Equilibrant Ltd. were commissioned by Quinn Automatic/DPS on behalf of Veolia to carry out concrete condition surveys, including recommendations for Life Cycle Management, of Northern Ireland Water Assets under Veolia’s control which included various Wastewater infrastructure. Part of the commission included Ballynacor Wastewater Treatment Works (WwTW) Interstage Pumping Station.
Ballynacor WwTW serves the catchment areas of Portadown, Lurgan and Craigavon in Northern Ireland. During refurbishment in 2007 a reinforced concrete Interstage Pumping Station was constructed to receive existing and proposed sewage flows into one structure to allow distribution of screened sewage to Primary Settlement Tanks. Defects in the reinforced concrete structure were observed after only a short service period and a consultant was appointed to carry out a visual condition survey in 2015.
Equilibrant Ltd. was instructed to carry out a Structural Investigation (SI) of the Interstage Pumping Station structure. The purpose of the investigation was to identify the cause, extent, severity and significance of the visually apparent deterioration of the internal concrete surfaces, and make recommendations for the life cycle management of the structure. Comparison was made with the findings of the previous inspection report to give an estimate of the rate of deterioration in conjunction with the testing. The SI comprised the following elements:
- Close visual Confined Space Inspection and delamination survey including photographic records;
- Local breakouts to inspect condition of reinforcement and conduct carbonation testing;
- Dust sampling for chloride, sulphate and cement analysis;
- Compressive strength testing of concrete cores;
- Petrographic examination of concrete cores;
- CSE Half-Cell Potential Surveys;
- Linear Polarisation Resistance [Corrosion rate measurements];
- Ferroscans to confirm reinforcement cover and distribution.
Previous inspection observed the internal concrete surfaces to also be in poor condition however no exposed reinforced was noted. Equilibrant Ltd. observed widespread spalling and exposed reinforcement thus noting that the concrete deterioration has been progressive in the intervening period between May 2015 and September 2017.
Based on chemical analysis and petrographic examination and the distinctive smell of hydrogen sulphate gas, Equilibrant Ltd. concluded that the internal reinforced concrete surfaces of the Interstage Pumping Station were suffering widespread Biogenic Sulphide Corrosion and the severity of the internal deterioration high. It is affecting the entire inner concrete surface area. However, the significance, at the time of inspection, was moderate. The remaining concrete, beyond the sulphate front, was in good condition and fit for use with compressive strengths in excess of 50N/mm².
Based on the findings of the Structural Investigation, Equilibrant Ltd recommended remedial works to restore the asset back to its as-built condition. Equilibrant Ltd. advised the client that early intervention would reduce ongoing maintenance costs and the longer the asset was left to deteriorate the more expensive the remedial works would cost. Remedial works were specified in accordance with the requirement of BSEN 1504.