how stiffness is affected by density. The results where as expected, as simply there was correlation between stiffness and density which was very evident across all temperatures. The only sample test where there appeared to be very little error, making evident the correlation between density and stiffness was the 40˚C test.
Fig 5.3
This graph does excellently display the correlation, as with an R² value of 0.997 there is very little deviation. The relationship is simply explained, the denser the material is, and the stiffer the material will be. However, during tests at lower temperatures the graphs did have more deviation. This may be down to a simple error during testing or possibly the sample was damaged. As I only tested one sample at each density I cannot confirm that this was a testing or sample error, although this is the most likely explanation, or less likely the results are correct.
Before I could begin testing any samples and determine how temperature effects asphalt mix properties, I first needed to decide what test best suited the requirements. Through research and help from Dr Woodward, I determined that ITSM testing would best suit the needs of this dissertation. I decided this as the apparatus would allow me to test the samples at varying temperatures as ITSM testing kit is set up inside a refrigerated incubator, allowing me to test a range of temperatures from 10˚C to 40˚C. 150mm diameter samples needed to be created and place in incubator to adjust to the temperature. These samples where first created using a gyratory compactor, another piece of equipment, which was required for this experiment.
From carrying out my research, comparing both modified and unmodified bitumen’s at non-standard test temperatures, it became quite clear how much of an effect on the results modified bitumen was having. The results of the modified samples proved how modifying bitumen can have a positive effect on stiffness results. Although I do believe that the results proved, the MD57 wearing course, and MD62 base course where both modified using different types of bitumen’s. This was evident due to how they performed at both the warmest and coldest temperatures. MD62 base course performed well during testing at the warmer temperatures. With results no less than 1876.5 MPa, they maintained a very high stiffness value when compared to the unmodified base course, which at its weakest had stiffness results of 575 MPa. In addition, the MD62 samples outperformed the unmodified at the colder tests as well maintaining a lower stiffness value of 14248.5 MPa, compared to the unmodified 18024.6 MPa. The MD57 samples were also clearly modified, as even at the 10˚C testing, the stiffness value never exceeded 7182 MPa. However, the samples did produce very low values at the 40˚C test. A lowest value of 305.5 MPa, which would leave this material very susceptible to rutting. At first I believed that this low value was due to the base course having a higher bitumen content, however this is contradictory with the results at 10˚C, which would I presume would be a lot higher if bitumen content was the only factor. The bitumen used in the MD57 samples was most likely modified for performance in colder climates, which would explain the poor performance at lower temperatures.
Chapter 6:
Conclusion
This dissertation has described the experimental program, test results, and findings of a project conducted to study the variation in asphalt mix properties at non-standard test temperatures using standard and modified bitumen’s. In this conclusion, I will assess if I have met my research objectives, which I set at the beginning of the project. The objectives where:
Early on in my research, I determined that the most suitable asphalt for testing would be asphalt concrete samples. This was mainly due to its popularity and worldwide use, meaning that this would most likely be the type of pavement used in adverse climates such as the Middle East or even colder climates like Canada and Scandinavia.
When I began carrying out my research, I made five 150mm diameter test samples with unmodified bitumen. They were base course samples so they contained large aggregate sizes. I did not however create any modified samples as these were provided to me from Lagan bitumen in Dublin. There was four base course samples (MD62) so I could compare modified and unmodified bitumen’s directly, as the bitumen content would be similar in both modified and unmodified samples. Wearing course samples also containing modified bitumen’s were also provided, so a comparison could be made between wearing course and base course.
I carried out ITSM testing on all samples with a temperature range of 10°C to 40°C. This was a very successful test as it perfectly illustrated the relationship between temperature and stiffness, and therefore the likely hood of deformation happening to the asphalt at the tested temperature could be determined. This trend continued on all samples, modified and unmodified. The results of testing made evident how large an effect modified bitumen can have on the asphalts performance to. I was able to compare the data and also looking at ITSM results, I could determine how likely permanent deformation was to occur as well.
In general, I believe this was a very worthwhile and interesting research project. The results of my experiments, although they were generally as expected, shocked as to how defined the differences in results were. I was happy with how well the experiments went. However I do believe there were areas that more research could have went into and more time could have been spent testing, this is discussed in chapter 7.
To conclude I believe I have achieved most of my aims and objectives that I set out at the beginning. The only area I have lacked in was exactly what methods of modifying bitumen are best suited to certain climates. However, I believe all other aspects including determining the mix properties of asphalt at different test temperatures have been achieved.
Chapter 7:
Recommendations for further works
There are many ways in which research project could achieve more detail and results that are more accurate. Throughout this dissertation, I have been focusing on the effects of temperature on asphalt pavement. This has led to interesting results proving the correlation between asphalt stiffness and temperature, and how density effects this. However I believe there are several ways in which further research could be carried out to see exactly how asphalt is effected, how modified bitumen alters the results and exactly what types of modified bitumen are best suited for certain climates.
