What are the effects of calcium hydroxide leaching from concrete?

Calcium hydroxide leaching from concrete is a significant issue that impacts both structural integrity and environmental safety. When water permeates through concrete, it dissolves calcium hydroxide (Ca(OH)₂), a byproduct of cement hydration, and carries it to the surface. This process, known as leaching, leads to several detrimental effects.

Firstly, leaching reduces the alkalinity of concrete, lowering its pH from around 12.5 to below 9. This weakens the passive layer protecting steel reinforcement, accelerating corrosion and compromising structural strength. Over time, this can cause cracks, spalling, and even catastrophic failure in severe cases.

Secondly, the leached calcium hydroxide reacts with atmospheric carbon dioxide to form calcium carbonate (efflorescence), creating unsightly white deposits on surfaces. While not structurally harmful, this affects aesthetics and may require costly cleaning.

Thirdly, the high pH of leachate can harm surrounding ecosystems. When calcium hydroxide enters water bodies, it raises pH levels, disrupting aquatic life and soil health. This is particularly concerning in urban runoff and construction sites near sensitive environments.

To mitigate leaching, proper concrete mix design, curing, and waterproofing treatments are essential. Using supplementary cementitious materials like fly ash or silica fume can also reduce calcium hydroxide content, enhancing durability.

Understanding these effects helps engineers and builders take proactive measures, ensuring longer-lasting and environmentally friendly concrete structures.