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Formwork removal time for concrete members using nominal mixes at different temperatures

By: Contributor(s): Publication details: Thane ACC LTD 2024Edition: Vol.98(4), AprDescription: 43-55pSubject(s): Online resources: In: Indian Concrete Journal - ICJSummary: A critical factor in the construction of reinforced cement concrete (RCC) structures is the timing of the safe removal of formwork. This time can be forecast using the maturity of concrete techniques and principles. Numerous academic publications suggest that formwork should be removed from the flexural members of RCC structures when concrete achieves at least 70 % of design strength. Early formwork removal might result in significant deformations or even failure. Nevertheless, delaying removal can cause construction delays that impact the profitability of the construction company and the use of the facility by the owner. Various countries’ codes, guidelines, and standards suggest stripping-time periods of different elements of RCC structures from twelve hours to thirty days. However, according to experiments conducted by authors, formwork for vertical concrete members must be stripped between 6 hours and 5.5 days, depending on the types of cement used and temperature ranges of 0°C to 45°C. Depending on the grade of the cement used and if the surrounding temperature is 45°C or 0°C, the time required to remove horizontal formwork ranges from 2.6 days to 124.4 days. Care must be taken when removing the formwork to prevent overstressing and damaging the concrete, especially when the ambient temperature is below 15°C. This is because many standard codes of practice are silent on the stripping time when the temperature is below 15°C. According to laboratory results conducted in this study at IIT Delhi, nominal mix cement concrete must have a compressive strength greater than 3.50 MPa to remove the vertical formwork in concrete made with ordinary Portland cement (OPC) and 3.25 MPa for Portland Pozzolana Cement (PPC).
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A critical factor in the construction of reinforced cement concrete (RCC) structures is the timing of the safe removal of formwork. This time can be forecast using the maturity of concrete techniques and principles. Numerous academic publications suggest that formwork should be removed from the flexural members of RCC structures when concrete achieves at least 70 % of design strength. Early formwork removal might result in significant deformations or even failure. Nevertheless, delaying removal can cause construction delays that impact the profitability of the construction company and the use of the facility by the owner. Various countries’ codes, guidelines, and standards suggest stripping-time periods of different elements of RCC structures from twelve hours to thirty days. However, according to experiments conducted by authors, formwork for vertical concrete members must be stripped between 6 hours and 5.5 days, depending on the types of cement used and temperature ranges of 0°C to 45°C. Depending on the grade of the cement used and if the surrounding temperature is 45°C or 0°C, the time required to remove horizontal formwork ranges from 2.6 days to 124.4 days. Care must be taken when removing the formwork to prevent overstressing and damaging the concrete, especially when the ambient temperature is below 15°C. This is because many standard codes of practice are silent on the stripping time when the temperature is below 15°C. According to laboratory results conducted in this study at IIT Delhi, nominal mix cement concrete must have a compressive strength greater than 3.50 MPa to remove the vertical formwork in concrete made with ordinary Portland cement (OPC) and 3.25 MPa for Portland Pozzolana Cement (PPC).

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