Thursday, 3 November 2016

Faster, Cheaper and Efficient: Constructing Concrete Lintels and Archs With ‘Exo-Reinforcement’ -Engr. Osaz’ ENOBAKHARE

Lintel beams provides structural support to the portion of the structure directly above them, (usually a wall) as well as aid the reduction of impact and stresses emanating from the use of the underlying member or components which are often doors and windows. 

Some archs also serve the same purposes while others are designed as ‘stand alone’.  The word ‘Exo-reinforcement‘ coined from the words ‘Exoskeleton’ and ‘Reinforcement’ is used here to describe the concept of introducing reinforcement to the external part of a concrete member instead of placing the reinforcing material internally. 
This is probably the first time this word is being used in public research space but the idea has spanned through ages. Essentially, exo-reinforced concrete saves construction time, money and also meets currently acceptable functional requirements for such member.

Mr Bode Araba (EPDM, Nigeria)
Mr. Bode Araba, Chief Executive at EPDM Nigeria, a research, training and project management firm based in Lagos has been visible in the corridor of promoting advancement in new or existing alternative methods of time-effective construction, which includes the use of variants of pre-cast exo-reinforced concrete building elements on a couple of successfully delivered projects that were directly under his watch. The method hasn’t gained prominence perhaps because most indigenous professionals are not receptive to changes or are simply skeptical about trying out new things.

Exo-reinforced concrete lintel beams like the regular types can come in precast or cast in-situ forms but it’s benefits are maximized when built pre-cast. Exo-reinforced archs are often cast in-situ because of their size and relative density but on sites where hoists and cranes are present, it’s okay for them to come pre-cast. 

To construct a pre-cast exo-reinforced concrete lintel beam, a sheet of anti-rust metal of about 6mm thickness and good strength is folded into a form of cuboid initially opened at both ends that fits perfectly into the provided space and level (taking the required span with adequate projections on both sides). 

This process can be done at the point of purchase of the metal or on site. A stopper (e.g. Polythene material) is then introduced at both open ends to stop any flow out. 

Concrete of adequate mix is poured into the fold and allowed to set for some hours. The stoppers are then removed to allow air into the concrete while the top leaves of the fold are welded together to hold firm. 

Once the exo-reinforced concrete lintel has gained sufficient strength, it is lifted and mounted to fit into the space provided. The same process applies to the construction of exo-reinforced archs except that the folding is done meticulously to take the required arch shape. 

On small sites, the lifting process can be done manually by means of thick ropes or by simply getting two laborers to lift it from both ends. These processes altogether can be completed for several numbers of lintel beams in a matter of hours saving the constructor the cost and time of installing and detaching timber or steel formworks and other associated works. 

After placement, a layer of mortar is introduced to the top of the member to receive the blockwall to be constructed over it. In the end, the member can be rendered (or plastered) along with the blockwall.

The same principle that works for regular reinforced concrete also applies to the exo-reinforced type, tension is resisted by the folded metal along its length while compression is resisted by the concrete within. 

Although from the structural engineering point of view, the way and manner at which the member provide resistance to stresses (in terms of shear force and the attendant bending moments) acting on it are slightly different. However it is still very safe to use exo-reinforced concrete for archs and beams provided you know what you are doing!          

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