Which of the following statements about construction joints in cement concrete is correct?
Correct Answer: B. Should not be provided at corners
📚 Detailed Explanation: Construction Joints Must NOT Be Provided at Corners
Why B is correct (“Should not be provided at corners”): This question asks you to pick the ONE correct statement. Options A, C, and D contain factual errors per IS 456 and standard practice. Only option B is correct: construction joints in cement concrete should not be located at corners, edges, or regions of high stress concentration.
Evaluation of Each Statement
| Statement | Correct? | Explanation |
|---|---|---|
| A. Joints should be located where shear force is LARGE | ✗ WRONG | Exactly the opposite of correct practice. Construction joints must be located where shear force (and bending moment) are minimum — typically the middle third of a span. Large shear at a joint surface demands high friction/interlock that a construction joint cannot reliably provide. |
| B. Should NOT be provided at corners | ✓ CORRECT | Corners are zones of stress concentration. When two surfaces meet at a corner, shrinkage and thermal stresses from two directions overlap, creating complex triaxial stress states. A construction joint here is a structural weak point exactly where the stresses are highest. IS 456 and standard practice prohibit construction joints at corners. |
| C. Should be located where bending moment is LARGE | ✗ WRONG | Again, exactly opposite to correct practice. High bending moment means high tensile/compressive stress across the joint plane. A joint here is prone to opening (tension side) or crushing (compression side). Always place joints at minimum BM locations. |
| D. Should be spaced at 3 m apart in huge structures | ✗ WRONG | The correct spacing for huge/massive structures is not less than 18 m apart (IS 456:2000), not 3 m. 3 m is far too small and would result in an impractical number of joints, significantly reducing structural integrity and increasing construction complexity. |
Why Corners Are Especially Vulnerable
| Stress Type at Corner | Effect |
|---|---|
| Stress concentration | Sharp re-entrant corners amplify stresses by 2–3× compared to adjacent regions |
| Biaxial restraint | Shrinkage/thermal movement restrained in two perpendicular directions simultaneously; compounded stress |
| Joint weakness | Construction joint provides ≈60–80% of parent concrete tensile strength at best; applying this weakness at highest-stress location risks premature failure |
Key Rule (IS 456:2000): Construction joints must be planned at positions of minimum shear force AND minimum bending moment. Corners, edges, and high-stress zones must be avoided. Spacing in huge structures: not more than 18 m, not 3 m.
- Construction joints must NOT be at corners — stress concentration + biaxial restraint make corners high-risk locations.
- Joints at large BM or SF positions (A and C) are wrong — exactly the opposite of IS 456 requirements.
- Spacing in huge structures = 18 m maximum, not 3 m.