The IS 6932 Part 7 (1973) standard outlines the prescribed procedure to evaluate building limes by measuring the compressive and flexural strength of lime-sand mortar specimens. It details the preparation, curing, and testing methods necessary for consistent assessment of lime's performance in construction applications. This code is pivotal for technical experts ensuring quality and reliability in lime-based mortars.
Overview
The IS 6932 Part 7 (1973) standard outlines the prescribed procedure to evaluate building limes by measuring the compressive and flexural strength of lime-sand mortar specimens. It details the preparation, curing, and testing methods necessary for consistent assessment of lime's performance in construction applications. This code is pivotal for technical experts ensuring quality and reliability in lime-based mortars.
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IS 6932 Part 7 (1973) introduces the testing methods for building limes, adopted by the Indian Standards Institution on March 22, 1973. The document integrates updated references including IS 2250:1981 for masonry mortar preparation, IS 712:1984 for lime specifications, IS 1070:1992 for reagent water standards, IS 650:1991 for building lime, and IS 460 (Part 1):1985 for sieves. It mandates specimen preparation following IS 2250:1981 and reporting results rounded as per IS 2:1960.
This section specifies the preparation of lime samples: approximately 1 kg of quicklime is crushed to pass through a 2.36 mm IS Sieve (per IS 460-1962). The quicklime is slaked isothermally for one hour, stirred, then sieved through an 850 micron sieve. Excess water is removed by hand pressing on filter cloth to achieve a water content between 60-65% by mass of dry hydrated lime. Moisture is determined by drying at 100 ±10°C until constant weight.
Distilled water conforming to IS 1070-1960 is mandatory for lime testing procedures to avoid contamination. Water used in slaking quicklime and preparing putty must be distilled. Moisture content is verified by oven drying at 100 ±10°C. The water content in lime putty is adjusted to 60-65% by mass of dry hydrated lime to ensure consistency.
Hydrated lime putty is prepared by mixing 500 g lime with 60-65% water, blending for five minutes, and passing twice through the IS 1625-1971 mixer. For mortar, 350 g of this putty is combined with 636-656 g of standard sand (about three times the dry lime mass) and mixed for ten minutes continuously. Quicklime preparation involves crushing, slaking, sieving, water adjustment, and mixing similarly. The fresh mortar is then used immediately for testing.
Mortar specimens are molded and stored undisturbed for 28 days in an environment maintaining at least 90% relative humidity and temperature of 27 ± 2°C. Specimens remain in molds covered with top and base plates, placed in a container. Temperature is monitored on at least 24 days to observe fluctuations. After curing, specimens are carefully removed for testing.
A total of 12 cube specimens are prepared, with 6 tested at 14 days and 6 at 28 days. After initial water curing for 7 days (or moist sand for Class B limes), cubes are tested with load applied steadily at 15 kg/min on the faces molded against the mold sides. The testing machine uses a self-adjusting platen without packing. Compressive strength is calculated as maximum load divided by cross-sectional area and expressed in kg/cm².
Specimens are immersed in water for 30 minutes prior to testing. They rest on two parallel rollers of 4 cm diameter spaced 8 cm apart. A third roller of 4 cm diameter applies load at the midpoint at a steady rate of 15 kg/min ±10%. No packing is used between rollers and specimen. The modulus of rupture is calculated using the formula t = k × (P / b d²), where k = 0.768, P is failure load, b is specimen width, and d its depth.
Test results are derived by averaging compressive strength values from six specimens. Strength is reported in kg/cm² with clear indication of the applied load area. Details regarding specimen preparation and any irregularities during testing are documented. The compressive strength formula is f_c = P/A, where P is load and A is cross-sectional area.
Key amendments include Amendment No. 3 (1985), which replaced IS 1625-1971 with IS 2250-1981 for mortar preparation and revised terminology. Amendment No. 4 (2010) updated several referenced standards to their latest versions including IS 712:1984, IS 1070:1992, IS 650:1991, and IS 460 (Part 1):1985. These revisions ensure alignment with current best practices and reaffirm the standard’s relevance.
Frequently Asked
The preparation starts with hydrated lime or quicklime. For hydrated lime, 500 g is mixed with 60-65% water by weight for 5 minutes and passed twice through the IS 1625-1971 mixer. Then, 350 g of putty is blended with three times its dry lime mass in standard sand (~636-656 g) for 10 minutes. For quicklime, about 1 kg is crushed to pass a 2.36 mm sieve, slaked isothermally for one hour, stirred, sieved through 850 micron sieve, excess water removed, and water content adjusted to 60-65%. The putty is then mixed with sand similarly. Mortar is used immediately for testing.
Specimens undergo initial curing in water or moist sand for 7 days. Six cubes are tested at 14 days after surface drying, and the remaining six continue curing for an additional 21 days before testing at 28 days. This schedule allows strength development assessment at two key intervals.
For compressive strength testing, the load is applied steadily at 15 kg/min without packing between the specimen and platens. For transverse strength (modulus of rupture), the load is applied through a third roller at 15 kg/min ±10%. These controlled rates ensure uniform application and reliable results.
Yes. Both hydrated lime and quicklime are acceptable. Hydrated lime is mixed with water and processed into putty, while quicklime is crushed, slaked, sieved, and adjusted for water content before mortar preparation. Both types are mixed with standard sand at a 1:3 ratio by dry hydrate mass and used immediately for strength testing.
The modulus of rupture (transverse strength) is calculated using the formula t = k × (P / b d²), where t is the modulus of rupture in kg/cm², P is the failure load in kg, b is the specimen width in cm, d is its thickness in cm, and k is a constant 0.768. Specimens are supported on two 4 cm diameter rollers spaced 8 cm apart, with load applied at midpoint by a third roller at 15 kg/min ±10%. Results are averaged over six specimens and expressed in kg/cm².
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