Chemical Approach to Formation of Calcite Precipitate from Recycled Concrete Aggregate Base Layers

Abstract

The use of recycled portland cement concrete aggregate in pavement base layers has been associated with the reduction of filter fabric permittivity and the accumulation of calcite precipitate and other materials in pavement subdrainage systems. A mechanism of portlandite dissolution within base-layer pore waters, followed by exposure to atmospheric carbon dioxide via subdrainage systems, and subsequent calcite precipitation is explored using chemical thermodynamic techniques. Ion activities and pH levels are estimated for the equilibrium states of rainwater entering the pavement, base-layer pore water isolated from the atmosphere, and subdrainage water exposed to the atmosphere. Results derived agree with field and laboratory observations of pH levels.