Behavior of Type K Shrinkage Compensating Concrete Under Various Forms of Mechanical Restraint

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Title: Behavior of Type K Shrinkage Compensating Concrete Under Various Forms of Mechanical Restraint

Author(s): Chris Ramseyer and Seth Roswurm

Publication: Special Publication

Volume: 307

Issue:

Appears on pages(s): 1-18

Keywords: Shrinkage compensating concrete, restrained expansion, Type K concrete, ettringite, expansive concrete, vibrating wire strain gage

Date: 3/1/2016

Abstract:
Shrinkage compensating concrete is one of the most common products currently used to mitigate the influence of drying shrinkage cracking in slabs, beams and other structural components. Type K expansive concretes have proved effective for prevention of structural and aesthetic damage due to tensile cracking in many modern applications. However, the ACI 223R-10 technical guide still indicates that a shrinkage compensating slab cannot expand adequately if it is surrounded on all sides by mature reinforced concrete. The objective of this project was to investigate whether the presence of a stiff external restraint condition, which may be provided by adjoining concrete, prevents a Type K expansive concrete slab from compensating for shrinkage. To investigate this behavior, the field condition of a slab-to-slab interaction was simulated using a steel restraint system with varying degrees of stiffness and amounts of Type K expansive cement component. Test frames were instrumented to evaluate the force and displacement responses of the Type K expansive concrete to the different boundary conditions provided by varying the steel restraint system. The results of this investigation support a conclusion contrary to that currently found in the ACI 223R-10 guiding document. This study concludes that a Type K expansive cement concrete does not suffer a severe reduction in shrinkage compensation in the presence of a very stiff boundary condition.