For any project involving concrete, formwork is a crucial step in the process. The formwork holds any concrete structures in place until it has fully set and can be stable on its own. This is especially critical in walls and columns that will need to stand upright and support buildings on their own. While some formwork remains in place permanently, concrete wall forms are typically removed once they are no longer needed.
While there is no straightforward answer to when these forms should be removed, there are some general guidelines that can help you avoid damage during a project. Some people want to speed up the timing, but planning for the appropriate setting time can be crucial.
Common Mistakes to Avoid
Concrete forms can fail to set correctly for any variety of reasons, ending in cracks and structural issues. However, these problems can generally be avoided by being aware of common downfalls.
One category of mistakes is around supplies themselves. Ordering the wrong amount of concrete, or the wrong type of concrete and admixtures, can lead to problems as your volumes are off, and carefully planned timelines may no longer apply. Similarly, the wrong water/cement ratio can probe problematic.
Many people also get too eager to move a project along quickly, which can lead to issues. Pouring concrete onto an improperly prepped site is common, and some workers will try to use formwork without fully finishing the freshly laid concrete.
Similarly, removing formwork before the concrete is fully cured is a sure way to have issues.
Estimating Removal Times
The rate at which concrete hardens and the concrete strength will depend heavily on the surrounding temperature, which is a large factor in formwork removal time. This means the season will be a consideration as you estimate time. For example, in winter there will likely be more time required for removal than the same project would require in summer.
Any structures that are subject to self-load and live load also require special attention, such as columns or beams. ea
In order to estimate the strength of concrete before formwork removal, it is best to carry out tests on concrete cubes or cylinders. These structures should be prepared with the same mix as the main structure and cured under the same circumstances of temperature and moisture. Once you have confirmed that the structure has enough strength to withstand the design load, that is when formworks should be removed. It is always better to leave formwork on for longer and allow extra time for curing when possible.
Signs Formwork Cannot Be Removed
If you are still unsure of the timing, there are some red flags you can watch for that signify it is not yet safe to remove your concrete wall forms. The goal is to avoid any issues like a collapse under the final design load, deflection of the structural member, or physical damage to the structural member.
You should always consider whether there is a risk of freeze-thaw damage or crack formations as a result of thermal contraction of concrete after the formwork striking. If there is a risk of any of these issues, it is recommended you delay the removal timeline of the formwork. In cases where the formwork needs to be removed for the sake of the project, insulating the structures well can help prevent this damage.
Factors to Consider in Strike Times
In order to properly determine striking time, it’s important to understand the characteristics of your concrete that may have an impact. Some of these factors include:
• Grade of concrete: high concrete achieves strength in shorter time
• Grace of cement: higher grades can help achieve higher strength in shorter time
• Type of cement: this can impact the strength development of concrete
• Temperature: higher temperatures lead to higher strength in shorter times
• Size of the concrete member: larger section members gain strength in shorter time
• Accelerated curing can be used to increase strength gain rate with applied heat
Further calculations can be done using information on the structure’s self-weight and construction loads during the process. If these can be calculated, it can help identify a safe point to remove concrete formwork.