Slabs are classified based on support conditions, shape, and structural systems. The type of slab influences reinforcement details, formwork requirements, and construction methodology.

• One-way Slab: Supported on two opposite sides with span ratio (long/short) > 2, with main reinforcement running along shorter span.
• Two-way Slab: Supported on all four sides with span ratio < 2, with main reinforcement in both directions.
• Cantilever Slab: Supported on one side only, extended outward with reinforcement at top.
• Flat Slab: Directly supported on columns without beams, may include drop panels or column capitals.

• Ribbed/Waffle Slab: Contains ribs in one or two directions with voids between, reducing self-weight.
• Hollow-core Slab: Precast with continuous voids to reduce weight while maintaining strength.
• Post-tensioned Slab: Contains tensioned tendons to improve load capacity and reduce thickness.
• Composite Slab: Uses profiled steel deck as permanent formwork with concrete topping.

• IS 456:2000: Code of Practice for Plain and Reinforced Concrete - Main code governing slab design and construction.
• IS 1786:2008: High Strength Deformed Steel Bars and Wires for Concrete Reinforcement.
• IS 2502:1963 (Reaffirmed 2018): Code of Practice for Bending and Fixing of Bars for Concrete Reinforcement.
• IS 10262:2019: Concrete Mix Proportioning - Guidelines.
• IS 516:1959 (Reaffirmed 2018): Method of Tests for Strength of Concrete.
• IS 13920:2016: Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces.
• SP 34:1987: Handbook on Concrete Reinforcement and Detailing.

Understanding the difference between main reinforcement and distribution reinforcement is crucial for proper slab construction.

• Main Bars: Carry the primary bending moment and are placed perpendicular to the direction of span (along shorter span in one-way slabs).
• Distribution Bars: Provide load distribution, control cracking, and are placed perpendicular to main bars (along longer span in one-way slabs).
• Reinforcement Ratio: In one-way slabs, distribution bars are typically 0.2% of gross sectional area or ≥ 20% of main reinforcement.
• Two-way Slabs: Both directions have main bars, with the reinforcement proportionate to the moments in respective directions.

• Bottom Reinforcement: Resists positive moment (tension at bottom) at mid-span and extends throughout the slab.
• Top Reinforcement: Resists negative moment (tension at top) at supports and corners.
• Continuous Slabs: Require top reinforcement at intermediate supports (typically extending 0.3L on either side of support, where L = effective span).
• Corner Reinforcement: Special top reinforcement at corners of two-way slabs to resist corner uplift.

Proper lapping of reinforcement is critical to ensure structural continuity and load transfer. IS 456:2000 provides detailed requirements for lapping.

• Lap Length Calculation: Min. lap length = Ld or 30d (whichever is greater) for tension bars, where Ld = development length, d = bar diameter.
• Bottom Bars Lapping: Preferably done at mid-span (away from maximum moment zone) or at supports for alternate bars.
• Top Bars Lapping: Preferably done away from supports (zone of maximum negative moment).
• Staggered Laps: Laps should be staggered, with not more than 50% of bars lapped at one section.
• Minimum Offset: Minimum clear distance between lapped bars = 2 × bar diameter.
• Binding: All laps must be securely tied with binding wire with minimum 3 ties per lap.

Proper positioning and maintaining cover for reinforcement is achieved using spacers and chairs.

• Cover Blocks: Precast cement concrete blocks (same grade as structural concrete) to maintain bottom cover.
• Chairs/Bar Supports: Metal or plastic supports to hold top reinforcement at correct height.
• Spacing of Spacers: Place at maximum 1.0m center-to-center in both directions.
• Chair Spacing: Maximum 0.75m center-to-center to prevent sagging of top reinforcement.
• Types of Chairs: Individual high chairs, continuous high chairs, or individual bar supports depending on slab thickness.
• Size Calculation: Chair height = slab thickness - (bottom cover + top cover + bottom bar diameter + top bar diameter).

