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 525m3 and 1,400 tons of product. In total, 14 bins, with a total capacity of approximately 7,350m3 and 19,600 tons of would be required material. Rocla suggested their ALFABLOC walling system.
Rocla Sales Engineer, Justin Kretzmar said “Rocla’s ALFABLOC range, that included 1.2m, 2.4m and 3m high blocks was immediately proposed as the best fit, however, a challenge remained in that the standard 3m 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, so a solution had to be found to increase this by almost 70%. This was quite a challenge, but not insurmountable “.
“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” commented Kretzmar.
Another challenge that needed to be considered was the lead time requirements of the client. As Rocla had previously never supplied to such a large project. With an existing production capacity more suited to projects requiring less than 100 blocks as opposed to this project of almost 500 of the new Heavy Duty units, including many 90° Corner blocks, Rocla’s in-house engineering and fabrication teams stepped up to 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 and having finalised block and layout designs with the client and navigated through all the project red tape, Rocla received an official order to supply and deliver
496 x Heavy Duty 3m Alfabloc’s, amounting to 1400 tons of concrete and 500 truck-loads, 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.
What is ALFABLOC
ALFABLOC is a very structurally efficient and versatile concept in design. In the majority of workingconditions the ALFABLOC units are lowly 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 added “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 ALFBLOC walling system to customers in the plastics, chemicals and packaging materials, construction, and mining sectors as temporary security measure for crowd control, security perimeter walling around sensitive storage areas on mines and manganese and other material stock piles.
Indeed, we ourselves have utilised the system at our manufacturing plant in Polokwane’s river sand bunker”.
“The system, which offers a quick and easy installation with limited downtime, has also found particular favour within the mining sector to ensure the separation of rock materials from equipment “concluded Kretzmar.
All Rocla concrete used in ALFABLOCS has a guaranteed 28-day strength of 35MPa which, coupled with a steel mesh will provide a solid barrier against intrusion. The steep slope and smooth off-shutter finish provide protection against climbing.
Rocla are the appointed exclusive license holders for their ALFABLOC, LBLOC and SHUTTABLOC systems for Southern Africa.
