How Long Can the Prefabricated Roof of a House Be Removed?
The formwork removal time for the prefabricated roof of a house is typically between 7 and 30 days, depending on factors such as temperature, concrete strength, and floor span. Removing the formwork too early may affect structural safety.
Temperature is a Key Factor Affecting Formwork Removal Time
The setting speed of concrete is closely related to temperature. In summer, when temperatures are higher, the hydration reaction of concrete accelerates, and its strength increases rapidly. Typically, it can meet the conditions for formwork removal within 7 to 10 days. In winter, when temperatures are below 5℃, the hydration reaction slows down, and strength growth is sluggish. The formwork removal time needs to be extended to 15 to 30 days, and even insulation measures (such as covering with cotton quilts or electric blankets) may be required to accelerate setting. If formwork is forcibly removed in low-temperature environments, the concrete may crack or deform due to insufficient strength.
Concrete Strength Must Meet Design Requirements
Before formwork removal, the concrete strength must be tested using a rebound hammer or same-condition curing test specimens. According to regulations, for floor slabs with a span of ≤2 meters, the strength must reach 50% of the design value; for spans of 2-8 meters, the strength must reach 75%; and for spans >8 meters, the strength must reach 100%. For example, for a 2-meter span floor slab made of C30 concrete (design strength of 30MPa), the strength may reach 15MPa (50%) in summer after 7 days, allowing formwork removal; in winter, the strength may only reach 10MPa after 15 days, requiring continued curing.
Floor Span Directly Determines Formwork Removal Time
The larger the span, the greater the bending moment and shear force that the concrete must withstand, and the higher the strength requirement. For small spans (such as balconies and canopies), due to their light self-weight, the formwork removal time can be appropriately shortened; for large spans (such as living rooms and bedrooms), the strength standards must be strictly followed. If the span exceeds 8 meters, even in summer, it is necessary to wait for more than 28 days to ensure structural safety.
Serious Consequences of Early Formwork Removal
If the formwork is removed before the concrete reaches the required strength, the concrete may sink or crack due to its self-weight or construction loads, and may even lead to collapse accidents. For example, a floor slab with formwork removed after 10 days in winter may develop through-cracks during subsequent renovation due to insufficient strength, affecting waterproofing and durability. In addition, after formwork removal, the concrete must continue to be cured for at least 14 days to prevent surface water loss and dry shrinkage cracks.
Recommendation: Before formwork removal, be sure to test the concrete strength and make a comprehensive judgment based on the ambient temperature and span. If there are doubts about the strength, extend the curing time or consult a structural engineer to ensure safety before proceeding with the next construction step.
