Methods of Test for Aggregates for Concrete, Part VII: Alkali Aggregate Reactivity
1963 Edition

Aggregate samples must be prepared by crushing and sieving to select particles passing a 300-micron IS sieve but retained on a 150-micron sieve. Fine aggregates require minimal crushing, while coarse aggregates should be crushed to a graded product representing the intended use. If the same quarried material is utilized for both sizes, testing focuses on the fine fraction unless the coarse material differs significantly. This ensures representative and standardized samples for alkali reactivity assessment.

Mortar specimens are cast in moulds in two layers, compacted using a tamper for uniformity. After 24 hours, specimens are removed and their initial length measured at 27 ± 2°C using a length comparator, maintaining consistent orientation. They are then stored vertically in containers at 38 ± 2°C above water, avoiding direct contact with water or container sides. Water is refreshed and the container cleaned at each measurement. Subsequent length measurements occur at specified intervals up to several months, with specimens and apparatus acclimatized before measurement. Expansion is calculated as the percentage length increase relative to the initial length.

The tests require Ordinary Portland Cement (OPC) with an alkali content of at least 1.0% expressed as the sum of Na2O plus 0.658 times K2O. This specification ensures a robust evaluation of the aggregate's alkali reactivity potential. Both high-alkali and low-alkali cements as per relevant standards should be used in testing to observe the aggregate's behavior under different alkali conditions.

The chemical method involves crushing and sieving aggregate to obtain particles between 150 and 300 microns. These are then immersed in a 1 normal sodium hydroxide solution and maintained at 80°C for 24 hours. The reaction extent is evaluated by analyzing changes in solution chemistry, such as dissolved silica content, using photometric techniques. This screening helps predict the aggregate's potential to cause deleterious alkali reactions in concrete.

Test results plotted on a graph with parameters R and S indicate potential harmful reactivity if the data point lies to the right of a defined boundary line. Points above a particular line segment between specified R and S values suggest possible alkali reactivity even with low mortar expansion. In such cases, the chemical test results are accepted unless further testing, such as mixing with inert aggregates, demonstrates innocuous behavior. This approach ensures reliable identification of potentially reactive aggregates.