design of a conductive self-heating concrete...

Michelle Ho REU 2009 – UH CIVE

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Design of a conductive self-heating concrete

system

Michelle Ho – REU student

Dr. Yilung Mo – REU Advisor

Dr. Gangbing Song – Faculty Mentor

Christiana Chang – Graduate Mentor

Final Report University of Houston, Houston, TX


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Table of Contents

1. Abstract pg. 3 2. Introduction pgs. 3-5

3. Literature Review pgs. 5-6

4. Experimental Setup pgs. 6-11

5. Results pgs. 11-15

6. Discussion pg. 15-16

7. Future Work pg. 16

8. Acknowledgements pg. 17

9. References pg. 17

10. Appendices pg. 18-21


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1. Abstract

This project attempts to eliminate the issue of deicing through an integrated self

conducting concrete system. A concrete block of three layers is designed, with a

conductive heating layer “sandwiched” between two regular mortar layers. The

conductive heating layer is made possible through the incorporation of chopped carbon

fiber, a well known conductive material. Three concentrations of carbon fiber were used,

at 1%, 1⅓%, and 1⅔% by mass of cement. A series of resistivity and heating tests were

conducted to test the effects of conductive concrete on deicing. It is found that as the

percentage of chopped carbon fiber increases, the electrical resistance decreases, thus

allowing more current flow in the system. Through this confirmation, the correlation

exists that as more conductive material is used in a concrete system, the higher the

electrical conductivity is, allowing heat to melt ice and snow. In the heating test, a

problem was discovered that as temperature decreased, resistance increased dramatically,

in which there was an insufficient amount of conductivity throughout the sample.

Additionally, a 20 V input yielded only .05 A and 1 W, which is not enough power to

heat up the concrete system. Due to such a large change in resistance when a sample was

frozen, a series of cooling and heating tests were made to explore the relationship

between resistance and temperature. It is found that as temperature increased, resistance

decreased, suggesting an inversely proportional relationship between them.

2. Introduction

For many years, drivers and construction workers have faced the perils and

inconveniencies of ice or snow accumulation on concrete roads. Car accidents due to


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slippery tires and hindrances on transportation in order to avoid these accidents have set

forth attempts to solve this problem by techniques of deicing.

Chemical substances, sodium chloride especially, have been used as a cheap

solution to decrease ice and snow buildup; yet, it has proven to cause more disadvantages

than advantages, such as deterioration on the reinforcing bars in bridge decks, damage on

concrete, destruction of vegetation, and major chloride pollution in groundwater (Tuan

2004; Williams 2000).

Due to the many shortcomings of sodium chloride, other chemicals were

proposed, such as potassium acetate, dispersed by a set automated spraying system.

Although Tuan proposed that it was more “green” – less harmful and more

environmentally conscious than salt, the different chemicals and spraying systems were

expensive, requiring a starting fee as much as $600,000. Additionally, each system

needed vast space, big storage tanks, and many other devices to ensure operation (Tuan

2008; Roosevelt 2004). Also, a chemical spraying system has an estimated lifespan of 5

years, which consumes time to replace, costs much money, and required frequent

maintenance (Tuan 2008).

Aside from using various chemicals as means of deicing, other techniques

involving a heating device were created, such as electric heating cables. These cables

were incorporated into ramps and bridge decks, and although they successfully melted 25

mm of snow per hour, the heating pipes were stripped out of the concrete overlay to

allow traffic flow (Tuan 2008). Moreover, the installation and operation of these pipes

were costly, in which power consumption required as high as $5/m2 (Cress 1995).


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Pipes with the flow of heating fluids were also used as an attempt to deice roads.

However, if a leak occurs, maintenance would be a hassle, even impossible, since the

heating pipes are embedded in concrete; also, the cost of circulation is extremely high.

Another type of heating pipes relied on the energy released from the condensation of

evaporated liquid and the latent heat of vaporization during phase transformation.

