How long does the standard mortar bar test take?

Observations are typically recorded over a long period, with readings taken at 1, 2, 3, 6, 9, and 12 months.

At what temperature are the mortar bars stored during the test?

They are stored in sealed containers over water at a controlled temperature of 38°C ± 2°C.

What expansion limits indicate a reactive aggregate in the mortar bar test?

Expansion exceeding 0.05% at 3 months or 0.1% at 6 months generally indicates potentially deleterious reactivity.

What is measured in the chemical method?

The test measures the reduction in alkalinity (Rc) and the amount of dissolved silica (Sc) after reacting the aggregate with a sodium hydroxide solution.

IS 2386 Part 7

: 2021

Methods of Test for Aggregates for Concrete - Part 7: Alkali-Aggregate Reactivity

CurrentSpecializedTesting MethodMaterials Science · Aggregates and Sand

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This standard details the testing methods to evaluate the potential alkali-aggregate reactivity (AAR) of aggregates intended for use in concrete. It outlines both the chemical method for rapid screening and the long-term mortar bar method for assessing deleterious expansive potential.

Covers methods for determining potential alkali-aggregate reactivity of aggregates, including the mortar bar method and chemical method.

Quick Reference Values

mortar bar test temperature38 ± 2 °C

chemical method test temperature80 ± 1 °C

potentially reactive expansion limit> 0.1% at 6 months

hazardous expansion early indicator> 0.05% at 3 months

comparator gauge length250 mm

Key Formulas

Expansion (%) = (Difference in length / Effective gauge length) × 100

Rc = (V1 - V2) × N × 10 (Reduction in alkalinity)

Practical Notes

The chemical method is a rapid screening tool; aggregates failing this test should not be outright rejected without confirmation from the more reliable long-term mortar bar test.

Alkali-aggregate reaction is highly dependent on moisture; therefore, testing is critical for aggregates used in dams, foundations, and marine structures.

If an aggregate is found to be reactive, risks can often be mitigated by using low-alkali cement or incorporating mineral admixtures like fly ash or GGBS.