The aggregate containing moisture in pores and having its surface dry is known as ……..
Correct Answer: D. saturated surface dry aggregate
📚 Detailed Explanation: Saturated Surface Dry (SSD) Condition
Aggregates exist in four standard moisture states, each defined by the distribution of water in and around the particles. The SSD condition is particularly important because it is the reference state used in concrete mix design calculations.
Why D (saturated surface dry) is correct: The SSD condition is precisely defined as: all internal pores are fully saturated with water, but the external surface of the particle is completely dry. In this state, the aggregate neither absorbs water from the mix (it's already saturated) nor contributes extra water (surface is dry). This makes SSD the ideal reference condition for calculating water absorption and for mix design water corrections.
Four Moisture States of Aggregate
| State | Pores | Surface | Effect on Mix |
|---|---|---|---|
| Oven-dry (OD) | Completely empty | Dry | Absorbs most mix water |
| Air-dry (AD) | Partially filled | Dry | Absorbs some mix water |
| Saturated Surface Dry (SSD) | Fully saturated | Dry | No absorption or contribution |
| Wet / Moist | Fully saturated | Wet film present | Contributes extra water |
Key Concepts for Students
- SSD is the reference state for all water absorption measurements: Water Absorption (%) = (SSD mass − OD mass) / OD mass × 100.
- On-site aggregate is rarely exactly at SSD; moisture correction is calculated as (actual moisture − SSD moisture) and applied to the batch water.
- Specific gravity of aggregate is most commonly reported in the SSD condition in Indian Standards (IS 2386 Part III).