Rapid Estimation of Water-Cementitious Ratio and Chloride Ion Diffusivity in Hardened and Plastic Concrete by Resistivity Measurement

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Title: Rapid Estimation of Water-Cementitious Ratio and Chloride Ion Diffusivity in Hardened and Plastic Concrete by Resistivity Measurement

Author(s): K. A. MacDonald and D. O. Northwood

Publication: Special Publication

Volume: 191

Issue:

Appears on pages(s): 57-68

Keywords: chloride resistivity; diffusivity; durability; fly ash; silica fume; slag

Date: 12/1/1999

Abstract:
The water/cementitious ratio of concrete is an important indicator of quality of concrete in the numerous ways that have been chosen to measure it. Low water/cementitious ratio concretes are high strength, low permeability, high durability and permanent concretes. It is also a property which is not frequently measured at the time of construction or on concretes which undergo distress during their service life due to the lack of standardized test methods and cheap test procedures for determining this property. In the present study, the use of electrical resistance measurements to estimate the water cementitious ratio and chloride ion diffusivity in terms of water cementitious ratio, compressive strength of concrete is explored. Both hardened and plastic concretes were studied, over a wide range of water/cementitious ratios. Supplementary cementing materials, paste volume fractions and admixture chemistries were varied as well. The results indicate that a rapid, field portable test can be used to estimate the water/cementitious ratio of plastic concrete delivered to the site, as well as samples of hardened concrete removed from structures. Use of the formation factor analogy to describe the pore system and measurements of the total pore volume allow an estimate of the transport properties of the concrete, such as diffusivity and permeability. Properties estimated by this technique are compared to those determined using the standard determination methods. The implications of using assumed pore solution characteristics are discussed. The method developed is potentially useful in both Quality Assurance and Quality Control testing of high performance structures. Additional work is required to develop a field test.