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Slab Construction Quality Check Procedure

Standard operating procedure for slab construction ensuring structural integrity, durability, and serviceability through proper inspection and testing methods in accordance with Indian Standards (IS Codes).

Structure Type: RCC Slab Quality Priority: High Validity: All Projects
1

Objective

To establish a comprehensive quality control procedure for Slab Construction, ensuring structural integrity, durability, and serviceability through proper inspection and testing methods in accordance with Indian Standards (IS Codes).

2

IS Code References

Inspection Stage IS Code Description
Formwork & Shuttering IS 14687:1999 Guidelines for Falsework
Reinforcement Checking IS 456:2000, IS 2502:1963 Concrete & Rebar Detailing
Concrete Mix Design IS 10262:2019 Mix Design & Aggregate Quality
Concrete Pouring & Vibrations IS 1199:1959, IS 4925:2004 Slump Test & Batching
Concrete Strength Testing IS 516:1959 Cube Test for Strength
Curing & Protection IS 7861:1981 Hot Weather Concreting
Final QA/QC Checks IS 456:2000 Tolerances & Quality Control
Safety Requirements IS 3764:1992 Safety Code for Construction
3

Pre-Casting / Pre-Pouring Inspection

A
Formwork & Centering Check
  • Ensure formwork material (plywood, steel, etc.) is as per IS 14687:1999
  • Check formwork dimensions, levels, and alignment as per drawings
  • Ensure formwork is clean, oiled, and tightly fixed to prevent leakage
  • Provide adequate supports (props, bracings, and scaffolding) to avoid deflection
  • Check for proper camber (if required) to counteract deflections
  • Verify formwork joints are tight and sealed to prevent grout loss
  • Check formwork surface is smooth to achieve required finish
IS 14687:1999 IS 1200: Part 5-1982
B
Reinforcement (Rebar) Inspection
  • Verify diameter, spacing, and number of bars as per structural drawings
  • Ensure cover blocks (20–30mm) are provided for proper cover
  • Check binding wire is used properly for securing bars
  • Verify lap length and anchorage as per IS 2502:1963
  • Ensure reinforcement is free from rust, oil, and dirt
  • Check for extra reinforcement around openings, cantilevers, and load-bearing areas
  • Verify main reinforcement and distribution steel placement
  • Check cranked bars at support points for proper bending
  • Ensure proper positioning of top and bottom steel mats
IS 456:2000 IS 2502:1963 IS 1786:2008
C
Slab Openings & Conduits Check
  • Ensure provisions for electrical conduits, pipes, and openings are made before casting
  • Check that conduits are properly secured and do not affect reinforcement positioning
  • Verify alignment of openings with architectural drawings
  • Ensure proper shuttering around openings to maintain shape
  • Check that openings don't exceed 1/3 of slab depth without additional reinforcement
  • Verify trimmer bars around large openings
IS 456:2000
D
Level & Alignment Check
  • Check level of slab formwork using water level or laser level
  • Ensure proper slope for drainage where required (bathrooms, balconies)
  • Verify thickness markings are consistent throughout the slab area
  • Check edge formwork for proper alignment and stability
  • Verify soffit level of slab matches structural drawings
  • Check props are properly shimmed and wedged
IS 456:2000
E
Safety & Support System Check
  • Verify adequate shoring and bracing as per IS 3764:1992
  • Check working platforms and safety railings are in place
  • Ensure props are properly sized for the load they will carry
  • Verify foundation of props is adequate and level
  • Check horizontal and diagonal bracing between props
  • Ensure access arrangements for concrete placement
IS 3764:1992 IS 14687:1999
4

During Concreting Inspection

A
Concrete Mix & Slump Test
  • Ensure approved concrete mix (e.g., M20, M25, M30) is used as per IS 10262:2019
  • Perform slump test (target 75–125mm for slabs) as per IS 1199:1959
  • Check for segregation and bleeding in the concrete mix
  • Ensure no extra water is added on-site, which may weaken the mix
  • Verify concrete temperature is within specified limits
  • Check concrete delivery time from batching plant
IS 10262:2019 IS 456:2000 IS 1199:1959
B
Concrete Placement & Vibration
  • Ensure concrete is placed within 30 minutes of mixing
  • Avoid free fall greater than 1.5m to prevent segregation
  • Use mechanical vibrators properly to compact concrete and remove air voids
  • Avoid over-vibration, which may lead to segregation and weak zones
  • Ensure concrete is placed continuously without cold joints
  • Check vibrator insertion depth and spacing
  • Ensure proper consolidation around reinforcement
IS 4925:2004 IS 456:2000
C
Level & Finishing Check
  • Ensure slab level matches approved structural drawings
  • Use leveling instruments to maintain an even surface
  • Properly finish slab using wooden or steel trowels to achieve the required texture
  • Provide proper slope (if required) for drainage purposes
  • Check levels at regular intervals during finishing
  • Ensure thickness tolerance is maintained (±10mm)
  • Check for proper surface finish as per specification
IS 456:2000
D
Quality Control During Pouring
  • Take concrete cube samples as per IS 516:1959 (minimum 6 cubes per 100 cum)
  • Check concrete doesn't displace reinforcement during placement
  • Ensure no formwork movement or bulging during pouring
  • Monitor weather conditions and take protective measures if needed
  • Check for proper consolidation at construction joints
  • Verify no honeycombing or voids formation
IS 516:1959 IS 456:2000
5

