Admixtures — identify the incorrect blanket statement about their effects Which of the following statements about concrete admixtures is NOT generally true?

Introduction / Context:Admixtures modify fresh and hardened properties of concrete, helping tailor workability, setting, strength, durability, and shrinkage. However, they have limits and must be selected judiciously for exposure conditions.

Given Data / Assumptions:

• Common admixture classes: accelerators, water reducers, superplasticizers, air-entrainers, pozzolanic/mineral additions.
• Normal structural concretes; not specialty polymer concretes or linings.
• Exposure may include moisture and mild chemicals but not severe acids without protective systems.

Concept / Approach:

Admixtures can accelerate hydration, reduce water demand, entrain air, or reduce permeability, thereby improving watertightness. Some help achieve higher strengths via lower w/c. However, no conventional admixture renders concrete “acid proof”; strong acids attack hydrated cement paste. Chemical resistance requires low permeability plus protective coatings or special binders.

Step-by-Step Solution:

Verification / Alternative check:

Durability design guides caution that acids degrade cementitious matrices; protective linings are necessary for aggressive acidic environments.

Why Other Options Are Wrong:

• (a), (b), (d) are achievable with appropriate admixture selection and mix design.
• “None of these” is wrong because (c) is demonstrably false.

Common Pitfalls:

• Over-relying on admixtures while neglecting cover, curing, and joints.

Final Answer:

Admixtures make concrete fully acid proof under aggressive chemical exposure.