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IS 6441:1998 Part 1 is the Indian Standard (BIS) for autoclaved cellular concrete blocks for masonry - part 1: specifications. This standard specifies the requirements for autoclaved aerated concrete (AAC) blocks for use in masonry. It covers materials, dimensions, tolerances, classification based on density, and key physical properties like compressive strength and drying shrinkage. It also outlines methods for sampling and testing to ensure conformity.
Specifies dimensions, quality, and physical requirements for autoclaved cellular concrete (AAC) blocks.
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Masonry and Bricks
Type
Specification
Amendments
This is a reaffirmation of the 1989 version. The standard itself is now withdrawn.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! This standard is WITHDRAWN. Users must refer to its replacement, IS 2185 (Part 3):2008, for current specifications.
! AAC blocks are lightweight and offer excellent thermal insulation but have lower compressive strength compared to dense concrete blocks, which must be accounted for in structural design.
! Due to their porosity, AAC blocks are highly absorbent. They should be protected from rain during storage and construction, and may require wetting before mortar application to prevent rapid water loss from the mortar.
EN 771-4:2011+A1:2015CEN (European Committee for Standardization), Europe
HighCurrent
Specification for masonry units - Part 4: Autoclaved aerated concrete masonry units
Specifies characteristics and performance requirements for AAC masonry units for structural and non-structural applications.
ASTM C1693 - 22ASTM International, USA
HighCurrent
Standard Specification for Autoclaved Aerated Concrete (AAC)
Covers autoclaved aerated concrete (AAC) intended for use as masonry units, both bearing and nonbearing.
AS/NZS 4455.1:2008Standards Australia / Standards New Zealand, Australia/New Zealand
MediumCurrent
Masonry units and segmental pavers and flags — Part 1: Masonry units
Broader standard for all masonry units but includes specific requirements and test methods for AAC units.
JIS A 5416:2018JSA (Japanese Standards Association), Japan
HighCurrent
Autoclaved lightweight aerated concrete panels and blocks
Specifies quality and performance for AAC blocks and panels used in walls, floors, and roofs.
Key Differences
≠IS 6441 uses a dual grading system (Grade 1/2 for quality and specific density ranges), whereas EN 771-4 uses a performance declaration system where manufacturers declare values for strength, density etc., and ASTM C1693 uses strength-based classes (AAC-2, AAC-4).
≠ASTM C1693 specifies a maximum drying shrinkage of 0.02%, which is significantly stricter than the IS 6441 limit of 0.05% for its highest quality (Grade 1) blocks.
≠EN 771-4 defines tolerance classes (e.g., T1 for thin-layer mortar) allowing for much tighter dimensional control (e.g., ±1.0 mm height) than the single set of general tolerances in IS 6441 (±3 mm height).
≠While IS 6441 provides thermal conductivity values as informative data linked to density, EN 771-4 requires the manufacturer to declare the thermal conductivity value as a key performance characteristic for regulatory CE marking.
Key Similarities
≈All standards are based on the same fundamental material definition: a cellular concrete made from cement/lime, fine siliceous aggregate, water, and an aerating agent, cured in a high-pressure steam autoclave.
≈The set of critical physical properties evaluated is consistent across the standards, focusing on compressive strength, dry density, dimensional stability (drying shrinkage), and dimensional accuracy.
≈The requirement for autoclaving is a mandatory and defining process step in all standards, recognized as essential for creating the stable crystalline structure of AAC.
≈All standards acknowledge the fundamental relationship where lower density results in improved thermal insulation but lower compressive strength, and this is reflected in their classification systems or property tables.
Parameter Comparison
Parameter
IS Value
International
Source
Compressive Strength (Avg. Min)
≥ 3.0 N/mm² (for Grade 1, Density 551-650 kg/m³)
≥ 4.0 MPa (580 psi) (for AAC-4 class)
ASTM C1693
Dry Density Range
551 to 650 kg/m³ (specific class)
Declared Gross Dry Density ± 50 kg/m³ (e.g., for a 600 kg/m³ declaration)
EN 771-4
Drying Shrinkage (Max)
≤ 0.05% (for Grade 1 blocks)
≤ 0.02%
ASTM C1693
Dimensional Tolerance (Height)
± 3 mm
± 1.0 mm (for Thin Layer Mortar Block, Class T1)
EN 771-4
Thermal Conductivity (Typical)
0.24 W/m·K (for density 551-650 kg/m³, informative)
Declared λ_10,dry value (e.g., ≤ 0.15 W/m·K for 600 kg/m³ density class)
EN 771-4
Moisture Content (at delivery)
No limit specified; test method is provided
Manufacturer to declare the value for equilibrium moisture content
ASTM C1693
Reaction to Fire
Considered 'non-combustible' (informative annex)
Class A1 (Non-combustible)
EN 771-4
⚠ Verify details from original standards before use
Key Values7
Quick Reference Values
Maximum drying shrinkage0.05 %
Minimum average compressive strength (Grade I)3.0 N/mm²
Minimum average compressive strength (Grade II)2.0 N/mm²
Tolerance on length (up to 600mm)± 3 mm
Tolerance on height/width (up to 300mm)± 3 mm
Density range for Grade I651-750 kg/m³
Density range for Grade II551-650 kg/m³
Tables & Referenced Sections
Key Tables
Table 1 - Dimensions of Blocks
Table 2 - Tolerances on Dimensions of Blocks
Table 3 - Physical Requirements for Autoclaved Cellular Concrete Blocks