Service-Life Performance Case Studies of Underground Reinforced Concrete Utility Vaults

Abstract

Underground reinforced concrete utility vaults play a vital role for the functioning of urban centers, providing space for all kinds of utility equipment. Underground structures are subjected to harsh environmental conditions that can impact their life and eventually trigger structural damage—potentially becoming hazardous to equipment and personnel carrying out routine inspections. A study was conducted to determine the main causes for deterioration in underground reinforced concrete structures observed during routine inspections in the southwest United States. Petrographic examinations of concrete samples cored from seven unique structures with significant damage showed that concrete carbonation has reached the reinforcing steel in some structures and there was evidence of minor sulfate attacks. Chloride ions were found at high concentrations, which had indications of being introduced through the concrete admixture. This is consistent with the practice of the precast industry around the 1960s–1980s to use calcium chloride admixtures to increase fabrication throughput. The presence of chlorides in the concrete matrix, coupled with gradual concrete carbonation, moisture, and oxygen, are the main causes of deterioration and damage observed in these structures.