Water testing is crucial for ensuring the durability of concrete because the quality of the mixing and curing water directly impacts the concrete’s long-term performance. Impurities in the water can interfere with the chemical hydration process, reduce strength, and cause deterioration over time.
How water quality affects concrete durability
Interference with hydration
- Impurities such as salts, organic matter, and industrial waste can disrupt the chemical reaction between cement and water that causes the concrete to harden and gain strength.
- Reduced bonding can occur if algae or organic materials are present, weakening the bond between the cement paste and the aggregates.
- Lower compressive strength is a direct result of improper hydration. Using poor-quality water can reduce concrete’s compressive strength by 10% to 30%, which is critical for structural integrity.
Corrosion of reinforcement
- Chloride contamination, often found in seawater or contaminated groundwater, can penetrate the concrete and cause the steel reinforcing bars (rebar) to corrode.
- Expansion and cracking result as the corroding rebar expands, creating internal stress that leads to cracking, spalling, and eventually, structural failure.
Chemical attacks
- Sulfate attack happens when sulfates in contaminated water react with the cement paste, causing the concrete to expand, crack, and lose strength.
- Efflorescence is the whitish salt deposit that appears on the concrete’s surface when impure water is used. While often aesthetic, it is a sign of poor water quality and can indicate larger issues.
- Surface scaling and a lower resistance to environmental factors, such as freeze-thaw cycles, can also be caused by impure water
Reduced workability
- Changes in setting time can occur. Some impurities, like certain salts or sugar, can either accelerate or retard the setting of the concrete, complicating construction and affecting its ultimate strength.
- Poor consistency can make concrete harder to place and consolidate, leading to a non-homogeneous mixture and a weaker structure.