How does the acidity of rainwater affect untreated concrete bench surfaces?

The acidity of rainwater, often caused by pollutants like sulfur dioxide and nitrogen oxides, can significantly impact untreated concrete bench surfaces. When rainwater has a low pH (typically below 5.6), it becomes acidic and reacts with the calcium compounds in concrete. This chemical reaction dissolves the binding materials in the concrete, leading to surface erosion, pitting, and loss of structural integrity over time.

The damage occurs in two main ways: first, the acid breaks down the calcium hydroxide in concrete, forming soluble salts that wash away. Second, it attacks the calcium silicate hydrate, which is responsible for concrete's strength. This process accelerates in areas with frequent acid rain exposure, causing rough textures, discoloration, and eventually cracks that compromise the bench's durability.

Without protective sealants or treatments, concrete benches exposed to acidic rainwater may show visible damage within 5-10 years, depending on rainfall frequency and pollution levels. Regular maintenance and pH-neutral cleaning can help mitigate these effects.