The cement whose strength is a little lower than the ordinary cement during the first three months but attains afterwards the same strength is known as:
🔬 Understanding Rate of Strength Gain
Different types of cement are engineered to gain strength at different rates. This is achieved by altering the proportions of the main Bogue's compounds. The key to this question is understanding which cement type is specifically designed for a slow rate of initial strength gain, which is directly linked to a low rate of heat generation (heat of hydration). This slow start is then compensated by a steady, long-term strength development that eventually catches up to ordinary cement.
đź“ť Detailed Analysis of Cement Types
(a) Low-heat Portland cement
This is the correct answer. Low-heat cement is manufactured by reducing the percentage of the fast-reacting, high-heat compounds—Tricalcium Silicate (C3S) and Tricalcium Aluminate (C3A)—and increasing the percentage of the slow-reacting Dicalcium Silicate (C2S). This composition results in a much slower rate of hydration and heat evolution. Consequently, its strength development is slow at the beginning (e.g., at 7 and 28 days), but because of the high C2S content, it continues to gain strength steadily and eventually reaches or exceeds the strength of Ordinary Portland Cement at later ages (e.g., 90 days and beyond).
(b) Rapid hardening Portland cement
This is incorrect. This cement is the exact opposite. It is designed with a high percentage of C3S to gain strength very quickly, far exceeding OPC at early ages.
(c) Portland blast furnace slag cement & (d) Portland pozzolana cement
These are plausible but less precise answers. Both of these blended cements also exhibit lower early strength and higher ultimate strength compared to OPC. This is due to the slower pozzolanic or slag reactions. However, "Low-heat cement" is the type that is specifically defined by the property described in the question—a slow initial hardening rate (due to altered clinker chemistry) that later catches up to OPC.
đź“Š Strength Gain Comparison
| Cement Type | Early Strength (e.g., 7 days) | Later Strength (e.g., 90 days) | Primary Reason |
|---|---|---|---|
| Low-Heat Cement | Lower than OPC | Equal to or Higher than OPC | High C2S, Low C3S content |
| Rapid Hardening Cement | Higher than OPC | Similar to OPC | High C3S content |
| Ordinary Portland Cement (OPC) | Standard (Baseline) | Standard (Baseline) | Balanced composition |
đź’ˇ Study Tips
- Low Heat = Slow Start: The name itself gives a clue. Low heat means a slow chemical reaction, which in turn means a slow start to strength gain.
- C2S is the Key: Remember that Dicalcium Silicate (C2S) is the "marathon runner." Cements with high C2S content (like Low-Heat Cement) will have low early strength but excellent long-term strength.
- Catch-up Effect: The defining feature described is the "catch-up" in strength. This is characteristic of cements that rely on C2S for their ultimate strength.