Cement Testing MCQ with answer and solution

Concept

Blaine air permeability cement fineness

Formula

S = (K / ρ) × (√(e³) / (1 - e)) × (√(t) / √(η))

Step-by-step solution

1. The Blaine Air Permeability test determines the specific surface area (fineness) of cement. 2. A known mass of cement is compacted into a test cell to form a permeable bed with specified porosity. 3. Air is drawn through the bed using a manometer, and the time taken for liquid to drop between marked levels is recorded. 4. Finer cement presents greater specific surface area and greater resistance to airflow, prolonging flow time. Answer: B

Explanation

The Blaine air permeability apparatus determines the specific surface area (fineness) of cement by measuring the time required for a fixed volume of air to pass through a compacted cement bed of standard porosity. Finer cement particles produce smaller capillary voids and greater resistance to air permeation, which elongates the flow time recorded in the manometer.

Why the other options are wrong

A) Laser diffraction measures particle size distribution, whereas Blaine apparatus determines specific surface area from flow resistance. C) Cement strength is evaluated using compressive testing machines on mortar cubes, not permeability. D) Sedimentation in water is used in the Wagner turbidimeter method, not the Blaine air permeability apparatus.

Shortcut

Blaine Air Permeability = Fineness from air flow resistance through compacted cement bed (cm2/g).

Common mistake

Confusing Blaine air permeability with compressive strength or particle sizing by laser diffraction.