Evaluating High Absorptive Materials to Improve Internal Curing of Concrete

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Title: Evaluating High Absorptive Materials to Improve Internal Curing of Concrete

Author(s): N. Delatte, D. Crowl, E. Mack, and J. Cleary

Publication: Special Publication

Volume: 256

Issue:

Appears on pages(s): 91-104

Keywords: aggregate absorption; compressive strength; cracking; high-performance concrete; internal curing; lightweight aggregate; maximum coarse aggregate size; ring-restrained cracking test; splitting tensile strength

Date: 10/1/2008

Abstract:
Some state highway agencies have implemented high-performance concrete (HPC) for bridge decks for durability rather than strength. While the low permeability of HPC is used to protect reinforcing steel and prevent corrosion, any concrete cracks can diminish the intended protection. One unintended consequence of HPC can be early-age cracking. This paper explores two ways to prevent bridge deck cracking - internal curing, and paste reduction by using an aggregate blend with a larger maximum size of aggregate. Results also apply to other classes of concrete used in transportation and other infrastructure. Mixtures were tested with large and small coarse aggregate. Fine lightweight aggregate (LWA) was added to some of the mixtures to reduce cracking tendency. The ring test, modifi ed from ASTM C1581, was used to determine the time of cracking of a concrete specimen due to drying and autogenous shrinkage against the restraint of the steel ring. Tests were carried out until cracking or for a maximum of 90 days. The strongest effect on cracking was due to the replacement of a small maximum size coarse aggregate (No. 8) with an aggregate blend of No. 8 and No. 57. Increasing the coarse aggregate absorption level from low to medium had a less dramatic effect, as did the introduction of LWA for internal curing to the low absorption coarse aggregate.