Air-entrained (entrained-air) concrete used in wall and roof linings provides which types of insulation benefits in buildings?

Introduction / Context:
Air-entrained concrete contains uniformly distributed microscopic air voids. While originally introduced to enhance freeze–thaw durability and workability, such voids and lower density can also contribute to thermal and acoustic performance in lightweight linings and blocks.

Given Data / Assumptions:

• Application: lining walls and roofs (non-primary structural layers).
• Air content increased via admixtures or foaming agents.
• Focus on insulation benefits rather than structural capacity.

Concept / Approach:
Entrainment creates countless closed, microscopic voids that reduce thermal conductivity compared with dense concrete, improving heat insulation. The porous internal structure disrupts sound transmission paths to some degree, aiding sound insulation (though specialized acoustic assemblies perform better). Hence, for lining purposes, both heat and sound insulation benefits are recognized.

Step-by-Step Solution:
Relate micro-voids to lower thermal conductivity → heat insulation.Relate discontinuities/voids to scattering and damping of sound waves → sound insulation.Therefore, select “both (a) and (b).”

Verification / Alternative check:
Thermal conductivity tables show lightweight/air-entrained concretes having lower k-values than normal dense concrete; acoustic tests show improved sound reduction indices in suitable assemblies.

Why Other Options Are Wrong:

• Picking only heat or only sound ignores the dual benefit.
• “Neither” contradicts known material behavior.

Common Pitfalls:

• Confusing air-entrained (micro voids) with aerated/foamed cellular concrete; both lower density, but production methods differ.

Final Answer:
both (a) and (b)