AVOIDING OVERFITTING IN INVERSE MODELING OF CHLORIDE MIGRATION IN CONCRETE

Author(s): Sreejith V. Nanukuttan, Neven Ukrainczyk, Des J. Robinson, and Eduardus A.B.
Koenders
Paper category: Proceedings
Book title: proceedings of the International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures
Editor(s): Miguel Azenha, Ivan Gabrijel, Dirk Schlicke, Terje Kanstad and Ole Mejlhede Jensen
ISBN:978-2-35158-171-4
e-ISBN: 978-2-35158-173-5
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 599-608
Total Pages: 10
Language : English

Abstract: Inverse analysis for reactive transport of chlorides through concrete in the presence of electric
field is presented. The model is solved using MATLAB’s built-in solvers “pdepe.m” and
“ode15s.m”. The results from the model are compared with experimental measurements from
accelerated migration test and a function representing the lack of fit is formed. This function
is optimised with respect to varying amount of key parameters defining the model.
Levenberg-Marquardt trust-region optimisation approach is employed. The paper presents a
method by which the degree of inter-dependency between parameters and sensitivity
(significance) of each parameter towards model predictions can be studied on models with or
without clearly defined governing equations. Eigen value analysis of the Hessian matrix was
employed to investigate and avoid over-parametrisation in inverse analysis. We investigated
simultaneous fitting of parameters for diffusivity, chloride binding as defined by Freundlich
isotherm (thermodynamic) and binding rate (kinetic parameter). Fitting of more than 2
parameters, simultaneously, demonstrates a high degree of parameter inter-dependency. This
finding is significant as mathematical models for representing chloride transport rely on
several parameters for each mode of transport (i.e., diffusivity, binding, etc.), which combined
may lead to unreliable simultaneous estimation of parameters.

Online publication : 2016
Publication type : full_text
Public price (Euros) : 0.00