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    RCON™   C ONCRETE E LECTRICAL R  ESISTIVITY M ETER    OVERVIEW Giatec RCON™ is an advanced tool for the electrical resistivity measurement of concrete using uniaxial  method. RCON™ employs AC impedance technique for the accurate and fast readings that can be continuously obtained using its customizable and user-friendly operating software for various concrete materials. The electrical resistivity of concrete can be simply related to their pore network characteristics such as pore size and their connectivity, moisture content in the pores and pore solution chemistry. In concrete materials, the electrical resistivity has been correlated well with important durability parameters such as permeability and diffusivity. In addition, this non-destructive test can be easily conducted on fresh or hardened concrete specimens at different ages or various stages of hydration in order to study workability, setting and durability performance of    concrete. The electrical resistivity method has also been applied to investigate corrosion of rebar in concrete, creep, aggregate segregation and freeze and thaw of concrete since they affect the pore network properties. FEATURES    Fast (<5 Second)     Accurate (±2%)     AC measurement (Galvanostatic)     Wide range of measurement frequencies (1Hz to 30kHz)    Phase detection (0-180 degree)    Stand alone operation    Continuous measurement    User-friendly PC software    Flexible sample holders    Customizable setup    USB connection to computer MEASUREMENT CONCEPT Giatec RCON ™  applies a small alternating current at intended frequencies without causing any disruption and measures the voltage between the two ends of the concrete specimen. The impedance (Z   ) can then be calculated from measured voltage and applied current values. In order to apply the current, two conductive plates are used as shown in Fig. 1. Concrete resistivity is then determined using the impedance value as follows:      Eq. 1  where  .cm] is the resistivity, A [cm 2  ] is the cross-sectional area of the specimen, L [cm] is the length of the specimen, and Z   is the impedance (resistance) measured by the device. Figure 1: Concrete specimen placed between two plates      The current signal generated by the device is sinusoidal. The voltage measured across the specimen is divided by the imposed current to obtain the impedance (See Fig. 2-a). Based on the value of the impedance, the current scale may vary from 10µA to 1 mA.  The phase of the impedance is calculated by determining the difference between the phase of the voltage and current (See Fig. 2-b).  APPLICATION RCON ™  is a unique tool to investigate the micro-structural properties of concrete including:  A)   P ERFORMANCE -B  ASED Q UALITY C ONTROL OF C ONCRETE   Concrete electrical resistivity techniques is a suitable replacement for the Rapid Chloride Permeability Test of concrete (as per ASTM C1202 or AASHTO 277) since there is a good correlation between the bulk electrical resistivity and durability performance of concrete (See Table 1). Therefore, this technique can be used for the performance-based quality control of concrete. Table 1: Rapid chloride permeability and bulk electrical resistivity values 1   Chloride Penetration 56-Day Rapid Chloride Permeability Charge Passed as  per ASTM C1202 (Coulombs) 28-Day Bulk Electrical Resistivity of Saturated Con crete (kΩ.cm)   High >4,000 <5 Moderate 2,000-4,000 5-10 Low 1,000-2,000 10-20  Very Low 100-1,000 20-200 Negligible <100 >200 a) Impedance measurement concept b) Measurement blocks Figure 2: Impedance measurement concept    B)   D IFFUSION OF CHLORIDE IN CONCRETE    An almost linear correlation between chloride diffusion coefficient determined through ponding test and conductivity (1/  , where   was measured using uniaxial technique with AC current at 1 kHz frequency) was reported by Ghods et al. (see Fig. 3) 2 . Similar findings have been reported by Sengul and Gjørv  3 .   C)   C ORROSION OF REBAR IN CONCRETE   Investigations have found correlations between concrete resistivity and both, the corrosion initiation and the propagation period. The corrosion rate often has an inverse correlation to the electrical resistivity. Hornbostel et al. 4  have gathered a comprehensive literature review on the relation of corrosion rate and electrical resistivity and the contributing factors. In general, higher electrical resistivity of concrete lowers the risk and the rate of corrosion (Table 2). Table 2: Relation between concrete resistivity and severity of corrosion 5 Resistivity (k    .cm) Severity of corrosion >20 Low corrosion rate 10-20 Low to moderate corrosion rate 5-10 High corrosion rate <5 Very high corrosion rate Figure 3- Relation between electrical conductivity and chloride diffusion coefficient of concrete for twenty mixture propotions 2     R² = 0.93 0 5 10 15 20 0.00 0.01 0.01 0.02 0.02    D   i   f   f  u  s   i  o  n   C  o  e   f   f   i  c   i  e  n   t   (  m    2    /  s  ₓ   1   0   -   1   2    ) Conductivity, 1/  , S ( ῼ .m) -1
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