Post-Pouring Inspection

A
Curing & Protection
  • Begin curing within 24 hours of pouring
  • Use water ponding, wet hessian cloth, or curing compound for at least 7–14 days
  • Protect fresh concrete from direct sunlight, heavy rain, and strong winds
  • Ensure entire slab surface is properly cured with no dry patches
  • Maintain curing water temperature between 5°C to 40°C
  • Check curing compound application rate if used
IS 7861:1981 IS 456:2000
B
Concrete Strength Testing
  • Collect cube samples (150mm x 150mm x 150mm) for compressive strength testing (IS 516:1959)
  • Test compressive strength at 7, 14, and 28 days
  • Ensure minimum characteristic strength (e.g., M20, M25) is achieved as per design
  • Maintain proper documentation of test results
  • Compare results with acceptance criteria
  • Take corrective action if strength is below specified limits
IS 516:1959 IS 456:2000
C
Surface Defects & Cracks Check
  • Inspect for cracks, honeycombing, or undulations on the slab surface
  • Perform hammer test to check for hollow or weak spots
  • Ensure minor defects are rectified using grout or epoxy mortar
  • Document all defects and corrective actions taken
  • Check for plastic shrinkage cracks and treat if necessary
  • Verify no structural cracks are present
IS 456:2000
D
Dimensional & Structural Stability Check
  • Measure slab thickness as per structural drawing
  • Ensure no excessive deflections or deviations after formwork removal
  • Verify supporting columns and beams are properly connected to the slab
  • Check edges and corners for proper finishing and alignment
  • Measure actual dimensions and compare with design
  • Check level tolerance within specified limits
IS 456:2000
6

Testing of Slab Concrete

Test Purpose IS Code Frequency
Slump Test Checks workability of concrete IS 1199:1959 Every batch/truck
Cube Strength Test Ensures required compressive strength IS 516:1959 6 cubes per 100 cum
Rebound Hammer Test Non-destructive test for surface hardness IS 13311:Part 2 As required
Ultrasonic Pulse Velocity Test Checks homogeneity and cracks IS 13311:Part 1 As required
Core Test Direct measurement of in-situ strength IS 516:1959 If cube results fail
Water Permeability Test Checks water tightness of concrete IS 3085:1965 For water retaining structures
Deflection Test Checks structural performance IS 456:2000 As per structural requirement
7

Common Defects & Remedial Measures

Defect Possible Cause Remedial Action
Cracks Thermal expansion, inadequate curing, shrinkage, overloading Epoxy injection, polymer modified cement, structural repair
Honeycombing Poor vibration, high slump, segregation, tight reinforcement Chipping and patching with grout, bonding agent application
Delamination Improper finishing, bleeding, over-troweling Remove loose material and resurface with overlay
Low Strength Poor mix design, excess water, inadequate curing, poor quality materials Core test, strengthening measures, structural assessment
Deflection Inadequate design, early formwork removal, overloading Additional supports, structural repairs, load restriction
Surface Dusting Poor finishing, inadequate curing, weak surface layer Surface hardener application, protective coating
Cold Joints Delay in concrete placement, improper construction joints Surface preparation, bonding agent, proper joint treatment
8

De-Shuttering Schedule

  • Slab side formwork: 24 hours after pouring (when concrete achieves sufficient strength)
  • Props and bottoms of slab:
• Slabs with spans up to 4.5m: 7 days
• Slabs with spans 4.5m to 6m: 14 days
• Slabs with spans above 6m: 21 days
  • Beam bottoms:
• Beams with spans up to 6m: 14 days
• Beams with spans above 6m: 21 days
  • Special Conditions:
• Hot weather: Reduce time by 25%
• Cold weather: Increase time by 50%
• Structural slabs: As per structural engineer's advice
  • Important Note: Retain 25% of props for an additional 7-14 days after removal for safety
IS 456:2000 Clause 11.3
9

Quality Parameters & Tolerances

Parameter Requirement Tolerance Testing Method
Concrete Grade As per design (M20/M25/M30) +15% of characteristic strength Cube test at 28 days
Slab Thickness As per structural drawings +10mm, -5mm Physical measurement
Level Tolerance As per architectural drawings ±5mm in 3m length Spirit level/Laser level
Surface Finish Smooth, no honeycombing ±3mm under 3m straight edge Visual inspection
Reinforcement Cover 20-30mm as per exposure ±5mm Cover meter
Crack Width No structural cracks Hairline cracks ≤0.3mm Crack gauge
10

QA/QC Checklist for Slab Construction

  • Approved structural drawings available and followed
  • Formwork properly installed, cleaned, and oiled
  • Shuttering level checked and maintained within tolerance
  • Props and supports adequate for the load
  • Reinforcement placed as per drawings (diameter, spacing, position)
  • Cover blocks placed at suitable intervals (1-1.5m c/c)
  • All electrical conduits and openings marked and secured
  • Approved concrete mix design followed
  • Slump test conducted within allowable range (75-125mm)
  • Concrete temperature within specified limits
  • Cube samples prepared for strength testing
  • Proper vibration and compaction during pouring
  • Level maintained during finishing
  • No cold joints formed during concreting
  • Curing started at the right time and continued for required period
  • De-shuttering done as per schedule
  • Surface checked for defects and remedial measures taken
  • Final dimensional checks completed and documented
  • Strength test results reviewed and accepted
  • All documentation completed and filed
11

Acceptance Criteria

Surface Finish: Smooth with no honeycombing, exposed rebar, or major voids
Level Tolerance: ±5mm from specified level in 3m length
Cracks: No structural cracks; hairline cracks not exceeding 0.3mm width
Compressive Strength: Minimum 99% of characteristic strength at 28 days
Deflection: Within permissible limits as per IS 456:2000 (span/250 or 20mm whichever is less)
Edge Alignment: ±10mm deviation from specified alignment
Dimensions: Thickness within +10mm and -5mm of specified value
Cover to Reinforcement: As per design requirement with tolerance of ±5mm
Water Tightness: No water penetration for water retaining structures
IS 456:2000 IS 516:1959
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