The River Island Sewage Pump Station faced two major challenges: as a sewage pump station the concrete required protection from microbial induced corrosion (MIC); and 9 m (30 ft) of the 12 m (40 ft) deep structure would be immersed in the surrounding water table.
The original design specified an epoxy coating as the inner liner of the concrete walls as well as an exterior waterproofing coating to protect the interior lining from negative side hydrostatic pressure “push off”. This combined system was found to be very expensive. In addition, the work required to maintain the integrity of the epoxy liner around the multiple penetrations of the lift station walls added to this cost.
Xypex Bio-San C500
admixture was proposed by PACE Advanced Engineering and then chosen by the City of Lathrop as an alternative to the specified system. Bio-San C500 contains Xypex’s antimicrobial crystalline technology
. This technology kills the Thiobacillus bacteria which cause the acid corrosion of concrete as well as preventing the infiltration of ground water and exfiltration of sewage liquid. As Bio-San C500 is added to the concrete at the time of batching, significant cost and construction schedule savings were achieved when compared to the initially specified epoxy coating: there was no need to install and detail the interior coating.
The structure is 12 m (40 ft) deep and situated in an area with a water table that sits at approximately 3.3 m (10 ft) below grade. The walls of the chambers are 900 mm (3 ft) thick and were cast using a taper tie secured, steel gang-forming system. While the concrete work was very good there were some minor imperfections that needed repair. Xypex Megamix II
with Bio-San was used for the minor repairs and to fill the 600 taper tie holes. As this high strength repair mortar also contains antimicrobial crystalline technology the repairs received the same MIC, sulfate and chemical resistance as the rest of the concrete treated with Bio-San C500.
The use of Xypex Bio-San based products in this lift station provided a very cost effective solution to the long term service life of this important piece of infrastructure.