This not only drives the ions but also gives an idea of its bindingstructure and how the pores are filled leading to a reducedpermeability. The setup is a simple, polycarbonate enclosure withNaOH and NaCl solutions on either sides and steel plates connectingthe sample and the connecting wires.
UNDERSTANDING THE CHLORIDE ION TRANSPORT RESISTANCE OF ALKALLI ACTIVATED BINDER SYSTEMS
Alexis N. Crain, Civil EngineeringMentor: Dr. Narayanan Neithalath, Associate Professor, Akash Dakhane, Graduate Research Student
School of Sustainability Engineering and the Built Environment
INTRODUCTION RESULTSEXPERIMENTAL PROCESS
The goal of this research it to determine the chloride ion permeabilityin alternative cement pastes such as slag and fly ash. Physical andchemical characteristics of conventional OPC are well known. Hencethe need to develop a more sustainable concrete that not only recyclessolid waste but also eliminates the need for costly infrastructuralmaintenance.
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BACKGROUND
Access of chloride ions into concrete causes deterioration in concretestructures and is a very costly structural damage issue. The majormechanism that carries the chloride ions to the level of reinforcingsteel is diffusion. When chloride ions reach steel, they destroy thepassivating layer around steel, and accelerate the electrochemicaldeterioration reactions of steel. The expansive corrosion products exerttensile stresses on the surrounding concrete, resulting in cracking.Cracking exacerbates the ingress of more moisture and ions, thusaccelerating further corrosion and subsequently compromises thestructural and functional properties, necessitating costly repair andrehabilitation.
NSSM Profiles of OPC and FA Pastes
Effect of Cl- ion Permeability on the Pore Connectivity of the Sample
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EIS – Nyquist Plot
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FUTURE WORK
• The binding process can be characterized by SEM and FTIR tounderstand the distribution and the interface of the chloride andthe hydrated fly ash particles
• Penetration depths should be studied to model the diffusion usingFick’s Diffusion coefficient
• Geopolymeric cementitious systems such as slag and metakaolincan be evaluated for the same.
This work consisted of three phases consisting primarily of studies ondurability and microstructural properties of alkali activated fly ashbinders, and determination of the changes in the material porestructure as a result of chloride transport.
PHASE 1: Characterizing Chloride Ion Diffusion
PHASE 2: Pore Structure of Alkali Activated Systems
PHASE 3: Analysis of Chloride Binding
In order to characterize the chloride ionpermeability the Non Steady StateMigration (NSSM) Test was performedwhere the binder samples werepounded by chloride ions under anelectrochemical gradient with anapplied voltage of 10 V for 24 hours.
To characterize penetration, the pore structuremust be evaluated. Thus the Mercury IntrusionPorosimetry was performed. Pore connectivity,size and distribution in the sample gives the ideaif the chloride binding has actually taken place toreduce the porosity of the sample. It can alsoindicate the refinement of the pore sizes.
After chloride binding has taken place, there arechanges in not only the physical properties butelectrochemical properties of the sample as well.Therefore, an Electrical Impedance Spectroscopywas done to find if the binding was stable, and ifit has reduced the connectivity of the pores
MIP of both sides and Middle sections
• Alkali activated Fly Ash of 8M NaOHindicated an increase in theimpedance after the NSSM test
• The NSSM test shows an early increasein current followed by a sudden dropat 7 hours indicating high resistance
• MIP indicates the critical pore sizeprofile is the same for the middle andthe chloride section with slightlysmaller pores
• The results suggest pore refinementand chloride binding
