CONTRACTOR Tamesis J.V.
DESCRIPTION Infilling 8 redundant digester tanks @ Beckton treatment works, Essex.
MIX DESIGN 700kg/m³ Foam Concrete
VOLUME 6000 m³
DURATION 23 days
The project consists of 8 cylindrical digester tanks which were redundant. Foam Concrete was used to infill the cone inside the tanks to a specific depth as required by the client. Once the cone was in filled the tanks were then demolished. Each tank base was filled in four lifts of 150m³ equating to a placed volume of 600m³, however 3 tanks required extra volume as they needed the floor to be higher than the rest. The volume of these were around 1000m³ each.
Since the lifts were of equal volume, each lift was thinner than the previous, as the cross sectional area of the cone increased. The maximum placing time for each 150m³ pour was 4 hours. This had to be completed prior to the initial set taking place. Also the fresh Foam Concrete had to be kept to a depth as such that the hydrostatic pressure did not cause collapse of the cellular structure of the Foam Concrete at the bottom of the lift. It was apparent that during the placement the initial sat was being accelerated by the residual heat of hydration from the layers below.
Accesses to inside the tanks were limited via 2×1 metre square holes for discharging the foam concrete. This was due to safety restrictions owing to the poor condition of the tank’s roof and the danger of falling debris. The discharge pipeline was lowered in to the tank and laid on the floor,pumping distance from the foam concrete batching plant varied from a few meters up to 200+ linear meters.
Pictures below show access of the discharge pipelines , together with a picture of 4 of the 8 tanks that required infilling.
THE EQUIPMENT USED
For this project FCL used 2 cement silos and our 10 meter long computerised batching plant. This was fed via cement tankers supplying a 70/30 blend of cement and pulverised fuel ash supplied in 30 ton deliveries supplying 4-5 loads daily at specific times throughout the day.
The picture below shows the first foam concrete pour in the cone of the digester tank.