J Barry, S Robertson & A Mesic, Freyssinet Australia Pty Ltd
The CBH Group is one of Australia’s leading grain organisations, a cooperative with operations including grain storage, handling and transport, to marketing shipping and processing, based in Western Australia. It has been established for 80 years and is owned and controlled by more than 4500 grain growers.
The CBH Geraldton base is located in the north of the state’s growing region and consists of receival and administration facilities, along with port terminals for export. As part of this receival facility, Geraldton has twenty four (24No) reinforced concrete grain silos which were constructed from slip formed concrete in the mid 1960’s. These silos were constructed as circular grouped silos in a bank of 8 x 3 No. interconnected/adjoining silos, each 36m in height and 13m in diameter, resulting in a plan layout of 100 metres long and approximately 40 metres wide. This layout formed internal star cells between the main silos which are used to store boutique grain. The walls of the silos are around 200mm thick and the wall reinforcement consists only of a centrally placed single mat.
In more recent years evidence of extensive vertical cracking was noted throughout the walls of these silos and this lead to various investigations and structural assessments. As is typically found for circular grain storage facilities of this type and age, it was concluded that the original design understanding was inadequate to cater for the peak loads occurring during grain outflow. The resulting structural cracking reflected this structural inadequacy, and given the marine environment in which the silos are located, also raised concern in regard to the long term durability of this structure.
Insufficient hoop reinforcement in the silo walls had resulted in extensive vertical cracking and led to restriction in grain loading and operation. As the silos are also located in a temperate marine location, 40 years of chloride ingress had also led to significant corrosion to the embedded reinforcement resulting in widespread delamination and spalling.