Improving Microwave Heating Characteristic of Asphalt Binder by Using Fly Ash

*Mert Atakan and Kürşat Yıldız* 

#### **Abstract**

 Previous studies have indicated that asphalt can heal itself, if it is allowed to rest enough. Current research on self-healing is focused on induction and microwave heating methods which provides with adding metallic fibers to asphalt mixture. However, any study about usage of fly ash to improve microwave heating of asphalt binder is not encountered. Because utilization rate of fly ash that is an environmental pollutant is 25% in the world, is required to find new field to use it. This chapter studies usability of fly ash as a microwave absorber in order to accelerate microwave heating of asphalt binder. In order to achieve this, specimens that contain fly ash at different ratio were prepared and microwave heating rate of these specimens were tested. These tests revealed that fly ash can accelerate microwave heating of bitumen, so it has a potential to improve self-healing of asphalt. The study also showed that below 20% of fly ash ratio by bitumen weight may not be enough to provide self-healing.

**Keywords:** microwave heating, self-healing, asphalt binder, fly ash, heating rate

#### **1. Introduction**

 Asphalt mixture, composed of aggregate, filler, and asphalt binder, is widely used for pavement construction in the world. The reasons of this choice are that it provides comfortable driving, its initial investment cost is relatively low, it reduces wheel noise, it needs less qualified labor, and it can be repaired fast. However, throughout service life, asphalt pavement exposed many effects such as climate effects, aging of bitumen, and traffic loads. Because of these effects, micro cracks occur and these cracks grow larger and bring about surface cracks, raveling, and potholes at last [1]. Deteriorations are usually repaired using conventional methods such as regional patch, filling the potholes, and rebuilding the pavement. These methods are insufficient due to both high cost and traffic disruption. New methods are needed to extend the service life of the pavement and to make the repair process less costly and faster.

Bazin and Saunier [2] revealed the self-healing phenomenon of asphalt in 1967. They reported that after the loading, asphalt can heal when it is allowed to rest, and temperature of the asphalt plays an important role in self-healing. After that, self-heling of asphalt has become a research focus.

 As the bitumen is very viscous material [3], it tends to flow through a micro crack just as capillary flow [4]. Thus, the crack heals as the bitumen fills in it. Little and Bhasin [5] explained the healing mechanism in 2007. They reported, as soon as external load removed, viscoelastic recovery occurs, regardless of the external load is large enough to damage the material or not. On the other hand, if the load is large enough to damage the material, healing occurs immediately after removal of external load. They also explained the difference between viscoelastic recovery and healing; "While the former is due to the rearrangement of molecules within the bulk of the material, the latter is due to the wetting and interdiffusion of material between the two faces of a nano crack to achieve properties of the original material".

 The healing process lasts until the material returns to its original state as long as the material is not exposed to the traffic load. Traffic load would make the cracks even worse. Furthermore, the process may last days at the ambient temperature [6]. In practice, however, it is not possible to stop the traffic to provide healing at the ambient temperature [7]. If asphalt concrete is exposed at higher temperature, healing rates are also enhanced [8, 9]. Moreover, a lot of researcher reported that cracks which are seen at winter disappear at summer [10]. In 2011, Garcia [4] reported that increasing the temperature of asphalt mix, increases the healing rates of the asphalt mix and there is a certain temperature and fixed heating time to provide self-healing of asphalt.

Self-healing of asphalt can be accelerated via some methods such as induction heating and microwave heating. Induction heating can heat electrically conductive materials such as metals by electromagnetic waves and adding such materials to asphalt mix makes it electrically conductive. Therefore asphalt mix can be heated by induction heating [7]. Much research on induction heating has been done [7, 10–18]. However, microwave heating has become a research focus recently. In 2013, Gallego and his colleagues [19] revealed microwave heating method and some studies on it has been done until now [15, 16, 19–29]. Different additives were used in asphalt mix to provide self-healing via microwave heating such as carbon nano tubes (CNT) [22], steel slag [21, 23, 29], carbon powder [27], and recycled asphalt pavement (RAP) [20, 28].

