Project Highlights

Society (Key Corp.) Tower – Cleveland, Ohio

In the early 1990’s Cleveland’s tallest building to be was designed with column concrete attaining a modulus of elasticity of 6.8 million psi (46.9 GPa) and a compressive strength of 12,000 psi (67.5 MPa). To achieve an optimized mix design with a reasonable amount of total cementitous quantity to limit shrinkage and creep potentials, an 8% silica fume addition played an integral part along with a 30% replacement value of slag cement, combined with a very low W/C of 0.24.

A single stage pump delivered this high performance concrete from the ground level to the floors above into column forms which were filled from the bottom up. Since there was no access to consolidate via mechanical vibration and vibrating forms were impractical, high concrete fluidity was required and specified as a minimum slump requirement of 10” (255 mm). A combination of a large dose of plant-added high range water reducer coupled with set balancing additives provided this negative water slump mix design the necessary workability. Spread, or slump flow as coined a decade later with the advent of self-consolidating concrete (SCC) was measured and expected to exceed 20” (510 mm) to assure proper in-place consolidation.

Society Tower; full height single stage concrete pumping and filling column from the bottom up

The average compressive strength achieved was in excess of 15,000 psi (103 MPa), well above specified performance, basically as a side effect to the more difficult performance of modulus of elasticity which in this case reached 7 million psi (48.3 GPa). Silica fume not only was instrumental in achieving the high modulus of elasticity requirement, but also to provide control in concrete viscosity, assuring a non-segregating SCC, well workable and long-distance pumpable high performance concrete.

Concrete Mix Design & Performance
Society ( Key Corp.) Tower, Cleveland, OH -1992

Mix Design Materials	lbs / yd3	kg / m3
Cement, Type I	685	406
Slag Cement (30% replacement)	285	169
Silica Fume ( 8 % addition )	80	47
Aggregates natural sand and traprock to yield; non-air-entrained
Water / Cementitious Ratio	0.24	0.24
High Range Water Reducer	2.3-3.5 gal / yd3	9 - 12 ltr / m3
3 day compressive strength	9,300 psi	64 MPa
7 day “	12,600 psi	87 MPa
28 day “	14,200 psi	98 MPa
56 day “	15,100 psi	104 MPa
56 day modulus of elasticity	7.0 x 106 psi	48 GPa

Society (Key Corp.) Tower
Cleveland, Ohio

Society Tower; full height single stage concrete pumping and filling column from the bottom up.