As a civil engineer or construction professional, having a solid grasp of various types of joints in concrete construction can make a significant difference in your project outcomes. This detailed article covers all the key aspects that every site engineer and civil engineering student should be familiar with.
VARIOUS TYPES OF JOINTS
1) Construction Joints
2) Expansion Joint And Contraction Joint
3) Cold Joint
CONSTRUCTION JOINTS:
Construction joints occur wherever concreting is stopped or delayed and when the fresh concrete placed against hardened concrete subsequently cannot be integrated into previous by vibrating. Horizontal construction joints occur at levels between two successive lift of concrete, whereas vertical construction joints occur where the structure of such length that is not feasible to place the entire length in one continuous operation.
Construction joints are required by the construction operation. Construction joint locations depend on the sequence of concreting operations or are part of the contract drawings. Construction joint location needs to be planned ahead of placing of concrete and should adhere to those pre-identified locations. Generally, they mark the top of a lift, the end of a monolith, or the end of a day’s work. They should be properly located and well bonded.
· When the work is to be interrupted, horizontal and vertical construction joints and bonding keys should be located in conformity with the relevant contract specifications/drawings.
· Construction joints should be located in the floor slab and beams near the middle of the span (where the shear is least) and should be vertical in the absence of provisions in construction drawings. In a column, the joint should be formed about 75 mm below the lowest soffit of the beams framing into it.
· Because construction joints frequently leak and degrade in the weather, as far as possible, they should be avoided. Before fresh concrete is placed. Existing concrete surface must be made rough by hacking or green cutting.
· The rough surface should be thoroughly wetted for about two hours and should be dried and coated with 1:1 freshly mixed cement – sand slurry, immediately before pacing the new concrete.
GREEN CUTTING FOR CONSTRUCTION JOINT TREATMENT:
Where a higher degree of quality of construction joint treatment is required as per contract specification/or drawings, green cutting should be applied. The entire construction joint should be treated by Green cutting using an air/water jet at a suitable pressure to remove the laitance from the green concrete surface to receive a subsequent pour of concrete over it. A suitable, approved brand of surface retarder should be used to retard the setting time of green concrete to a depth of 5 to 8 mm. Green cutting should b done only after the final set of concrete so that the additional water available from the air-water jet used for green cutting on the surface does not harm the quality of the concrete. Prior to the commencement of the green cutting operation, a mockup should be made for each grade of concrete, with different types of cement and different kinds of exposure of the proposed construction joint.
EXPANSION AND CONTRACTION JOINTS:
Expansion and contraction joints should be strict as per the relevant construction drawings only. Line and level of water – stop and expansion boards, if any at these joints should be safeguarded from damage or dislocation during the placing and consolidation of concrete.
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Conclusion
Understanding various types of joints in concrete construction is a fundamental part of becoming a competent civil engineer. We have tried to cover every important aspect in this article so you can confidently apply this knowledge in real-world construction scenarios. Stay tuned to CivilNotess for more valuable content tailored for civil engineering professionals.
❓ Frequently Asked Questions (FAQ)
What is the ideal concrete mix ratio for general construction?
For general construction purposes, a 1:2:4 mix ratio (cement:sand:aggregate) is commonly used. However, the specific ratio depends on the structural requirements and the grade of concrete specified by the design engineer.
How long does concrete take to cure completely?
Concrete typically reaches about 70% of its strength within 7 days and achieves its design strength (close to 100%) in 28 days under proper curing conditions. However, curing should continue for at least 7 to 14 days for best results.