Formworks may be permanent or temporary in nature that holds and support viscous or wet concrete in place as it dries up. For the starting-out builders or construction workers, getting yourself well versed with the quality issues of formworks would be an edge.
Normally, for walls, columns, and footing steel and phenolic or plywood panels are used. These formworks are supported by scaffolds and bracings which are strictly calculated to hold the weight it carries. Serious injuries may happen if the quality of formwork is compromised. Aside from the safety threats, these may also be grounds for quality concerns later on. Thus, formworks should be strictly checked before concreting.
If it is used in a high-rise building, especially in the construction of slab. It will be inspected by the formwork inspector before you can pour concrete on the slab and provided that the formwork inspector shall issue a “certificate of inspection.” It will also be inspected by the Municipality Inspector to ensure that the slab is ready to receive concrete.
There are various quality issues of formworks known to the construction industry. Some of it are as follows.
1. Vertical surfaces not straight
This usually happens to vertical structures like columns. Scaffold and bracing failures would cause curved or not straight surfaces. Should there be nails or protruding materials on the formworks, it should be hammered down carefully to avoid hollowness or wavy concrete output. Although this may not be observed right away wait until the painting works commence.
To rectify, operatives usually, use stone grinders to the bulged area. Just imagine the savings builders could have saved if the formworks and scaffolds were just installed properly.
The quality assurance and quality control engineer should make sure that it is well erected.
2. Unmaintained formworks cause flaking and uneven surface
This is true to retaining walls or walls wherein the formworks used has laitance concrete not cleaned. After the removal of the unmaintained formworks, flaking on the structure may be observed. Dirt, dust, and dirty concrete bits diminishes the quality of cast concrete. Thus, it is really important to clean the formwork before using it.
To do this, for the new formworks, the forms surfaces are treated with a non-staining mineral oil or other lubricant approved by the quality engineer. Any excess lubricant should be satisfactorily removed before placing the concrete. If correctly done, the surface of casted concrete should be as smooth as paper sheet. Meaning, no more rectification, and your structure are already ready for painting preparation.
For used formworks, lightly tap the surface to remove concrete laitance. Other builders also power wash their formworks.
Maintenance for formworks is relevant for project savings. If properly maintained in good condition, particularly as to the size, shape, strength, rigidity, tightness, and smoothness of surface, these for dramatically decrease the project’s overhead expenses. Thus, this does good for the project cash flow and profit.
3. Formwork terminations not properly plugged or terminated
Especially for beams and walls, these terminations should be properly blocked out to prevent the wet concrete from coming out of the forms. By experience, a formwork termination wasn’t terminated properly causing spillage of ready-mixed concrete. The completion of the concrete was delayed as we have to rectify the unplugged termination and additional concrete was added due to spillage. Thus, concrete wastage was increased causing a lot of money because of one single mistake.
It is advisable to thoroughly check terminations prior to concreting works. Also, if you cannot monolithically pour a beam, see to it that it is as per structural code. Normally, beams may be terminated but on the one-fourth of its entire length from the concrete column. Check the structural notes on the plan for the specifications.
4. Formworks and accessories carelessly dropped upon dismantling
Upon the direction of the engineer concerning the removal of formworks, see to it that strategic formwork removal is followed and this work should be done with care so as to avoid injury to the concrete.
To prevent overspending on formworks and scaffolds, its accessories such as clamp, wedges, and ties should be loosened not immediately but gradually. The bolts and c-clamps shouldn’t be dropped carelessly to avoid deformation. Thus, lessening the need to purchase additional accessories.
Therefore, this one is the most common source of quality issues of formwork that the engineer should look at.
If the lean concrete hasn’t reached its designed strength yet, there should be no heavy loading on it. Moreover, its scaffolds should be removed or dismantled yet to prevent hairline cracks, especially for beams.
It is also important that an experienced supervisor or formworks engineer is onsite during the installation of formworks. Its bolts and clamps should be properly tightened to prevent misalignment or bulging on cast concretes. In the case of roof slabs and suspended slabs, forms should remain in place until the test cylinders attained its minimum comprehensive requirement as designed. Depending on test results or as required, formworks for suspended slabs shouldn’t be removed for periods of time until directed by the engineer.
Formworks should always meet its purpose, that is to conform to the established alignment and grades before and after the casting of concrete. Thus, it is advisable to have the survey team check the placed formworks first before the concreting works. Otherwise, it would mean serious legal concerns for casted concrete protruding property lines not part of the building or structure.
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In maximum, how many times we can use the same shutter for concrete casting if it is maintained?