Monitoring corrosion levels of fly ash concrete reinforcement using electromagnetic method

Abstract

This research aims to study the monitoring of corrosion levels in steel reinforcement bars in fly ash concrete byusing the electromagnetic method. This method is proposed as a new non-destructive methodology for corrosionlevel inspection of steel bars immersed in fly ash concrete. An alternating current with a frequency of 100 kHz isapplied to generate changing magnetic flux. This method is also used to generate a magnetic flux in the excitationcoil and the root mean square voltage (Erms) depends on the total magnetic reluctance of the sensing coiltouching the fly ash concrete. In this research, the first specimen group of fly ash concrete is mixed with variousaggregate levels of 0%, 20% and 40% of fly ash weight, respectively without rebar. The second specimen groupof fly ash concrete is mixed with various aggregate levels of 0%, 20% and 40% of fly ash weight, respectively, withrebar. Each subgroup is composed of 12 specimens. All specimens are immersed in water for 90 days and thendried for 7 days. In addition, the second specimen subgroup is divided into 4 groups which are normal, low,medium, and high times of corrosion determined by the length of time the specimens are immersed in NaCl 5%solution with electric current used to accelerate the corrosion level. An electric current density of 400 μA/cm2 isapplied for 0 hours, 48 hours, 96 hours, and 144 hours, respectively. Each group includes three pieces. Theresults of the electromagnetic method for identifying types of fly ash concrete for various aggregate levels usedin this research are 0%, 20% and 40% of fly ash weight, respectively without rebar. The values of the fly ashconcrete are found to be 2.80V, 2.79V and 2.75V, respectively. This method could identify the corrosion levels ofthe second group with rebar at medium to high levels of fly ash concrete, which are 0% and 20%. The Erms valuesof the steel rebars are 2.920V, 2.890V 2.923V, and 2.897V, respectively. The average steel loss are 1.94%, 3.09%1.81%, and 2.75%, respectively. The corrosion levels of the 40% fly ash concrete could only be measured at thehigh corrosion level, and thevalues of this fly ash concrete is 2.950V. The average steel loss is 1.46%.

Keywords : Electromagnetic, Reinforcing, Magnetic reluctance, Concrete, Corrosion