Critical infrastructure is regularly exposed to saltwater, deicing salts, and chemicals that can threaten construction materials and long-term durability. Bridges, parking decks, marine structures, and industrial facilities must be built with concrete that can withstand that chloride exposure.
ASTM C1876 provides a standardized way to measure how well concrete resists the flow of electrical current, also known as bulk electrical resistivity or conductivity. By simulating how harmful chloride ions can penetrate concrete, we can determine concrete durability.
In this guide, we simplify the basics of ASTM C1876:
- Understanding Bulk Electrical Resistivity and Conductivity
- Recommended Equipment
- ASTM C1876 Test Preparation, Procedure & Results
Understanding Bulk Electrical Resistivity and Conductivity
Bulk Electrical Resistivity: How much concrete resists the flow of electrical current. High resistivity indicates the material is less likely to allow chloride penetration and is highly durable.
Bulk Electrical Conductivity: As the inverse to resistivity, conductivity is how easily electrical current flows through concrete. High conductivity demonstrates more vulnerability to chloride-based wear and tear.
Bulk electrical resistivity or conductivity is a material property used to estimate concrete’s permeability to chloride ions.
To measure these properties according to ASTM C1876, you will need the following equipment.
Recommended Equipment
A simulated pore solution, saturated with Calcium Hydroxide created by adding 7.6 g of dry NaOH, 10.64 g of dry KOH, and 2.0g of dry Ca(OH)2 to a 1 L container, and adding deionized water to the 1 L mark.
A sponge and electrically conductive fluid.
A conductivity test device. Devices vary in waveform (AC/DC), voltage, and frequency, but should be capable of applying a consistent field across the entire cross-section of the specimen and measure the voltage drop across the specimen ends to three significant digits.
Stainless steel electrically conductive plate electrodes made with the same nominal diameter at the ends of the specimens to be tested and between 6mm and 8mm thick. They will be positioned on opposite ends of the concrete specimen.
Electrical cables to connect the plate electrodes to the test device. Either two insulated cables or one insulated cable with two conductors made of 18 AWG stranded copper wire will suffice.
A non-electrically conductive specimen holder for tests conducted horizontally, or a non-electrically conductive surface for tests conducted vertically, such as a rubber or plastic base or mat at least 3mm thick and with a cross-sectional area larger than that of the plate electrodes.
A caliper to measure specimen diameter.
A diamond saw or one with a silicone-carbide cutting edge to trim the ends of the core without introducing cracks.
A set of verification resistors or a cylindrical verification cell containing multiple precision resistors, which can be provided by some equipment suppliers.
Personal protective equipment (PPE) that is routinely checked for vulnerabilities.
Electrical properties vary with temperature, so assuring consistency with a temperature sensor is key.
You can get everything you need for ASTM C1876 with the Giatec RCON™ Bulk Electrical Resistivity Testing Complete Package.
With these items, you’re ready to conduct a test assessing bulk electrical resistivity or conductivity according to ASTM C1876.
ASTM C1876 Test Preparation, Procedure & Results
#1 Select and Prepare Specimens
- If testing molded cylinders, prepare specimens casted and cured according to ASTM C192 or C31. If testing cores, prepare specimens in accordance with ASTM C42.
- Obtain a minimum of two specimens from cores or cylindrical mold casts and saw the ends.
#2 Measure Specimens
- Use the caliper to measure and record the two cross-sectional diameters at each end of each specimen in meters to the nearest 0.001m. In total, you’ll need four specimen lengths taken at 90° to each other.
#3 Submerge Specimens
- Before handling solution elements, you should review the proper safety precautions and use suitable PPE.
- Submerge two prepared specimens in an 18L or 20L bucket with a sufficient amount of the simulated pore solution—enough to cover specimens with 35mm-40mm of solution. Replace solution if cloudy.
- Saturate specimens until the time of testing for at least 6 days (or from the time of demolding in the case of molded cylinders). Use the temperature sensor to maintain a temperature of 23.0 ℃ ± 2.0 ℃.
#4 Set Up the Testing Device
- Prior to the specimen test time, verify the accuracy of measurements made by the testing device over the range of expected values of resistivity or conductivity by using your set of verification resistors or verification cell.
- Remove the test specimen from the solution container and rinse with running tap water while rotating the specimen and removing the solution with your hands. Blot off excess liquid and transfer to the specimen holder or place into a test device designed to hold specimens vertically. Do not leave the specimen exposed to air for longer than 5 minutes before performing tests.
- Input the specimen dimensions into the conductivity test device.
- Saturate the sponges with the electrically conductive fluid and apply to each electrode to ensure electrical contact with the surface of the concrete. Connect the electrodes to each end of the specimen.
#5 Run the Test
- Perform tests at 1kHz, unless otherwise specified by the specifier of the test. Your conductivity test device will send an electrical signal through the concrete and measure the voltage and current from which you can calculate ion passage.
- After allowing the readings to stabilize for 2 to 5 seconds, record the values. For test devices that measure resistance, measure the electrical resistance of at least two precision resistors with a range that includes the expected specimen resistance. Some testing apparatus display electricity or resistivity calculations once specimen dimensions are input. If using these devices, select on the verification cell at least two values of each to account for the range of the specimens being tested. To pass verification, the readings should be within 2% of the known values.
- Remove the electrodes from the specimen, reapply the electrodes, and repeat the measurement. Make at least two repeat measurements, and record the final average.
#6 Interpret and Report Results
- Determine the bulk electrical resistivity in accordance with the type of test device used.
- High resistivity = lower ion penetration = better durability
- High conductivity = more ion movement = potential durability concerns
- Report the source of the core, identification number, type of concrete, specimen description, curing history, age of specimen, and the type of test device used (including the operating frequency for devices with variable frequency).
Conclusion
ASTM C1876 gives engineers a reliable way to measure concrete’s resistance to ion movement—one of the clearest indicators of long-term durability. By testing bulk electrical resistivity or conductivity, you can quickly identify how well a concrete mix will stand up to saltwater, deicing salts, and/or industrial chemical exposure.
This standard provides a practical test for protecting structures, reducing maintenance costs, and ensuring safety over decades of service. Please review the current standard for the most up-to-date guidelines.
Forney has the machines and accessories necessary for ASTM C1876. Shop the Forney store today.