Fly ash is a by-product which is generated by combustion of coal at the thermal power station and it is known as a environmental pollutant [30]. Blissett and Rowson [31] estimated that 750 million tons of fly ash is produced annually worldwide and Wang [32] predicted that fly ash utilization rate is about 25%.Therefore, in order to deal with this environmental pollutant, it is necessary to find new fields where fly ash can be used in. In this chapter, fly ash was used as an additive for asphalt binder in order to accelerate microwave heating of asphalt binder, since fly ash is much more affected from microwaves than bitumen or aggregate is.

#### **2. Materials and methods**

#### **2.1 Material description**

 In order to prepare specimens, 50/70 penetration grade bitumen supplied from Kırıkkale oil refinery was used. The fly ash which was mixed with bitumen was supplied from Çayırhan Thermal Power Plant. The fly ash type was chosen randomly by taking into consideration the amount of metal oxides. The chemical composition of the fly ash based on another study is given in **Table 1**. According to same study, blaine fineness of fly ash is 2830 cm<sup>2</sup> /g. The microwave oven which is used in the experiment has 800 W output power and 2450 MHz frequency same as any microwave ovens.

*Improving Microwave Heating Characteristic of Asphalt Binder by Using Fly Ash DOI: http://dx.doi.org/10.5772/intechopen.87836* 


**Table 1.** 

*Chemical composition of the fly ash (%) [33].* 

#### **2.2 Preparation of specimens**

 In order to prepare specimens, 30 g of bitumen were put in each beaker and fly ash was weighed. Both fly ash and bitumen were heated at 150°C in the drying oven before mixing together them. After that, 150°C bitumen which is in the beaker was put on the heater and hot fly ash was added in it and the bitumen had been stirred with a stick until they mixed homogeneously (**Figure 1**). Finally, they were left to cool for one night.

 Fly ash ratio was chosen variable from 2 to 50% by weight of bitumen and they were named from FA2 to FA50. Besides, a control specimen which contains 0% of fly ash was generated. Apart from that, a specimen generated contains 2% of steel wool in order to confirm heating effect of metallic fibers and named SW2 (**Figure 2**).

#### **2.3 Testing of microwave heating characteristic**

Microwave heating test was used in order to determine microwave heating rates of different samples. Microwave output power employed 800 W. First, samples were heated for 20 seconds and measured its temperature. As the immersion thermometer works slowly, it waited for 1–2 minutes to read the temperature of specimen. After that, specimen was heated another 20 seconds and it went on six times

**Figure 1.**  *Preparation of the specimens.* 

**Figure 2.**  *Steel wool used in the specimen.* 

**Figure 3.**  *Measuring the temperatures of asphalt specimen.* 

in total to reach 120 seconds. Same experiment was repeated for 40 seconds breaks and 60 seconds breaks, until reach 120 seconds in order to eliminate errors.

 While measuring the temperature via the immersion thermometer, the specimen was cooled at the same time. Therefore, the temperatures which were gauged were lesser than it should be. To solve this problem, temperatures were measured quickly with an infrared thermometer and compared with the immersion thermometer (**Figure 3**). According to values obtained from infrared thermometer, measured temperatures enhanced 5%, in order to compensate cooling.

#### **3. Results and discussion**

These tests showed that microwave heating rate of bitumen increased as fly ash ratio increase. According to infrared thermometer values, there was a difference between top surface and bottom surface of the bitumen sample at the rate of up

*Improving Microwave Heating Characteristic of Asphalt Binder by Using Fly Ash DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 4.**  *Microwave heating rate of asphalt binder specimens.* 

 to 30–40%. This means that additives did not mix with bitumen homogeneously; instead they settled at the bottom of the beaker. We faced the same problem with the specimen which contains 2% steel wool. The bottom surface of the specimen reached 90°C in 20 seconds via microwave heating, while top surface barely exceeds the ambient temperature. To get rid of the problem, asphalt mix may be used instead of merely asphalt binder.

Tests indicated that little amount of fly ash such as 2 or 4% is not very effective to improve heating rate of bitumen. Therefore, high amount of fly ash such as from 20 to 50% was used subsequently.

