Water required for hydration only — compute for 500 kg of cement Assume chemically bound (hydration) water demand is 0.23 times the weight of cement. For 500 kg of cement, how much water is required for hydration only (excluding water to fill gel pores)?

Introduction / Context:
Cement hydration consumes a portion of the mixing water chemically. A widely cited value for the water required for the chemical reaction (not including water held in gel pores) is about 0.23 times the weight of cement. Understanding this helps explain why low water–cement ratios are possible without starving hydration if proper curing is provided.

Given Data / Assumptions:

• Hydration water demand = 0.23 * weight of cement.
• Cement mass = 500 kg.
• Excludes additional water to fill gel pores (which would raise total to roughly 0.36–0.38 * cement).

Concept / Approach:
The mass of water needed for chemical combination is computed directly by multiplying the cement mass by the hydration fraction (0.23). This is a straightforward proportion calculation used in concrete technology to discuss water partitioning between chemical binding and capillary/gel storage.

Step-by-Step Solution:

Verification / Alternative check:
If the question asked for water for complete hydration plus gel-pore water, the estimate would be about 0.36–0.38 * 500 = 180–190 kg, which is distinct from this hydration-only value.

Why Other Options Are Wrong:

• 105, 125, 135, 150 kg: do not equal 0.23 * 500; these are off by ≥10 kg or represent different assumptions.

Common Pitfalls:
Confusing hydration water (≈0.23) with total internal water at complete hydration (≈0.36–0.38); using these values interchangeably in mix design.

Final Answer:
115 kg