Core TradesQuestion 63 of 700
A large slab pour is interrupted for 3 hours when the concrete supply is delayed. When placement resumes, a visible line forms where fresh concrete meets the partially set concrete. This cold joint is BEST prevented in future pours by:
a.Planning continuous delivery and placing/vibrating fresh concrete into the previous lift before it takes initial set
b.Adding extra water to the delayed concrete
c.Increasing the slab thickness
d.Waiting until the first section fully hardens before continuing
Explanation
A cold joint forms when a new lift is placed after the prior concrete has begun to set, so the two do not knit together. Prevention is continuous placement and revibrating fresh into the previous layer before initial set. Adding water weakens concrete; thickness is irrelevant; deliberately waiting for full hardening guarantees a cold joint.
Law Reference: 2025 CA Building Code, Chapter 19 (Concrete)Practice all 700 questions free — no signup required.
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