Although it was able to perform the task of deicing sufficiently, the system was too

complex and costly to build, with approximately 40% of the total cost used on drilling.

Aside from pipes, lamps have also been utilized as a form of heat on the underside of a

bridge deck in Denver, Colorado; however, it proved to be ineffectual in power with a

high lagging time (Cress 1995).

Although many methods have been attempted to prevent the danger of icy and

slippery roads, the issue of designing an efficient and economical means for deicing

remains. Moreover, forming a system with a lesser amount of maintenance is significant

in reducing cost and saving time. This paper presents the integration of an electrically

conductive concrete system to solve the problem of deicing, cost, and efficiency.

3. Literature Review

Yehia et al 1998 revealed that out of the various deicing methods used in

communities today, such as road salting and heat pipes, utilizing a conductive concrete

system is an optimal choice, in which it provides a cost sufficient and efficient deicing

performance, homogeneous and constant heating, and an efficient mechanical strength

and conductivity (Yehia and Tuan 1998). Moreover, Yehia et al 2000 showed that

conductive concrete performs as a semiconductor for the concrete structure, in which the

addition of more electrically conductive material in concrete triggers higher electrical


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conductivity and heat generation when hooked up to a power source (Yehia, Tuan, and

Ferdon, et al. 2000; Sun, Li, and Mao 1997). Also, the heating rate and temperature

increases when current circulates throughout the conductive layer, and in turn the

conductivity will rise as a result of increased temperature. Again, in turn, the increase of

conductivity will trigger more current circulation; therefore, heat generation through this

result promotes resistive heating which melts ice and snow (Tuan 2004). In order to

obtain optimal results, it is significant to take note that the resistivity of the conductive

concrete must not exceed 103 Ω.cm (Yehia, Tuan, Ferdon et al 2000). Thus, in this

project, designing the model to output resistance to be less than that value is a significant

concern.

Carbon fiber is one of the best conductive materials to incorporate into the

conductive concrete system, in which its electrothermal effects, compression and

temperature sensibility, mechanical and physical characteristics exceed others (Sun, Li,

and Mao 1997; Tang et al 2006; Tang et al 2002). Therefore in this project, carbon fiber

will be used to optimize the results of conductivity, temperature effects, and so on.

4. Experimental Setup

Two distinct types of concrete mortar were used in this experimental project.

Table 1 below shows the two different versions of concrete and its ratios composition.

The dimensions of this conductive concrete system were designed to be 15 cm x 15 cm x

16 cm. Each sample consists of three layers of concrete, in which the top layer, 10 cm

tall, and the bottom layer, 3 cm tall, were made of regular concrete mortar, while the

middle layer, 3 cm tall, was composed of conductive concrete mortar, which is regular

concrete mortar incorporated with chopped carbon fiber (CCF) measured by percentage


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by mass of cement. In order to create three layers of mortar and bond them together

simultaneously, each layer was mixed and poured followed by the next layer after

allowing the first layer to settle for thirty minutes, into a half solid form. After mixing

and pouring the mortar into a mold, it was allowed to dry overnight. Each sample was

wrapped in damp towels for one day and then allowed to dry for two days.

Table 1: Two different types of concrete mortar

Mortar Type Water: Cement Cement: Sand %CCF Admixture

Regular mortar 1:2 1:1 N/A

Electrically conductive

mortar

1:2 1:1 1, 1⅓, 1⅔

A thermocouple was glued onto the center of the surface of each sample to

measure the amount of heat loss or gain in that external area. Another thermocouple was

placed in the center of the top layer to measure the internal temperature of the concrete

mortar for comparison with the surface temperature. Four electrodes were placed in each

sample in symmetrical spacing for the purpose of transferring voltage in the conductive

concrete layer. Figure 1 displays the complete diagram of one side of each sample

including the location of the electrode slots, partial dimensions of the concrete mortar

block, dimensions of the three concrete layers, and location of the imbedded

thermocouple.


