Final answer:
The suitability of concrete mixtures with fixed aggregate ratios can vary because different construction scenarios require concrete with different properties. Adjusting the aggregate ratios is crucial for the workability, finish, and structural integrity of concrete in specific applications.
Step-by-step explanation:
The fixed ratios of fine aggregate to coarse aggregate in concrete mixtures can lead to issues because different construction scenarios require different properties in the concrete used. A fixed ratio does not take into account the need for adjustments based on specific project requirements. For example, if the mix is not sufficiently workable, it can be difficult to properly place and consolidate, resulting in issues such as poor compaction or the presence of air voids.
While not all options might be applicable, the correct answer to why it is not suitable for all concrete mixtures when the amount of fine aggregate and coarse aggregate is fixed is mostly related to: C) Affects workability. Adjusting the amounts of fine and coarse aggregates in concrete is essential to achieve the right workability, finish, and structural integrity for the intended application.