This part of IS 2386 specifies the methods for determining the surface moisture in aggregates. It details both the drying method and the displacement (pycnometer) method, which are critical for adjusting batch water quantities during concrete production to maintain the design water-cement ratio.
Describes methods for determining the surface moisture content of aggregates, including the displacement method.
Quick Reference Values
oven drying temperature100 to 110 °C
pycnometer capacity1000 ml
sample weight displacement method1000 g (approximate)
weighing balance accuracy0.5 g or 0.1 percent of test load
Key Formulas
Surface Moisture (%) = (Weight of surface water / Weight of saturated surface-dry sample) × 100
Percentage of surface moisture (Displacement Method) = [ (V - W/G) / (W - V) ] × 100 — where V = weight of water displaced, W = weight of sample, G = specific gravity of SSD aggregate
Practical Notes
The specific gravity of the aggregate in a saturated surface-dry (SSD) condition must be accurately known (via IS 2386 Part 3) before using the displacement method.
Surface moisture fluctuates with weather and storage conditions; daily or per-shift testing is highly recommended at concrete batching plants.
Always deduct the total surface moisture contributed by both fine and coarse aggregates from the free mixing water added to the concrete batch.