Time domain reflectometry for measuring watercement ratio of concrete

Title: Time domain reflectometry for measuring watercement ratio of concrete
Author(s): Xiong Yu, Vincent P. Drnevich, Jan Olek
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess
Print-ISBN: None
e-ISBN: 2912143926
Publisher: RILEM Publications SARL
Publication year: 2004
Nb references: 24
Language: English

Abstract: Water-cement ratio is an important property for concrete strength and durability so getting reasonably accurate measurements of it for freshly mixed concrete is of great practical importance. The much larger dielectric constant of water compared with other ingredients in fresh concrete makes it strongly related to water content. On the other hand, the high ion content in the pore solution of the fresh concrete strongly affects the electrical conductivity. Time Domain Reflectometry (TDR) provides fast and accurate measurement of both dielectric constant and electrical conductivity. Simple calibration equations are proposed that relate water content to the dielectric constant and cement content to the electrical conductivity. Thus, TDR can measure both water content and cement content simultaneously, from which water-cement ratio can be calculated. Since both dielectric constant and electrical conductivity are somewhat temperature dependent, temperature compensation factors are required to adjust for temperature effects. The TDR system for this application is similar to that used for measurements in soils and consists of a TDR tester, cable and disposable, permanently inserted measurement spikes which penetrate approximately 135 mm into the surface of the fresh concrete. The concrete can be tested in place or in test specimens. In addition, a thermocouple is used to make temperature measurements in the curing concrete, which provides data for the temperature compensation factors. This paper presents the basic principles, testing system, and preliminary test results for use of TDR to determine water-cement ratios of the fresh concrete.

Online publication: 2004-03-25
Classification: Measuring W/C and Porosity
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143926.014