Formwork or Shuttering is indispensable in both private and commercial construction projects. This unique feature serves the purpose of a mould for concrete features in the project. And the mixed concrete is poured into the formwork to take shape. It also holds it together until the concrete is cast and dry. At the same time, before you remove the formwork, you must be sure that the concrete structure is strong enough to bear the weight of the part where the formwork was holding. Visit https://www.bkhgroup.com.au/formwork/ to read about Striking Formwork.
As crucial as the formwork is to construction, the project manager and other stakeholders need to understand some basic principles of using them. However, this article will only focus on what special formwork is, how to remove the formwork and the minimum period it may take. So, let us follow carefully.
What is Striking Formwork?
Whenever you hear of Striking formwork, it refers to removing the formwork after the concrete has been cast and set. When the concrete has achieved its recommended strength and other properties to support its weight and the pressure exerted on it, the formwork or shuttering has served its purpose. In other words, shuttering removal is also essential for the curing process to work.
When you evaluate the formwork after removal, which is still valuable for reuse, you can safely keep it for future projects. At the same time, depending on the side forms and the removed case of slabs and beams, you may allow the formworks to stay in the place for more extended periods.
Factors that affect the Period of Striking of Formwork
Striking of the formwork has a designated time that must be removed, and this fantastic time depends on many factors. At the same time, the unique period and related factors may also vary from one building project to another. In addition, some critical controlling factors that determine when the formwork or shuttering is to be removed are listed below.
- Concrete type in the structure
When concrete contains a blast furnace slag (GGBS) or pulverized-fuel ash (PFA), such concrete can take a relatively longer striking period. On the other hand, the standard Portland cement concrete and similar ones may not take as long as the earlier mentioned cement types. GGBS and PFA cement types take a longer time to gain enough strength against the OPC. But the implication is also that when it finally gains enough power, it can become reliable. Meanwhile, employing rapid hardening types of cement can significantly reduce the level to which the concrete can attain strength while speeding up the hardening process.
- The weather of casting concrete
When the weather is cold, the rate of setting the concrete and attaining stiffness can be delayed when trying to reduce the striking time. For instance, ground slabs can take more time to gain strength and stiffness than the typical weather concreting process for concrete structures. It is also different from delaying troweling operations. When you have higher stability in the concrete, it also shows a shortened period of striking off the formwork.
- Exposure conditions of the site
When the temperature of the structures increases, it takes a reduced required time to remove the formwork from the concrete. At the same time, it is also capable of the proper strength to withstand the exerted weight. It can also attain this power level more quickly as long as you can effectively control the cracking of the structure from affecting the inner concrete.
- The best method for curing concrete
When the concrete inside the formwork is well cured, then the process can effectively reduce the striking time before the formwork is removed. And as soon as the formwork structure is removed from the formwork, the concrete curing should begin. The curing of the concrete should be secured when there are the right insulations in place that can protect the structure’s surface against extreme temperature changes.
- Treatment and admixtures to concrete
As a stakeholder in using concrete formwork, you can also reduce the striking time when adding some admixtures to the concrete structures. For example, some of the recommended admixtures are accelerators that efficiently reduce the setting time of the cast concrete.
Essential factors to consider before removing formwork
Before even planning to strike out formwork from a structure, certain aspects must be held sacrosanct. Some of these factors are mentioned below.
- When using slabs and beams, you can remove fit formwork conveniently in-situ with the strength of the concrete to be 10 N/mm2. On the other hand, it should be able to take up to two times of the stress or weight that will be exerted on it
- In general, the best practice of removing shuttering is to be done after assurance that it is strong enough under all conditions. The strength must be self-supporting and capable of bearing loads that are imposed on it
- To access the internal strength of the cast concrete, you should also perform all the pull-out tests for the cubes through standard procedures. They can also be cured under similar conditions as the in-situ concrete, as achieved by matching the cube samples when immersed in water. The water temperature is also compared to the structure.
- The proprietary quick-strip is also a valuable component in removing the shuttering that has completed its job. This process also can be done by propping or disturbing the structure in any way.
- When the weather is cold, concrete formworks for walls, beam sides and columns must be given more than enough time. The reason is that if this striking of the formwork is done too early, you may still find what we know as ‘green concrete’ underneath it, and it can be easily damaged.
- All striking processes for formwork must be carefully carried out to avoid all kinds of damage due to inaccurate projections. In the case of early removal that is found to be wrong, the repair of the damage is to be carried out immediately on the formwork. It may include obliterating the formwork and reinstalling it.