Consider the following statements regarding aggregates : 1. Dry aggregates absorb water from the mixing water and thus affect the workability 2. Aggregates containing surface moisture contribute extra 3. The free moisture content in fine aggregate result in reduction of volume 4. The free moisture content in coarse aggregate result in bulking of volume
Try it first: pick an option, then read the explanation.
Correct answer: A. Statement 1 and 2 are correct
Detailed Explanation: Moisture States of Aggregate — Analysing the Statements
Aggregate moisture condition significantly affects the effective water content of the concrete mix. There are four standard moisture states: oven-dry, air-dry, saturated surface dry (SSD), and wet (surface moisture present). The correct moisture adjustment ensures the intended water-cement ratio is achieved in the field.
Why A (Statements 1 and 2 are correct) is correct: Statement 1 is correct — oven-dry or air-dry aggregates absorb water from the mix, reducing free water and workability; this must be compensated by adding extra water. Statement 2 is correct — wet aggregates with surface moisture contribute extra water to the mix, raising the w/c ratio and reducing strength if uncorrected. Statements 3 and 4 are WRONG — bulking (volume increase) occurs in fine aggregate (sand), NOT coarse aggregate. Coarse aggregate does not exhibit bulking. Statement 3 reverses this (says FA reduces volume) — incorrect. Statement 4 says CA bulks — also incorrect.Moisture States and Their Effects
| Moisture State | Effect on Mix Water | Correction Needed |
|---|---|---|
| Oven-dry | Absorbs most water from mix | Add extra water |
| Air-dry | Absorbs some water from mix | Add some extra water |
| SSD | No absorption or contribution | None (reference state) |
| Wet (surface moisture) | Contributes extra water | Reduce mix water |
Key Concepts for Students
- Bulking occurs only in fine aggregate (sand) — capillary tension in surface moisture films causes fine particles to push apart. Coarse aggregate particles are too heavy for this effect.
- All concrete mix designs reference aggregate in the SSD condition as the baseline; field corrections are made for deviations from SSD.
- Statements 3 and 4 are classic exam distractors — they swap the roles of fine and coarse aggregate.