Concrete Construction – Stripping time for slab formwork (excluding props) According to standard site practice for normal Portland cement and moderate ambient conditions, after how many days may the soffit formwork (sheathing) of slabs be removed while keeping the props in place for continued support?

Difficulty: Easy

Correct Answer: 4 days

Explanation:


Introduction / Context:
Formwork removal (stripping) must balance construction speed with the early-age strength gain of concrete. For slabs, a common practice is to remove only the soffit sheathing first while leaving props (supports) in place to carry loads until the concrete becomes sufficiently strong. Knowing the indicative stripping time prevents early-age cracking and deflection problems.



Given Data / Assumptions:

  • Normal Portland cement and typical site temperatures (no accelerated curing).
  • Item asked: slab soffit formwork removal while retaining props.
  • Service loads are not placed until the element reaches adequate strength; props remain to sustain self-weight.



Concept / Approach:
Standard guidance distinguishes three actions: removing vertical forms to walls/columns (earliest), removing slab/beam sides (early), and removing slab soffit sheathing while keeping props (intermediate), followed by final removal of props (latest). For slabs, the sheathing can generally be removed after a short but safe period, with props left to carry the member until later ages.



Step-by-Step Solution:
Identify that only the sheathing is to be removed; props remain.Adopt indicative practice where soffit sheathing of slabs may be struck after a few days, commonly taken as about 3–4 days in general guidance.Select the closest standard choice from the options provided: 4 days.



Verification / Alternative check:
Engineering handbooks present typical ranges (with props left in place) of approximately 3–4 days for slab sheathing, longer for beams, and still longer until props are fully removed. Local codes and specifications may specify exact values depending on span, temperature, and cement type.



Why Other Options Are Wrong:

  • 1–2 days: generally too early for safe sheathing removal in ordinary conditions.
  • 7–14 days: these are more consistent with prop removal thresholds or longer spans; excessive for only striking sheathing with props left.



Common Pitfalls:
Confusing sheathing striking with prop removal; ignoring effects of low temperatures or slow cement on strength gain; not checking span-dependent requirements.



Final Answer:
4 days

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