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IS 15648:2006 is the Indian Standard (BIS) for pulverized fuel ash for lime-pozzolana mixture applications.. This standard specifies the requirements for pulverized fuel ash (fly ash) for use as a pozzolanic material in lime-pozzolana mixtures. It covers the essential chemical and physical properties, such as fineness, lime reactivity, and chemical composition, to ensure the quality and performance of the ash for producing materials like mortars, plasters, and masonry blocks.
Pulverized fuel ash for lime-pozzolana mixture applications.
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Building Limes and Gypsum Products
! This standard is for fly ash used with lime, which is different from IS 3812 that covers fly ash for use with Portland cement. The key differentiator is the 'lime reactivity' test specified herein.
! Lime-pozzolana binders have slower strength gain compared to ordinary Portland cement. This characteristic must be considered in project timelines, particularly for formwork stripping and load application.
! Controlling the 'Loss on Ignition' (LOI) is critical, as high unburnt carbon content can adversely affect workability, increase water demand, and lead to inconsistent color in the final product.
Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
Specifies chemical and physical requirements for fly ash, but for use in concrete rather than lime mixtures.
EN 450-1:2012European Committee for Standardization (CEN), Europe
HighCurrent
Fly ash for concrete - Part 1: Definition, specifications and conformity criteria
Defines and specifies fly ash for use in concrete, sharing many core chemical and physical test parameters.
AS/NZS 3582.1:2016Standards Australia / Standards New Zealand, Australia/New Zealand
MediumCurrent
Supplementary cementitious materials, Part 1: Fly ash
Covers fly ash for use as a cementitious material in concrete, sharing fundamental pozzolanic characterization.
BS 3892-1:1997British Standards Institution (BSI), UK
MediumWithdrawn
Pulverized-fuel ash. Specification for pulverized-fuel ash for use with Portland cement
Former UK standard for fly ash use in cement applications, influential on the Indian standard's development.
Key Differences
≠The primary scope of IS 15648 is specifically for 'lime-pozzolana mixture applications', whereas major international standards like ASTM C618 and EN 450-1 are for the use of fly ash in 'concrete' (i.e., with Portland cement).
≠IS 15648 specifies a mandatory 'Lime Reactivity' test, requiring a minimum compressive strength of 4.0 N/mm² on a lime-fly ash mortar. International standards use a 'Strength Activity Index' with Portland cement, which measures performance in a different chemical system.
≠IS 15648 provides a single grade for fly ash. In contrast, ASTM C618 classifies ash into Class F and Class C based on chemical composition (CaO content), and EN 450-1 has categories based on fineness and loss on ignition.
≠The limit for Loss on Ignition (LOI) in IS 15648 is a strict maximum of 5.0%, while ASTM C618 allows up to 6.0% (though purchasers often specify lower) and has provisions for higher LOI if performance is proven.
Key Similarities
≈All standards mandate a minimum content for the sum of key oxides (SiO₂ + Al₂O₃ + Fe₂O₃) to be around 70%, ensuring the material has sufficient pozzolanic compounds.
≈Fineness is a critical parameter in all standards, commonly measured by the percentage of material retained on a 45-micron sieve, as it directly influences the rate of pozzolanic reaction.
≈All standards include a soundness test (e.g., Le Chatelier expansion or autoclave expansion) to ensure the hardened material is dimensionally stable and will not undergo deleterious expansion over time.
≈There is a common emphasis on limiting deleterious substances that can affect long-term durability, such as Sulphur Trioxide (SO₃) and Magnesia (MgO), with comparable maximum limits.
Parameter Comparison
Parameter
IS Value
International
Source
Sum of Oxides (SiO₂ + Al₂O₃ + Fe₂O₃), % min
70.0
70.0 (for Class F)
ASTM C618
Sulphur Trioxide (SO₃), % max
3.0
3.0
EN 450-1
Loss on Ignition (LOI), % max
5.0
6.0
ASTM C618
Fineness (retained on 45 µm sieve), % max
34
34 (for Class F and C)
ASTM C618
Reactivity Test
Lime Reactivity: Min 4.0 N/mm² compressive strength
Strength Activity Index with Cement: Min 75% of control at 28 days
ASTM C618
Soundness by Le Chatelier, mm max
10
10
EN 450-1
Magnesia (MgO), % max
5.0
5.0
ASTM C618
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Lime reactivity at 28 days, min4.0 N/mm²
Fineness by Blain's air permeability method, min250 m²/kg