• Measuring tape (30m & 5m).
• Chalk line/chalk powder.
• Spirit level.
• Marker pen/paint.
• Plumb bob.
• String/thread.
• Slab reinforcement drawing.

• Verify beam top levels are as per drawing.
• Mark slab thickness above beam top level.
• Mark locations for any drops, openings, or cutouts.
• Indicate position of services (electrical conduits, plumbing sleeves).
• Mark locations for any inserts or embeds.
• Indicate construction joint locations if applicable.
• Verify all dimensions against the drawing.

• Mark main bar spacing on formwork or shuttering edges.
• Mark distribution bar spacing perpendicular to main bars.
• Indicate extra reinforcement zones (near supports, openings).
• Mark locations for top reinforcement chairs.
• Double-check spacing against Bar Bending Schedule.

• Timber Formwork: Traditional system using wooden planks and runners.
• Plywood Formwork: Water-resistant plywood sheets with timber or metal framing.
• Steel Formwork: Steel sheets and frames, suitable for repetitive use.
• Aluminum Formwork: Lightweight, high precision system for rapid construction.
• Table/Flying Formwork: Large pre-assembled units for rapid cycling.
• Proprietary Systems: DOKA, PERI, MIVAN, etc.

• Set up primary supports/props at required spacing (typically 0.9-1.2m).
• Install secondary beams/runners perpendicular to primary beams.
• Place formwork sheets/boards on secondary beams.
• Apply release agent evenly on formwork surface.
• Install edge formwork with proper bracing.
• Provide camber if specified in drawings (typically L/500).
• Seal all joints to prevent grout leakage.
• Install sleeves for services and blockouts for openings.

• Verify reinforcement grade, diameter, and length as per BBS.
• Check bar bending for compliance with shape codes.
• Inspect bars for rust, oil, or contaminants.
• Prepare adequate cover blocks and chairs.
• Verify formwork is clean, level, and ready.

• Place cover blocks at 1.0m centers.
• Lay main bars first, maintaining specified spacing.
• Place distribution bars perpendicular to main bars.
• Secure intersections with binding wire.
• Provide extra reinforcement near openings as per drawing.
• Check and confirm spacing and cover before proceeding.

• Install chairs/bar supports at specified spacing (typically 0.75m).
• Place top main bars in the correct direction.
• Lay top distribution bars perpendicular to main bars.
• Secure all intersections with binding wire.
• Verify top cover is maintained throughout.
• Install additional reinforcement at corners as specified.

• At Supports: Extend bottom bars into supports by min. development length.
• Top Reinforcement Extent: Extend minimum 0.3L from face of support (L = effective span).
• Around Openings: Provide additional U-bars at corners and extra parallel bars.
• At Free Edges: Provide edge beams or thickened edges with U-bars.
• Corner Reinforcement: Provide additional top bars at 45° to prevent corner lifting.

• Use rigid PVC conduits (min. 2mm thick) for electrical wiring.
• Place conduits between top and bottom reinforcement layers.
• Avoid placing conduits in highly stressed areas (column strips).
• Secure conduits to reinforcement with binding wire.
• Minimum 20mm clearance between conduits and reinforcement.
• Maximum diameter of conduits limited to 1/3 of slab thickness.

• Install proper sleeves for all penetrations.
• Provide 15-25mm clearance around pipes for movement.
• Seal sleeves to prevent concrete leakage.
• For large openings (>150mm), provide additional reinforcement.
• Avoid clustering of sleeves in one area.

Typical concrete for slabs is M20 or M25 grade, designed for good workability and finish.

• Obtain approval of reinforcement from structural engineer.
• Verify formwork stability, alignment, and levels.
• Check concrete mix design approval.
• Verify cover blocks and chairs are properly placed.
• Ensure electrical conduits and sleeves are secured.
• Arrange for concrete cube samples for testing.
• Check availability of vibrators, screeds, and finishing tools.
• Plan pouring sequence and ensure adequate labor.
• Arrange for proper lighting if concreting extends to evening.
• Prepare curing arrangements.

