Concrete technology — primary factor controlling strength of cement concrete Among the following, the property that primarily governs hardened concrete strength is:

Introduction / Context:
The water–cement (w/c) ratio is the cornerstone of concrete mix design. While aggregate grading, cement content, admixtures, and curing matter, it is the w/c ratio that most directly controls paste porosity and thus compressive strength and durability.

Given Data / Assumptions:

• Normal weight aggregates and standard curing are assumed.
• Strength is measured at a standard age (for example, 28 days).
• Other parameters are within typical ranges and do not represent pathological extremes.

Concept / Approach:
At a given cement type, decreasing the w/c ratio reduces capillary porosity in the hydrated cement paste, producing higher strength and lower permeability. Excess water beyond that needed for hydration leaves voids after evaporation, weakening concrete. Thus, w/c ratio is a first-order variable in strength prediction models.

Step-by-Step Solution:
Relate w/c ratio to porosity: lower w/c → denser paste → higher strength.Recognize cement quantity effect is secondary if w/c stays constant; more cement at the same w/c mainly affects paste volume, not intrinsic strength.Consider water quality: must meet standards, but normal potable water alone does not set strength.Therefore, water–cement ratio primarily governs strength.

Verification / Alternative check:
Empirical strength–w/c relations (for example, Abram-type relations) show monotonic strength increase as w/c decreases within practical ranges.

Why Other Options Are Wrong:
Water quality matters for durability and setting but not as the primary strength control.

Aggregate quantity affects workability and economy; cement quantity without w/c control does not guarantee strength.

Curing temperature affects rate of strength gain but w/c dictates ultimate potential at a given age.

Common Pitfalls:
Chasing high cement content instead of optimizing w/c; ignoring curing leading to unrealized strength; using high w/c to ease placing at the expense of strength.

Final Answer:
Water–cement ratio