lime-pozzolana mixture
1983 Edition

IS 4098 categorizes lime-pozzolana mixtures into three types based on their application in masonry mortars and foundation concrete: LP 7 for masonry mortars up to Grade MM 0.5 and foundation concrete; LP 20 for masonry mortars up to Grade MM 2 and foundation concrete; and LP 40 for masonry mortars up to Grade MM 5. The mixtures use Class C hydrated lime combined with pozzolanic materials such as burnt clay or fly ash, and may include up to 5% Type IV gypsum to enhance setting and strength. Pozzolana must demonstrate a lime reactivity of at least 4 N/mm² according to IS 1727. These classifications ensure suitability for different structural strength requirements.

The standard permits the use of Class C hydrated lime (IS 712-1984) combined with pozzolana materials which can be burnt clay, fly ash (IS 3812-1981), or rice husk ash. Production can be carried out through intergrinding in ball or tube mills or by blending powdered components. Additionally, Type IV mineral gypsum (IS 1290-1973) may be incorporated up to 5% to accelerate setting times and improve early strength. Strict chemical limits are imposed, including maximum free moisture of 5%, minimum free lime of 22%, maximum carbon dioxide of 5%, sulphate content not exceeding 3%, and magnesium oxide capped at 8%. These specifications ensure the mixture's performance and durability per IS 4098.

Sampling of lime-pozzolana mixtures should involve collecting material from at least 12 different bags or, if fewer, from each bag, combining equal portions to form a composite sample weighing a minimum of 5 kg. Samples must be stored in airtight containers prior to laboratory testing. Quality control tests include chemical analyses for moisture content (max 5%), free lime (min 22%), carbon dioxide (max 5%), sulphate (max 3%), and magnesium oxide (max 8%). Physical testing covers fineness (maximum 15% retained on 150-micron sieve for certain types), setting time (initial minimum 2 hours and final maximum varying by type), compressive strength after 7 and 28 days, water retention (minimum 65%), and soundness (maximum 1% autoclave expansion). These procedures ensure the mixture meets IS 4098 standards.

Chemically, lime-pozzolana mixtures must have free moisture content not exceeding 5%, free lime content at least 22%, carbon dioxide limited to 5%, sulphate content below 3%, and magnesium oxide under 8%, as tested according to referenced IS methods. Physically, the mixtures (types LP40, LP20, LP7) have specific requirements: fineness must be at most 15% retained on 150-micron sieve (except LP7 where it's not specified), initial setting time should be at least 2 hours, final setting time must not exceed 24 hours for LP40, 36 hours for LP20, and 48 hours for LP7. Compressive strength requirements range from minimum 0.3 N/mm² at 7 days (LP7) to 4 N/mm² at 28 days (LP40). Water retention should be at least 65%, and soundness (autoclave expansion) not more than 1%. These parameters ensure proper performance in construction.

Per IS 4098 Clause 7.1, lime-pozzolana mixtures should be stored in weatherproof buildings that protect the material from moisture and damp conditions, thereby preventing deterioration. Storage areas must provide easy access for inspection and identification. The mixtures are typically stored in bags made from jute, multi-ply paper, HDPE, or cloth, which should be clearly marked with the manufacturer's details and net weight, and maintained in good condition upon delivery to avoid contamination or moisture ingress. Proper storage safeguards the mixture’s quality and reactivity essential for effective use in construction projects.