IS 6925:1973 is the Indian Standard (BIS) for methods of test for concrete admixtures. This standard outlines the methods of test for evaluating concrete admixtures. It provides procedures to assess the effect of an admixture on the properties of fresh concrete (like workability, water content, and setting time) and hardened concrete (compressive strength and drying shrinkage) by comparing a test mix against a control mix.
Prescribed methods for testing the performance and compliance of chemical admixtures for concrete.
Overview
- Status
- Superseded — superseded by IS 6925:1996
- Usage level
- Rare
- Domain
- Materials Science — Admixtures and Chemical Products for Concrete
- Type
- Testing Method
Also on InfraLens for IS 6925
Practical Notes
! This standard is officially WITHDRAWN. The testing methods have been incorporated into IS 9103:1999 'Concrete Admixtures — Specification'. For all current purposes, refer to IS 9103.
! The effectiveness of an admixture is highly dependent on the type and brand of cement, aggregates, and ambient conditions. These tests are comparative and results are specific to the materials used.
! Test results, especially setting time and strength, are very sensitive to temperature. Maintaining the standard test temperature of 27 ± 2°C is critical.
Frequently referenced clauses
concreteadmixturescementwater reducing admixturesretarding admixturesaccelerating admixtures
International Equivalents
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Key Values5
Quick Reference Values
Minimum water reduction for water-reducing admixture5% (for same workability)
Minimum 7 & 28-day compressive strength compared to control mix90% of control
Maximum 1-year compressive strength compared to control mix125% of control
Initial setting time deviation from control mixNot more than 30 mins earlier or 90 mins later
Maximum drying shrinkage at 28 days compared to control mix135% of control
Key Formulas
Water Reduction (%) = [ (Water in control mix - Water in test mix) / Water in control mix ] * 100
Tables & Referenced Sections
Key Clauses
Clause 3 - General Requirements for Testing
Clause 4 - Tests on Fresh Concrete
Clause 4.2 - Workability and Water Content
Clause 4.3 - Setting Time
Clause 5 - Tests on Hardened Concrete
Clause 5.2 - Compressive Strength
Frequently Asked Questions4
Is IS 6925 still a valid standard?+
No, it has been withdrawn by BIS. It is superseded by IS 9103:1999, which includes both the specifications and test methods for admixtures.
How is the performance of a water-reducing admixture assessed according to this standard?+
By comparing a test mix with the admixture to a control mix. The test mix must achieve the same workability with at least 5% less water and have a 28-day compressive strength of at least 90% of the control mix (Clauses 4.2 & 5.2).
What equipment is used to test the setting time of concrete with admixtures?+
The Vicat apparatus is used to test the setting time on a cement paste made with a portion of the mixing water and admixture from the concrete mixes, as per Clause 4.3.
What is the main principle of testing in this standard?+
The main principle is comparison. An admixture's effect is measured by comparing the properties of a 'test mix' containing the admixture with a 'control mix' (or reference mix) made with identical materials but without the admixture.
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