High-strength concrete is required in engineering projects that have concrete components that must resist high compressive loads. High-strength concrete is typically used in the erection of high-rise structures. It has been used in components such as columns (especially on lower floors where the loads will be greatest), shear walls, and foundations. High strengths are also occasionally used in bridge applications as well.
In high-rise structures, high-strength concrete has been successfully used in many U.S. cities. A high-rise structure suitable for high-strength concrete use is considered to be a structure over 30 stories. Not only has special concrete made such projects feasible due to load capacity, it has also allowed for the reduction of column and beam dimensions. Lower dead loads result, reducing the loads associated with foundation design. Also, owners benefit economically since the amount of rentable floor space, primarily on the lower floors, increases as the space occupied by the columns decreases. It is estimated that a 50-story structure with 4-foot diameter columns using 4000 psi concrete can reduce column diameters by approximately 33% by using 8000 psi concrete (Peterman).
High –strength concrete is occasionally used in the construction of highway bridges. High-strength concrete permits reinforced or prestressed concrete girders to span greater lengths than normal strength concrete girders. Also, the greater individual girder capacities may enable a decrease in the number of girders required. Thus, an economical advantage is created for concrete producers in that concrete is promoted for use in a particular bridge project as opposed to steel.
The following table gives high-strength mixes that are commercially available:
aMaximum aggregate size: mixes 1-5,at ½ in. (12.7mm);mix 6, 1 in. (25mm)
bWeight of total water in mix including water in admixture.
cTests on 6 x 12 in. cylinders.
Table 7.4 (Nawy)