Analysis and Performance of PCCP Mortar Coating
The evaluation of cement mortar coatings on prestressed concrete cylinder pipes (PCCP) may include such techniques as petrographic examination, material testing, and environmental testing of soil and groundwater. Petrographic analysis includes a microscopic examination of polished and thin sections, and in some cases, scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDXS). Material testing includes the evaluation of absorption, density, and chloride content of the mortar coatings. Testing of groundwater and soil are used to establish the level of corrosivity of the environment and to identify the need for additional protective measures. This paper discusses mechanisms of mortar coating degradation in aggressive environments that may render the coating ineffective for protecting the prestressing wires against corrosion. Deterioration may involve the chemical alteration or transformation of the cement paste, due to loss of mortar alkalinity, or expansive reactions within the cement paste, and corrosion of the prestressing steel. The impact of chloride ion permeation on the corrosion rate of embedded steel is also discussed.
