Question

Portland cement does not contain (1) \(\mathrm{Ca}_{3} \mathrm{~A} \mathrm{l}_{2} \mathrm{O}_{6}\) (2) \(\mathrm{Ca}_{3} \mathrm{SiO}_{5}\) (3) \(\mathrm{Ca}_{2} \mathrm{SiO}_{4}\) (4) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)

Short answer

(4) \(\text{Ca}_3 (\text{PO}_4)_2\)

Step-by-step solution

Understand Portland cement composition

Portland cement is a common type of cement used in construction. It primarily contains compounds of calcium, silicon, aluminum, and iron. The main compounds in Portland cement are: 1. Tricalcium silicate 2. Dicalcium silicate 3. Tricalcium aluminate 4. Tetracalcium aluminoferrite.

Identify the compounds in the options

Review the chemical formulas of each option: (1) \(\text{Ca}_3 \text{Al}_2 \text{O}_6\) is tricalcium aluminate (2) \(\text{Ca}_3 \text{SiO}_5\) is tricalcium silicate (3) \(\text{Ca}_2 \text{SiO}_4\) is dicalcium silicate (4) \(\text{Ca}_3(\text{PO}_4)_2\) is tricalcium phosphate.

Compare options with Portland cement composition

Compare the provided compounds with those known to be in Portland cement: - \(\text{Ca}_3 \text{Al}_2 \text{O}_6\) (tricalcium aluminate) is present in Portland cement. - \(\text{Ca}_3 \text{SiO}_5\) (tricalcium silicate) is present in Portland cement. - \(\text{Ca}_2 \text{SiO}_4\) (dicalcium silicate) is present in Portland cement. - \(\text{Ca}_3(\text{PO}_4)_2\) (tricalcium phosphate) is not typically present in Portland cement.

Determine the correct answer

Based on the comparison, it is evident that \(\text{Ca}_3(\text{PO}_4)_2\) (tricalcium phosphate) is not present in Portland cement.

Key concepts

Tricalcium Silicate

In the world of Portland cement, tricalcium silicate, known chemically as \(\text{Ca}_3\text{SiO}_5\), plays a crucial role. This compound significantly affects the early strength development of cement. When Portland cement is mixed with water, tricalcium silicate undergoes a chemical reaction called hydration. This reaction produces calcium silicate hydrate and calcium hydroxide, which contribute to the hardening and strength of the cement.

Here are some key points to remember about tricalcium silicate:

• Reacts quickly with water.
• Responsible for the initial setting and early strength of cement.
• Produces a lot of heat during the hydration process, which can be beneficial in colder climates.

This makes tricalcium silicate an essential ingredient in achieving the desired performance of Portland cement in construction.

Dicalcium Silicate

Dicalcium silicate, or \(\text{Ca}_2\text{SiO}_4\), is another critical component of Portland cement. Unlike tricalcium silicate, dicalcium silicate reacts more slowly with water. It plays a significant role in the long-term strength development of cement. The slow hydration process of dicalcium silicate ensures that the concrete continues to gain strength over time.

Here are some important characteristics of dicalcium silicate:

• Reacts slowly with water.
• Contributes to the long-term strength of cement.
• Produces less heat during the hydration process.

This makes it ideal for constructions requiring prolonged strength development, such as large structures like dams and bridges.

Tricalcium Aluminate

Among the main compounds of Portland cement, tricalcium aluminate, or \( \text{Ca}_3\text{Al}_2\text{O}_6 \), is known for its fast-reacting properties with water. The reaction of tricalcium aluminate with water produces a significant amount of heat, which can be beneficial in speeding up the setting time of the cement. However, excessive tricalcium aluminate can lead to undesirable properties, such as increased susceptibility to sulfate attack.

Key points about tricalcium aluminate include:

• Reacts very quickly with water.
• Contributes to the rapid setting of cement.
• Produces a lot of heat during the hydration process.
• Can be adverse in environments where sulfate attack is a concern.

This component is balanced carefully in the composition of Portland cement to achieve optimal performance and durability.