Which of the following types of joints is a temporary joint left between subsequent concreting operations?
Correct Answer: B. Construction joint
📚 Detailed Explanation: Construction Joint is the Temporary Joint Between Successive Pours
Why B (Construction joint) is correct: A construction joint is the interface formed when fresh concrete is placed against concrete that has already hardened or partially set. It arises whenever concreting work is deliberately or unavoidably halted — at the end of a working day, due to equipment failure, or between planned lifts of a large structure. It is a temporary joint in the sense that it is not pre-designed to allow movement; rather, it is a consequence of the construction sequence.
The Four Main Types of Joints in Concrete Works
| Joint Type | Purpose | Designed / Temporary? | Allows Movement? |
|---|---|---|---|
| B. Construction Joint | Interface between successive concreting operations; work stoppage joint | Temporary (unplanned or planned work-stoppage) | No — monolithic behaviour intended |
| A. Isolation Joint | Separates a structure from adjacent structures or foundations to prevent stress transfer | Designed (planned) | Yes — vertical movement; allows differential settlement |
| C. Contraction Joint | Controls and localises shrinkage cracking in slabs and pavements | Designed (planned) | Partial — groove or weakened plane allows controlled crack |
| D. Expansion Joint | Accommodates thermal expansion/contraction of long or large structures | Designed (planned) | Yes — full gap with compressible filler |
Construction Joint Details
| Aspect | Detail |
|---|---|
| Location (beams/slabs) | Within the middle third of the span — where shear force and bending moment are minimum |
| Location (columns) | Horizontally, 10–15 cm below the junction with a beam or haunch |
| Surface preparation | Old concrete surface must be roughened (wire brushing / chipping), cleaned, and moistened before placing new concrete; bond coat of cement slurry may be applied |
| Direction in slabs | Perpendicular to the main reinforcement; reinforcement continues across the joint unbroken |
| Key requirement (IS 456) | Joint surface must be free of laitance; roughened to expose aggregate; shear key or rebars ensure load transfer |
- Construction joint = temporary interface formed when concreting is stopped and restarted.
- Located at positions of minimum shear force and bending moment (middle third of span in beams/slabs).
- Surface must be roughened, cleaned, and wetted before resuming concreting to ensure bond.