Rapid Migration Test

Rapid Migration tasteThe RMT involves subjecting a 4-inch (102- mm) diameter by 2- inch (51-mm) thick saturated samples to an outdoor(a) electrical potential to force chlorides ions to migrate into the exemplars (NT BUILD 492 1999). To account for convince cover justifications, the sign menstruation flow by the specimen is measurable and the applied voltage is adjusted accordingly. The samples are fit into silicone refuge sleeves where one of the offices of the specimens is immersed in a 0.3 N NaOH (1.2% NaOH) dissolver and the other side to a 10 percent NaCl solution. After a specified duration, the samples are removed and axially split into 2 pieces. A depth of chloride sagacity is determined in one half of the specimen using a colorimetric technique spraying silver nitrate solution on the freshly cut surface.The originally proposed mode called for the cover sample to be exposed to a voltage gradient for 8 hours, after which the specimen is sliced and sprayed wit h an indicator for chlorides, AgNO3 to determine the depth of chloride penetration. This time period bes the part difficult to fit into a normal working day of a testing ground. Consequently, Tang and Nilsson revised their method to use variable voltages and test durations depending upon the initial reliable measured (NTBuild 492). This improved test was standardized as a Nordtest procedure.The standardized method NTBuild 492 still presented further problems. The most critical is the protracted time duration of the test (as long as 4 years in some cases) and the wide range of applied voltage that must be used. A simplified testing protocol was developed in which the effect of several different voltages and test durations were evaluated (Hooton, Thomas and Stanish 2001). Based on the results of their research, a fixed test duration of 18 hours was selected, with a transforming applied voltage. The voltage selected for the test is based on the initial current value for that s ample under a 60-volt potential. The new proposed voltage values were selected to avoid chloride break done that would occasionally occur in the NTBuild 492 procedure2.2.6 get hold RESISTIVITY TEST USING THE FOUR-POINT WENNER PROBE (FM 5-578)Concrete conductivity is fundamentally related to the permeability of fluids and the diffusivity of ions through a porous material (Whiting and Mohamad 2003). As a result, the electrical resistor can be used as an indirect measure of the ease in which chlorides ions can penetrate concrete (Hooton, Thomas and Stanish 2001). The resistivity of a saturated porous medium, such as concrete, is mainly measured by the conductivity through its pore solution (Streicher and Alexander 1995).Two procedures have been developed to determine the electrical resistivity of concrete. The first method involves passing a direct current through a concrete specimen placed between two electrodes. The concrete resistance between the two electrodes is measured. The ac tual resistance measured by this method can be reduced by an unknown standard due to polarization at the probe contact interface. The second method solves the polarization problem by passing an alternating current (AC) through the sample. A convenient tool to measure using this method is the quatern -point Wenner Probe resistivity meter (Hooton, Thomas and Stanish 2001). The set up utilizes quadruplet equally spaced surface contacts, where a small alternating current is passed through the concrete sample between the outer pair of contacts. A digital voltmeter is used to measure the potential difference between the two inner electrodes, obtaining the resistance from the ratio of voltage to current (see Figure 5). This resistance is then used to calculate resistivity of the section. The resistivity of a prismatic section of length L and section area A is devoted by= A.RLwhere R is the resistance of the specimen calculated by dividing the potential V by the applied current I.The r esistivity for a concrete cylinder can be calculated by the undermentioned formula .d21V =4LIwhere d is the cylinder diameter and L its length (Morris, Moreno and Sages 1996). Assuming that the concrete cylinder has homogeneous semi-infinite geometry (thedimensions of the element are king-size in comparison of the probe spacing), and the probe depth is far little than the probe spacing, the concrete cylinder resistivity is given byV =(2. .a)Iwhere a is the electrode spacing (see Figure 5). The non-destructive nature, speed, and ease of use make the Wenner Probe technique a promising alternative test to stipulate concrete permeability.Current Applied(I)PotentialMeasuredConcrete rise upaaa(V)to be TestedEquipotential linesCurrent turn tailLinesFigure 5. Four-point Wenner Probe Test Setup.Results from Wenner Probe testing can vary significantly if the degree of saturation or conductivity of the concrete is inconsistent. Techniques to turn over more uniform saturation, such as vacuum saturation or submerging in water overnight, can be performed in the laboratory. However, the laboratory pre-saturation procedure still presents some inconsistencies. The known conductivity of the added solution changes when conflate with the ions (mainly alkali hydroxides) still present in the concrete pores after the drying go (Hooton, Thomas and Stanish 2001). To overcome this problem, Streicher and Alexander (1995) suggested the use of a high conductivity solution, for example 5 M NaCl, to saturate the sample so that the change in conductivity from the ions remaining in the concrete is insignificant.