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Figure 1:Dimensions in cm and locations of electrodes and thermocouple

For the purpose of comparison and diversity, two different types of electrodes

were used as shown in Figures 2 and 3. One of each type of electrode and percent CCF

was produced, resulting in a total of 6 concrete mortar samples. One type of electrode,

aluminum wire mesh, is more permeable than the other, zinc perforated metal sheets. The

effect of permeability on thermoconductivity is compared through recording and

analyzing resistance in the results.


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Figure 2:Aluminum wire mesh

Figure 3:Zinc perforated metal sheet

For the resistivity test, the two point probe method was utilized by means of the

outermost electrodes near the corners. Voltage was inputted in an increasing stepwise

configuration, starting at 5V, increasing at 1V per 20 seconds, through the electrodes, for

220 seconds, in order to record the values of current feedback. It is important to control

and input voltage in a stepwise function to avoid thermal shock in the concrete (Tuan

2004). By plotting current versus voltage and fitting a linear regression line on the graph,

the slope of the equation of that line was recorded as resistance. Five trials of the


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resistivity test were conducted for each sample. Figure 4 is an example of a mortar block

hooked up with a power supply during the two point probe method testing.

Figure 4:Sample hooked up to a power supply

In the heating test, at first, a sample was used to input 20 V. The power was read

to be 1 W, which is too small of an amount for sufficient heat and conduction, and when

a sample was frozen, its resistance unexpectedly increased dramatically. Thus instead, a

series of heating and cooling tests were made to investigate the correlation between

resistance and temperature. Two wire mesh samples, 1% and 1⅔% CCF, were used; not

all samples were tested due to time restraints, where each test consumed at least about 5

hours.

The samples used for testing were wrapped with two layers of insulation sheets to

ensure more accurate results. During each cooling test, the sample was placed in a

freezer, in which temperature and current were recorded every ten minutes until a

sufficient amount of data was taken to plot a graph and confirm a correlation. In each


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heating test, the already frozen sample was taken out of a freezer, in which temperature

and current were recorded every ten minutes until around 16oC was achieved.

5. Results

Table 2 reveals the average resistance of each five trials of the resistivity test,

along with the standard deviation.

Table 2: Average Resistance and Standard Deviation

Average Resistance (Ω) Standard Deviation

Zinc Mesh Zinc Mesh

428.46 401.87 17.16 16.00

372.68 334.59 14.44 16.09

350.27 304.77 5.83 6.46

Figure 5 below plots Resistance (Ohms) versus % CCF by Mass of Cement of

each resistance data point of the five trials of each sample. Appendix A shows the entire

set of data points in the form of a table.


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Resistance (Ohm) vs. % CCF by Mass of Cement

0

50

100

150

200

250

300

350

400

450

500

0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80

% CCF by Mass Cement

Resis

tan

ce (Ω

)

Zinc Mesh

Figure 5: Resistance (Ohms) vs. % CCF by Mass by Cement

Figure 6 plots the average resistance (Ohm) versus % CCF by Mass of Cement,

along with the standard deviation of each point.


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Average Resistance (Ohm) vs. % CCF by Mass of Cement

0

50

100

150

200

250

300

350

400

450

500

0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80

% CCF by Mass of Cement

Resis

tan

ce (Ω

)

Zinc Mesh

Figure 6: Average Resistance (Ohms) vs. % CCF by Mass of Cement

Figure 7 reveals the correlation between resistance (Ohm) and temperature(oC)

along with the standard deviation of each point for the cooling test of both wire mesh

samples of 1% and 1⅔% CCF.


