Tools for assessing damage in concrete affected by AAR coming from fine and coarse aggregates
Over the last few years, comprehensive management programs for the diagnosis and prognosis of alkali-aggregate reaction (AAR) in aging concrete structures were developed in North America, based on a series of laboratory test procedures. Although promising, these lab-procedures presented several parameters whose impacts were not completely understood, which significantly reduced their applicability for the appraisal of deteriorated concrete structures in service. In this context, it has been suggested that two lab-tools, the Stiffness Damage Test (SDT) and the Damage Rating Index (DRI) could reliably assess the condition of concrete affected by AAR. This paper presents the condition assessment of 25, 35 and 45 MPa AAR affected concrete specimens incorporating fine and coarse reactive aggregates and presenting different distress degrees (i.e. expansion levels from 0.05 to 0.30%) through the use of an innovative multi-level approach. Results show that both SDT and DRI are suitable for assessing damage in AAR affected concrete through their output parameters. Yet, they present a complementary character, which illustrates the need for a multi-level approach.
Evaluation of the Stiffness Damage Test (SDT) as a tool for assessing damage in concrete due to alkali-silica reaction (ASR): Input parameters and variability of the test responses
Abstract The Stiffness Damage Test (SDT) is an interesting tool for assessing damage in concrete affected by alkali-silica reaction (ASR). It has been found that the use of a fixed loading over the test limits its ability to reliably appraise the distress level of concrete samples, mainly when different concrete strengths and aggregate types are used. However, there is currently very limited data on the influence of various input parameters on the test responses. This paper thus presents a critical evaluation of several input parameters of the SDT. Parameters such as the core’s environmental conditions, the samples’ characteristics and the samples conditioning history seem to influence significantly the cyclic test output results. Otherwise, different types of surface preparation and the specimens’ size (i.e. specimens’ diameter) did not seem to clearly modify the test analyses.
Détérioration de fondations de pylones d'ancrage de lignes de transport d'électricité par des réactions alcalis–granulats, performance mécanique et réparation du béton
A number of concrete tower foundations that support power lines over the St. Lawrence River in the Quebec City area were showing deterioration related to alkali–aggregate reactions. The aggregates involved are siliceous limestones commonly exploited in the area. Many foundations have been cored down to the rock basement and samples were taken all along the cores for petrographic examination and mechanical testing. These studies show that the concrete presents some mechanical weaknesses but only in the first decimeters close to the surface, even if the entire mass of the concrete foundations is affected by alkali–aggregate reactions. The results also suggest that the deterioration is isotropic in the concrete and that the compressive strength is affected as much as the tensile (Brasilian) strength. Various types of corrective measures were applied to the deteriorated components: sealing of cracks, removing of the deteriorated concrete and replacement with a new concrete containing silica fumes in addition ...