Question

In concreting the foundation of a high-rise building, describe the potential issues that could arise related to the following factors: the types of Portland cement, the Water to Cement (W/C) ratio, the most often used admixtures and the concrete slump test.

Answer 1

There is no specific type of cement which is used in concrete on high rise buildings. It's the concrete which have modified properties.

Waste materials from power plant like fly ash are used in the production of portland pozzolana cement. It is used in mass concrete constructions like high-rise buildings, under water concrete structures such as bridges, piers, dams etc. The heat of hydration rate is lower in this type of cement. Because of lower heat of hydration, it is also used in brickwork and plaster work.

OPC is not usually used keeping the environment in mind, Portland Pozzolona Cement is a better choice.

OPC (Ordinary Portland Cement) is used for all general purposes and widely used for all ordinary concrete work, mortar, plaster etc.

Hence use OPC or PCC for the concreting of the high rise building according to the site location and the temperature

Retarders can be used in the cement if they have to transported to site via transit mixer or to reduce heat of hydration due to mass conreteing. Plasticizers or super plasticizers are used to obtain same amount of workability for the concrete with lesser use of water thereby not harming strength.

the strength of the concrete depends solely on the relative quantity of water compared with the cement. In other words, the strength is a function of the water to cement ratio (w/c) where w represents the mass of water and c represents the mass of cement.
It is known as abrhams law

Reducing the water content of concrete, and thereby reducing the w/cm, leads to increased strength and stiffness, and reduced creep. The drying shrinkage and associated risk of cracking will also be reduced. The concrete will have a lower permeability or increased water tightness that will render it more resistant to weathering and the action of aggressive chemicals. The lower water to cementitious materials ratio also improves the bond between the concrete and embedded steel reinforcement.

Slump tests should be made periodically on freshly mixed mortar immediately prior to the mortar being conveyed to the lining machine.

A concrete slump test should be done as described in ASTM C 143. A slump test is widely used to check the workability and consistency of concrete.