What is the minimum grade of concrete for precast shell units?

Grade M15 is the minimum specified in Clause 3.2.

What are the typical dimensions for a standard shell unit?

A common size is 1220 mm x 1220 mm, with a thickness of 25 mm at corners and a central rise of 115 mm (Table 1).

When can the shell units be lifted from the moulds?

Only after the concrete has attained a cube strength of at least 7.5 N/mm² (Clause 4.8).

What is the minimum thickness for the concrete screed on top?

The levelling course (screed) must have a minimum average thickness of 20 mm (Clause 7.1).

IS 6332

: 1984

Code of practice for construction of floors and roofs using precast doubly-curved shell units

CurrentSpecializedCode of PracticeBIMStructural Engineering · Building Construction Practices incl. Painting, Varnishing

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This standard outlines the construction practices for floors and roofs using precast doubly-curved reinforced concrete shell units. It covers the requirements for materials, casting, handling, stacking, erection, and the laying of in-situ concrete or screed to form a composite structural system.

Code of practice for construction of floors and roofs using precast doubly-curved shell units

Quick Reference Values

Minimum grade of concrete for precast unitsM15

Minimum thickness of shell at corners25 mm

Typical reinforcement for 1.22m x 1.22m unit6 mm dia mild steel bars at 150 mm c/c both ways

Minimum average thickness of levelling course (screed)20 mm

Minimum cube strength before demoulding7.5 N/mm²

Minimum cube strength before handling/erection15 N/mm²

Practical Notes

Proper curing of precast units is critical to prevent shrinkage cracks and achieve the required strength before handling and erection.

Accurate alignment of units during erection is essential for the structural integrity of the composite floor/roof diaphragm.

The in-situ concrete screed is not just a leveling course but a structural component that provides composite action; its quality and bonding are vital.