OF By Rajiv KumarADG IRICEN Reference Codes IS
OF By Rajiv Kumar/ADG, IRICEN
Reference Codes • IS 456: 2000 – – Plain & reinforced cement concrete- code of practice (fourth revision) Amendments up to 4 • IS 1791: 1985 – – General Requirements for batch type concrete mixers • IS 2505: 1992 – – Concrete Vibrators-Immersion Type : General Requirements • IRUSS: 2019 – – Indian Railway United Standard Specification
Production Stages Concrete is a combination of Cementitious Material, Aggregates and water along with Admixtures, if required. Production Stages Proportioning Mixing Transportation Placement Compaction Curing
Mixing of Concrete • Stages of Charging Ingredients Sequence Of Charging Ingredients: 1. 25% of water, 2. 50% of CA, 3. 50% of FA, 4. 100% of Cement, 5. 50% of CA, 6. 50% of FA, 7. 75% of water. • Mixing Time 25 -30 revolutions (About 1. 5 -2 minutes) are sufficient. • Hand Mixing Cement + FA + CA + Water
Transportation & Placement • Transit time should be a design parameter. Method of transportation should be decided in advance for deciding suitable admixture. • Mix should be suitable for method of placement • Placement temperature should be 5 -400 C. • It should remain cohesive during placement without any segregation. • Concrete shall not be freely dropped into place from a height exceeding 1. 5 metres. • Subsequent layer should be placed when concrete is still in plastic state (within 30 min) for monolithic construction
Compaction Mechanical Compaction Vibrations are imparted by mechanical means resulting into temporary liquefaction and air bubbles come on top and escape. Type 1. 2. 3. 4. 5. Internal vibrations External vibrations Table vibrations Platform vibrations Surface vibrations
Mechanical Compaction Internal Vibration Needle vibrator is used Most commonly used technique. Available in 25 -90 mm dia and 30 to 65 cm length (IS: 2505) Frequency 100 -270 Hz(IS: 2505) Effective for thickness upto 45 cm(3. 3. 6/IRUSS) Generally 3500 -5000 rpm
Internal Vibration • Radius of influence is around 10 times of needle dia. • For effective compaction, spacing between vibrator insertions should be within 1. 5 times of Radius of Influence. • Preferably 100 mm immersion in earlier layer of concrete (in plastic state) CBC, clause 8. 3. 3. • Vibrator withdrawal from concrete should be gradual to fill up the voids.
Mechanical Compaction Surface Vibration Also called Screed Board Vibrators Action is similar to tamping Effective upto 15 -30 cm depth.
Importance of Compaction
Curing • Curing is the process of promoting hydration for development of strength and controlling temperature.
Effect of Curing (OPC)
Effect of Curing (PPC)
Curing : Important Points IS: 456 clause 13. 5 covers details time period for curing. 7/10 days moist curing, covered with wet hessian/similar material for OPC/PPC concrete, preferably 14 days. Not less than 10 days in hot & dry weather. CBC clause 8. 4. 1 stipulates minimum 14 days moist curing. Also if temperature is going below 5 degree C then additional blanketing material to keep concrete at 10 degree C or above. CBC clause 8. 4. 3 covers Steam curing – Generally 18 hrs. cycle, to complete all activities within 24 hrs, with temperature rise @ 22 -32 C/hr to max temp. 66 -88 C is allowed.
Curing : Important Points 1. Curing should be started immediately after setting when surface is still moist. 2. Uninterrupted curing should be ensured. 3. Curing is to replenish the lost moisture, hence Humid climate or rainy season is not the sufficient reason for not doing curing 4. It can not be made measurable item in contract. The best way is to educate the person responsible for curing. 5. Sea water shall not be used for curing due to harmful salt content. 6. Exposed surfaces of concrete shall be kept continuously damp for a period of 14 days from the date of placing of concrete. (Para 3. 3. 9. 3 of IRUSS) 31
Quality Control in Production IS: 456 clause 10 It is for quality control for concrete production IS: 456 clause 10. 1 - Quality Assurance Measures • Consistent with planned requirement • Adequate strength • Serviceabity • Durability IS: 456 clause 10. 1. 2 - Quality Assurance Plans • Input • Production process • Output
Quality Control in Production IS: 456 clause 10. 1. 3 – Quality Assurance Documentation • Records of inspection • Test reports of materials and concrete samples, • Nonconformity reports & remedial action, • Statistical analysis of final test results for Quality assurance. Other sub clauses are for batching precaution, w/c ratio, mixing & workability monitoring & control QUALITY CONTROL Ref in CBC clause 5. 6 covers this quality aspect. CBC clause 5. 6. 1 mentions that DEN’s competency certificate needed for the person to execute and supervise concrete work. CBC clause 5. 7 covers in brief about RMC also.
THANKS
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