Self healing of cracks in concrete: from a model material to usual concretes

Title: Self healing of cracks in concrete: from a model material to usual concretes
Author(s): Sébastien Granger, Ahmed Loukili, Gilles Pijaudier-Cabot, Mouloud Behloul
Paper category : conference
Book title: 2nd International RILEM Symposium on Advances in Concrete through Science and Engineering
Editor(s): J. Marchand, B. Bissonnette, R. Gagné, M. Jolin and F. Paradis
Print-ISBN: 2-35158-003-6
e-ISBN: 2351580028
Publisher: RILEM Publications SARL
Publication year: 2006
Nb references: 12
Language: English

Abstract: This paper deals with the self healing of cracks phenomenon, in concrete, and especially with its role on mechanical properties. In a first phase, an experimental program, including mechanical tests, acoustic emission investigation and SEM observations, is carried out on an ultra high performance concrete, considered as a model material. This concrete is characterized by its low Water/Cement ratio, which implies that the quantity of potential reactive compounds in the microstructure upon cracking is very high. Prismatic notched specimens are damaged under three points bending and then totally immerged in water for different ageing times, so as to activate the self healing phenomenon, only possible in presence of water. After this ageing phase, the mechanical behaviour of the healed specimens is characterized by means of three points bending tests. A fast recovery of global stiffness and a slight improvement of structural strength are thus highlighted, depending on the time of ageing. Acoustic emission is also performed on this model material. In order to follow the micro-cracking processes and to show that the mechanical contribution of the self healing is related to the precipitation of crystals in the pre-existing crack, the specimens are instrumented with an acoustic emission system, during all the tests. 2D location maps of micro-cracks are thus obtained and clearly show the micro-cracking of the newly formed crystals for healed specimens. The analysis of the cumulative number of detected events, and of the energy extracted from each detected signals highlight the two damage regimes for healed specimens, the newly formed crystals damage followed by the continuation of the pre-existing crack propagation. This research work on the model concrete is completed with microscopic investigations by SEM, which show that new C-S-H have precipitated in the cracks. The same mechanical tests are then applied to usual concretes, and the influence of mix design on the phenomenon is analysed. Four different concretes, with Water/Cement ratio from 0.3 to 0.5, and including silica fume or not, are analysed, and the mechanical behaviour of healed specimens from these concretes is characterized.

Keywords: self healing, acoustic emission, sem, mechanical properties

Online publication: 2006-08-02
Classification: 3.3 Theme 3: Monitoring, Repair and Maintenance of Concrete Structures
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2351580028.094