Phd Plan

PhD plan

1 Introduction

My goals and contribution to the program

My main goal is to broaden my theoretical foundation in the fields of electrochemistry, corrosion and concrete in order to support experimental findings. I plan to summarize other experimentalists work and find ways to use their ideas. My intention is to build on previous work done and to search the missing knowledge that combines electrochemistry and concrete science.

I believe that my background in chemistry in addition with my knowledge in micellar chemistry and experimental experience corresponds with your needs. Micellar chemistry can help in the understanding of the mechanism of the PEO-PS bilayer adsorption on the anode and CaO core release from nano-aggregates due to pH drop. The adsorption effectiveness is related to the hydrophilicity – hydrophobicity ratio of surfactants, which determines mainly the type of developed interactions at the interface of anode – surfactant species (monomers and micelles). The durability and aesthetic appearance of concrete may be improved by the addition of hydrophobizing agents as a consequence of reduced water permeability. Hydrophobizing agents lead to less water absorption at the same time as they let water vapour out. This may lead to a dryer interior over time and thereby reduced rate of detrimental reactions needing liquid water as reaction medium. The ingress of water born aggressives like chlorides will be reduced (in particular in marine splash zones), but also corrosion rates may be decreased. Carbonation rates may, however, be somewhat increased.

Furthermore there is a certain point in the concentration of a surfactant called critical micellar concentration (cmc). Above this point surfactants aggregate in the form of micelles. Cmc is affected by factors like temperature, pH, salt concentration, etc. Salt presence generally affects the folding of polymers, by lowering cmc, so it is probably a concern for PEO-PS blocks. Chemical factors such as ionic strength which decrease the critical micelle concentration of the polymer blocks may improve the coating stability. The non-ionic polyethylene oxide derivative is also one of the most important detergent and does not suffer from drawbacks, i.e. functions very well in acid solutions. The use of other pH sensitive polymeric micellar shells may cause protonation on low pH values and thus turn them into monomers. I believe these points could be further investigated.

Objectives and significance:

The use of novel self healing cement-based layers for cathodic protection is an ambitious project that raises quite significant scientific challenges. This project is considered with a high feasibility based on investigations and indication that materials show superior properties in the presence of nano-aggregates. Recent studies shows calcium silica hydrate CSH gel contained in cement is a nanostructured material. Therefore a nanoscale investigation of the properties of the cement layer is required as well.

The new idea of this proposal is increasing the durability of the anode/concrete cover zone in reinforced concrete, by means of a self-healing mechanism. The novel material is a modified cement matrix that supplies excess Ca ions when needed and will stop or slow down calcium migration. The result from the self healing process will be restored properties of this interface and increased durability. Apart from practical applications there is also great importance from an intellectual point of view. The inspiration comes from biological systems, which have the ability to heal after being wounded. Recent advances in materials chemistry and nanoscale fabrication techniques have enabled biologically inspired materials systems that mimic many of these remarkable functions.

2 PhD thesis and methodology

A.    Literature study, establishing properties of concrete

Concrete has many properties that makes it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for its properties like hydration, strength and durability to be optimal.

Water and cement initially form a cement paste that begins to react and harden. This paste binds the aggregate particles through the chemical process of hydration. In the hydration of cement, chemical changes occur slowly, eventually creating new crystalline products, heat evolution, and other measurable signs [1]. The properties of this hardened cement paste, called binder, control the properties of the concrete. It is the inclusion of water (hydration) into the product that causes concrete to set, stiffen, and become hard. Since the main hydrate of cement is the nano-structured calcium silica hydrate (CSH) it is essential to investigate its properties on a nano-scale. The strength of the concrete is related to the water to cement mass ratio and the curing conditions. A high water to cement mass ratio yields a low strength concrete. This is due to the increase in porosity (space between particles) that is created with the hydration process.

Durability is a very important concern in using concrete for a given application. Concrete provides good performance through the service life of the structure when concrete is mixed properly and care is taken in curing it. Water, although important for concrete hydration and hardening, can also play a role in decreased durability once the structure is built. This is because water can transport harmful chemicals to the interior of the concrete leading to various forms of deterioration.

Methods for studying the concrete bulk matrix are microscopy (SEM and TEM) as well as mechanical tests. A rough estimation of the time for the implementation of this part of research will be 3-4 months.

B.     Tailoring properties of nanoaggregates

PEO-block-PS vesicles are nanostructured materials that will be used for the transportation of CaO in hostile (e.g. less alkaline) environment. These polymer aggregates will release CaO in the cement matrix after detrimental external influence. The release of CaO is needed as an excess source of Ca²⁺ to cover up the missing Ca ions, because of their depletion during the formation of Ca(OH)₂ on lower pH. These micelles contribute to the restructure of the pore space in the cement matrix and alter the cement hydration mechanisms due to their specific amphiphilic properties [2]. The nano-composite can be studied by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM).

Bilayers are particularly impermeable to water and ions, which allows them to regulate water, salt concentrations and pH by pumping ions across their shells. Furthermore there is evidence [2] that the hydrophobic interaction of the micelles shell is able to significantly reduce water permeability even in low polymer concentration. Therefore it is necessary to set a lower limit for water permeability by means of PEO-b-PS concentration. This part of the research will initially improve the properties of the anode/concrete interface and will reduce the risk of bond weakening, and will probably take less than 4 months.

