Design and Construction of an Internally Cured Slab

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Title: Design and Construction of an Internally Cured Slab

Author(s): Robert T. Bates, Erik Holck, Miles Dee, Michael King

Publication: Special Publication

Volume: 290

Issue:

Appears on pages(s): 1-10

Keywords: Concrete water tank, internal curing, post-tensioned slab, shrinkage cracking

Date: 9/14/2012

Abstract:
Constructing large capacity, monolithically placed water storage tank slabs is a complex proposition. Previously, specifying low-shrinkage concrete mixes and monolithic placement of the slab within a specified time period was the prescribed method, yet shrinkage cracking still occurred. We felt more could be done to improve concrete placing and finishing, reducing shrinkage cracking and enhance durability. An investigation on the use of an Internally Cured Concrete mix on the floor and roof slabs of the Denver Water 10-Million Gallon [MG] (38-Million Liter [ML]) Lone Tree Tank No. 2 that Bates Engineering Inc. was designing was pursued. The tank floor and roof slab are each about 61,000 ft2 (5,700 m2) and would be monolithically placed. Laboratory trial batches performed determined plastic and hardened characteristics of the ICC as compared to traditionally proportioned mix designs. Tests performed in the laboratory included: compressive strength and drying shrinkage (ASTM C 157(1), modified 7-day saturation). An ICC mix was selected based on durability expectations. Results of the floor slab placement were successful and only two shrinkage cracks were observed, 7-day and 28-day compressive strength tests, workability and consistency surpassed expectations. As a result, it was decided to use ICC concrete on the remaining structural components.