No Ordinary Warehouse


No Ordinary Warehouse

24 hours to make a floating concrete floor


The land around Christchurch International Airport is a hive of new construction activity: by a current count, there are nine new builds underway on airport or airport-adjacent land at present, with at least another five mooted.

Some of this development is the effect of the city-wide rebuild and a regeneration of the economy, and some, as in the case of Arrow’s current airport warehouse project, comes from one company’s expansion drive. EBOS competes with major multinationals such as Nestle and Mars, and its growth in 2017 has necessitated heavy investment in storage, with new buildings in Brisbane and Sydney alongside Arrow’s specialised project, a high-spec, 3,680m² warehouse adjacent to the airport in Christchurch.



The warehouse is a rare beast both for its size and the relatively unusual aspects of its massive base. Project manager Brian Macmillan, who took the reins when he joined Arrow in early July, describes the mammoth task of making a single-pour, 500 cubic meter concrete floor: “It started with the post-tensioned slab at the base and the tendons that run through it for weight-bearing and longevity.

“We did the pour on 26 October starting at 3am, and when I arrived on-site beforehand there were already 15 trucks lined up. We used concrete from three plants and had the largest concrete pump in the South Island inside the building and a second pump outside.”

The concrete flow continued unceasingly until 3pm that day, and the finishing touches took another 11 hours. The pre-pour preparation involved ensuring that the tendons were coordinated to avoid conflicting with the parts of the floor where heavy racking would be bolted down, and laser levelling of all the gravel and sand to council-approved standard.



Then came another clever feat of engineering. The post-tensioning tendons Brian refers to are pre-stressing steel cables inside plastic ducts or sleeves, positioned before the concrete is placed. Two days after the pour, the post-tensioning experts slightly stressed the new floor by pulling on the tendons, and a week later they put 32 tonnes of tension on each tendon, anchoring them to the outer edges of the concrete and shrinking the whole floor inward by 20 millimetres.

After a special surface coating of Ashford Formula to give it even more strength, the floor was finally done, and ready for service loads to be applied. Brian says, “The floor will keep moving slightly for another four years or so until it finally settles. Because it’s independent and floating in the middle of the building, it won’t come under any stress if the building moves around it.”

Within the warehouse is also something remarkable – a vault, resembling a bank vault, which will store high-value restricted items. Brian says, “The security factor is unique in this job – we installed 250 pre-cast panels for the vault, with vibration sensors on every panel to detect if an attempt is made to cut into it.”



The EBOS warehouse build started in June 2017 and will finish at the end of January 2018.