Shrinkage-Free Mortars for Repairing Damaged Concrete Structures

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Title: Shrinkage-Free Mortars for Repairing Damaged Concrete Structures

Author(s): S. Collepardi, G. Corazza, G. Fazio, S. Monosi, and R. Troli

Publication: Special Publication

Volume: 239

Issue:

Appears on pages(s): 375-388

Keywords: expansive agent; repairing mortar; shrinkage-reducing admixture

Date: 10/1/2006

Abstract:
Shrinkage-compensating mortars are in general pre-mixed cementitious materials which contain expansive agents among the various powder ingredients. The role of the expansive agent, in the form of dead burnt calcium oxide (CaO) or calcium sulfo-aluminate (CSA), is to produce a compressive stress in the repairing mortar due to the restraint exerted by the metallic reinforcements or the friction of the rough concrete substrate. To be successful, the mortar must be carefully wet cured because the expansion can occur only in the presence of water due the hydration of the CaO or CSA based expansive agent. In the absence of careful wet curing, the repairing work can be unsuccessful because there would not be any useful precompression from restrained expansion. The present work is devoted to study the behavior of mortars containing CaO or CSA as expansive agents combined with a Shrinkage-Reducing Admixture (SRA) in the presence and in the absence of wet curing. Due to the synergistic action of the SRA with the expansive agent, the restrained expansion can occur even in the absence of any wet curing. However, this action in much more effective when SRA is combined with CaO rather than with CSA.