Question

Which of the following is not a property of ferrocement?

• A. Impervious nature
• B. Capacity to resist shock
• C. No need to formwork
• D. Strength per unit mass is low (It's high)

Hint:

\textbf{Ferrocement:} Thin-shell concrete with multiple layers of wire mesh reinforcement and rich cement mortar.
\textbf{Key Properties:}
\textbf{High strength-to-weight ratio} (i.e., strength per unit mass is high).
Good impact resistance and toughness.
Relatively impervious to water.
Can be molded into complex shapes.
Often requires simpler or less formwork than conventional concrete.
The statement "Strength per unit mass is low" is incorrect; it's actually high.

Answer 1

The Correct Option is D

Ferrocement (or Ferro-cement) is a type of thin-shell reinforced concrete construction. It consists of a rich cement mortar mix applied over multiple layers of closely spaced wire mesh reinforcement (e.g., chicken mesh, welded wire mesh). This creates a thin, strong, and durable composite material. Properties of Ferrocement:
High strength-to-weight ratio: Ferrocement is relatively lightweight but has good tensile and flexural strength due to the high degree of reinforcement dispersion. This means its strength per unit mass is high, not low. (This contradicts option d).
Impervious nature (Good water tightness / Low permeability - Option a): The dense cement mortar matrix and closely spaced mesh reinforcement contribute to making ferrocement relatively impervious to water, especially if properly cured and finished. This makes it suitable for water-retaining structures like tanks, boats, and roofs. So, (a) is generally a property.
Capacity to resist shock and impact (Good impact resistance - Option b): The multiple layers of mesh reinforcement help to distribute impact loads and provide good toughness and resistance to cracking and shattering from shock or impact. So, (b) is a property.
Ease of forming complex shapes: Ferrocement can be easily molded into curved or complex shapes because the mesh reinforcement can be readily bent and shaped before mortar application.
Formwork requirements (Option c "No need to formwork"): While ferrocement can be applied over a shaped armature of mesh, often some form of temporary backing or simple mold (formwork) is used, especially for larger or more complex elements, to support the fresh mortar until it sets. For very thin or self-supporting mesh structures, extensive formwork might be reduced or eliminated compared to conventional concrete, but saying "no need to formwork" for all cases is an overstatement. However, it often requires \textit{less complex or less robust formwork} than traditional reinforced concrete for similar shell-like structures. If "no need" is interpreted as "significantly less need or simpler formwork," it has some validity.
Good crack control: The closely spaced reinforcement helps to distribute cracks, keeping them very fine.
Durability and corrosion resistance (if well made). The question asks which is NOT a property of ferrocement. Let's re-evaluate the options:
(a) Impervious nature: Generally true, it's relatively watertight.
(b) Capacity to resist shock: Generally true, it has good impact resistance.
(c) No need to formwork: This is often cited as an advantage, meaning simpler or minimal formwork compared to conventional concrete. While not always strictly "no" formwork, it's a characteristic feature of its construction method for many shapes.
(d) Strength per unit mass is low: This is incorrect. Ferrocement is known for having a high strength-to-weight ratio. It is strong for its relatively low weight. So, if "strength per unit mass is low" is stated as a property, that statement is false, making it the answer for "NOT a property". Therefore, the statement that is NOT a property of ferrocement is that its strength per unit mass is low. In fact, it is high. \[ \boxed{\text{Strength per unit mass is low}} \]