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This not only drives the ions but also gives an idea of its binding structure and how the pores are filled leading to a reduced permeability. The setup is a simple, polycarbonate enclosure with NaOH and NaCl solutions on either sides and steel plates connecting the sample and the connecting wires. UNDERSTANDING THE CHLORIDE ION TRANSPORT RESISTANCE OF ALKALLI ACTIVATED BINDER SYSTEMS Alexis N. Crain, Civil Engineering Mentor: Dr. Narayanan Neithalath, Associate Professor, Akash Dakhane, Graduate Research Student School of Sustainability Engineering and the Built Environment INTRODUCTION RESULTS EXPERIMENTAL PROCESS The goal of this research it to determine the chloride ion permeability in alternative cement pastes such as slag and fly ash. Physical and chemical characteristics of conventional OPC are well known. Hence the need to develop a more sustainable concrete that not only recycles solid waste but also eliminates the need for costly infrastructural maintenance. 0 50 100 150 200 250 0.00 5.00 10.00 15.00 20.00 25.00 Current (mA) Time (Hours) NSSM at 10V for 24 h FA1 FA2 OPC1 OPC2 BACKGROUND Access of chloride ions into concrete causes deterioration in concrete structures and is a very costly structural damage issue. The major mechanism that carries the chloride ions to the level of reinforcing steel is diffusion. When chloride ions reach steel, they destroy the passivating layer around steel, and accelerate the electrochemical deterioration reactions of steel. The expansive corrosion products exert tensile stresses on the surrounding concrete, resulting in cracking. Cracking exacerbates the ingress of more moisture and ions, thus accelerating further corrosion and subsequently compromises the structural and functional properties, necessitating costly repair and rehabilitation. NSSM Profiles of OPC and FA Pastes Effect of Cl - ion Permeability on the Pore Connectivity of the Sample -4 -3 -2 -1 0 1 2 3 4 20 30 40 50 60 70 Z'' Z' EIS – Nyquist Plot Before NSSM1 Before NSSM2 Before NSSM3 After NSSM1 After NSSM2 After NSSM3 FUTURE WORK • The binding process can be characterized by SEM and FTIR to understand the distribution and the interface of the chloride and the hydrated fly ash particles • Penetration depths should be studied to model the diffusion using Fick’s Diffusion coefficient • Geopolymeric cementitious systems such as slag and metakaolin can be evaluated for the same. This work consisted of three phases consisting primarily of studies on durability and microstructural properties of alkali activated fly ash binders, and determination of the changes in the material pore structure 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 ion permeability the Non Steady State Migration (NSSM) Test was performed where the binder samples were pounded by chloride ions under an electrochemical gradient with an applied voltage of 10 V for 24 hours. To characterize penetration, the pore structure must be evaluated. Thus the Mercury Intrusion Porosimetry was performed. Pore connectivity, size and distribution in the sample gives the idea if the chloride binding has actually taken place to reduce the porosity of the sample. It can also indicate the refinement of the pore sizes. After chloride binding has taken place, there are changes in not only the physical properties but electrochemical properties of the sample as well. Therefore, an Electrical Impedance Spectroscopy was done to find if the binding was stable, and if it has reduced the connectivity of the pores MIP of both sides and Middle sections • Alkali activated Fly Ash of 8M NaOH indicated an increase in the impedance after the NSSM test • The NSSM test shows an early increase in current followed by a sudden drop at 7 hours indicating high resistance • MIP indicates the critical pore size profile is the same for the middle and the chloride section with slightly smaller pores • The results suggest pore refinement and chloride binding
