Soundness test of aggregate

The soundness test (IS:2386 Part V) measures the resistance of aggregate to disintegration by weathering, such as freezing and thawing, wetting and drying, and salt crystallisation. It uses repeated immersion in a saturated solution of sodium sulphate or magnesium sulphate.

Apparatus

Wire-mesh baskets, containers for the solution, IS sieves (as per the aggregate size), oven (105-110 degrees C), balance and a hydrometer. Solution: saturated sodium sulphate with specific gravity 1.151 to 1.174 (or magnesium sulphate, 1.295 to 1.308).

Procedure

1. Wash and oven-dry the aggregate, separate it into the standard fractions and weigh the specified amount of each (for coarse aggregate, for example, 300 g of 10-4.75 mm, 1000 g of 20-10 mm and 1500 g of 40-20 mm; for fine aggregate, 100 g of each fraction).
2. Immerse the sample in the solution for 16 to 18 hours at 27 +/- 1 degrees C, so that the solution covers it by at least 15 mm.
3. Remove it, drain for 15 minutes, and dry it in the oven at 105-110 degrees C to constant weight (a drying period of about 4 to 8 hours); cool to room temperature.
4. This forms one cycle; repeat the cycle five times.
5. After the last cycle, wash the sample free of salt (checked with the barium chloride test), dry it, and sieve each fraction on the sieve on which it was originally retained.
6. Weigh the retained material and find the loss.

$$\text{Soundness loss}\ (\%) = \frac{W_1 - W_2}{W_1}\times 100$$

where $W_1$ = initial weight and $W_2$ = final retained weight. The weighted average loss of all fractions is reported.

Significance

• It shows the durability of aggregate under climatic changes; it is useful in places with freezing weather (the hills and high-altitude areas of Nepal).
• Limits: loss not more than 12% with sodium sulphate and 18% with magnesium sulphate after five cycles (IS/IRC/NRS 2070).