Bricks and Clays – Effect of Constituents on Drying and Burning In the composition of good brick earth, excess of which constituent leads to undue shrinkage and warping of raw bricks during drying and burning?

Difficulty: Easy

Correct Answer: Alumina (clay fraction) in excess

Explanation:


Introduction:
Understanding how each constituent of brick earth affects behavior during drying and firing is crucial for quality bricks. This question focuses on warping and shrinkage defects that appear when the clay fraction is not balanced properly.


Given Data / Assumptions:

  • Typical constituents: alumina (clay), silica (sand), lime, iron oxide, magnesia.
  • Observation: shrinkage and warping during drying and burning are being linked to a specific excess constituent.
  • We assume standard kiln practices and controlled firing curves.


Concept / Approach:

Alumina imparts plasticity and workability, but too much plastic clay causes large drying shrinkage. Without sufficient sand (silica) as a non plastic temper, bricks deform and warp as water leaves and during sintering.


Step-by-Step Solution:

1) Identify the role of each constituent in green strength and firing behavior.2) Recognize that alumina rich mixtures show high plasticity and high shrinkage.3) Balance with silica to control shrinkage; otherwise warpage occurs.4) Thus, excess alumina is the cause of shrinkage and warping noted in the question.


Verification / Alternative check:

Standard brickmaking texts note that silica reduces shrinkage and helps maintain shape, while alumina increases plasticity and shrinkage.


Why Other Options Are Wrong:

Lime excess risks cracking or melting but is not the primary shrinkage driver. Iron oxide influences color and vitrification. Magnesia can improve color and reduce warpage at small amounts. Sand in excess reduces shrinkage rather than causing it.


Common Pitfalls:

Confusing the role of lime or iron oxide with the plasticity controlled by alumina and silica balance.


Final Answer:

Alumina (clay fraction) in excess

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