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IS 10049:1981 is the Indian Standard (BIS) for the manufacture of lime-based blocks. This standard outlines the procedures for manufacturing lime-based building blocks, suitable for masonry. It specifies the requirements for raw materials like lime and aggregates, details the mixing, moulding, and curing processes, and sets the minimum physical properties such as compressive strength, density, and drying shrinkage for the finished blocks.
Code of practice for the manufacture of lime-based blocks
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Building Limes and Gypsum Products
! Curing is a critical step; unlike cement, lime gains strength slowly through carbonation, requiring a controlled environment.
! The quality of lime (as per IS 712) and aggregate has a direct and significant impact on the final block's performance.
! These blocks are generally suitable for non-load-bearing or partition walls due to their moderate strength characteristics compared to concrete blocks.
EN 771-2:2011+A1:2015CEN (European Committee for Standardization), Europe
MediumCurrent
Specification for masonry units - Part 2: Calcium silicate masonry units
Covers finished masonry units made from lime and siliceous aggregates, but specifically for autoclaved products.
ASTM C73 - 19ASTM International, USA
MediumCurrent
Standard Specification for Calcium Silicate Brick (Sand-Lime Brick)
Specifies requirements for bricks made from sand and lime, but hardened by high-pressure steam (autoclaving).
BS 187:1978BSI (British Standards Institution), UK
HighWithdrawn
Specification for calcium silicate (sandlime and flintlime) bricks
Was the direct British predecessor for calcium silicate units before harmonization with European standards.
Key Differences
≠Curing Method: IS 10049 allows for moist air curing or low-pressure steam curing, whereas modern equivalents like EN 771-2 and ASTM C73 are for autoclaved calcium silicate units, which are cured under high-pressure steam. This results in significantly different chemical bonding and physical properties.
≠Standard Type: IS 10049 is a 'Code of Practice for Manufacture', detailing the process of making the blocks. EN 771-2 and ASTM C73 are 'Product Specifications', focusing on the performance requirements and testing of the final product, leaving manufacturing methods to the producer.
≠Performance Levels: Due to the non-autoclaved curing, the typical compressive strength values specified and achieved under IS 10049 are substantially lower (e.g., 3.5 - 10 MPa) than for standard autoclaved calcium silicate bricks (often 15 - 30+ MPa).
≠Material Flexibility: IS 10049 is more general, allowing for lime to be mixed with 'suitable fine aggregate' which can include sand or pozzolanic materials like fly ash. International standards are typically more specific to a 'sand-lime' (calcium silicate) composition.
Key Similarities
≈Core Raw Materials: All standards are based on the same fundamental constituents: a calcareous binder (lime) and a siliceous aggregate (sand, fly ash, etc.).
≈End Use Application: The blocks produced under all these standards are intended for use as masonry units in the construction of walls and partitions.
≈Fundamental Properties: All standards recognize and specify limits for key performance indicators such as compressive strength, water absorption, and dimensional stability (drying shrinkage).
≈Manufacturing Concept: The basic manufacturing sequence of mixing raw materials, moulding them into a block shape, and then curing/hardening to gain strength is common to all standards.
Parameter Comparison
Parameter
IS Value
International
Source
Compressive Strength (Average)
Class L35: 3.5 N/mm² (MPa) min. Other classes exist.
Grade MW: 17.2 MPa min. Grade SW: 31.0 MPa min.
ASTM C73
Water Absorption (by weight)
Max 20%
Grade MW: Max 15%; Grade SW: Max 10%
ASTM C73
Drying Shrinkage
Max 0.15%
Typically ≤ 0.04% for autoclaved units (not always a mandatory parameter in ASTM, but is in EN 771-2).
EN 771-2
Density Classification
Not explicitly classified by density; density is a result of the mix.
Specifies gross dry density classes, e.g., Class D 1.8 is 1610 to 1800 kg/m³.
EN 771-2
Minimum Lime Content
Binder not less than 12.5% of the weight of dry aggregate.
Not specified; performance-based standard focuses on final product properties, not mix design.
ASTM C73 / EN 771-2
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Minimum average compressive strength (28 days)3.5 N/mm²
Minimum compressive strength of individual unit (28 days)2.8 N/mm²
Maximum block density1800 kg/m³
Maximum drying shrinkage0.15 %
Maximum water absorption (24-hour immersion)20 % by mass
Tables & Referenced Sections
Key Tables
Table 1 - Physical Requirements of Lime-Based Blocks