• Perform slump test before placement (75-100mm recommended).
• Cast cube samples for 7 and 28-day strength tests.
• Start pouring from farthest point and progress systematically.
• Pour in strips or panels based on planned sequence.
• Avoid concrete fall from height exceeding 1.5m.
• Use needle vibrators at 400-600mm intervals to compact concrete.
• Avoid over-vibration to prevent segregation.
• Check level continuously during pouring.
• Use screed boards to achieve uniform level.
• For large slabs, use defined construction joints with proper detailing.

• Wait until bleeding water disappears before finishing.
• Use wooden float for initial leveling.
• For smooth finish, use steel trowel.
• For non-slip finish, use broom or textured roller.
• Check levels with straight edge during finishing.
• Ensure appropriate slopes for drainage where required.
• Apply curing compound or cover with wet burlap once concrete has set.

• Ponding: Create earth bunds and pond water (most effective method).
• Wet Covering: Use wet burlap/gunny bags kept continuously moist.
• Curing Compounds: Apply membrane-forming compounds after final set.
• Duration: Minimum 7 days for OPC concrete, 10 days for PPC/PSC concrete.
• Water Quality: Use clean, potable water free from impurities.

IS 456:2000 (Clause 11.3) specifies minimum periods before formwork removal:

• Check concrete strength before removal (by cube tests or NDT).
• Remove formwork gradually without shock or vibration.
• For large spans, start removal from center and move to supports.
• Leave re-shoring/back-propping in place for required duration.
• Inspect concrete for any defects immediately after formwork removal.
• Continue curing even after formwork removal.

• Slump test: For workability check (75-100mm for slabs).
• Cube test: 7 and 28-day compressive strength (IS 516).
• Steel reinforcement testing: Tensile strength, bend test.
• Level survey: To check final slab thickness and levels.
• Cover measurements: Using cover meter.
• Surface regularity: Using 3m straight edge.
• Non-Destructive Testing (NDT): Rebound hammer test (IS 13311 Part 2) or Ultrasonic Pulse Velocity (UPV) test (IS 13311 Part 1) for in-situ concrete quality assessment.

• Approved architectural and structural drawings (latest revisions).
• Reinforcement inspection records and Bar Bending Schedule (BBS).
• Formwork inspection records and approval.
• Concrete mix design approval and concrete pour cards.
• Concrete cube test reports (7-day and 28-day strength).
• Material test certificates for cement, aggregates, and steel.
• Daily progress reports and site diaries.
• Level survey reports for formwork and finished slab.
• Curing records (method, duration, start/end times).
• Photographic evidence at critical stages (formwork, rebar, concreting).
• Records of any site instructions, non-conformities, and remedial actions.

Effective on-job training quality relies heavily on continuous supervision and immediate correction of deviations. The site engineer and quality control team play a pivotal role.

• Pre-Pour Checklist: Implement a mandatory checklist before every concrete pour covering formwork, reinforcement, and service installations.
• Visual Inspection: Regular visual inspection of rebar cage for correct spacing, cover, and binding before and during concrete placement.
• Slump Test Verification: Site engineer must personally witness and approve slump tests for every concrete delivery.
• Vibration Monitoring: Ensure proper use of vibrators to achieve full compaction without segregation or honeycombing. Train labor on correct vibration techniques.
• Level Monitoring: Continuously check slab levels during concrete pouring to avoid undulations and ensure correct thickness.
• Curing Supervision: Strict supervision of curing methods and duration. Emphasize the importance of continuous moisture.
• Immediate Rectification: Any non-conformity (e.g., misplaced rebar, formwork deflection) must be identified and rectified immediately before proceeding.
• Toolbox Talks: Conduct daily toolbox talks with labor and supervisors on critical quality aspects for the day's work.