What is recommended for a concrete retaining wall exposed to corrosive soil to resist sulfate attack?

For a concrete retaining wall exposed to corrosive soil, particularly one that contains sulfates, the use of Type V cement is recommended due to its formulated resistance to sulfate attack. Type V cement contains a lower percentage of tricalcium aluminate, which significantly improves its ability to withstand the effects of sulfates compared to other types of cement.

Additionally, a water-to-cement (W/C) ratio of 0.35 is advantageous because it contributes to a denser and less permeable concrete mix. Lower permeability is crucial in this scenario, as it helps prevent the ingress of sulfate-laden water, thereby reducing the risk of sulfates attacking the concrete matrix and causing deterioration.

Other options listed in the question do not provide the same level of protection. For instance, Type II cement offers moderate resistance to sulfate attack but is not as effective as Type V when dealing with aggressive environments. A higher W/C ratio, such as in one of the other options, would lead to increased permeability, making the concrete more vulnerable to sulfate penetration and subsequent damage.

Therefore, the combination of Type V cement along with a W/C ratio of 0.35 stands out as the best solution for ensuring the longevity and durability of concrete structures in corrosive soil conditions.