Induction heating of electrically conductive porous asphalt ... - TU Delft

ARTICLE IN PRESS 

Construction and Building Materials xxx (2010) xxx–xxx 

Contents lists available at ScienceDirect 

Construction and Building Materials 

journal homepage: www.elsevier.com/locate/conbuildmat 

Induction heating of electrically conductive porous asphalt concrete 

Quantao Liu a, *, Erik Schlangen a , Álvaro García a , Martin van de Ven b 

a Delft University of Technology, Faculty of Civil Engineering and Geosciences, Micromechanics Laboratory (MICROLAB), Stevinweg 1, 2628 CN Delft, The Netherlands 

b Delft University of Technology, Faculty of Civil Engineering and Geosciences, Road and Railway Engineering, Stevinweg 1, 2628 CN Delft, The Netherlands 

article 

info 

abstract 

Article history: 

Received 24 August 2009 

Received in revised form 15 December 2009 

Accepted 16 December 2009 

Available online xxxx 

Keywords: 

Porous asphalt concrete 

Steel fibers 

Steel wool 

Electrical resistivity 

Indirect tensile strength 

Induction heating 

In this research, an electrically conductive porous asphalt concrete, used for induction heating, was prepared 

by adding electrically conductive filler (steel fibers and steel wool) to the mixture. The main purpose 

of this paper is to examine the electrical conductivity and the indirect tensile strength of this 

conductive porous asphalt concrete and prove that it can be heated via induction heating. It was found 

that, to make porous asphalt concrete electrically conductive, long steel wool with small diameter is better 

than short steel fibers with bigger diameter. However, steel fibers with short length and big diameter 

have better strength reinforcement capability than steel wool with long length and small diameter. It was 

also proved that conductive porous asphalt concrete containing steel wool can be easily heated via induction 

heating. Finally, 10% (by volume of bitumen) of steel wool type 000 was proposed as an optimal content 

in porous asphalt concrete to obtain an optimal conductivity, a good induction heating rate and an 

acceptable indirect tensile strength. It is expected that the autogenous healing capacity of asphalt concrete 

will be enhanced with the increase of temperature during induction heating. 

Ó 2009 Elsevier Ltd. All rights reserved. 

1. Introduction 

Porous asphalt concrete is the most commonly used surface 

wearing course in the Netherlands due to its excellent performance 

in noise reduction and water drainage. However, the biggest defect 

of porous asphalt concrete is its poor performance in terms of 

durability compared with dense graded asphalt concrete. The average 

lifetime of porous asphalt is of approximately 11 years [1], 

much shorter than the lifetime of a dense asphalt mixture. The 

main durability problem of porous asphalt concrete is called raveling 

[2], which is the loss of aggregates from the surface layer of the 

pavement and has a negative effect on the general performance of 

the pavement [3]. Part of the damage due to raveling is the result of 

errors in the production and processing methods, including poor 

control of asphalt temperature during production, variations in 

the mixture composition, the presence of weak aggregates in the 

asphalt mixture or insufficient filler fraction in the mixture [1]. 

However, the majority of the raveling damage is the result of the 

material properties themselves [4]. Aggregates in the porous asphalt 

mixture are hold together by the binder. Due to ageing hardening 

(temperature cycles, wetting–drying, ultra-violet and traffic 

loading) or due to extreme cold weather conditions, the stiffness of 

the binder increases, the relaxation capacity decreases, the binder 

* Corresponding author. Tel.: +31 (0) 15 2788078. 

E-mail address: quantao.liu@tudelft.nl (Q. Liu). 

becomes more brittle, the self healing potential and fracture resistance 

of the bitumen decreases, and cracking of the interface between 

aggregates and the binder occurs. Small cracking on 

highway runway can mean the start of some big distresses. Then, 

the traffic load will remove aggregate particles from the surface 

layer. After the first stones are removed, more stones will follow 

at a higher rate [5]. This will increase the noise levels in the road 

and reduce the traffic comfort. 

It is well known that asphalt concrete is a self healing material 

[6,7]. As Little and Bhasin explain [6], healing occurs only after a 

stress or strain is induced, which is sufficiently large to generate 

damage. Immediately after the load that generated the damage 

has been removed, and both faces of the crack are in contact, the 

diffusion of molecules from one face to the other starts. This process 

will happen, while there are not more loads, until the micro-crack 

has completely disappeared and the repaired material 

has the level of strength of the original material. The problem 

comes because it is difficult to stop traffic circulation on a road 

to allow enough self healing recovery at ambient temperature. It 

is also well known that the amount of healing increases when 

the material is subjected to a higher temperature during the rest 

period [7,8]. Increasing the temperature will enhance the healing 

effect of the asphalt concrete. 

