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.
Alkali-silica reaction: understanding the phenomenon
The alkali-silica reaction in cementitious composites occurs through the chemical association of the solution contained in the matrix pores, which is strongly basic and rich in alkalis, and the reactive phases of some aggregates. For the process to begin, high relative humidity and a high concentration of total alkalis are required. The degradations resulting from this reaction involve expansion, cracking, exudation and decreased mechanical performance of the structure, which can cause it to break depending on the magnitude of the phenomenon. Understanding the reaction development process is necessary to propose measures that can effectively extinguish or mitigate the occurrence. One of the measures widely studied is the incorporation of supplementary cementitious materials in concrete. In Brazil, technical regulations already exist that recommend the use of these cementitious materials. The Northeast region of the country is a major producer of fly ash and granulated blast furnace slag, but not all of this material is destined for other industries. The article in question is a compendium of technical information from relevant research developed about alkali-silica reaction. His contribution is in the didactic approach that allows the understanding of students in the engineering area and professionals who do not have the expertise in the subject in order to stimulate future research on the use of supplementary cementitious materials in Northeast Brazil, mainly.
ANALYSIS OF BOLT′S ANCHORING QUALITY BASED ON WAVELET NEURAL NETWORK
The dynamic response of bolt achieved by impact-echo method can be effected easily by some factors.It′s difficult to classify bolt′s anchoring quality according to the dynamic response of bolt.In this paper,a new analytical method of bolt′s dynamic response is put forward.The new analytical method combing with advantages of wavelet analysis and artificial neural network is presented.Firstly,the dynamic response of bolt by numerical simulation software FLAC3D is obtained.Secondlyt,he features are extracted from the dynamic response of bolt by wavelet analysis.Thirdlyt,hese features are fed into the artificial neural network for training.Finallyt,his artificial neural network to classify the bolt′s anchoring quality intelligent according to the dynamic response of bolt is employed.In order to validate this new analytical method,some practical signals of bolt′s dynamic response are used for the test.The results indicate that the new analytical method is practicable.