Investigating the effect of polyurethane additive on bitumen adhesive fatigue behavior

Dissertation for Master's degree

in the field of road and transportation civil engineering

Abstract

     Asphalt damage is one of the problems that are the concern of road and transportation engineers today, and every year huge costs are spent on the repair and maintenance of asphalt roads. Many efforts have been made to increase the resistance and life of asphalt, among these efforts is improving the properties of bitumen. The use of polymers in modifying the properties of bitumen is very common and is expanding day by day. Thermoplastic elastomers and reactive polymers are among the families of polymers that have significant effects on bitumen properties. In this research, thermoplastic polyurethane (TPU), synthesized polyurethane (PU) has been used as a modifier additive in bitumen. The tests of penetration degree, softening point (R&B), thin crust glaze (RTFO), aging acceleration chamber (PAV), dynamic shear rheometer (DSR), bending beam rheometer (BBR) and Fourier transform infrared spectroscopy (FTIR) were performed on modified samples with different shapes of polyurethane family. The results of these tests showed that polyurethane reduced the degree of penetration and increased the softening point of bitumen, which modified bitumen had higher hardness and viscosity, and as a result, less thermal sensitivity. Polyurethane has also increased the high performance temperature of base bitumen and increased its resistance against permanent deformation and has been able to give higher performance levels to base bitumen. At medium temperature, bitumens modified with polyurethane showed better performance and greater resistance to fatigue than base bitumen. At low temperatures, although polyurethane had a very small positive effect on bitumen performance, it could not add performance category to bitumen at low temperature. The results of the FTIR test showed the urethane bonds in the modified bitumen, which confirmed the formation of bonds in the bitumen and determined its chemical structure. Keywords: bitumen, polyurethane, isocyanate, polyal, bitumen foam. They are asphalt [1]. Traffic loading causes damage such as rutting [2] and fatigue cracks [3]; And environmental factors such as temperature are the main cause of cryogenic cracks. Depending on factors such as load size, contact surface, temperature and hardness and thickness of the pavement, traffic loading can cause tension [4], compression [5], shear [6] or a combination of them at different points of the pavement. Usually, the repetition of these stresses and strains leads to pavement damage. Fatigue cracks are actually small cracks that increase with continuous loading in the pavement system and finally expand in the form of fatigue cracks. The accumulation of these cracks eventually causes the pavement to break. Therefore, the ability to predict pavement behavior against fatigue phenomenon is important. Since the fatigue phenomenon occurs mostly in the bitumen phase [7] related to the asphalt mixture [1], therefore, tests related to the fatigue behavior of bitumen can be used.

1-2- Statement of the problem

     Every year, a lot of expenses are considered for repairs and maintenance of roads, most of which are spent on removing and repairing the cracks created in the pavement. Cracks in the pavement are one of the most important modes of failure and one of the main factors in reducing the service level of the pavement. Among the types of cracks, we can mention reflective, contraction and fatigue cracks. Cracks are caused by various factors such as traffic load, temperature changes and settlement of the underlying layers. Basically, the main cause of cracking is temperature changes, and traffic causes cracks to propagate and spread further.

At high temperatures, rutting is the main mode of failure in asphalt concrete, but cracks in asphalt pavement usually occur at low temperatures because asphalt becomes brittle at low temperatures, and this causes the asphalt to crack without much deformation. Also, low temperature causes bitumen in asphalt concrete to become harder and as a result reduce the fatigue life.

One of the main ways to increase the ability of asphalt to resist damage is to prepare quality materials and modify the properties of bitumen. Improving the properties of bitumen makes bitumen have better elastic and viscous properties, as well as higher shear modulus, and consequently better performance.Many additives from different families including polymers (elastomers [8], plastomers [9] and reactive polymers [10]), fibers, fillers, nano materials, etc. are used to modify the properties and performance of bitumen in asphalt mixture. In this research, the use of polyurethane polymer [11] as an additive to improve the performance of bitumen against the phenomenon of fatigue by temperature scanning test is considered. In addition, the effect of this additive on the chemical structure of bitumen has been investigated by Fourier infrared spectrometry test, as well as its effect on bitumen resistance against permanent deformation at high temperature and cryogenic cracks at low temperature and thermal sensitivity of bitumen. Polyurethane is the general name for polymers that have urethane linkages. Urethane bonds are formed from the reaction of isocyanate group [12] with polyols [13]. In polyols, groups such as hydroxyl [14] (OH), which has active hydrogen, reacts with an isocyanate group and creates urethane bonds.

1-3- Hypothesis

Different modifiers, depending on their type, have different effects on the physical and mechanical properties of bitumen, which can lead to different functional properties in bitumen. Therefore, it is predicted that by adding a suitable modifier to bitumen, it is possible to increase stiffness, elasticity and viscosity. 1-4- Research objectives The main objective of this research is to investigate the effect of adding polyurethane polymer on the adhesive fatigue behavior of bitumen at medium temperature. Another goal of this research is to investigate the effect of this material on the performance of bitumen at high and low temperatures and thermal sensitivity of bitumen. It is also considered to determine the urethane bonds formed in the bitumen matrix.

1-5- Thesis structure

     This thesis is compiled in 6 chapters. The content of each chapter is summarized in the following. Chapter 2- Review of the past literature of the subject: In this chapter, the history and basics of bitumen and its modification, its purpose and history, and the types of experiments related to bitumen and their applications are discussed. Also, the important issues and cases related to the types of common modifiers have been described. Chapter 3- Materials, Materials and Test Plan: To achieve the research objectives, a plan of materials, materials and the test plan necessary to collect the required data was prepared. The details of this program and its steps along with the materials and equipment used in this research are given in this chapter. Chapter 4 - Results and analysis: In this chapter, the results obtained from various tests conducted on bitumen are discussed and analyzed. Chapter 5 - Conclusions and suggestions: General conclusions and suggestions for the continuation of the research are given in this chapter. Chapter 6 - Resources: In this chapter, various sources are used. It is introduced in this research.

Chapter 2

A review of the past literature of the subject

-1- The history of bitumen and its modification

Sumerians, Assyrians and many previous civilizations used bitumen widely. The beginning of the modern bitumen industry can be attributed to the year 1712 when natural bitumen stones were discovered in France. At that time, bituminous materials were simply spread in the form of lumps on the surface of the local roads, and gradually they were ground and compacted under the traffic. This technique was quite successful and in a short period of time, improvements were made in the work, in the form of powdering and heating the material before use. Then the asphalt was compacted and solidified by pounding and flattening, which was known as dense asphalt [1] and was used in the streets of Europe. Compared to dirt roads, such streets were very durable, healthy and interesting; Their only drawback was that they were loose, unstable and slippery [2] with the beginning of heavy traffic. [2] [

     The first cases of bitumen modification date back to 1843 AD. In the 1930s, experimental bitumen modification projects were implemented in Europe, and in the 1950s, the use of neoprene latex [3] as a bitumen modifier began in North America. [3] In 1963, the first modified bitumen test roads were built in France, in order to know the behavior of modified bitumen with various natural and synthetic rubbers. [4] In the late 1970s, Europe modified bitumen. Tar was before America