Conductive concrete is a category of concrete containing electrically 

conductive components to attain stable and high electrical 

conductivity. The first attempt of making an electrically conductive 

concrete road for deicing dates back to the 1950s. Besides, very 

0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. 

doi:10.1016/j.conbuildmat.2009.12.019 

Please cite this article in press as: Liu Q et al. Induction heating of electrically conductive porous asphalt concrete. Constr Build Mater (2010), doi:10.1016/ 

j.conbuildmat.2009.12.019


2 Q. Liu et al. / Construction and Building Materials xxx (2010) xxx–xxx 

recently Sherif et al. [9] and Tuan [10] made conductive concrete 

containing steel fibers and shavings for bridge deck deicing. 

Electrically conductive asphalt concrete is a relatively new 

functional material developed to achieve electrical conductivity. 

To reach this property, conductive filler or fibers should be added 

to the mixture. Wu et al. [11] made the first electrically conductive 

mixture by adding conductive carbon fibers, carbon black or graphite 

to the asphalt concrete. They demonstrated that the conductivity 

is proportional to the volume of conductive filler or fibers 

added. An excess of conductive particles can cause the degradation 

of the asphalt concrete properties, such as the strength or the 

workability of fresh materials. Finally, they showed that adding 

conductive fibers to the mixture is much more effective to increase 

the conductivity than adding conductive filler. In addition, García 

et al. [12] show how the conductivity is proportional to the volume 

of aggregates in the mixture and how there is an optimum volume 

of electrically conductive particles for each mixture. These authors 

explain the conductive mechanism by means of the percolation 

theory. With a low volume of conductive particles in the mixture, 

the resistivity of asphalt concrete is that of a non conductive material, 

but when the volume of conductive particles is above the percolation 

threshold, the resistivity drops and the sample becomes 

conductive. 

It is theoretically feasible to repair cracks in asphalt concrete 

before they become too big to be healed. The use of fibers to 

reinforce binder has long been in practice. In this research, conductive 

steel fibers are added to the asphalt mixture and induction 

heating is used to increase the temperature locally, just 

enough to increase the asphalt healing rates and repair microcracks 

or the bond between aggregates and binder. The main 

objective of using conductive fibers is to increase the conductivity 

of binder so that micro-cracks can be healed via induction 

heating. Induction heating in the asphalt industry is a novel technique 

originally developed by García et al. [12]. In this method, 

the power supply sends alternating current through the coil, generating 

an alternating electromagnetic field. When the conductive 

asphalt specimen is placed under the coil, this electromagnetic 

field induces currents flowing along the conductive loops formed 

by steel fibers. The induced current dissipates heat by the Joule 

effect. This method can be repeated if damage returns. Traditionally, 

in conductive roads, heat was generated due to the electrical 

resistance in the conductive particles when connected to a power 

source, but in this occasion, authors are trying to make porous 

asphalt concrete appropriate for induction heating and the subsequent 

healing of cracks. This method has the advantage of having 

high volumetric heating rates. Another advantage of using fibers 

is that they will probably improve the ageing behavior and the 

resistance to water damage of bitumen by achieving thicker binder 

film and by preventing drain-off of the mastic. This may improve 

significantly the raveling resistance of porous asphalt 

concrete. 

This will be the first time that this induction heating technique 

is applied to porous asphalt concrete. The objectives of this research 

are: 

To study the effect of steel fibers volume content on the electrical 

conductivity of porous asphalt concrete. 

To investigate the effect of the steel fibers volume content on the 

indirect tensile strength of porous asphalt concrete. 

To analyze the effect of steel wool volume content on the heating 

rate of porous asphalt concrete. 

To explore the relationship between electrical conductivity and 

induction heating in porous asphalt concrete. 

To optimize the type and volume content of steel fibers to obtain 

a good electrical conductivity and a high induction heating rate 

in porous asphalt concrete. 

2. Experimental method 

2.1. Materials 

The aggregates used to make porous asphalt concrete specimens were quarry 

material (Bestone, Bremanger Quarry, Norway) (size between 2.0 and 22.4 mm 

and density 2770 kg/m 3 ), crushed sand (size between 0.063 and 2 mm and density 

2688 kg/m 3 ), and filler type Wigro 60 K (size < 0.063 mm and density 2638 kg/m 3 ). 

