Dr.-Ing. Pietro Carrara
Effects of the exposure to aggressive environments on the concrete behavior from multiscale analysis
The aging of the concrete structures is particularly susceptible to aggressive environments, in particular to the penetration of chemicals such as chloride or sulphate ions and carbon dioxide. Hence, a reliable modeling of the diffusive properties of the concrete is mandatory to schedule efficient maintenance as well as to estimate the service and ultimate life of concrete structures. However, this is a non-trivial task because the diffusion process is a multiscale problem since the mass transport is influenced by different factors acting at different length scales. Moreover, the interactions between the aggressive chemicals and the mechanical properties of the concrete can take place at different length scales as well: chlorides induce steel rebars corrosion at the macroscale but the penetration speed is influenced by the cement paste microstructural arrangement. The presence of sulphate ions leads to harmful reactions with the aggregates (alkali-aggregates reactions), which should be studied at the mesoscale. Also, carbonation due to the presence of carbon dioxide affects the cement paste microstructure, altering its mechanical behavior. In this framework the adoption of a numerical multiscale approach is mandatory to correctly reproduce the real aging processes keeping the computational effort into acceptable limits.
Main goal of the present work is to to study the penetration of the aggressive chemicals into the concrete as well as the consequences on the concrete mechanical behavior. In the first part of the project, the diffusive behavior of chloride ions at different length scales will be studied and a homogenization approach will be proposed in order to establish a connection between different length scales. In particular, we aim at defining the diffusivity at the macroscale starting from the microstructural arrangement of the cement paste. Then, the method will be extended to different aggressive species and to different situations (e.g., non-saturated media) and it will be coupled with the expected mechanical performances of the concrete. In this part of the project, an efficient way to consistently upscale the effects of damage on the global mechanical behavior will be studied (e.g. using the transformation field analysis technique). Throughout the work, a key role will be played by the execution and analysis of experimental tests in order to calibrate and/or validate the proposed numerical models.
Publications within the framework of the RTG:
Publications in peer-reviewed scientific journals:
P. Carrara, R. Kruse, D.P. Bentz, M. Lunardelli, T. Leusmann, P.A. Varadya and L. De Lorenzis. Improved mesoscale segmentation of concrete from 3D X-ray images using contrast enhancers. Cement and Concrete Composites, 93: 30-42, 2018.
P. Carrara and L. De Lorenzis. Chloride diffusivity of the interfacial transition zone and bulk paste in concrete from microscale analysis. Modelling and Simulation in Materials Science and Engineering 25, 045011, 2017.[ DOI ]
P. Carrara and L. De Lorenzis. Consistent identification of the interfacial transition zone in simulated cement microstructures. Cement and Concrete Composites 80, S. 224-234, 2017.[ DOI ]
P. Carrara, T. Wu, R. Kruse and L. De Lorenzis. Towards multiscale modeling of the interaction between transport and fracture in concrete. RILEM Letters 1, S. 94-101, 2016.[ DOI ]
P. Carrara, L. De Lorenzis and D.P. Bentz. Chloride diffusivity in hardened cement paste from microscale analyses and accounting for binding effects. Modelling and Simulation in Materials Science and Engineering 24, 065009, 2016.[ DOI ]
Conference contribution with publication in conference proceedings:
P. Carrara and L. De Lorenzis. Chloride diffusion and binding in hardened cement paste from microscale analyses. Proc. of International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service life of Cement-Based Materials and Structures, Lyngby, Denmark, 2017.
P. Carrara, T. Wu and L. De Lorenzis. Chloride diffusivity of hardened cement paste from multiscale modeling. Proc. of International workshop Durability and Sustainability of Concrete Structures, Bologna, ltaly, 2015.