Autoclaved reinforced cellular concrete floor and roof slabs
2006 Edition

Per IS 6073, the materials approved for producing autoclaved cellular concrete slabs include inorganic binders such as lime and cement, or a blend thereof; finely powdered silicon dioxide sources like sand; aluminium powder as the gas-forming agent; water; and optional harmless additives. The cement must comply with applicable IS specifications (e.g., IS 269 for Ordinary Portland Cement). The additives should not interfere with the autoclaving process and must be chemically safe. This combination supports the formation of lightweight, durable cellular concrete through steam curing under pressure.

IS 6073 defines form tolerances for autoclaved reinforced cellular concrete slabs as follows: length and width deviations allowed up to ±5 mm; thickness variation up to ±3 mm; squareness, measured by diagonal differences, limited to ±5 mm; and warpage restricted to a maximum of 3 mm per meter. These tolerances ensure proper fit and structural integrity. For detailed graphical representations, refer to Figure 2 within the standard.

The ultimate load is established by the manufacturer and must meet or exceed the minimum specified by IS 6073. Testing involves applying half the design load for 30 minutes at the quarter points of the effective span, followed by the full design load (including self-weight) maintained for another 30 minutes. The slab is then inspected for cracking and measured for mid-span deflection. While the code does not explicitly state safety factors, it implicitly requires that the ultimate load capacity exceed the design loads, providing a safety margin typically ranging between 1.5 and 2.0.

Compressive strength testing per IS 6073 requires preparing three cube samples from the slab, conducting tests according to IS 6441 (Part 5), and ensuring the mean strength meets or exceeds the class minimum with no individual sample below 85% of the average. Thermal conductivity is measured on a single slab sample following IS 3346's two-slab guarded hot plate method, with results not exceeding the maximum values defined for each class. Samples are tested in an air-dried condition post load-deflection and ultimate load tests, ensuring compliance with specified criteria.

IS 6073 advises storing slabs on wooden planks or suitable supports to prevent direct ground contact, with separate stacking for different densities or shapes. Handling must follow manufacturer instructions to avoid damage, with special attention to marked lifting points and hole-making provisions. Cutting slabs is prohibited without engineer authorization. Damaged slabs should be rejected to maintain structural integrity. Improper storage or handling can cause permanent warping or twisting, so care must be taken to preserve slab quality before installation.