Question

Q3. A heavily reinforced and massive concrete structure is to be designed for a coastal location in Alaska. As a consultant to the primary contractor, write a report on the choice of cement type, aggregate size, admixtures, mix proportions, concrete placement, and concrete curing procedures.

Answer 1

As a project consultant I would like to recommend following for the massive marine structure-

1. Cement- For coastal region with cold climate, the best cement will be High Alumina cement, as it has more resistance to chemical attack due to marine environment, it also has a high heat of hydration to resist against cold climate.
2. Aggregate size- The best suitable size of Aggregate for massive structure near cold coastal region is 20mm or more with angular shape which provides the structure more strength. As density of concrete increases its strength also increases.
3. Admixture- Admixtures like plasticizers, air entrainers and accelerators are required to develop the massive structure. Plasticizers like lignosulphonic acids are used to loss of workability. Air entrainers are used to improve resistance from freezing and thawing in cold region. Accelerators also accelerate the rate of setting in very cold condition.
4. Mix proportion- For such marine structure strength mix should be M-40 or above with minimum cement ratio not less than 360. And maximum free water cement ratio will be 0.40 for better structure durability and strength.
5. Concrete placement- To achieve quality concrete, we have to secure homogeneity of concrete and avoid segregation of concrete during transportation and placement. Concrete should be placed in layers of 350-450 mm thickness for massive structure. Delaying in placing of concrete upto critical extent may results in gain of ultimate compressive strength.
6. Concrete curing procedure- The main objective of curing is to increase durability and impermeability of concrete. It also reduces shrinkage of concrete. The most suitable method of curing for such marine and cold climate is Steam Curing, since steam curing procedure increases the rate of strength development. It also increases the resistance to sulphate action and to freezing and thawing.

I think this solution might be helpful to u to understand the basics, have a nice day.