Finally, the bitumen used was 70/100 pen, obtained from Kuwait Petroleum, with 

density 1032 kg/m 3 . 

Besides, two different types of electrically conductive fibers were mixed in the 

asphalt. The first one was steel fibers (called steel fiber type 1), with a diameter between 

0.0296 mm and 0.1911 mm. The second one was steel wool type 000 with 

diameters between 0.00635 mm and 0.00889 mm. These fibers had to be chopped 

by hand, always by the same operator. Both types of fibers had an approximate density 

of 7.8 g/cm 3 . These fibers had an electrical resistivity of 7 10 7 X cm. To find 

the size distribution of the conductive fillers, more than 100 fibers of each type 

were checked by taking photographs under the optical microscope and measuring 

their length with an image processing program, obtaining the distribution shown in 

Fig. 1a and b. 

2.2. Porous asphalt design 

Porous asphalt PA 0/16, the most commonly used mixture in the Netherlands, 

was used in this research. The mixture composition was fixed based on the Dutch 

Standard, RAW 2005 (Table 1) and Gyratory compactor was used to compact the 

mixture. These specimens have a diameter of 100 mm and a variable thickness between 

77.40 and 84.22 mm. 

The maximum theoretical density of the mixture was 2.569 g/cm 3 . It was calculated 

as the total weight divided by the total volume of all the materials before compaction. 

After mixing, the maximum theoretical density of the loose mixture was 

measured using an ultrapycnometer 1000 (America, Quantachrome Instruments), 

a 

Percentage % 

b 

Percentage % 

70 

60 

50 

40 

30 

20 

10 

0 

25 

20 

15 

10 

5 

0 

0 0.125 0.25 0.5 1.0 2.0 

Size of steel fiber mm 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 

Size of steel wool mm 

Fig. 1. Size distribution of steel fiber type 1 (a) and steel wool type 000 (b). 




Q. Liu et al. / Construction and Building Materials xxx (2010) xxx–xxx 3 

Table 1 

Composition of PA 0/16 mixture for Gyratory specimen based on the Dutch standard 

(RAW 2005). 

Sieve size 

(mm) 

Density 

(g/cm 3 ) 

which is an instrument for measuring the true volume and density of powders, 

foams and bulk solids. The maximum theoretical density measured with this apparatus 

was 2.571 g/cm 3 , very close to the previously calculated value. The maximum 

theoretical density of the mixture changes with the variation in volume of steel 

wool in the mixture and can be computed according to the total weight and volume 

of all materials in the mixture. The standard calls for a minimum of 20% of air voids 

content. In this case, the air voids content was assumed to be 21%. Based on the 

maximum theoretical density, the calculated density of the specimen after compaction 

and the weight of the mixture, the Gyratory compactor can control the height 

of the specimen to obtain the ultimate target density. The air voids content can be 

computed after molding the specimens by determining their dimensions (to compute 

their volumes) and weights. The maximum and assumed densities of the mixtures 

with different volume contents of the fibers (the fiber–bitumen volume ratio) 

were calculated to obtain the same air void content in all samples studied. The air 

voids content for all specimens after compaction was around 21%. 

2.3. Electrical resistivity tests 

The electrical resistivity measurements were done at room temperature 20 °C. 

The samples, with diameter 100 mm and thickness 50 mm were cut from the Gyratory 

compacted specimens. After cutting, the samples were placed in an oven at 

40 °C during 8 h to remove the moisture and prevent the steel fibers rusting on 

the surface of the samples. Inside the sample, the steel fibers do not corrode, because 

they are completely coated with bitumen. A digital multimeter was used to 

measure the resistance below 36 10 6 X. A resistance tester was used to measure 

the resistance higher than this value. Two electrodes made of 100 mm square copper 

plates were connected with resistance tester when testing resistance. Both electrodes 

were placed at both ends of the test sample to measure the electrical 

resistance. A small pressure was applied to the copper electrodes to obtain a good 

contact with the surface of the sample. The total contact resistance between the two 

electrodes was about 0.4 X, which is negligible with respect to the great resistances 

studied (higher than 100 kX in the samples). The electrical resistivity was obtained 

from the second Ohm-law by 

q ¼ RS 

ð1Þ 

L 

where q is the electrical resistivity, L is the internal electrode distance in meter, R is 

the measured resistance in omega and S is the electrode conductive area in square 

meter. The electric field is assumed constant and the end-effects considered 

negligible. 

