Corrosion Resistance Test
Objective and Significance
To evaluate the ability of rebar to resist corrosion when exposed to corrosive environments, ensuring its longevity and structural integrity in concrete structures.
- Corrosion of rebar can lead to severe structural damage, compromising safety and increasing maintenance costs.
- Understanding the corrosion resistance of rebar helps in selecting the appropriate type of rebar for different environmental conditions, enhancing the durability and lifespan of concrete structures.
Aim
To determine the corrosion resistance of rebar by simulating accelerated corrosive conditions and assessing the extent of corrosion over a specified period.
Apparatus
- Electrochemical Cell: Typically consists of a working electrode (rebar sample), a counter electrode (platinum or graphite), and a reference electrode (saturated calomel electrode or silver/silver chloride electrode).
- Electrolyte Solution: Often a 3.5% sodium chloride (NaCl) solution to simulate seawater conditions.
- Potentiostat/Galvanostat: To control the voltage and current during the electrochemical testing.
- pH Meter: To measure the pH of the electrolyte solution.
- Weighing Balance: To measure the initial and final weight of the rebar samples.
- Sandpaper: For cleaning and preparing the rebar surface.
- Deionized Water: For rinsing the rebar samples.
- Immersion Tank: For submerging the rebar samples in the electrolyte solution.
- Timer: To record the duration of the test.
Procedure
- Sample Preparation:
- Cut the rebar into specified lengths (typically 10-15 cm).
- Clean the rebar samples using sandpaper to remove any surface rust or contaminants.
- Rinse the samples with deionized water and dry them thoroughly.
- Initial Measurements:
- Weigh the cleaned rebar samples and record their initial weights.
- Setting Up the Electrochemical Cell:
- Prepare a 3.5% NaCl solution as the electrolyte.
- Place the rebar sample (working electrode) in the electrochemical cell.
- Insert the reference and counter electrodes in the cell.
- Connect the electrodes to the potentiostat/galvanostat.
- Testing:
- Set the potentiostat to apply a constant voltage (often -0.5 to -1.0 V vs. the reference electrode) to simulate corrosive conditions.
- Monitor and record the current response over time to assess the corrosion rate.
- Alternatively, immerse the rebar samples in the NaCl solution for a specified period (e.g., 30 days) without electrochemical equipment to observe natural corrosion.
- Post-Test Analysis:
- Remove the rebar samples from the solution.
- Rinse the samples with deionized water and dry them.
- Weigh the samples again to determine the final weight.
- Calculate the weight loss due to corrosion.
- Microscopic Examination (optional):
- Perform a microscopic examination to analyze the corrosion patterns and identify the type of corrosion (e.g., pitting, uniform corrosion).
Result
- Weight Loss Calculation:
- Calculate the weight loss due to corrosion using the formula:
Weight Loss=Initial Weight−Final Weight
- Corrosion Rate:
- Calculate the corrosion rate (in mm/year) using the weight loss, surface area of the rebar sample, exposure time, and density of the rebar material. The formula for corrosion rate (R) in mm/year is:
R=534×W/A×T×DR
where:
- W = Weight loss in milligrams
- A = Surface area in cm²
- T = Time of exposure in hours
- D= Density of rebar material in g/cm³
