The PhD candidate: Judy Yuen Wah Luong

Title of the PhD project: Durability of Concrete with Novel Composite Cements for the Norwegian Market

Objectives

The aim of the PhD project is to achieve better understanding of the degradation mechanisms of future Zero Carbon emission Concrete (ZCC) made with novel composite cements (CEMII/C). By that to obtain essential knowledge to optimize the design of future ZCC with respect to resistance against long-term degradation. The focus will be on the resistance against carbonation and chloride intrusion.  

Background    

Cement is by far the largest contributor to the carbon footprint of concrete, and the CO₂ emission from the cement production stands for a significant part of the global CO₂ emission. In conjunction with the Norwegian government’s goal of reducing the total CO₂ emission in Norway by 55% by 2030, Norcem, as one of the major cement producers in the Norwegian market, has the goal of reducing the CO₂ emission from their products to a level that gives zero emission throughout their life cycle by 2030. In order to obtain zero net CO₂ emission concrete, it is estimated that Norcem needs to reduce the CO₂ emission per unit concrete by 75% compared to current levels (2022).

A major part of the CO₂ emission originates from the production of Portland clinker in cement. Carbon capture and storage technology, as well as an increase usage of alternative fuel in the production of cement, are measures that are already been implemented in Norcem’s business strategy in order to reduce the CO₂ emission. However, to obtain zero net CO₂ emission concrete, it is also necessary to apply measures that allow to reduce the cement content in concrete and to replace in a greater extent Portland clinker with alternative materials, so-called supplementary cementitious materials (SCMs). R&D is necessary to provide knowledge for development of new and improved products in terms of carbon footprint. The innovation project ZeroCarbCon initiated by Norcem will form the basis for future development.

The research that will be performed in the ZeroCarbCon project, will be based on the results from another innovation project by Norcem. The NewSCem project was established in 2018 and finished in 2022. In this project, a large selection of SCMs were evaluated as clinker substitution with levels up to 35 weight-%, based on results from performance testing and field exposure. The three most promising materials turned out to be calcined clay, non-ferrous slag and natural volcanic pozzolan. These materials will be further investigated in the ZeroCarbCon project. Since the new cement standard allows application of cement with clinker substitution up to 50 weight-%, the SCMs will be evaluated based on corresponding substitution levels in the ZeroCarbCon project.  

The development of the novel composite cements with up to 50 weight-% of clinker substitution (CEM II/C), allows the development of future ZCC. However, it is necessary to gain more knowledge about these new products in order to develop products that will meet the requirements from the industry, in terms of the mechanical and durability properties. The understanding of the durability of these new products are especially important as there have been significant changes on the current regulations on concrete durability recently and further changes are expected in the nearest future. A critical review of these changes as well as recommendations of concrete combination of the novel composite cements will be given in the ZeroCarbCon project.

Research questions    

Two of the most important degradation mechanisms in reinforced concrete, thus often define its durability properties, is corrosion induced by carbonation and corrosion induced by chlorides. The main study in this PhD project will be on the resistance of future ZCC with CEM II/C cement against carbonation and chloride ingress. The aim is to explain the chemical processes behind these two degradation mechanisms for the novel concretes, thus to provide essential knowledge to predict the durability properties and to form the basis for development of future ZCC.

A great number of different CEM II/C cement with different combination of SMCs and levels of clinker substitution will be tested. The aim is to study the effect of the levels of clinker as well as the effect of the different SMC combinations on the carbonation and chloride ingress rate. The most promising combinations will be further tested with varying water-cement ratio in order to provide a basis for the new durability classification of concrete, where the exposure resistance classes (ERC) are introduced. This allows us to determine the maximum water-binder ratio for the different classes related to carbonation, XRC classes, and classes related to chloride ingress, XRDS classes.

Collaboration    

The PhD project is part of the innovation project ZeroCarbCon, in which several companies and institutions are involved. Essential results from research and development work conducted by the other parties in the project can be utilized in the PhD project.

In this project, the PhD student will have a close collaboration with SINTEF, who will be responsible for the execution of the laboratory testing and field testing. The student will assist in some of the testing. Furthermore, the student will interpret the results from the testing and put them in context with current models and regulations.

The PhD student will also have a collaboration with NPRA. NPRA has since the 1990s systematically collected data from well-documented fields tests. The field data that will be harvested for the study in the ZeroCarbCon project, on the other hand, are based on only 1-5 years field exposure. Through the collaboration, the student will have access to and be able to supplement with long-term data from NPRA to verify possible models.
    
Tasks    

The PhD project can be divided into 5 main tasks.

1.    Literature review
Understand the underlying models and assumptions behind the regulations related to carbonation and chloride ingress given in the current concrete standards NS-EN206 and NS-EN1992.

2.    Accelerated lab testing – phase I:
Prepare a testing matrix in which different combinations of SMCs
and replacement levels of clinker will be systemically varied. The model cements from this matrix will be tested for the resistance against carbonation and chloride ingress, by performing accelerated testing at the laboratory.

3.    Accelerated lab testing – phase II:
The most promising model cements will be further tested through accelerated laboratory testing where the water-cement ratio will be systematically varied. The study will form the basis for the new durability classification of concrete according to NS-EN1992, as this classification includes the maximum water-cement ratio for the different classes. The additional laboratory testing will provide data to determine the maximum water-cement ratio for the XRC classes related to carbonation and XRDS classes related to chloride ingress.  

4.    Field exposure and long-term field data
The most promising model cement will also undergo long-term field exposure to carbonation (field station at Voll in Trondheim) and chloride ingress (NPRA’s field station in Bergen). The aim is to imitate the different environments corresponding to the different exposure classes given in the standards, e.g XC1-XC4 for carbonation and XS1-XS3 for chloride ingress. New field data will be studied in conjunction with long-term field data from earlier projects (data from NPRA).

5.    Mechanism study
Use advanced methods, e.g. SEM, TGA and XRD, on a selection of samples to explain potential deviating behaviors among the concrete samples and understand the underlying mechanisms. The study will likely be performed in collaboration with PhD student Johan Dalene, who also will be a part of the ZeroCarbCon project and will study the microstructure and reaction phases of the novel concretes.

Supervision

Main supervisor: Klaartje De Weerdt (NTNU)
Co-supervisor: Knut Ose Kjellsen (Norcem)
Supporting supervisors: Øyvind Bjøntegaard (NPRA), Tobias Danner (SINTEF), Malene Thostrup Pedersen (NTNU)