2.4. Indirect tensile strength test 

RAW spec. 

% retained 

Cumm. 

% ret. 

% ret. by 

weight 

Weight 

(g) 

22.4–16.0 2.778 0–7 4 4 48 

16.0–11.2 2.774 15–30 25 21 252 

11.2–8.0 2.762 50–65 57 32 384 

8.0–5.6 2.765 70–85 80 23 276 

5.6–2.0 2.781 85 85 5 60 

2.0–0.063 2.688 95.5 95.5 10.5 126 



heating samples were the same as the ones used to measure the electrical resistivity. 

The cylindrical samples cut from Gyratory specimens were used to avoid the 

problem of binder concentration on the surfaces of samples and to get a higher 

heating efficiency for that thinner samples mean less temperature difference between 

the top and the bottom of the samples. The distance between the coil of 

the induction machine and the top surface of the heating sample was about 

32 mm. Each sample studied was heated for 3 min and its temperature change 

was measured with a 640 480 pixel, full color infrared camera. 

3. Results and discussions 

3.1. Effect of conductive fiber volume content on the electrical 

resistivity of porous asphalt concrete 

The effect of steel fiber (type 1) volume content on the resistivity 

of porous asphalt concrete samples is shown in Fig. 3. The resistivity 

of the samples shows three stages: high resistivity stage, 

with fiber volume content less than 10%; transit stage, with fiber 

volume content from 10% to 20%; and low resistivity stage, with fiber 

volume content higher than 20%. Samples with less than 10% of 

fibers exhibited insulating behavior, with resistances higher than 

10 9 X m. During the transit stage (between 10% and 20% of fibers), 

the electrical resistivity of the sample suffered a sharp decrease 

from 10 9 X m to 4.7 10 4 X m. It was discovered that, for the steel 

fiber type 1, 20% fibers are needed to make the porous asphalt concrete 

electrically conductive. 

In addition, when drying the sample after cutting, it was found 

that plain samples, without steel fibers, glued a little bit to the 

plate bellow, showing drainage of binder in the sample. However, 

samples with steel fibers did not show this phenomenon, which 

shows that the steel fibers could prevent the drainage of binder. 

3.2. Effect of conductive fiber volume content on the indirect tensile 

strength of porous asphalt concrete 

The effect of steel fibers volume content on the indirect tensile 

strength (ITS) of porous asphalt concrete is shown in Fig. 4. The ITS 

of the plain porous asphalt concrete studied was 2.06 MPa. The ITS 

of porous asphalt concrete increased with the volume of steel fibers 

until a maximum of 2.62 MPa with a steel fibers content of 

11%. Adding more fibers to the mixture results in a decrease of 

the ITS, because too many fibers reduce the mastic film thickness, 

causing a bad adhesion between the asphalt components. Finally, 

samples with 20% of steel fibers (the one with highest electrical 

1,00E+10 

ITS MPa 

2.80 

2.60 

2.40 

2.20 

2.00 

1.80 

1.60 

0 5 10 15 20 25 

Fiber volume content % 

Fig. 4. Effect of steel fiber type 1 volume content on the ITS of porous asphalt 

concrete. 

conductivity), had a maximum tensile strength of 2.03 MPa, close 

to that of the plain porous asphalt concrete. 

3.3. Electrically conductive mechanism in porous asphalt concrete 

Broken porous asphalt samples after indirect tensile test were 

observed under the microscope to check the fibers distribution. 

The conductive mechanism was explained according to the percolation 

theory [15]. Fiber distribution in samples with different contents 

of steel fibers is shown in Fig. 5. When 5% of steel fibers is 

added to the mixture, they are uniformly distributed and do not 

contact each other, having a similar resistivity to that of an asphalt 

concrete sample without fibers. When more steel fibers are added 

to the mixture, they start contacting each other, which causes to a 

gradual decrease in the resistivity. If the fiber volume content 

reaches more than 10% (percolation threshold), the first conductive 

paths are formed in the sample. This corresponds to a sharp decrease 

of resistivity. Beyond the percolation threshold, the conductive 

network develops and spreads gradually in three dimensions 

with the increase of the volume content of the steel fibers. When 

the fiber volume content is more than 20%, steel fibers contact each 

other in all directions and many conductive networks and passages 

are formed, corresponding to a very low value of resistivity at 

which adding more steel fibers does not reduce the resistivity of 

sample any more. 

