What is the main difference between normal-weight and lightweight concrete?

• A. Weight: lightweight uses lighter aggregates to reduce density; properties may differ in strength and insulation.
• B. Lightweight concrete is always stronger than normal-weight.
• C. Normal-weight concrete uses lighter aggregates.
• D. Weight only affects setting time, not strength.

Answer: (A)

The main idea here is density driven by the aggregate. Lightweight concrete uses lightweight aggregates (like expanded clay, shale, pumice, or similar materials) to lower the overall unit weight of the mix. That reduced density also changes other properties, so its strength and thermal insulation can be different from normal-weight concrete.

Why this answer fits best: it directly states that the key difference is weight, caused by lighter aggregates, and notes that strength and insulation can differ as a result. It captures the tradeoffs you deal with when choosing lightweight versus normal-weight concrete.

Why the other statements aren’t correct: lightweight concrete is not inherently stronger than normal-weight concrete; strength depends on mix design and materials, and lightweight mixes are not guaranteed to be stronger. Normal-weight concrete does not use lighter aggregates. And weight affects more than just setting time—it also influences strength, stiffness, and other performance characteristics.