Title:
Active Confinement of Concrete Members with Self-Stressing
Composites
Author(s):
Neven Krstulovic-Opara and Patrick D. Thiedeman
Publication:
Materials Journal
Volume:
97
Issue:
3
Appears on pages(s):
297-308
Keywords:
active confinement; fiber-reinforced concrete; high-strength
lightweight aggregate concrete; prestressing; self stressing; shape memo-ry
alloys.
DOI:
10.14359/4625
Date:
5/1/2000
Abstract:
The paper presents the results of an exploratory investigation on the use of self-stressing composites for active confinement of concrete members with the goal of maximizing member strength and ductili-ty. Self-stressing composites are made with memory materials which have a unique capability of temporarily freezing elastic deformation. Deformation recovery is triggered with heat or electricity. When strain recovery is physically restrained, large prestressing stresses, i.e., active confinement, is generated. No jacks or other mechanical devices are needed to introduce active confinement. Therefore, the use of self-stressing composites permits application and change in active confine-ment at any time after the member has hardened. This decreases the work effort associated with active confinement, and also permits its use in applications not practically feasible using conventional pre-stressing methods. One such example, in which self-stressing stay-in-place formwork actively confined the member core after it was cast-in- place, was explored in the presented research. The effects of active confinement on increasing strength and ductility of both normal-strength and high-strength lightweight concretes (HS-LWC) were explored, with the main focus being on HS-LWC. To maximize strength and ductility of HS-LWC, a combination of active confinement with self-stressing composites and addition of steel fibers was considered. Two types of confinement were explored: confinement with continuous memory fibers only, and confinement with a combination of continu-ous memory fibers and slurry infiltrated fiber-mat concrete (SIM-CON). Applications in both retrofit and new construction were con-sidered. In both cases, active confinement was successfully applied using the proposed approach. The confinement effectively restrained microcracking and improved crack stability, leading to improved strength, ductility, and toughness of tested specimens.