Passive layER FailuRe Mechanisms (PERFoRM)

Primary investigator: Professor Susan Bernal Lopez, Supervisor
Co-investigator: Dr Juan Pablo Gevaudan, Marie Skłodowska-Curie Fellow

The Marie Skłodowska-Curie, Passive layER FailuRe Mechanisms (PERFoRM) project aims to unveil how in-service environmental conditions influence the stability of the passive layer on steel rebar embedded in concretes based on low-carbon cementitious materials, such as Near-neutral Salt Activated Slag materials (NnSAS), when exposed to environmental threats (e.g., CO2). NnSAS materials a subset of alkali-activated materials that offer high carbon emission savings, compared to other construction materials. However, their long-term performance is largely unknown, especially in the case of their corrosion mechanisms in embedded reinforcement.

PERFoRM will implement non-destructive techniques (NDTs), such as micro-computerized tomography, for the in-situ diagnosis of steel reinforced concretes (i.e., pore structure characterization); along with cutting-edge electrochemical techniques to determining corrosion rates closely resembling in-service concrete structures. The main scientific focus areas of the PERFoRM project are:

• Developing novel durability wireless embedded (D-WirE) sensors for in-situ tracing of aggressive ions (e.g. chlorides) and monitoring of internal factors (e.g. relative humidity, pH) in concrete.
   
• Ground-breaking work monitoring chemical and physical changes induced by carbonation/chloride penetration in NnSAS mainly using NDTs.
   
• Advanced characterisation of the passive layer growth, breakdown, and failure rates of steel rebars embedded in NnSAS.
   
• Creation of service-life models by incorporation of in-situ carbonation and chloride penetration regression models.

The PERFoRM project has developed unique insights on the development and application of sensor networks, characterization of the pore network of NnSAS materials, and the corrosion performance of carbonated alkali-activated slag materials. Moreover, the PERFoRM project, through the use of thermodynamic and electrolyte conductivity simulations, has provided new insights into the formation, establishment, and maturity mechanisms of passive layers in salt and alkali-activated materials.

The innovative research results from the PERFoRM project have been integrated with collaborative programmes coordinated by the European Federation of Corrosion (EFC) Work Programme 11 as well open-research data resources by the University of Leeds, hence, providing a direct route to international awareness and utilisation of the fellowship outcomes.

MSCA Fellowship training

The PERFoRM project provided a multitude of opportunities for research training in the areas of corrosion thermodynamics and kinetics, micro-computerized tomography and image analysis, and advanced microscopy techniques.

The project provided also provided the opportunity for interaction with scientific and technical committees of RILEM (TC CAM) and EFC (WG 11) to advance the understanding of passive layer generation and breakdown due to environmental aggressors. The materials characterization support were provided by the Research team in the host institute, and the original research contributions have been prepared for publication in peer-reviewed journal as well as presented at international conferences.

Research training objectives

The main research training objectives for realizing the impact of the research project were the following:

Training in fundamentals of corrosion science

The Fellow attended the Corrosion Science and Corrosion Control for Infrastructure (CSC2I) Technical course at TU-Delft (Netherlands) on October 21-25, 2019. In this course, the Fellow was trained on the theoretical fundamentals of the thermodynamics and kinetics of corrosion science.

The Fellow also learned about the implementation of electrochemical techniques in the laboratory needed to perform and accomplish the research objectives of the project. To supplement this training, the Fellow undertook individual study of the theoretical underpinnings of advanced electrochemical techniques. These studies centered on the understanding of the mixed potential theory and how sulphide species (HS-) may affect the electrochemical responses measured in slat-activated slag materials.

Training on non-destructive techniques and sensors for diagnosing and monitoring of concrete structures

The Fellow attended the technical courses on Thermo Scientific Amira-Avizo and Pergeos Software for the analysis of micro-scale computerized tomography (non-destructive characterization technique) datasets at the Henry Royce Institute of the University of Manchester on August 5-6, 2019.

On August 16th, 2019, the Fellow joined Professor Muhammed Basheer on a technical visit to City University London to establish fibre optic sensor manufacturing at UNIVLEEDS as part of the establishment of a sensors laboratory in School of Civil Engineering.

Training on advanced materials characterization (real-time monitoring and sensing corrosion)

The Fellow participated in the Royal Microscopy Society course on TEM fundamentals and sample preparation at UNIVLEEDS on July 8th-10th, 2019. Additionally, the Fellow organized the Advanced Microscopy and Computational Techniques in the Multi-Scale Characterisation of Porous Media Colloquium in association with the UNIVLEEDS Bragg Centre for Materials Research, Institute of Fluid Dynamics, and UKCRIC on January 30th, 2020. Keynote speaker of this event was Prof. Catherine Davy from L’École Centrale de Lille (France). This event also served to strengthen international research collaborations for the Fellow.

The research training activities, which contributed to the overall work programme are briefly described:

• Literature review on the effect of the ionic conductivity of highly reductive pore solutions of slag based AACs. It was evident steel surface metallurgy (grain size, grain density) along with the ionic conductivity of the pore solution affect the establishment, stability, and maturity of passive layers.
   
• The research activities of the project on the following aspects commenced after technical courses and training on material characterization and corrosion fundamentals were successfully completed.
   
