SPECIAL CONCRETEElectrically Conductive Concrete

Presented by,R.V.Subbulakshmi,M.Suriyaa,B.E Civil IIIrd year,A.V.C College of Engineering,Mannampandal.

ABSTRACT

• Although concrete has existed in various forms over most of recorded

history, it is a material that still has opportunities for exciting

developments.

• Over a number of years, many unsuccessful research efforts were made

to develop concrete that could combine good electrical conductivity

with the excellent engineering properties of normal concrete mixes.

• The Institute for Research in Construction (IRC) has succeeded in

achieving this challenging goal, with electrically conductive concrete

(“conductive concrete” for short), a patented invention that offers future

promise for use in a variety of construction applications.

INTRODUCTION

• Ongoing IRC research is now focused on optimizing conductive

concrete formulations for the best combination of strength, electrical

properties, and production methods at the lowest possible cost,

leading ultimately to commercial development and widespread use.

• Due to its electrical resistance and impedance, a thin conductive

concrete overlay can generate enough heat to prevent ice formation

on a paved surface when connected to a power source.

• The heated deck of Roca Spur Bridge was the first implementation

in the world using conductive concrete for de-icing.

CONDUCTIVE CONCRETE

• Conductive concrete is cement based composite that contains

electronically conductive components in a regular concrete matrix

designed to enable stable and relatively high conductivity.

DESCRIPTION

• The Conductive Concrete Mix contains carbon, graphite products,

steel fibers.

• In addition to the cement, fly ash, silica fume, fine aggregate, coarse

aggregate, water and super plasticizer are used.

• The conductivity is usually several orders of magnitude higher than

that of normal concrete.

• Normal concrete is effectively an insulator in the dry state, and has

unstable and significantly greater resistivity characteristics than

conductive concrete, even when wet.

CHARACTERISTICS

• The conductivity value is stable. The effects of moisture content,

hydration time and temperature on conductivity are insignificant.

• It is lightweight: conventionally mixed, conductive concrete has a

density of about 70 percent that of normal concrete.

• Conductive concrete is chemically compatible with normal concrete,

bonding well with it if used as an overlay.

• Thermal stability is comparable to that of normal concrete. The

colour of conductive concrete is a darker grey, reflecting its

carbon content.

HEAT TRANSFER ANALYSIS

• With the apparent physical and thermal properties of the conductive

concrete the power consumption in using conductive concrete can

be determined.Composition Mass

density(kg/m3)Heat capacity Thermal

conductivity

Steel 7850 0.42 47.0

Conventional

concrete

2300 0.88 0.87

Conductive

concrete

3133 0.71 4.40

WORKING PRINCIPLE

• A three-phase, 600 A and 220 V AC power source is available from

a power line nearby.

• In a control room a microprocessor monitors and controls the

deicing operation .

• The system includes four main elements: (1) a temperature-sensing

unit, (2) a power-switching unit, (3) a current-monitoring unit, and

(4) an operator-interface unit.

• Different power supply schemes such as using solar energy with

a backup battery, microwave power, and DC power, are being

evaluated for cost-effectiveness.

METHODOLOGY• The temperature-sensing unit takes and records the thermocouple readings of the slabs

every 15 minutes.

• A slab's power will be turned on by the controller if the temperature of the slab is below 40 degrees Fahrenheit and turned off if the temperature is above 55 degrees Fahrenheit.

• The power-switching unit controls power relays to perform the desired on/off function.

• To ensure safety, a current-monitoring unit limits the current going through a slab to a user-specified amount.

• The operator-interface unit allows a user to connect to the controller with a computer.

• The operator interface displays all temperature and electrical current readings of every slab in real time.

• A user also has the option of downloading controller-stored data into a spreadsheet. 

CONSTRUCTION SEQUENCE

• A 4-inch thick inlay of conductive concrete was cast on top of a 10½ inch thick regular reinforced concrete . The inlay consists of 52 individual 4-by-14-foot conductive concrete slabs.

• In each slab, two angle irons were embedded for electrodes. Coupling nuts were welded to one end of the angle irons for making an electrical connection.

• A thermocouple was installed at the center of each slab at about ½ inch below the surface to measure the slab temperature.

• The power cords and thermocouple wiring for each slab were secured in two PVC conduits, accessible from junction boxes along the centerline of the bridge deck.

• Two 31½-by-31½-foot-by-1/4 inch angle irons spaced about 3 feet apart were embedded in each slab for electrodes in a back-to-back fashion.

PROCEDURE

• The 52 slabs were energized in an alternating fashion to avoid a power surge.

• Groups of two slabs were started up in turn at three-minute intervals and

energized at 208 V for 30 minutes.

• This alternating process of energizing the slabs was followed throughout the

storm.

• The maximum current recorded varied between seven and 10 amps, with an

average of eight. Peak power density delivered to the slabs varied between 33

to 52 W/ft2 with an average of 42 W/ft2.

• Energy consumed by the conductive slabs during the three-day period varied

from 47 to 70 kW-hr, with an average of 58 kW-hr per slab.

• Total energy consumption was about 3,000 kW-hr.

MIX DESIGN

• The mix design used in this project contained steel fibers and carbon

products for conductive materials.

• Steel fibers of variable lengths amounted to 1½ percent and the

carbon products of different particle sizes amounted to 25 percent

per volume of the concrete.

• The mix also included crushed limestone of ½ inch maximum size

and fine aggregate.

ADVANTAGES

• This method of heating would eliminate or dramatically reduce the

need for using salt, thus providing an effective and environmentally

friendly alternative.

• Conductive concrete itself is the heating element, and thus is able to

generate the heat more uniformly throughout the heated structure.

• The conventional de-icing methods require nearly 5 hours but this

technique requires just an hour. Hence the time consumption is less.

FUTURE

• Design better concrete system to solve icing problem in polar

regions.

• The execution of this project may provide a solution for the free

flow of traffic bringing much relief to the travelling public.

• Conductive Concrete has the potential to address a wide variety of

applications, including grounding, heating, cathodic protection of

reinforcing steel in concrete structures such as bridges and parking

garages, and electromagnetic shielding.

CONCLUSION

• This promising new technology should prove to be a valuable

tool in the fight against icy conditions on roadways.

• Thus the concept of using conductive concrete is highly feasible

for melting the ice on pavements.

REFERENCE• http://www.newsgd.com/news/picstories/content/images/attachement/jpg/

site26/20080204/0010dc53fa040910b7cd05.jpg

• http://www.fhwa.dot.gov/PAVEMENT/recycling/fach01.cfm

• Electrically Conductive Concrete Michelle Ho University of Houston Cullen

College of Engineering smho@uh.edu

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

Nebraska.” IABSE Symp., San Francisco, 449–454. • Roosevelt, D. S. 2004.

• Conductive concrete Heating Layer on Effectiveness of Deicing[J].” Journal fo

Wuhan University of Technology – Mater. Sci. Ed. Volume 17. Issue3.41-45.

THANK YOU

Questions