 The sample which contains 2% of steel wool reach approximately 90°C at the bottom and 24°C at the top in 20 seconds. When the temperature is balanced, it was around 50°C which is quite higher than the all samples with fly ash.

Garcia [4] reported that below certain temperatures, healing cannot occur because bitumen behaves non-Newtonian fluid. However this certain temperature changes with the type of bitumen and usually healing can start between 30 and 70°C [34]. In our study, 20% and higher fly ash ratio was enough to reach 30°C in 40 seconds and 50% fly ash ratio was enough to exceed 40°C in 40 seconds (**Figure 4**). In order to confirm whether this temperature is sufficient or not to self-heal, further experiments are required such as determining healing index of asphalt mix containing fly ash or comparing the viscosity of asphalt binder containing fly ash.

The effect of the fly ash to mechanic properties of asphalt was not evaluated. However, it is observed that high amount of fly ash may reduce its ductility. According to previous study, high amount of fly ash rate gives rise to a drop at ductility and penetration of the asphalt, whereas its softening point is rising [35].

#### **4. Conclusions and recommendations**

 In the chapter, contribution of the fly ash to microwave heating of bitumen was researched. A sample with 2% of steel wool was also tested in order to compare the results. From the outcome of our investigation, it is possible to conclude that:


### **Acknowledgements**

The authors would like to thank their colleagues Prof. Dr. Salih Yazıcıoğlu and Assoc. Prof. Dr. Osman Şimşek for their contribution in conducting some of the experiments for the research. Besides, the authors also would like to thank to their colleagues Tech. Osman Aydın for his technical assistance.

### **Author details**

Mert Atakan\* and Kürşat Yıldız Faculty of Technology, Department of Civil Engineering, Gazi University, Ankara, Turkey

\*Address all correspondence to: mertatakan@gazi.edu.tr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Improving Microwave Heating Characteristic of Asphalt Binder by Using Fly Ash DOI: http://dx.doi.org/10.5772/intechopen.87836* 

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**295**

**Chapter 25**

(ICFs)

**Abstract**

A Comparative Study between

and Insulated Concrete Forms

*Nehal Atlam and Mukaddes Darwish*

(ICFs) properties of the resilient masonry walls system.

masonry walls system, masonry, buildings

**1. Introduction**

Concrete Masonry Units (CMUs)

This chapter aims a comprehensive comparative study in order to assess the success of a resilient masonry walls system for major successful buildings in the United States and guide for the selection of optimum materials for each building. Many essential parameters, which control building behaviors such as durability, acoustical privacy, structure configurations, fire and wind resistance, material type, energy use, and cost of the assembly have been analyzed. The mentioned analysis is performed on 10 major buildings, for which the data were available. The results of the analyzed data identified the similarities of the used materials. The learning outcomes of these analyses can be used to improve building strategies for the designs of existing buildings and new buildings. A case study in Gulf Coast, Mississippi is investigated. The procedure for selection of this case study can be utilized as the decision criterion for similar cases of resilient walls system design, and as the main essential factor that lead to the optimum way of building these kind of buildings. Principal component analysis (PCA) is used to correlate the commonly used materials within concrete masonry units (CMUs) and insulated concrete forms

**Keywords:** concrete masonry units (CMUs), insulated concrete form (ICFs), resilient

Within the building industry complexity, there is a growing interest in new technologies that promise to deliver efficiency, cost savings, durability, and productivity increase to the construction projects. Increasingly, new construction method is emerging, and it called resilient masonry walls system. Using sustainable (resilient) masonry walls system in the construction industry provides safe and a healthy environment, durability, fire, flood, and wind resistance. The key success of a resilient masonry walls system for major successful buildings in the United States and guide future depends on selective optimum materials for each building. Concrete masonry units (CMU) and insulated concrete forms (ICFs) are the most versatile products in the construction industry [1, 2]. These products are not diametrically opposite, they have clear overlaps.

Despite this, the main differences between CMU and ICF can be defined.

#### **Chapter 25**
