The Water Absorption Test determines the percentage of water absorbed by coarse aggregates, providing an indication of pore structure, density, and suitability for high-quality concrete and asphalt works.
To determine the Water Absorption (%) of a coarse aggregate sample using SSD and Oven-dry mass values.
Repeat the procedure on another sample and take the average.
Water Absorption (%) = (A − B) / B × 100 Where: A = SSD Mass of aggregate B = Oven‑Dry Mass of aggregate
If:
Water Absorption (%) = (2045 − 2000) / 2000 × 100
= 45 / 2000 × 100
= 2.25%| Aggregate Type | Max Water Absorption (%) |
|---|---|
| Coarse Aggregate (Normal concrete) | ≤ 2% |
| Fine Aggregate (Sand) | ≤ 3% |
For high-performance or severe exposure concrete, stricter limits may apply.
The Water Absorption Test is covered under IS 2386 (Part 3) – Specific Gravity, Density, Voids, Absorption and Bulking. This test provides insight into the internal pore structure of aggregates, which directly affects concrete durability, water demand, and long‑term performance. Aggregates with excessive pores tend to absorb more water, which may lead to reduced compressive strength and increased shrinkage. By determining absorption, engineers calibrate mix water content accurately to achieve the target workability and strength parameters.
The SSD (Saturated Surface Dry) condition is critical because it represents the state where internal pores are full of water while the exterior surface is dry. This allows mix water calculations to remain accurate. If aggregates are not brought to SSD before batching, they either absorb mix water (leading to lower workability) or contribute excess water (making the mix too wet). The SSD condition ensures correct water‑cement ratio, the single most important factor governing concrete strength.
Water absorption is directly linked to aggregate quality. Aggregates with low absorption are denser and more durable, making them suitable for high‑strength and long‑life structures. On the other hand, aggregates with high absorption may lead to increased permeability, reduced freeze‑thaw resistance, and potential durability issues. Additionally, when absorption is high, the concrete mix becomes unpredictable without proper adjustments, affecting slump, cohesiveness, and compaction.
In site conditions, aggregates stored in open yards exhibit varying levels of moisture. Regular absorption testing helps determine free moisture correction during batching to maintain consistent mix quality. For automated batching plants, entering accurate absorption values ensures the batching software adjusts water content correctly. This prevents issues such as plastic shrinkage, excessive bleeding, or segregation in fresh concrete.
| IS Code | Description |
|---|---|
| IS 2386 (Part 3) | Methods of Test for Aggregates – Specific Gravity, Density, Voids & Water Absorption |
| IS 383 | Specification for Coarse and Fine Aggregates for Concrete |
| IS 456 | General concrete requirements & material quality guidance |
For most concrete works, water absorption should be ≤ 2%. Lower values indicate denser and more durable aggregates.
SSD ensures that aggregate pores are filled without free surface water. This prevents errors in mix design water calculations.
Yes. Aggregates with high absorption draw water from the concrete mix, reducing effective W/C ratio and causing poor workability and potential strength loss.
Typically during material approval and periodically during construction to ensure consistent aggregate quality.
Yes. Dense rocks like basalt and granite have low absorption. Porous rocks like sandstone and lightweight aggregates have higher absorption.