When testing the unmodified samples, I should have created at least four samples at each number of gyrations. This potentially could have eliminated any errors found. Such as unmodified sample 3, this did not fit the trend at some temperatures and therefore disturbing the R² value. If more samples had of been created, I could have eliminated any outstanding results to get a better determination of exactly how density effects asphalt stiffness.
Also when carrying out the ITSM testing, it could have been beneficial to use smaller differences in temperature for testing. This would have led to much more accurate data in terms of exactly how sensitive to temperature asphalt really is. For instance, could a change as small as 1 or 2˚C make a noticeable difference during testing. The smallest increment I used was 5˚C, which did fit almost perfectly into the data exactly where, would be predicted. I would be interested in seeing would the results be as accurate for smaller temperature changes.
Another interesting adjustment that could have been made would to be to test several different types of modified bitumen at the range of temperatures. I would be interested in seeing exactly what types of bitumen are best suited to certain temperatures, and are there some less effected by temperature than others. Also more research into the different reactions of base course and wearing course to temperature, and is it directly affected by bitumen content.
Test that I also believe would be a worthwhile and interesting experiment would be to perform some sort of wheel tracking test on asphalt samples. If carried out at varying temperatures this would provide very interesting data, hopefully showing exactly how asphalt deforms under loading, at non-standard test temperatures. This would however involve a lot more work. As wheel tracking is a destructive test, new samples would need to be created for testing at every temperature. In addition, samples containing modified and unmodified bitumen could be created along with testing base course against wearing course samples. This would involve creating dozens of samples and be a time costly experiment; however, I do believe the results would be very worthwhile and interesting. This would be an even better indication of what asphalt specimen is best suited to different climates.
Chapter 8:
References
.. (2013). Who, what, why: When does tarmac melt?. Available: http://www.bbc.co.uk/news/magazine-23315384. Last accessed 4th Nov 2016
.. (2014 ). Polymer Modified Bitumen. Available: http://www.bitumina.co.uk/polymer-modified-bitumen.html. Last accessed 20th April 2017.
.. (2015). ADVANTAGES OF ASPHALT. Available: http://www.eapa.org/promo.php?c=171. Last accessed 4th Dec 2016.
.. (2016). Drainasphalt. Available: http://www.aggregate.com/products-and-services/asphalt/drainasphalt/. Last accessed 4th Dec 2016.
.. (2016). HOT ROLLED ASPHALT (HRA). Available: http://www.kilsaran.ie/build/product/hot-rolled-asphalt-hra/. Last accessed 7th Dec 2016.
.. (2016). STONE MASTIC ASPHALT (SMA). Available: http://www.kilsaran.ie/create/product/stone-mastic-asphalt-sma/. Last accessed 4th Dec 2016.
Anil Srivastava and Ronald van Rooijen. (2000). Bitumen performance in hot and arid climates. Available: http://www.e-asfalto.com/datoseuropa/Bitumen%20performance%20in%20hot%20and%20arid%20climates.htm. Last accessed 5th Dec 2016.
Dave VanDeusen. (2015). Low Temperature Cracking in Asphalt Pavements. Available: http://www.dot.state.mn.us/mnroad/projects/Low_Temp_Cracking/. Last accessed 6th Dec 2016.
Eva Remisova (2013). Resistance to Permanent Deformation in Binder Content and Film Thickness Viewpoint. Slovakia: ..
H. B. Takallou, R. G. Hicks, D.C. Esch . (1987). USE OF RUBBER-MODIFIED ASPHALT PAVEMENTS IN COLD REGIONS . Available: http://www.asphaltrubber.org/ARTIC/International/RPA_A1118.pdf. Last accessed 4th Nov 2016.
Mihai O. Marasteanu Xue Li Timothy R. Clyne Vaughan R. Voller David H. Timm David E. Newcomb. (2004). Low Temperature Cracking of Asphalt Concrete Pavements. Available: http://conservancy.umn.edu/bitstream/handle/11299/792/1/200423.pdf. Last accessed 6th Dec 2016.
N. Baldo, M. Dal Ben, M. Pasetto. (2010). Indirect Tensile Test for the Determination of the Stiffness and the Resilient Modulus of Asphalt Concretes: Experimental Analysis of the EN 12697 -26 and the ASTM D 4123 Standards . Available: http://data.abacus.hr/h-a-d/radovi_s_kongresa/nagoya_japan_2010/90383.pdf. Last accessed 8th Dec 2016.
N. Baldo, M. Dal Ben, M. Pasetto. (2010). Indirect Tensile Test for the Determination of the Stiffness and the Resilient Modulus of Asphalt Concretes: Experimental Analysis of the EN 12697 -26 and the ASTM D 4123 Standards . Available: http://data.abacus.hr/h-a-d/radovi_s_kongresa/nagoya_japan_2010/90383.pdf. Last accessed 8th Dec 2016.
