Hickam Sewer Lift Stations
Services Applied by VCS Engineering
Project Description
Sewer Lift Stations No. 1 and No. 1A are located in the Joint Base Pearl Harbor Hickam in Honolulu, Hawaii. Lift Station No. 1 was constructed in 1936, and the date of construction for Lift Station No. 1A is unknown, except that it was built after No. 1. The lift stations have been showing signs of deterioration, such as concrete cracking and spalling. SSFM International led a team in evaluating and rehabilitating these lift stations and reached out to VCS to provide support relating to the service life evaluation of the reinforced concrete.
Project Scope
VCS conducted a concrete material and corrosion assessment of the superstructure and substructure elements using several non-destructive and material sampling techniques:
- Hammer sounding
- Ground penetrating radar survey to determine rebar cover-depth
- Corrosion potential survey
- Concrete resistivity testing
- Carbonation depth testing
- Concrete chloride concentration
- Petrographic analysis
Project Solution
After completion of the field work and data analysis VCS concluded that microbially-induced corrosion (MIC) is the primary cause of concrete deterioration in the lift stations. Visual assessment of the concrete inside the lift stations showed surface scaling at the top of the lift stations which is characteristic of MIC. MIC was also identified by the petrographic analysis in the wet well cores. Reinforcement in the lift stations was also at risk for chloride-induced corrosion. Corrosion potential testing identified areas of active corrosion in both lift stations, and chloride concentrations in excess of the corrosion initiation threshold were measured in 62% of the collected cores. VCS recommended to apply a chemically resistant coating to the interior concrete surfaces of the lift stations to protect the concrete from MIC and install targeted cathodic protection in the areas of sound concrete that are actively corroding.