C.    Development and testing (sample preparation, conditioning and monitoring).

Development and testing will be the main experimental activity of the whole project. The electrochemical behavior of the novel cathodic system will be studied will be studied with techniques like potential mapping, potentiodynamic polarization (PDP), polarization resistance (PR), electrochemical impendence spectroscopy (EIS), cyclic voltametry (CVA) etc. These techniques will help to evaluate how the product layers influence the electrochemical behavior of the steel in cement extract. The evaluation of the electrochemical behavior of the steel surface, in terms of deriving polarization resistance, should take into account the crystallinity, morphology, and composition of the surface layers, that can be investigated by scanning electron microscopy and energy dispersive X-ray analysis [3]. Electrochemical measurements are also employed to monitor the electrochemical process at the steel–paste interfaces.

Cyclic voltammetry is a useful method for investigating the mechanisms of surface oxidation/reduction behavior of steel in an alkaline environment, as the concrete pore solution. CVA results can indicate high corrosion resistance when the peak potential initially shifts anodically. EIS on the other hand is a much more complicated technique that measures the impedance of a system over a range of frequencies. Therefore we can have information on the frequency response of the system, including the energy storage and dissipation properties. EIS measurements can provide equivalent electrical circuit, used to represent the investigated systems and interfaces.

D.    Characterization (evaluating necessary alterations in the synthesis of nano aggregates and/or testing optimized concentrations and properties).

Characterization methods like SEM, infared spectroscopy and X-ray spectroscopy (XRD) can be used for this part of the work. Combined characterization provides information for the structural alterations induced by cathodic protection (CP), and help to explain the efficiency of CP techniques. Microscopic and image analysis techniques render possible quantitative characterization of the composite microstructure at various interfaces, including structural morphology of steel corrosion and cement hydration products, pore structure, as well as the interfacial transition zones between cement paste and aggregate or bulk cementitious matrix and steel [4]. SEM observations provide evidences that supports the existence of other mixtures or substances in the protected mortars.

E.     Evaluation results (involving CP efficiency, morphology and composition of the layers).

Once the initial search (described above) has been performed, the next phase is the evaluation of laboratory results. This stage is used to verify if experimental data and simulations produce sensible results. At this point possible problems or experimental data flaws may be revealed. Consequently the assessment of critical parameters and dominant factors in terms of up-scale of the tests, is essential.

F.     Modeling cement hydration in the modified systems

The final part of the project will be a modeling approach. The main objective is the application of existing models of cement hydration and ion transprort mechanisms to the modified systems studied in the Thesis.

G.    Thesis

Finally, at the end of all simulations and experiments will be the writing of the thesis.

3 Research time plan

Project Implementation

The preliminary work plan is as presented in Table 1, including main milestones.

Table 1. Preliminary schedule of the milestones of the project
Year 1 months				Year 2 months				Year 3 months				Year 4 months
1-3	4-6	7-9	10-12	1-3	4-6	7-9	10-12	1-3	4-6	7-9	10-12	1-3	4-6	7-9	10-12
A
	B
	C
						D
							E
										F
													G

Milestones:

A: Literature study, establishing properties of concrete

B: Tailoring properties of nano-aggregates

C: Development and testing (sample preparation, conditioning and monitoring).

D: Characterization (evaluating necessary alterations in the synthesis of nano aggregates and/or testing optimized concentrations and properties).

E: Evaluation results (involving CP efficiency, morphology and composition of the layers). Assessment critical parameters and dominant factors in terms of up-scale of the tests

F: Modeling cement hydration in the modified systems

G: Thesis

4. Publication & conference presentation expected

Each step described above covers subjects of my work that can be published. I believe that I am able to publish three or four papers per year. Most of concrete properties were studied thoroughly in the past therefore one paper on establishing the surface and electrochemical properties of concrete specimens could cover this subject. Tailoring properties of the nano-agregates perhaps can be presented in two papers. Development and testing, characterization and evaluating results would be subjects to further publication. I also plan to attend meetings or conferences in order to present research. 

5. References

[1] Fahlman, M., “Materials Chemistry”, Springer, (2007)

[2] Koleva, D., A., van Breugel, K., Zhou, G., Ye, J., Chamululu, G., and Koenders, E., A., B., “Porosity and Permeability of Mortar Specimens Incorporating PEO113–b–PS218 Micelles”, ACI Materials Journal, 267, 101-110, (2009)

[3] Koleva, D., A., de Wit, J., H., W., van Breugel, K., Lodhi, Z., F., and van Westingc., E., “Investigation of Corrosion and Cathodic Protection in Reinforced Concrete I. Application of Electrochemical Techniques” Journal of The Electrochemical Society, 154 (4), 52-61, (2007)

[4] Koleva, D., A., van Breugel, K., de Wit, J., H., W., ., and van Westingc., E., Copuroglu, O., Veleva, L., Fraaij, A., L., A., “Correlation of microstructure, electrical properties and electrochemical phenomena in reinforced mortar. Breakdown to multi-phase interface structures. Part I: Microstructural observations and electrical properties”, Materials Characterization, 59, 290 – 300, (2008)