Monitoring crack movement in polymer-based self-healing concrete through digital image correlation, acoustic emission analysis and SEM in-situ loading

A study was performed to assess the fitness of continuous monitoring methods to detect failure due to excessive strain on polymers bridging moving cracks in the context of self-healing concrete. Testing of several polymer precursors with distinct properties also allowed conclusions regarding the requirements for polymers in this application. Acoustic emission (AE) analysis was performed in parallel with digital image correlation (DIC) at the macro-scale. In addition, a micro-scale study was performed with tensile tests inside an SEM chamber. Detection of failure through AE analysis coupled with DIC was possible only in case of failure due to brittle fracture of a rigid foam after 9% strain, which generated high-energy acoustic events. Direct observation of interfaces with SEM insitu loading allowed determination of failure of a rigid foam due to cracking of the polymer matrix and detachment at the interface with the cementitious matrix, with an onset at 5% strain and complete detachment at 16% strain. For a flexible, continuous film of polymer, detachment occurred before 50% strain. Assuming adequate adhesion, polymers with high elongation (>100%) and modulus of elasticity much lower than 10 MPa are required if cracks subjected to a realistic amplitude of movement are targeted. (C) 2016 Elsevier Ltd. All rights reserved

Autonomous regeneration of concrete structures by incorporation of self-healing mechanisms

info:eu-repo/semantics/publishe

Visualization of the healing process on reinforced concrete beams by application of Digital Image Correlation (DIC)

A hot topic in research recently is the manufacture of an advanced concrete system enhanced by Self-Healing (SH) characteristics. In general, material science is focused on the establishment of smart engineering concrete and cementitious composites that can extend their service life and remain durable and strong even when phenomena of decay appear. In the case of this study, formation of damage and recovery of the mechanical properties is investigated by application of an encapsulated healing agent. On experimental level, it is imperative to implement an optical, non- contact and on-line capturing optical technique to visualize and compare the crack propagation at the loading and reloading (when the initial cracks are filled by the healing agent) stage. For that reason, optical measurements by application of Digital Image Correlation (DIC) are performed during tests. Processing images captured by a 2-digital cameras system during all the loading stages of four-point bending tests give a full-field vies of the crack displacement and strain profiles. A step further, the visualization of the cracking phenomena by DIC offers a useful tool to apply fracture theories of concrete on healing systems

Acoustic Emission Activity for Characterizing Fracture of Marble under Bending

The present paper occupies with the acoustic emission (AE) monitoring of fracture of marble. The specimens belong to two different material types and were tested in three-point bending after being ultrasonically interrogated. Consequently, they were repaired by means of suitable epoxy agent and mechanically re-loaded. Apart from the well-known correlation of pulse velocity to strength, which holds for the materials of this study as well, AE provides some unique insight in the fracture of the media. Parameters like the frequency content of the waveforms, and their duration among others show a transition in relation to the load. According to their strength class, the specimens exhibit distinct AE characteristics even at low load, enabling to judge their final strength class after having sustained just a small percentage of their ultimate capacity. More importantly, the AE activity during reloading indicates the quality of repair; specimens with good restoration of strength, exhibited similar AE activity to the intact specimens, while specimens with lower repaired capacity exhibited random behavior. This work discusses the passive monitoring of marble fracture and shows that AE parameters that have been used to successfully characterize cementitious materials, provide good results in monolithic materials like marble as well. It is suggested that AE monitoring during a proof loading can provide good information on the potential strength class, which is especially useful for repaired specimens, where the pulse velocity cannot be easily used

Detecting the activation of a self-healing mechanism in concrete by acoustic emission and digital image correlation

Autonomous crack healing in concrete is obtained when encapsulated healing agent is embedded into the material. Cracking damage in concrete elements ruptures the capsules and activates the healing process by healing agent release. Previously, the strength and stiffness recovery as well as the sealing efficiency after autonomous crack repair was well established. However, the mechanisms that trigger capsule breakage remain unknown. In parallel, the conditions under which the crack interacts with embedded capsules stay black-box. In this research, an experimental approach implementing an advanced optical and acoustic method sets up scopes to monitor and justify the crack formation and capsule breakage of concrete samples tested under three-point bending. Digital Image Correlation was used to visualize the crack opening. The optical information was the basis for an extensive and analytical study of the damage by Acoustic Emission analysis. The influence of embedding capsules on the concrete fracture process, the location of capsule damage, and the differentiation between emissions due to capsule rupture and crack formation are presented in this research. A profound observation of the capsules performance provides a clear view of the healing activation process