Cement composition and quality – which compound should be higher? Good quality Portland cement generally contains a higher percentage of which compound for early strength development?

Introduction / Context:
Ordinary Portland cement (OPC) performance depends on the relative proportions of its clinker compounds. Among these, tricalcium silicate (C3S) and dicalcium silicate (C2S) dominate strength development, while tricalcium aluminate (C3A) strongly affects setting and sulfate resistance. Identifying which compound correlates with higher early strength and, thus, is typically favored in many general-purpose cements is essential for civil engineering practice.

Given Data / Assumptions:

• We consider general-purpose OPC used in buildings and infrastructure.
• “Good quality” here refers to cements targeting robust early strength and workable setting behavior under standard conditions.
• Gypsum regulation of C3A is assumed as normal for OPC.

Concept / Approach:

C3S hydrates relatively quickly and is chiefly responsible for early strength (from 1 to ~28 days). C2S hydrates more slowly and contributes to later strength. Excess C3A can harm sulfate resistance and cause flash setting without gypsum. C4AF has modest contributions to strength and color. Therefore, higher C3S is characteristic of many good early-strength cements used in ordinary construction.

Step-by-Step Solution:

Verification / Alternative check:

OPC formulations with higher C3S content routinely show faster early strength gain, which aligns with standard mix design expectations and field performance in formwork removal schedules and early loadings.

Why Other Options Are Wrong:

C2S: Beneficial for later strength, but not the target for higher early strength.

C3A: Too high a percentage impairs sulfate resistance and risks flash set; gypsum is required to moderate it.

C4AF: Minor effect on strength; not a primary determinant of “good quality.”

All of the above: Incorrect because their effects are not equally desirable; C3S is the key for early strength.

Common Pitfalls:

Equating early strength exclusively with C3A due to fast reaction; forgetting gypsum’s regulatory role; ignoring long-term vs early strength contributions.

Final Answer:

Tricalcium silicate (C3S)