Concrete materials — definitions of free water and total water in mix design In concrete technology, select the correct statement(s) regarding the terms “free water” and “total water” used in batching and water–cement ratio calculations.

Introduction / Context:Understanding water accounting in concrete is essential to control the water–cement ratio, which governs strength, durability, shrinkage, and permeability. Terms like free water and total water appear in mix design, site adjustments, and moisture corrections for aggregates.

Given Data / Assumptions:

• Aggregates may be oven-dry, air-dry, saturated surface-dry (SSD), or wet with surface moisture.
• Water added at the mixer and surface moisture on aggregates both contribute to effective mixing water.
• Aggregates absorb some water internally up to their absorption capacity.

Concept / Approach:

Free water is the water that remains available in the paste for workability and hydration after deducting aggregate absorption. Practically, it is the water added at mixing plus any surface moisture contributed by wet aggregates. Total water includes free water and the portion of water that is absorbed into the aggregates during mixing to reach SSD condition.

Step-by-Step Solution:

Verification / Alternative check:

Site moisture correction sheets compute batch water by starting from target free water, then adjusting for aggregate moisture (deduct if dry, reduce if wet) to keep the intended water–cement ratio constant.

Why Other Options Are Wrong:

• (c) contradicts standard definitions.
• (e) ignores that total water necessarily includes absorbed water.

Common Pitfalls:

• Confusing SSD condition with free water. SSD has zero surface moisture but contains absorbed water.
• Not compensating batch water for wet or dry aggregates, causing unintended strength loss or poor workability.

Final Answer:

Both (a) and (b) are correct.