Durable and Environmental design of Monitored COncrete structures in Marine environment – DEMCOM

The aim of the DEMCOM project is to tackle all these challenges through the major issue that affects marine concrete structures integrity: alteration by chloride ingress. For this purpose, this project will be divided in four Tasks (T). The methodological approach, described by the figure, is the conducting line of the DEMCOM project.

Task 1 is dedicated to the management of the project.

The main objective of Task 2 (T2) is to drive an experimental campaign with slag blended concrete slabs instrumented with the recently developed resistivity sensor designed for monitoring resistivity profiles over the whole thickness of a concrete structure. It is intended to address new scientific challenges: i) measuring and analyzing the electrical, conductive and capacitive phenomena, in order to extract not just one but two complementary observables, resistivity and chargeability, and their distribution in the material with a single probe ii) it would be possible to evaluate the kinetics of water and chloride penetration for concrete slabs exposed to tidal iii) analysing these outpouts data to get the input of the transport model integrating the processes of chloride and liquid transport.

Task 3 (T3) is the main part of the project. It has to combine durability modeling and multi-scale modeling by validating modeled results with experimental results obtained in T2 by monitoring. T3 is dedicated to develop a multi-scale model to estimate the concrete transport properties (input of the durability model) from the concrete compounds (technological parameters), as required for combination with LCA and LCP models. Indeed one challenge of the project is that the durability and LCA/LCP models should use the same inputs which are technological parameters and environmental parameters. This will be developed in the case of other binders than Portland cement as slag.

The key ingredients are respectively: 1) an appropriate hydration model to determine the amount of each phase, 2) a morphological model to describe their geometrical organisation and repartition across different length scales and 3) a suitable homogenization schemes to successively upscale the macroscopic properties of interest from those of each phase at the microscopic scales

Task 4 will be devoted to the combination of durability LCA and LCP models for identifying the most favorable material solution. To optimize the design also by reducing the calculation time of the method, Sensitivity Analysis (SA) will be developed to identify the action levers for maximize service life and minimize environmental impacts and costs. Different scenario will be studied for giving recommendations dedicated to the designers to also accept environmental LCA combined with LCP analysis as decision-making tool. Advice includes optimum concrete mix design to meet specific surrounding conditions, corrosion protection for reinforcing steel by considering LCA LCP analysis.

The results are published in scientific papers or in conferences. All are available on hal site(https://hal.science/search/index?q=demcom). The data are available on

entrepot.recherche.data.gouv.fr/dataverse/anr-demcom

The work carried out has led to significant advances in understanding the behavior of slag-containing concretes (hydration, resistivity, durability, and LCA) exposed to marine environments.

Monitoring resistivity during drying and water imbibition phases demonstrated the influence of slag on the concrete microstructure, pore solution composition, and transport properties. Calibration of the resistivity measurements made it possible to determine the degree of saturation and indirectly estimate water permeability, which is an input parameter of the durability model.

Imbibition tests using salt water and fresh water also made it possible to independently determine water content and chloride content profiles, by exploiting their different penetration kinetics. Consequently, chloride diffusion coefficients were estimated as a function of the degree of saturation, which is an essential input parameter for the durability model, as demonstrated by the sensitivity analysis performed. Artificial tidal exposure tests conducted on instrumented concrete specimens confirmed the potential of resistivity measurements for monitoring chloride ingress over time in unsaturated conditions, by adapting the geometrical factor. However, resistivity tomography did not make it possible to distinguish chloride concentration profiles from saturation profiles on a single concrete specimen.

In parallel, an advanced hydration kinetics model for slag-containing cements was developed based on an experimental database compiled from the literature. This model makes it possible to predict the evolution of porosity and the chemical composition of the materials as a function of their formulation, and to estimate the effective chloride diffusion coefficient using homogenization techniques. This approach was validated against a database of diffusion coefficients measured in cement pastes. Upscaling to concrete is currently underway to enable coupling between the LCA and durability models.

The work on the life cycle assessment of cement made it possible to identify the main levers for reducing environmental impacts. Replacing clinker with slag appears to be the most effective lever, although its application is limited by the availability of resources. Increasing cement fineness is also a promising strategy for reducing concrete consumption while maintaining its mechanical performance and durability.

The coupling between the LCA and durability models is not yet operational, as the upscaling to concrete is still under development.

under sonstruction

This interdisciplinary project deals with Durability Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) of Reinforced Concrete (RC) structures under marine environment like wharf, bridges, floating wind turbines etc… The objective is to develop a new eco design method to maximize service life and minimize environmental impacts and costs of RC structures submitted to chloride ingress. In the context of changes of structure uses, climatic environment and service life prolongation, the Non Destructive Evaluation (NDE) during inspection coupled with durability model and, LCA and LCC decision diagram can bring very useful tools for structure managers. These stakes require NDE results to be directly integrated in durability models to improve the health diagnosis and thus the service life prognostic by minimizing environmental impacts and costs. Sensitivity Analysis will be developed and used to determine which action levers have to be modified to this aim.