sulfateexpansion

Sulfate expansion is a phenomenon that occurs in hardened cementitious materials, such as concrete, when they are exposed to sulfates. This process involves a chemical reaction between sulfate ions and certain components of the cement paste, primarily calcium hydroxide and calcium aluminate hydrates. The reaction leads to the formation of expansive products, most notably ettringite.

The ingress of sulfates typically occurs through external sources, such as soil, groundwater, or seawater, which can contain significant concentrations of sulfate salts. When these sulfates come into contact with concrete, they can penetrate the porous structure of the material. Once inside, the sulfates react with the alkalis and calcium compounds released during cement hydration.

The formation of ettringite is the primary driver of sulfate attack. Ettringite crystals occupy a larger volume than the original cementitious matrix. As these crystals grow within the pores and microcracks of the concrete, they exert internal tensile stresses. Over time, these stresses accumulate, leading to cracking, spalling, and a general loss of strength and durability of the concrete. The rate and severity of sulfate expansion depend on factors such as the type and concentration of sulfate, the permeability of the concrete, the ambient temperature, and the presence of protective coatings or admixtures.