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Resistance vs Temperature (Cooling)

0

500

1000

1500

2000

2500

3000

-10 -5 0 5 10 15 20 25

Temperature (°C)

Resis

tan

ce (Ω

)

Cooling 1% CCF

Cooling 1.67% CCF

Figure 7: Resistance (Ohm) vs. Temperature (oC) [Cooling]

Figure 8 shows the correlation between resistance (Ohm) and temperature(oC) for

the heating test of both wire mesh samples of 1% and 1⅔% CCF along with the standard

deviation of each point. Appendix B shows a table of the entire set of heating and cooling

data.


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Resistance vs. Temperature (Heating)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

-15 -10 -5 0 5 10 15 20

Temperature (°C)

Resis

tan

ce (Ω

)

1% CCF Heating

1.67% CCF Heating

Figure 8:Resistance (Ohm) vs. Temperature (

oC) [Heating]

6. Discussion

By analyzing Figure 5, one is able to correlate resistance and percent CCF as an

inversely proportional relationship. This relationship in the graph reveals that by

increasing the amount of conductive material in the mortar block, resistance generally

decreases as more current is to allowed flow through the system. Figure 6 strongly

emphasizes this conclusion, where there exists only a small range in standard deviation,

despite some overlapping, in which a linear regression line can be easily traced amongst

the three data points for the two different electrodes. Hence, by increasing the amount of

conductive material in a concrete system, one could expect a decrease in resistance, thus

better thermal conductivity by allowing more current flow for better resistive heating.

Additionally, it can be observed that in Figures 5 and 6, the samples with

aluminum wire mesh as electrodes had lower resistivity than those with zinc perforated


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metal sheets. Through this observation, it can be analyzed that the use of a more

permeable type of electrode induces better conductivity and resistive heating.

Figures 7 and 8 reveal an inversely proportional relationship between resistance

and temperature, in which as temperature increases, resistance decreases, vice versa. A

sudden analysis of this relationship between resistance and temperature was unexpected

since the original purpose of this project was to examine the heating properties and

effects of electrically conductive concrete. This correlation, which came about by the

observation of a striking increase in resistance with a decrease in temperature, may

possibly be explained only in a molecular level. However, it may also be the cause of

several factors, such as the design of the mortar sample, applying amounts of CCF that is

too small for efficient conductivity, and so on. Revisions to solve this problem is

discussed in the future work section.

7. Future Work

Since this project is the start of a series of other projects and the CCF was difficult

to mix into the concrete batch, only three small percentages of CCF were initially added.

However, since such a small percentage of CCF provided extreme outputs of low current

and high resistance, in the future projects, a higher amount of the addition of CCF will be

considered, along with a new method to mix the CCF in a more efficient and uniform

way. Sonication and compaction will be also be considered to eliminate entrapped air

bubbles in non-solidified concrete mixtures. In addition, specific course aggregates,

whether fine or course, will be added to create actual concrete instead of mortar to better

mimic a real life environment.


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8. Acknowledgements

The research study described herein was sponsored by the National Science

Foundation under the Award No. EEC-0649163. The opinions expressed in this study are

those of the authors and do not necessarily reflect the views of the sponsor.

9. References

Cress, M. D. 1995. “Heated bridge deck construction and operation in Lincoln,

Nebraska.” IABSE Symp., San Francisco, 449–454. Roosevelt, D. S. 2004. “A bridge deck anti-icing system in Virginia: Lessons learned

from a pilot study,” Final Rep. No. VTRC 04-R26, Virginia Transportation Research Council, Charlottesville, Va.

Sun Mingquing, Li Zhuoqiu, and Mao Quizhao. 1997. “Study on the Electrothermal

Property of CFRC[J].” Journal of Wuhan University of Technology. V 19. Issue 2. 72-74.

Tang, Zuquan. June 2006. “Influential Factors on Deicing Performance of electrically Conductive Concrete Pavement.” Journal of Wuhan University of Technology – Mater. Sci. Ed. Volume 21. No 2.