3.4. Effect of bitumen content on the electrical resistivity of porous 

asphalt concrete 

Resistivity Ω.m 

1,00E+08 

1,00E+06 

1,00E+04 

0 5 10 15 20 25 


Fig. 3. Effect of steel fiber type 1 volume content on the resistivity of porous asphalt 

concrete. 

When fibers are added to the mixture, the thickness film of 

mastic around the aggregates is reduced. This can have a negative 

effect on the mechanical properties of asphalt concrete pavements 

so, to ensure the durability of this porous asphalt, bitumen content 

needs to be increased. In this section, higher bitumen contents 

were used to check how the electrical conductivity of porous asphalt 

concrete was affected. The fiber content was fixed at 20% in 

the mixture (for optimal electrical conductivity purpose) and the 

bitumen content was gradually increased from 4.5% to 5.4%. The effect 

of bitumen content on the electrical resistivity of porous asphalt 

concrete samples is shown in Fig. 6. An increase in the 

bitumen content causes a reduction in the electrical resistivity of 

porous asphalt concrete. Furthermore, ITS reductions from 

2.03 MPa to 1.40 MPa were also observed with the increase on 

bitumen content. 





Fig. 5. Steel fibers distribution in the porous asphalt concrete samples. 

1,00E+05 

2.1 

1,00E+11 

Steel fiber type 1 


1,00E+04 

Resistivity 

ITS 

1.9 

1.7 

1.5 

ITS MPa 


1,00E+09 

1,00E+07 

1,00E+05 

Steel wool type 000 

1,00E+03 

1.3 

4.2 4.5 4.8 5.1 5.4 5.7 

Bitumen content % 

Fig. 6. Effect of bitumen content on the electrical resistivity and ITS of porous 

asphalt concrete. 

1,00E+03 

0 5 10 15 20 25 


Fig. 7. Effect of fiber volume content on the resistivity of the porous asphalt 

concrete. 

3.5. Effect of different type of fibers on the electrical resistivity and ITS 

of porous asphalt concrete 

2.80 

2.60 

Steel fiber type 1 

Steel wool type 000 

Fibers size determines the number of fibers per unit of batched 

weight and the number of fibers per cubic meter of asphalt concrete. 

Since the total weight, rather than the absolute size determines 

the cost of the fibers, the question arises whether a large 

number of short fibers are more effective than the same weight 

of long fibers. To answer this, steel wool type 000 instead of steel 

fiber type 1 was used to check if it is better to improve both electrical 

conductivity and mechanical properties of porous asphalt 

concrete. 

Comparisons between the effect of steel wool type 000 and steel 

fiber type 1 volume content on the resistivity and indirect tensile 

strength of porous asphalt concrete can be seen in Figs. 7 and 8, 

respectively. The high resistivity stage and the low resistivity stage 

have almost the same values for both steel wool type 000 and steel 

fiber type 1 at 10 9 X m and 10 4 X m, respectively. However, the 

transition of the steel wool type 000 curve begins at 8%, exhibiting 

a lower percolation threshold than that of the steel fiber type 1 at 

10%. Besides, the transition curve of steel wool type 000 is sharper 

than the one of steel fiber type 1 and reaches the low resistivity 

stage at 10% of volume of steel wool type 000, much earlier than 

that of steel fiber type 1 at 20% of volume of steel fibers. So, steel 

ITS MPa 

2.40 

2.20 

2.00 

1.80 

1.60 

0 5 10 15 20 25 


Fig. 8. Effect of fiber volume content on the ITS of porous asphalt concrete. 

wool type 000 is much more effective than steel fibers type 1 to enhance 

the electrical conductivity of porous asphalt concrete. 

