Development of Chemical Deficiencies in Post-Tension Grout Materials

PT construction provides efficient bridge with advantages in construction, economy, and serviceability. In bonded post-tensioned systems, the introduction of stresses to the reinforced concrete element is made through tensioned high-strength steel strand that are encapsulated in a cementitious grout. The hardened grout provides corrosion protection by the presence of the alkaline pore water to passivate the steel strand and by creating a barrier from external contaminants. However, there have been documented cases of strand corrosion relating to deficiencies of the grout materials. Segregation of thixotropic grouts allowed for the development of chemically deficient grouts (characterized as having high sulfate concentrations) in vertically-deviated tendons in part attributed to an upward moisture and ion mobility. The Schupak pressure bleed test and vertically-cast grout specimens was utilized to assess the performance of grout materials subjected to adverse construction practices including prehydration and addition of excess mix water. Results indicated that there is limited availability of sulfate ions upon initial grout casting but would still be able to accumulate via transport of the free water. Greater pressures and vertical deviations allowed for greater moisture transport and sulfate accumulation.