New homes, commercial and public buildings, apartment blocks and other modern structures are increasingly being constructed using formed concrete to replace the more traditional construction materials. In many Mediterranean countries it is the norm to see grey concrete skeletons going up two or more floors and a complete roof already tiled before a brick is even laid. We take a look at the basic construction methods used in formed concrete buildings from laying the foundation and floor, to formed pillars, upper floors and stairwells. Then we look at the final touches in walls, doors and windows.
When a building is constructed using the formed concrete method, all supporting parts are made from steel reinforced, formed concrete. This includes the foundations, floor slabs, support posts, joists, vigas and roof covering.
The building is erected part by part. The foundation trenches are dug and then lined with wooden boards joined together, which are known as forms, to encase the concrete. Pre-formed steel mesh cages in the shape of long square section open tubes are then laid in the trenches for the foundations. This is followed by the flat steel mesh mats that are laid to reinforce the floor slab. The points set out in the plans for the support posts are then each fitted with four short lengths of steel rebar rods tied in vertically in preparation. More wooden forms are put in place above the foundations surrounding the floor area to encase the concrete for the floor slab. Once all preparations are complete, the concrete is poured over the entire area in one go, thereby creating a combined floor and foundation which is solid and very strong.
Once the concrete has set, the vertical posts are formed using steel plates that fit together with holes and lugs to form the shuttering for the square pillars. The long square section steel mesh cages are dropped inside and tied with wire to the vertical lengths of rebar that were left protruding from the slab. The shuttering is brought up to the specified height and then each column is checked with a spirit level to ensure each is perfectly vertical. Sometimes they have to be moved slightly and held in place with poles to ensure they don’t move. The columns are then filled with concrete and left to set.
Once the columns are ready, there are two popular methods of creating the floor above.
One is by shuttering the complete floor area. This is more difficult, as the entire floor is created by laying wooden boards side by side and fixed together in place. This entire area then has to be supported in mid-air by a forest of adjustable steel posts. The pillars are left exposed as they will be continued up to the next floor. Steel rebar rods are again left to protrude above the proposed level of concrete. The sides are made by screwing vertical boards to the floor boards, creating an entire formed box to hold the concrete. Again, steel mesh is laid across the boards and concrete is poured and allowed to dry.
The other method is to lay support beams horizontally around the circumference and inner support sections of the first floor connecting each concrete pillar. These beams are shuttered using connected wooden boards and steel mesh cages laid along them. The pillars are left exposed with rebar rods protruding as above. When the concrete is completely set, specially pre-formed reinforced concrete vigas are laid across the beams at intervals. The vigas are supported with adjustable steel poles. Between the vigas are laid large, hollow clay bricks specially formed for this purpose to form a network across the entire floor. The sides are then formed with wooden shuttering, steel mesh mats are laid across the whole area and concrete is poured to form the floor.
Once the first floor is completely set, whichever method is used, the next rise is constructed as above. The adjustable steel supports and the wooden shuttering boards are then removed from the lower floor and re-used for each new floor. More floors are stacked one above the other until the planned height of the building is reached. Finally the roof section is put in place. This is also formed using one of the above methods. The exposed roof surface is then treated to make it waterproof and then clay tiles clad its surface.
Once the whole structure is complete and the concrete is fully set all the steel supports and shuttering boards are removed. Then the bricklayers complete the brickwork for the walls. The completed walls are then usually covered with a cement render and painted. The interior walls are similarly covered either with cement render or plaster and painted.
Interior floors are usually covered with marble, terracotta or ceramic tiles according to the building’s specification. Doors and windows are fitted last using wooden, steel or plastic (uPVC) frames.
This is basically how the vast majority of buildings are constructed using the formed concrete method. The information in this article is meant to give a general idea and insight into this popular construction method and is not meant as a construction manual. However, next time you are walking past a construction site and see this method put into practice, you will have an understanding of what is actually going on and why.