In Fig. 8, it can be seen that the indirect tensile strength curve 

versus volume of steel wool type 000, has the same shape as the 

curve for steel fiber type 1. Additions of steel wool type 000 below 

4% by volume increase the ITS of the samples, but too much steel 





Fig. 9. Induction heating image of a sample with 10% steel wool type 000. 

wool results in a decrease of the maximum strength of porous asphalt 

concrete. Steel wool type 000 offers a much weaker reinforcement 

than steel fiber type 1. The maximum ITS of samples 

containing steel wool type 000 happens at around 4% with a value 

of 2.27 MPa, only slightly higher than the ITS of plain samples 

without steel wool at a value of 2.06 MPa and much lower than 

the maximum ITS of samples containing about 11% steel fibers at 

a value of 2.62 MPa. It is very interesting to note that the ITS of 

samples with optimum electrical conductivity containing 10% of 

steel wool type 000 and 20% of steel fiber type 1 are 1.99 MPa 

and 2.03 MPa, very close to each other. So, steel wool type 000 

and steel fiber type 1 have the same effect on the ITS of porous asphalt 

sample at their respective content for optimal electrical conductivity. 

From the point of view of the electrical conductivity, 

steel wool type 000 has better performance than steel fibers. 

3.6. Induction heating of porous asphalt concrete 

To study the induction heating of porous asphalt concrete, samples 

containing steel wool type 000 were used. Fig. 9 shows an 

induction heating image of the sample with 10% steel wool. All 

samples have the similar images like this. On the top surface of 

the sample, clusters of steel wool work as small heaters. This corresponds 

to the shining dots on the surface of the sample in Fig. 9. 

The image shows uniform temperature in the horizontal direction. 

This is because the magnetic field is constant at the same distance 

from the coil. The temperature of the sample decreases from top to 

bottom. It was also found that samples had a higher heating rate 

when they were closer to the coil of the induction machine. The 

reason for this is that the magnetic field is stronger close to the 

coil. Finding the optimum distance between the pavement and 

the coil will be a topic for future study. 

The temperatures of all the samples with different steel wool 

volume contents were recorded and used to analyze the effect of 

the steel wool content on the heating rate of porous asphalt samples 

(Fig. 10). The plain sample without steel wool was almost not 

heated in 3 min because of the very low heating speed. Below 10% 

of steel wool in the mixture, the temperature reached increased 

with the increase of the volume content of steel wool. The samples 

could be heated, even if hey were not conductive, but the heating 

rate was lower. The temperature cannot be increased any more 

when the steel wool volume content is above 10%. This value coincides 

with the minimum in the resistivity curve in Fig. 8. The minimum 

resistivity will result in a maximum Joule heat in the 

sample; hence the temperature will be also a maximum. Adding 

steel wool above 10% does not improve the heating and will result 

in a decrease of the indirect tensile strength, as shown in Fig. 8. So, 

Temperature ºC 

160 

140 

120 

100 

80 

60 

40 

20 

0 

10% is the optimal volume content of this type of steel wool to heat 

easily porous asphalt concrete. 

4. Conclusions 

30s 

90s 

150s 

0 2 4 6 8 10 12 14 16 

Steel wool volume content % 

It was found that long steel wool type 000, is better than short 

steel fiber type 1 to make porous asphalt concrete electrically conductive. 

However, short steel fibers have better strength reinforcement 

capacity than steel wool. The mechanisms of electrical 

conductivity and induction heating are explained in this paper. 

10% (by volume of bitumen) of steel wool type 000 is proposed 

as an ideal content to make porous asphalt concrete conductive 

and for a fast induction heating. Besides, this value gives an acceptable 

indirect tensile strength to porous asphalt concrete. Adding 

more bitumen for durability purpose can increase the electrical 

conductivity of porous asphalt concrete, but it can also decrease 

its indirect tensile strength. It is expected that the self-healing 

capacity of asphalt concrete will be enhanced with the induction 

heating, although this is a matter for future study. 

5. Further research plan 

60s 

120s 

180s 

Fig. 10. Effect of steel wool type 000 volume content on the heating rate of porous 

asphalt concrete. 

It has been proved that the electrically conductive porous asphalt 

concrete can be heated quickly with induction energy. However, 

work needs to be done to detect the healing effect of this 

porous asphalt concrete. The idea is to introduce some damage 





to the porous asphalt concrete samples, and then heat the samples 

with induction energy to see if the damage can be healed or not. 

Strength recovery can serve as a healing index and CT scanning 

can serve as a method to see the cracks occurring and closing inside 

the material. In addition, more researches related to practical 

implementation of this kind of material will be done. 

Acknowledgements 

The scholarship from the China Scholarship Council is acknowledged. 

The technical support of Prof. Klaas van Breugel, Prof. A.A.A. 

Molenaar and Marco Poot are also appreciated. Furthermore, the 

authors would like to express thanks to Global Material Technologies 

for their technical expertise and advices about steel wool. 

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