ROCLA’S engineering department was recently approached by a client in the mining sector for a product suggestion to create 3m high storage bins for material with a bulk density of 2,700 kg/m3. This material would also be required to be stored at a 25° angle of repose, above the bin wall height, extending up to almost 6.2m above floor level in the centre of the bins. Accordingly, each three-sided bin would need to store approximately 525 m3 and 1,400 tons of product. In total, 14 bins, with a total capacity of approximately 7,350 m3 and 19,600 tons would be required. Rocla suggested its Alfabloc walling system.
Rocla sales engineer, Justin Kretzmar said: “Rocla’s Alfabloc range, which includes 1.2 m, 2.4 m and 3 m high blocks was immediately proposed as the best fit. However, a challenge remained in that the standard 3 m high blocks have a maximum rated bulk density for stored material of only 1,600 kg/m3 in free-standing orientation with 25° repose loading. Therefore, a solution had to be found to increase this by almost 70%. This was quite a challenge, but not insurmountable,” he says.
“Our engineering team determined that anchoring the blocks with chemical anchors to an engineered surface-bed and re-designing and increasing the steel reinforcement in the blocks, thereby creating a heavy-duty range of Alfablocs, was the successful solution to achieve the required loading,” said Kretzmar.
The client’s lead time posed an additional challenge. Rocla had never supplied such a large project and had existing production capacity suited to projects requiring less than 100 blocks as opposed to this project’s requirement of nearly 500 new heavy-duty units, as well as many 90° corner blocks. Rocla’s inhouse engineering and fabrication teams “stepped up to the plate”. They not only built new moulds, but also redesigned them to speed up stripping, preparation and production to ensure that all moulds could be cycled daily.
Twelve months after the product request was lodged, the block and layout designs finalized with the client and the project red tape navigated; Rocla received an official order to supply and deliver 496 x heavy-duty 3 m Alfablocs, amounting to 1400 tons of concrete and 500 truckloads, including all the anchorage components, which included 1,984 resin capsules, threaded rod studs, washers and nuts.
Production started almost immediately with the existing moulds and increased incrementally as additional moulds were completed and introduced into the system. The last blocks were delivered almost a year after receipt of the order, in March 2024.
Alfabloc applications
Rocla says Alfabloc is a very structurally efficient and versatile concept in design. In the majority of working conditions, the Alfabloc units are minimally stressed and provide a robust retaining structure. With granular materials, which generally provide the most onerous loadings, the Alfabloc unit has additional stability generated by the frictional force down the face of the wall.
Experience has shown the Alfabloc units can withstand significant misuse by mechanical plant used to move retained material. However, as with all relatively thin-walled concrete structure, they will suffer damage with persistent and negligent striking by mechanical plant.
Kretzmar says, “The foundation for the Alfabloc system is usually the new or existing concrete surface bed onto which stored materials will be contained. The loads imposed by the Alfabloc units are usually no more than the wheel loads imposed by the mechanical plant utilised to move the stored material. However, depending on the nature of the stored material, the units can either be placed onto the concrete surface bed or bolted into place.”
To assist in the spread of load horizontally, the units have a concrete tongue-and-groove joint that runs the full length of overlap between adjacent blocks. Additionally, as and when required for organic stored materials, painted or galvanised plate can be installed across these joints to completely seal them.
Fitting of a top channel not only assists to join the blocks, but also provides a platform onto which any number of other security devices can be attached, such as steel arms for razor wire or CCTV installations. For security installations the cavity inside the Alfabloc offers a perfect secure location for the placement of cables.
“We have supplied our Alfabloc walling system to customers in the plastics, chemicals and packaging materials, construction, and mining sectors.”