Pavement Interactive. (2009). HMA Performance Tests. Available: http://www.pavementinteractive.org/article/hma-performance-tests/. Last accessed 8th Dec 2016.
People for Proper Policing. (2005). A summary of road surfacing options and characteristics.Available: http://www.properpolicing.org.uk/articles/A%20summary%20of%20road%20surfaces%20options.pdf. Last accessed 4th Nov 2016.
Phillip Blankenship. (2015). How much does density matter?. Available: http://asphaltmagazine.com/how-much-does-density-matter/. Last accessed 20th April 2017.
S.K. Khanna & C.E.G. Justo. (2015). TYPES OF FAILURES OF FLEXIBLE PAVEMENT. Available: http://civilblog.org/2015/09/18/10-different-types-of-failures-of-flexible-pavement/. Last accessed 5th Dec 2016.
W. Vonk and R. Hartemink. (2004). the softening point and the SBS content. Available: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.511.3240&rep=rep1&type=pdf. Last accessed 5th Dec 2016.
Zhang Qi-sen , Chen Yu-liang , Li Xue-lian. (2009). Rutting in Asphalt Pavement under Heavy Load and High Temperature. Available: http://www.nlcpr.com/RuttingAsphaltPavementHeavyLoadHighTemp.pdf. Last accessed 6th Dec 2016.
Chapter 9:
Appendix
“I hereby declare that this is all my own work and does not contain unreferenced material copied from any other source. I have read the University’s policy on plagiarism in the Student Handbook and understand the definition of plagiarism (below). If it is shown that material has been plagiarised, or I have otherwise attempted to obtain an unfair advantage for myself or others, I understand that I may face sanctions in accordance with the policies and procedures of the University. A mark of zero may be awarded and the reason for that mark will be recorded on my file.
Definition of Plagiarism
Plagiarism is the act of taking or copying someone else’s work, including another student’s and presenting it as if it were your own. Typical plagiarists use ideas, texts, theories, data, created artistic artefacts or other material without acknowledgement so that the person considering the work is given the impression that what they have before them is the student’s own original work when it is not. Plagiarism also occurs where a student’s own previously published work is re-presented without being properly referenced. Plagiarism is a form of cheating and is dishonest.
I hereby declare that with effect from the date on which the dissertation /project is submitted to the University of Ulster I permit the University to allow the dissertation/project to be copied in whole or in part without reference to me on the understanding that such authority applies to the provision of single copies made for study purposes or for inclusion within stock of another library. This restriction does not to the copying or publication of the title and abstract of the dissertation/project.
IT IS A CONDITION OF USE OF THIS DISSERTATION/PROJECT THAT ANYONE WHO CONSULTS IT MUST RECOGNISE THAT THE COPYRIGHT RESTS WITH THE UNIVERSITY AND THAT NO QUOTATION FROM THE DISSERTATION/PROJECT AND NO INFORMATION DERIVED FROM IT MAY BE PUBLISHED UNLESS THE SOURCE IS PROPERLY ACKNOWLEDGED.”
Signed………………………………………
Date…………………………………………
Faculty of Art Design and the Built Environment
Research Governance Assessment Form
SECTION 1: Please complete the following details in full:
STUDENT NAME: Ruairi McElduff
STUDENT NO: B00660263
COURSE TITLE: Civil Engineering (BSc)
MODULE: CIV525
DISSERTATION TITLE: Asphalt Mix Properties At Different Test Temperatures
ASPECT INVOLVING HUMAN CONTACT: No
START DATE : October 2016 COMPLETION DATE: May 2017
SUPERVISOR: Dr David Woodward
Please consult the Universities Policy on Research involving human participants and answer the following question by selecting YES or NO.
| Does your project involve human participants or subjects in any way? This includes interviews, focus groups and questionnaires or observation or research interventions of any kind. | YES/NO |
If you have answered NO to the question above then the research does not require Filter or Ethical Review and your project can proceed immediately. Please sign and date the declaration below. If you have answered YES to the question then you must proceed to section 2 of this application form.
Declaration by the Student and Supervisor: I have taken the Universities Policy on Research involving human participants into account and confirm that the assessment above is accurate and that the project does not require review by the Filter or Ethical Committee.
| Student Signature: | Date: |
| Supervisor Signature: | Date: |
Section 1 of this form should be bound into the project, dissertation or thesis and a paper copy should be sent by internal mail to the Chair of the Filter Committee, Dr Cherie Driver, Belfast Campus.
Any significant change to your dissertation will require a further assessment and you should seek guidance on this from your supervisor.
Please note that the consequence of embarking on research involving human subjects without having received filter committee approval is failure of the dissertation.
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