Electrical Resistivity Measurements for Quality Control During Concrete Construction

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					 ACI MATERIALS JOURNAL                                                                                          TECHNICAL PAPER
Title no. 105-M61


Electrical Resistivity Measurements for Quality Control
During Concrete Construction
by Ozkan Sengul and Odd E. Gjørv

For the production of new concrete structures in severe environments,            durability design and performance-based quality control
requirements to chloride diffusivity are increasingly being used as              have been introduced.3,4 Current experience with such
a performance-based specification for concrete durability. As a                  durability design is also very promising.5 As a result,
basis for the concrete quality control during concrete construction,             specifications to both chloride diffusivity and concrete
however, the testing of chloride diffusivity is both time-consuming
and elaborate. Therefore, the relationship between chloride                      cover are given that provide the basis for performance-based
diffusivity and electrical resistivity of the given concrete based on            concrete quality control during concrete construction. The
the Nernst-Einstein equation should first be established. Then the               control of the chloride diffusivity is based on migration
chloride diffusivity can indirectly be controlled by routine-based               testing, and although such testing can be completed within a
measurements of the electrical resistivity during concrete                       relatively short period of time, it is both elaborate and
construction. There are several test methods for measuring the                   requires at least 2 to 3 days of testing. Therefore, at an early
electrical resistivity of concrete. Also, there are several factors that         stage of the concrete construction work, the current guidelines
may affect such measurements. To provide more information about                  for durability design require that the Nernst-Einstein relationship
some of those factors that may affect the results and establish some
simple procedures for a routine-based quality control of the electrical          between the chloride diffusivity and the electrical resistivity of
resistivity during concrete construction, an experimental program                the given concrete is established. Based on this relationship,
was carried out. The test program was mainly based on the                        the routine-based concrete quality control of the specified
four-electrode (Wenner) testing of the electrical resistivity and                chloride diffusivity can then be indirectly carried out by
included different probe spacing and different geometry of the test              regular control measurements of the corresponding electrical
specimens. For comparison, some two-electrode measurements                       resistivity.1 Normally, this testing is carried out by use of the
were also carried out. To describe the effect of the various factors             four-electrode (Wenner) method as an additional, nondestructive
that may affect the resistivity, the test results are mostly presented           test on the same concrete specimens as those that are used for the
as relative resistivities obtained by the two different test methods.
The results show that, for given testing conditions, the electrical
                                                                                 regular testing of the 28-day compressive strength. In principle,
resistivity obtained by the Wenner method is different from that                 however, the two-electrode method can also be used for quality
obtained by the two-electrode method. It was concluded, however,                 control of the electrical resistivity.
that for a given type of concrete specimen with given moisture and                  For all porous materials, the Nernst-Einstein equation
temperature conditions, the Wenner method appears to be a suitable               expresses the relationship between the electrical resistivity
and reliable test method for performance-based quality control of                and ion diffusivity, as shown in the following equation6
electrical resistivity, and hence concrete durability, during
concrete construction.
                                                                                                                  R⋅T                      ti
                                                                                                          D i = --------------- ⋅ -------------------
                                                                                                                              -                     -                   (1)
Keywords: chloride diffusivity; electrical resistivity; four-electrode method;                                      2         2 γ ⋅c ⋅ρ
quality control; two-electrode method; Wenner method.
                                                                                                                Z ⋅F                 i       i



                     INTRODUCTION                                                where Di is diffusivity for ion I; R is gas constant; T is absolute
  For specification of concrete durability, current codes and                    temperature; Z is ionic valence; F is Faraday constant; ti
practice are mostly based on some simple and prescriptive                        is transfer number of ion I; γi activity coefficient for ion
requirements to concrete composition and execution of                            I; ci is concentration of ion i in the pore water; and ρ is
concrete work, the results of which are neither unique nor                       electrical resistivity.
easy to verify and control during concrete c
				
DOCUMENT INFO
Description: For the production of new concrete structures in severe environments, requirements to chloride diffusivity are increasingly being used as a performance-based specification for concrete durability. As a basis for the concrete quality control during concrete construction, however, the testing of chloride diffusivity is both time-consuming and elaborate. Therefore, the relationship between chloride diffusivity and electrical resistivity of the given concrete based on the Nernst-Einstein equation should first be established. Then the chloride diffusivity can indirectly be controlled by routine-based measurements of the electrical resistivity during concrete construction. There are several test methods for measuring the electrical resistivity of concrete. Also, there are several factors that may affect such measurements. To provide more information about some of those factors that may affect the results and establish some simple procedures for a routine-based quality control of the electrical resistivity during concrete construction, an experimental program was carried out. The test program was mainly based on the four-electrode (Wenner) testing of the electrical resistivity and included different probe spacing and different geometry of the test specimens. For comparison, some two-electrode measurements were also carried out. To describe the effect of the various factors that may affect the resistivity, the test results are mostly presented as relative resistivities obtained by the two different test methods. The results show that, for given testing conditions, the electrical resistivity obtained by the Wenner method is different from that obtained by the two-electrode method. It was concluded, however, that for a given type of concrete specimen with given moisture and temperature conditions, the Wenner method appears to be a suitable and reliable test method for performance-based quality control of electrical resistivity, and hence concrete durability, during concrete c
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