Tang, Zuquan, Li Zhouqiu, Hou Zuofu, et al. 2002. “Influence of Setting of Electrical

Conductive concrete Heating Layer on Effectiveness of Deicing[J].” Journal fo Wuhan University of Technology – Mater. Sci. Ed. Volume 17. Issue 3. 41-45.

Tuan Christopher Y. March 2008. “Roca Spur Bridge: The Implementation of an

Innovative Deicing Technology.” Journal of Cold Regions Engineering (U. of Nebraska). Volume 22 Issue 1, 1-15.

Tuan, Christopher Y. 2004. “Electrical Resistance Heating of Conductive concrete

Containing Steel Fibers and Shavings.” ACI Materials Journal, V. 101, No. 1. 65-71.

Williams, D., Williams, N., and Cao, Y. (2000). “Road salt contamination of ground water in major metropolitan area and development of a biological index to monitor its impact.” Water Research, 1 (34), 127-138.

Yehia, Sherif and Tuan, Christopher Y. 1998. “Bridge Deck Deicing.” Transportation

Conference Proceedings, Department of Civil Engineering, University of Neraska-Lincoln. 51-57.

Yehia, S. A., Tuan, C, Y., Ferdon, D., and Chen B. 2000. “Conductive Concret Overlay for Bridge Deck Deicing: Mixture Proportioning Optimization, and Properties.” ACI Materials Journal. V. 97, No. 2. 172-181.

10. Appendices

Appendix A: Resistive testing data points


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Table 3: Resistive testing data points

Measured

Resistance

% CCF Zinc (Ω) Mesh (Ω)

1.00 432.19 383.28

1.00 400.35 393.44

1.00 425.87 424.06

1.00 443.19 411.49

1.00 440.72 397.09

1.33 389.57 325.24

1.33 357.76 330.28

1.33 358.90 316.18

1.33 372.78 356.82

1.33 384.37 344.43

1.67 347.64 314.52

1.67 343.28 301.29

1.67 347.95 306.21

1.67 357.54 297.18

1.67 354.95 304.66

Appendix B: Cooling and heating test data points

Figure 9: Cooling data of 1% CCF

Current (A) Temperature (°F) Resistance

(Ω) Temperature (°C)

0.044 68 454.68 20.00

0.042 67 476.33 19.44

0.039 67 512.97 19.44

0.039 66 512.97 18.89

0.036 67 555.72 19.44

0.034 65 588.41 18.33

0.031 62 645.35 16.67

0.028 58 714.50 14.44

0.025 55 800.24 12.78

0.024 53 833.58 11.67

0.023 50 869.83 10.00

0.02 46 1000.30 7.78

0.02 44 1000.30 6.67

0.017 42 1176.82 5.56

0.017 40 1176.82 4.44

0.015 39 1333.73 3.89

0.015 38 1333.73 3.33

0.014 36 1429.00 2.22

0.015 35 1333.73 1.67

0.013 34 1538.92 1.11


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0.013 33 1538.92 0.56

0.013 31 1538.92 -0.56

0.012 30 1667.17 -1.11

0.012 29 1667.17 -1.67

0.012 28 1667.17 -2.22

0.012 26 1667.17 -3.33

0.011 25 1818.73 -3.89

0.01 25 2000.60 -3.89

0.01 24 2000.60 -4.44

0.01 22 2000.60 -6.11

0.01 21 2000.60 -6.11

0.01 21 2000.60 -6.11

0.009 20 2222.89 -6.67

0.009 19 2222.89 -7.22

0.009 19 2222.89 -7.22

0.009 19 2222.89 -7.22

0.008 18 2500.75 -7.78

0.008 18 2500.75 -7.78

Figure 10: Heating data of 1% CCF

Current (A) Temperature (°F) Resistanc (Ω) Temperature (°C)

