Title page for ETD etd-92598-152639


Type of Document Master's Thesis
Author Pokkuluri, Kiran S.
Author's Email Address kpokkulu@vt.edu
URN etd-92598-152639
Title Effect of Admixtures, Chlorides, and Moisture on Dielectric Properties of Portland Cement Concrete in the Low Microwave frequency Range
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
Al-Qadi, Imadeddin L. Committee Chair
Flintsch, Gerardo W. Committee Member
Niles, Jerome A. Committee Member
Riad, Sedki Mohamed Committee Member
Schnoedt, Heinrich Committee Member
Keywords
  • Electromagnetic waves
  • Nondestructive evaluation
  • Portland Cement Concrete
  • Coaxial Transmission Line
  • Dielectric properties
Date of Defense 1998-09-21
Availability unrestricted
Abstract
The use of electromagnetic waves as a nondestructive

evaluation technique to evaluate Portland cement concrete

(PCC) structures is based on the principle that a change in

the structure, composition, or properties of PCC results in

a change in its dielectric properties. The coaxial

transmission line is one of the few devices that can

measure the dielectric properties of PCC at a frequency

range of 100-1000 MHz. A coaxial transmission line

developed at Virginia Tech was used to study the effect

of moisture, type of aggregate, water/cement ratio, curing

period, admixture type (microsilica, superplasticizer, and

shrinkage admixture), and chloride content on the dielectric

properties of PCC.

Measurements were conducted in the time

domain and converted to the frequency domain using Fast

Fourier Transform. The research found that an increase in

the moisture content of PCC resulted in an increase in the

dielectric constant. Mixes containing limestone aggregate

had a greater dielectric constant than those containing

granite. The dielectric constant decreased with curing

period due to the reduction in free water availability.

Mixes containing higher water/cement ratios exhibited a

higher dielectric constant, especially in the initial

curing period. The admixtures did not significantly

affect the dielectric constant after one day of curing.

After 28 days of curing, however, all three admixtures

had an effect on the measured dielectric constant as

compared to control mixes. Chloride content had a

significant effect on the loss part of the dielectric

constant especially during early curing. A relationship

was also established between the chloride permeability

(based on conductance measurements) of PCC and its

dielectric constant after 75 days of moist curing.

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