Code of Practice for Construction of Floor and Roof with Joists and Filler Blocks, Part IV: With Precast Hollow Clay Block Slab Panels
1981 Edition

According to the standard, design loads for hollow clay block slab panels are considered in two phases: first during construction handling and erection, and secondly for service conditions. The panels must support their own weight treated as simply supported slabs, along with any superimposed loads such as floor finishes and live loads. Additionally, the average crushing strength of the hollow clay blocks is reduced by 20% to accommodate variability, and permissible stresses are determined following IS 456-1978 to ensure safety under operational conditions.

Hollow clay blocks used in precast slab panels must comply with IS 3951 (Part II) - 1975 for structural hollow clay blocks. They should preferably conform dimensionally to the recommended figures within the standard. Prior to casting, the blocks must be thoroughly soaked and allowed to become skin-dry. Blocks are placed with their shorter face resting on the platform and bonded with a 10 mm thick 1:3 cement-sand mortar. Mortar layers sandwich the blocks with reinforcement positioned in longitudinal grooves, maintaining a maximum panel height of 600 mm. Vertical joints are staggered using half units, ensuring the face with main reinforcement is vertical and forms the ceiling surface. The average crushing strength is considered with a 20% reduction for design purposes, and permissible stresses are assigned based on IS 456-1978.

Casting of slab panels should be carried out on a level platform shielded from direct sunlight and strong winds to prevent rapid drying. Following casting, panels require water curing for a minimum of 14 days, succeeded by an additional 14 days of air curing. Panels must only be lifted after 28 days from casting, and during transportation, they should be handled vertically or horizontally with the reinforcement face down to avoid damage. For installation, panels are positioned side by side over a finished, level support, and joints are filled and finished with 1:2 cement-sand mortar to ensure proper bonding and integrity.

The recommended joining methods include placing slab panels side by side on a finished level support and filling any gaps with 1:2 cement-sand mortar, finished with rule pointing. To provide structural continuity, negative reinforcement bars are embedded in longitudinal grooves at the slab tops, projecting 60 mm from panel ends and lap welded with adjacent panels' reinforcement. Alternatively, a 120 mm wide in-situ concrete joint can be provided between panels with negative reinforcement placed over supports to achieve partial continuity. Mortar and concrete quality must comply with the relevant IS standards to ensure strength and durability.

In addition to IS 6061 Part 4, several Indian Standards govern the materials and finishing for floors and roofs constructed with hollow clay block slabs. These include IS 1196-1978 for bitumen mastic, IS 1197-1970 for rubber finishes, IS 1198-1958 for linoleum, IS 1443-1972 for cement concrete tiles, IS 2114-1962 for terrazzo, IS 2115-1980 for mud phuska, IS 2571-1970 for in-situ cement concrete, IS 4631-1968 for epoxy resin, IS 5318-1969 for PVC finishes, and IS 5766-1970 for brick finishes. Selecting the appropriate finishing materials as per these standards ensures compatibility and durability of the floor or roof system.