0.013 8 1539.31 -13.33

0.013 11 1539.31 -11.67

0.014 15 1429.36 -9.44

0.015 18 1334.07 -7.78

0.016 20 1250.69 -6.67

0.018 23 1111.72 -5.00

0.02 24 1000.55 -4.44

0.024 33 833.79 0.56

0.024 33 833.79 0.56

0.024 35 833.79 1.67

0.025 38 800.44 3.33

0.026 39 769.65 3.89

0.028 42 714.68 5.56

0.031 43 645.52 6.11

0.032 45 625.34 7.22

0.032 46 625.34 7.78

0.032 47 625.34 8.33

0.034 47 588.56 8.33

0.034 49 588.56 9.44

0.035 50 571.74 10.00

0.035 51 571.74 10.56

0.036 51 555.86 10.56

0.038 53 526.61 11.67


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0.039 54 513.10 12.22

0.038 53 526.61 11.67

0.039 54 513.10 12.22

0.039 55 513.10 12.78

0.04 56 500.28 13.33

0.041 56 488.07 13.33

0.041 57 488.07 13.89

0.042 58 476.45 14.44

0.041 57 488.07 13.89

0.039 59 513.10 15.00

0.042 59 476.45 15.00

0.043 59 465.37 15.00

0.043 62 465.37 16.67

Figure 11: Cooling data of 1⅔% CCF

Current (A) Temperature (°F) Resistance (Ω) Temperature (°C)

0.048 69 416.79 20.56

0.042 66 476.33 18.89

0.042 66 476.33 18.89

0.042 65 476.33 18.33

0.039 65 512.97 18.33

0.036 63 555.72 17.22

0.036 62 555.72 16.67

0.035 60 571.60 15.56

0.029 55 689.86 12.78

0.028 52 714.50 11.11

0.026 50 769.46 10.00

0.025 48 800.24 8.89

0.025 46 800.24 7.78

0.024 42 833.58 5.56

0.022 40 909.36 4.44

0.02 39 1000.30 3.89

0.017 37 1176.82 2.78

0.018 34 1111.44 1.11

0.017 33 1176.82 0.56

0.017 33 1176.82 0.56

0.015 32 1333.73 0.00

0.015 31 1333.73 -0.56

0.014 28 1429.00 -2.22

0.014 29 1429.00 -1.67

0.014 26 1429.00 -3.33

0.014 27 1429.00 -2.78

0.014 25 1429.00 -3.89


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0.014 25 1429.00 -3.89

0.014 23 1429.00 -5.00

0.013 22 1538.92 -5.56

Figure 12: Heating data of 1⅔% CCF

Current (A) Temperature (°F) Resistance (Ω) Temperature (°C)

0.013 7 1538.92 -13.89

0.013 13 1538.92 -10.56

0.016 13 1250.38 -10.56

0.016 17 1250.38 -8.33

0.018 19 1111.44 -7.22

0.019 21 1052.95 -6.11

0.022 23 909.36 -5.00

0.024 26 833.58 -3.33

0.025 27 800.24 -2.78

0.026 31 769.46 -0.56

0.027 33 740.96 0.56

0.028 36 714.50 2.22

0.029 37 689.86 2.78

0.031 40 645.35 4.44

0.031 42 645.35 5.56

0.034 43 588.41 6.11

0.035 44 571.60 6.67

0.035 46 571.60 7.78

0.037 47 540.70 8.33

0.037 49 540.70 9.44

0.039 49 512.97 9.44

0.039 51 512.97 10.56

0.039 51 512.97 10.56

0.04 54 500.15 12.22

0.04 53 500.15 11.67

0.042 53 476.33 11.67

0.044 54 454.68 12.22

0.043 55 465.26 12.78

0.043 55 465.26 12.78

0.044 55 454.68 12.78

0.045 56 444.58 13.33

0.045 57 444.58 13.89

0.045 57 444.58 13.89

0.046 57 434.91 13.89

0.047 59 425.66 15.00

0.048 60 416.79 15.56

0.049 61 408.29 16.11

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