Concrete Strength Record Jumps 36%
by Kneeland A. Godfrey, Jr., Sr. Ed.;Serial Information: Civil Engineering—ASCE, 1987, Vol. 57, Issue 10, Pg. 84-86
Document Type: Feature article
Abstract:
A Seattle building now going up has 19,000 psi concrete, the strongest ever in conventional structures. It costs three times as much as conventional concrete, so will not be widely used. At least six changes from conventional concrete mix design led to the strength. Only 14,000 psi, or about 75% of the concrete's strength was needed as strength; the rest was needed to achieve the desired elastic modulus or stiffness, which helps minimize wind sway of the completed building. The building's 18 cylindrical columns have no conventional reinforcing, but each has a permanent steel shell and welded to its inside face, shear studs. The innovations were used to cut cost of the structure�by an estimated 30% of the $30 million structural cost. Many changes were made from conventional quality control: 18 cylinders for each 100 cu yd of concrete, six times the usual, with strengths measured at ages up to 1 year; smaller, 4 in. diameter by 8 in. long test cylinders; replacement of capping compound in test cylinders with an end-grinding procedure; and replacement of fog-room curing with lime-water immersion curing. When placed, the column concrete is not vibrated�it is not necessary because concrete for two-floor column pours is pumped in from the bottom of the lift, assuring good concrete mixing.
Subject Headings: Concrete | Strength of materials | Cylinders | Concrete columns | Buildings | Benefit cost ratios | Steel columns
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