Code of practice for the manufacture of lime-based blocks
1981 Edition

IS 10049 recommends the following weight-based mix proportions for lime-pozzolana blocks: For LP 20 grade, lime to fine aggregate to coarse aggregate is 1:1:2 with 11% water; for LP 40 grade, the ratio is 1:2:4 with 10% water. When lime and pozzolana are used separately, with lime reactivity at 40 kgf/cm², the proportions are 1 lime : 2 pozzolana : 3 fine aggregate : 6 coarse aggregate with 11% water; for 80 kgf/cm² lime reactivity, the mix is 1:2:6:12 with 10% water. These ratios exclude cinder aggregates and water is calculated as a percentage of total material weight.

The standard permits the use of natural or crushed stone as coarse aggregate conforming to IS 383-1970, burnt clay brick aggregates complying with IS 3068-1975, and fine aggregates meeting IS 383-1970 specifications. Cinder aggregates are also allowed if they comply with IS 2686-1977 and do not exceed 20 mm in size. These specifications ensure material quality for strength and durability in lime-based blocks.

According to IS 10049, immediately after molding, blocks should be transferred with base plates to a covered shed to protect from sun, wind, and rain. Lime-pozzolana blocks require an initial drying phase of at least 96 hours, while lime-cement blocks need 18 hours before further handling. Subsequently, blocks must be stacked and kept moist through regular water spraying for a minimum curing period of 28 days to achieve the desired strength and durability.

For quality blocks, the mixing process should include adding just enough water to obtain workable consistency without causing aggregate segregation. Thorough blending of lime, pozzolana or cement, and aggregates is essential. During moulding, mechanical or electrical machines should be used; the mould should be filled with a 20% surcharge above its top, followed by compaction through vibration or mechanical tamping. The surface must then be leveled off uniformly to produce dimensionally accurate blocks.

Water used must be clean, free from harmful impurities, and generally potable. The water's pH should not be below 6 to prevent adverse chemical effects in the blocks. Additionally, the quantity of water should be just sufficient to achieve proper mix consistency without causing segregation. Adhering to these water quality standards is crucial for the longevity and strength of the manufactured blocks.