Water Absorption (Aggregate & Brick)

Water absorption is the increase in weight of a dry porous material after soaking, expressed as a percentage of its dry weight — a direct measure of accessible porosity and hence durability and mix-water behaviour. For coarse/fine aggregate it is tested per IS 2386 Part 3; for bricks by 24-hour immersion per IS 3495 Part 2.

High aggregate absorption means more internal voids — weaker, frost/AAR-prone stone, and aggregate that draws mix water (free water = added water − absorption), so absorption must be allowed for when computing the effective water-cement ratio. IS limits aggregate absorption broadly to ≤2% (often ≤1% for high-grade concrete). For bricks, IS 1077 limits 24-h absorption (≈≤20% for common burnt-clay bricks, lower for higher classes); excessively absorptive bricks rob mortar of water, weakening the bond, and signal under-burning.