Cement choice for marine exposure — structures in sea water For the construction of structures exposed to sea water, which cement type is generally preferred among the following options?

Introduction / Context:
Sea water contains sulphates, chlorides, and magnesium salts that can attack concrete and reinforcement. Selecting an appropriate cement helps limit permeability and chemical reactivity and reduces thermal cracking in mass sections such as sea walls and piles.

Given Data / Assumptions:

• General marine exposure with adequate cover, low w/c ratio, and good curing.
• Within the listed choices only; sulphate-resisting Portland cement is not included.
• Durability prioritized over rapid early strength.

Concept / Approach:

Portland-pozzolana cement (PPC) lowers calcium hydroxide content and permeability via pozzolanic reaction, improving resistance to sulphate/chloride ingress compared with ordinary or rapidly hardening cements. Quick-setting and rapid-hardening cements favor speed, not durability in aggressive environments. Low heat cement reduces temperature rise but does not, by itself, address chemical ingress as effectively as PPC within the given options.

Step-by-Step Solution:

Verification / Alternative check:

Marine durability guidance commonly recommends PPC, blended cements, or SRPC; since SRPC is absent here, PPC is the best choice among the options.

Why Other Options Are Wrong:

• Quick-setting/rapid-hardening: higher heat, faster set, not superior durability.
• Low heat cement addresses thermal issues rather than ion ingress primarily.

Common Pitfalls:

• Neglecting cover, w/c control, and curing; cement type alone cannot ensure durability.

Final Answer:

Portland-pozzolana cement (PPC).