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Quality Check For formwork - Every Engineer should know |
Today we are going to see all the things which engineers should check while placing and after Fixing the formwork.
Check To be done Before Placing Formwork.
(i) Quality of the Formwork.
The First thing a site engineer should ensure is the condition of the formwork they are going to use.
The formwork should not have major defects such as
l Holes - If there are large number of holes, There will be chances of leakage of slurry from them which will lead to honeycombing to the structure and loss of durability of the concrete as the cement will move out of the formwork due to which there will not be adhesive bond in a small portion of the structure from where the slurry is moved out.
l No Bends - If the shuttering boards are bend, than the Engineer should not allow shuttering team to place the Board. The demerit of bend boards are once the concrete is poured and is set, as soon as you remove the board, you will see uneven surface of concrete in bend form. So it should be avoided
l Quality Of the Formwork - Every Formwork have limited number of repetitions or in easier words we can say the limited number of times a formwork can be repeated or used. Normally the 12mm class 1 Plywood boards which we normally use in conventional methods can be repeated for 5-7 times, same for Ply-boards of 18mm they can easily be repeated for 12-15 times or more based on the time we remove the formwork after poring. So, If the quality of board is degraded or bulged due to absorption of water, than the use of those Formworks should be avoided. The demerit of it is when we will pour the concrete, there will be pressure to the board which they wont be able to resist, resulting in undulation of the concrete finish.
l Joints - While Formwork making , The joints should be smooth on a same plane, as if the joints are uneven we may see lines at the joint areas after removing of formwork.
l Diagonality/Perpendicularity - The Formwork should be checked diagonally and the corners perpendicularity. This is done because if we place a formwork whose diagonality or perpendicularity is not maintained, There will be space between the joints of the formwork.
(ii) Check For Shuttering Oil.
The engineer should ensure proper application of shuttering oil to the surface of the formwork. There is a merit and demerit of application of shuttering oil.
l The merit is that when we apply shuttering oil to the formwork, the concrete does not stick to the surface of the formwork, resulting in giving a smooth finish.
l Demerit is when we apply excess of shuttering oil to the surface, while compaction the air bubbles get stick to the surface of the formwork later shows small holes in concrete after removing the formwork.
(iii) Ensure proper surface.
The area where we are going to place the shuttering should be clean, there should not be any dead chips, or any site waste else it will be hard to clean it after placement of the formwork.
(iv) Reinforcement
There are times when because of the reinforcement we are unable to place formwork or there are times when we may get less cover. So we should identify the area before placement and rectify that as early as possible. Even we should check for Dry chips concrete on the reinforcement and remove them before placing of formwork
Checking to be done Before pouring Concrete
The checking should be done in the same order below.
(i) Check For Plumb
It is a process in which the verticality of formwork is checked. The Board is fixed at the bottom, at the starter, We always take the reference of the starter to check the verticality of the board at the top ( We should never check in middle or anywhere, just the starter and top of the formwork where we are about to pour concrete). It is Mandatory the reading of the top and bottom should match with each other, only after that we can have assurance that the board is vertical. Normally we take tolerance of +/- 2-5mm.
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| Check For Plumb |
On the second lift we should ensure that there is a starter, If by chance we don’t have starter than we must ensure to check the bottom reference point from the previous lift starter. There are many chances when the shuttering team don’t listen to check from the last lift starter, but we should insist them to do so.
This method is suitable for -Columns, Beams, Shear Walls, Retaining Walls, Core-walls, Slab sides etc.
(ii) Check for Line
After we are done with Plumb we should check the line. As we know that the formwork is Vertical or straight at the corners by plumb method, than we tie a thread at corners connecting each other to maintain the verticality at the top. The dimension of the top corner is taken as the reference and line is checked and maintained by taking the reading at every 1-1.5m making the reading similar to the reference reading.
The method is done for Beams, Walls.
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| Check for Line |
(iii) Check for Level
This Method is done to check the bottom level of Beam, Slabs or any horizontal surface. The process can be done with 2 method
1. By using auto level machine.
In this process we take the reference from the reduce level, and on ever 1-1.5m we place the leveling staff and check the level.
2. With Help of Thread
In the process of thread, the span should not be too long else the thread may show sagging tendency at the center.
In this process the thread is tied in X manner above the area to be checked at a certain level take 1 meter above from slab level and with the help of leveling tape, the slab or beam bottoms are leveled.
To make it understand easier, Imagine above the top of slab you tied a thread at 1 meter from the slab level. Now if you invert the level tape from the thread to the slab you will get 1m + thickness of the slab. A tolerance of +/- 5mm is ignores but if you get more than that it should be rectified.
(iv) Check for Dimensions
The Dimensions with respect to drawings should be checked,
For columns - Length, width & Diagonals should be checked
For Lift area - They are very delicate thing, Life should be given most attention in checking, same for this also length, breadth and diagonals should be checked.
For Slabs - Length and breadth should be checked.
For Beams - The depth and breadth should be checked.
(v) Check For Supports
After the Plumb, line and level is checked, the supports are tighten up and the engineer must ensure the checks before pouring the concrete.
(vi) Check For any openings
Engineer should check if there is any openings like holes , at corners or in bottom of the formwork. If anything found than should be rectified by jamming it will concrete, plywood, Forms etc taking care about the finish to be maintained.
Checks to be Done After Pouring of concrete.
1) Once the concrete pouring is complete, The plumb should be checked again.
2) The line Should be checked (though it is hard to rectify be atleast can do something than nothing).
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