Title:
Structural Mechanics Methodology in Diagnosing and Assessing Long-Term Effects of AAR in R/C Structures
Author(s):
A. Danay
Publication:
Materials Journal
Volume:
91
Issue:
1
Appears on pages(s):
54-62
Keywords:
air; alkali-aggregate reactions; concretes; deformation; expansion; gravity dams; laboratories; petrography; post-tensioning; reinforcing steels; stresses; Materials Research
DOI:
10.14359/4450
Date:
1/1/1994
Abstract:
Alkali-aggregate reactivity in massive reinforced concrete structures often tends to develop at a very slow rate, with little if any of its characteristic signs. The visible symptoms, excessive distortions and cracking, are ambiguous and common to other root causes of structural distress. When suspected, possibly because it is perceived primarily as a chemical rather than structural problem, AAR diagnosis is traditionally delegated to laboratory testing. Being largely qualitative and far from infallible, as well as often devoid of a meaningful structural assessment, this approach may result in wrong or delayed diagnosis, with extremely costly consequences where large projects such as power generating facilities are involved. A new approach is proposed, based primarily on a structural in situ rather than laboratory investigation, and focusing on detecting the major structural symptoms of concrete swelling, namely, dimensional changes, build-up of concrete compressive stresses, and post-tensioning effect on reinforcing bars. The key diagnostic tools are overcoring tests for concrete stresses, reinforcing bar in situ test, and regression analysis on structural deformation-monitoring data, when available, all requiring detailed structural analysis simulation. The proposed methodology has been successfully applied to a major hydraulic power generating project, in which previous investigations have failed for 20 years to identify the root cause of continuing operational and structural problems, resulting in costly outages and maintenance.