Which is not considered as a constituent of portland cement?

Options

A. `Ca_2SiO_4`
B. `Ca_3SiO_5`
C. `Ca_3Al_2O_6`
D. `CaSiO_3`

Answer

To determine which compound is not considered a constituent of Portland cement, we need to analyze the options provided:

1. **Aluminium Oxide (Al2O3)**: This is a common constituent of Portland cement, as it contributes to the cement's properties.

2. **Calcium Silicate Oxide (CaO)**: This is also a major component of Portland cement, specifically in the form of calcium silicates, which are crucial for the cement's strength.

3. **Ca3SiO4 (Tricalcium Silicate)**: This is one of the primary compounds found in Portland cement and is responsible for the strength development.

4. **Sodium Oxide (Na2O)**: While sodium oxide can be present in small amounts, it is not a primary constituent of Portland cement.

5. **Potassium Oxide (K2O)**: Similar to sodium oxide, potassium oxide is not a major component of Portland cement.

6. **Gypsum (CaSO4·2H2O)**: Gypsum is added to Portland cement to control the setting time and is considered a constituent.

From the analysis above, the compounds that are not considered primary constituents of Portland cement are Sodium Oxide and Potassium Oxide. However, among the options, Sodium Oxide is the most commonly recognized as not being a significant constituent.

### Final Answer:
**Sodium Oxide (Na2O)** is not considered a constituent of Portland cement.