• The Fellow developed a database on micro-computerized tomography of near-neutral salt activated slag materials, which was leveraged and analyzed for the successful completion of one M. Eng. individual dissertation.
  
  The data revealed the differences between mass transport processes because of material design differences. The two (2) datasets are critical to assess the mass transport and pore structure network analysis of both Na2CO3 and Na2SO4 activated slag materials.
  
  Additionally, the Fellow produced long-timescale aged near-neutral salt activated slag materials (540 days) critical to inform service-life models and performance-based materials designs. Aged materials are available for long-term phase assemblage characterization as well as mechanical and mass transport performance of near-neutral salt and alkali activated slag materials.
  
  This data information is crucial to inform the development of novel service life models for low-CO2 cementitious materials by validating long-time scale predictions.
   
• Available long-term data on the carbonation effects on the corrosion mechanisms led to the first reported long-term studies (335 days) on the CO2-induced (carbonation) corrosion performance of reinforced alkali-activated slag/metakaolin blended concretes.
  
  Results indicated that the addition of metakaolin to alkali-activated slag concretes caused short-term (<158 days) beneficial improvements to the corrosion protection of embedded reinforcement. However, these benefits are not long lasting, and by 221 days of exposure, metakaolin-containing alkali-activated slag concretes experienced increases in the corrosion rate likely due to the breakdown of a porous intermediary film.

The research is continuing at the University of Leeds, and is currently led by Professor Susan A Bernal in the School of Civil Engineering. The project will capitalize on the innovative findings of passive layer formation mechanisms to probe further the specific role of sulphide species within the first three days of the passive layer establishment process.

The research topic on passive layer formation and breakdown mechanisms within low-CO2 cementitious materials continues to remain quite popular with global research attention. The Fellow aims to further investigate research questions opened through the implementation of this project in his future academic career as an Assistant Professor at the Pennsylvania State University.

This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 839436. 

Impact

The PERFoRM project has permitted a range of technical and training objectives to be attained. These outcomes will contribute to the expected impact of the project highlighted in the original research proposal. Immediate impacts arising are summarized below:

• New insights into the engineering application of wireless sensor technology and data processing challenges have been highlighted by the Fellow in a high-impact publication in Science.
  
  These will assist the scientific community by not only identifying the current challenges to sense, collect, and process data-to-information, but also spark new cross-disciplinary collaborations in the field of cementitious materials, electrical and computer engineering.
   
• New understanding of the effect of the ionic conductivity of highly reductive pore solutions of both alkali- and salt-activated slag materials where novel relationships between the pore solution chemistry of these materials was established with the steel metallurgical variables and the establishment, stability, and maturity of passive layers.
  
  More specifically, this work presented the mechanisms of passive layer formation based on the redox potential of the pore solution, which is established after 72 hours to be a highly reducing redox potential.

Publications and outputs

The project has the following publications and outputs:

Peer-Reviewed Journal Publication

Gevaudan, J.P.; Bernal, S.A.; Provis, J.L.; “The Relationship Between the Chemistry of Pore Solutions in Alkali-Activated Slag Materials and the Formation of the Passive Layer in Embedded Reinforcement.” In review. To be submitted to RILEM Technical Letters. 2021.

Gevaudan, J.P.; Mundrah, S.; Guerrero, M.E.; Mejia de Gutierrez, R.; Provis, J.L.; Bernal, S.A; “Carbonation-Induced Corrosion of Embedded Steel Reinforcement in Alkali-Activated Slag and Metakaolin Concretes.” In review. To be submitted to Cement and Concrete Research. 2021. (Impact Factor = 8.328)

Peer-Reviewed Conference Publication

Gevaudan, J.P.; Bernal, S.A.; “Chloride-induced Corrosion of Steel Reinforcement in Alkali-Activated Slag/Metakaolin Blended Concretes” International RILEM Conference on Microstructure Related Durability of Cementitious Composites (Microdurability). TU – Delft, The Netherlands. Published. 2021.

Scientific Perspective

Napolitano, R., Reinhart, W. and Gevaudan, J.P., 2021. Smart cities built with smart materials. Science, 371(6535), pp.1200-1201. (Impact Factor = 41.845)

Technical Reports

Mundrah, S.; Gluth, G.; Gevaudan, J.P., Bernal, S.A, et al. “A critical assessment on the applicability of electrochemical methods for testing corrosion of steel bars embedded in alkali-activated materials.” European Federation of Corrosion (EFC) Work Programme 11 within the Steel Corrosion in Alkali-Activated Materials Task Group. 2021.

Invited Talks

Gevaudan, J.P.; Bernal, S.A.; “Electrochemical Characterisation of Corrosion Mechanisms in Alkali-Activated Materials.” 3rd Yorkshire Cement and Concrete research meeting. January 20, 2020.

International and National Conference Participation

39th Cement and Concrete Science Conference (Bath, United Kingdom).

5th Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures (Potsdam, Germany).

Other dissemination

Additionally, the fellow organized the Advanced Microscopy and Computational Techniques in the Multi-Scale Characterisation of Porous Media Colloquium in association with the UNIVLEEDS Bragg Centre for Materials Research, Institute of Fluid Dynamics, and UKCRIC on January 30th, 2020. Keynote speaker of this event was Prof. Catherine Davy from L’École Centrale de Lille (France).