Geopolymer-based moisture sensors for reinforced concrete health monitoring

Abstract Moisture plays a critical role in reinforced concrete corrosion, underpinning structural degradation which costs the global economy a staggering $350 bn per year (0.5% GDP). Both moisture sensors and repair materials that limit water ingress are required, but monitoring and maintenance are often viewed as separate challenges. This paper outlines a first-time demonstration of moisture sensors based on low calcium fly ash geopolymers — a class of cementitious, electrolytically conductive repair materials. Electrochemical impedance spectroscopy and equivalent circuit models are used to understand and optimize the electrical response of geopolymer sensors to water content and temperature. Moisture and temperature precisions of 0.1 wt% and 0.1 °C are demonstrated respectively, and sensor drifts over 20 min periods were found to be within 1–3%. Sensor responses were also shown to be repeatable to within 3% between wetting and thermal cycles. Results from spectrometry and chromatography analyses link this repeatability to the minimal ion leaching from the sensors. The study demonstrates the feasibility of moisture sensing using geopolymers, and furthers our current understanding of the role of moisture in the ionic conductivity of alkali-activated materials. This work is anticipated to be the first stage in developing 2D, distributed sensor-repairs for concrete structures, and other chemical sensors that support concrete structural health monitoring and prognostics.

[1]  Göran Hedenblad,et al.  Moisture permeability of mature concrete, cement mortar and cement paste , 1993 .

[2]  Kurt V. Heber.  Humidity measurement at high temperatures , 1987 .

[3]  Neil G. Thompson,et al.  CORROSION COST AND PREVENTIVE STRATEGIES IN THE UNITED STATES , 2002 .

[4]  J. S. Kim,et al.  Solid state water vapor sensor for robotics applications , 1988, Proceedings. 1988 IEEE International Conference on Robotics and Automation.

[5]  E. Zdankiewicz,et al.  Micromachined water vapor sensors: a review of sensing technologies , 2001 .

[6]  Transient moisture profiles in cover-zone concrete during water absorption , 2018, Cement and Concrete Research.

[7]  Ji Zhou,et al.  A study on electrical conductivity of chemosynthetic Al2O3–2SiO2 geoploymer materials , 2008 .

[8]  L. J. Parrott,et al.  Moisture profiles in drying concrete , 1988 .

[9]  David A Lange,et al.  Relative Humidity in Concrete: What does it mean? , 2006 .

[10]  L. D. Miron,et al.  Concrete Durability: Cementitious Materials and Reinforced Concrete Properties, Behavior and Corrosion Resistance , 2017 .

[11]  Pawel Niewczas,et al.  Hybrid optical-fibre/geopolymer sensors for structural health monitoring of concrete structures , 2015 .

[12]  Kenneth T. V. Grattan,et al.  Demonstration of a fibre-optic sensing technique for the measurement of moisture absorption in concrete , 2006 .

[13]  Noboru Yamazoe,et al.  Humidity sensors: Principles and applications , 1986 .

[14]  B. Yadav,et al.  Opto-electronic humidity sensor: A review , 2015 .

[15]  A. Hamilton,et al.  Ambient Cured Fly Ash Geopolymer Coatings for Concrete , 2019, Materials.

[16]  M. Baghini,et al.  A critical review of soil moisture measurement , 2014 .

[17]  Mohamed Saafi,et al.  Temperature and moisture monitoring in concrete structures using embedded nanotechnology/microelectromechanical systems (MEMS) sensors , 2008 .

[18]  Jonathan Knappett,et al.  Craig’s Soil Mechanics , 1974 .

[19]  A. Lasia.  Electrochemical Impedance Spectroscopy and its Applications , 2014 .

[20]  Pa Wedding,et al.  The Electrical Resistivity of Concrete with Emphasis on the Use of Electrical Resistance for Measuring Moisture Content , 1979 .

[21]  J. Deventer,et al.  Geopolymer technology: the current state of the art , 2007 .

[22]  José Marcos Ortega,et al.  Moisture Distribution in Partially Saturated Concrete Studied by Impedance Spectroscopy , 2013 .

[23]  Mohamed Saafi,et al.  Graphene/fly ash geopolymeric composites as self-sensing structural materials , 2014 .

[24]  Hao Wang,et al.  Fly ash-based geopolymers: The relationship between composition, pore structure and efflorescence , 2014 .

[25]  David A Lange,et al.  Relative Humidity in Concrete , 2006 .

[26]  D. Miranda,et al.  Considerations on electrical impedance measurements of electrolyte solutions in a four-electrode cell , 2016 .

[27]  Fernando Pacheco-Torgal,et al.  Alkali-activated binders: A review: Part 1. Historical background, terminology, reaction mechanisms and hydration products , 2008 .

[28]  Grzegorz Fusiek,et al.  Geopolymeric thermal conductivity sensors for surface-mounting onto concrete structures , 2016 .

[29]  Minqiang Li,et al.  A novel conductive humidity sensor based on field ionization from carbon nanotubes , 2007 .

[30]  Ricardo P Nogueira,et al.  On the intrinsic electrochemical nature of the inductance in EIS: A Monte Carlo simulation of the two-consecutive-step mechanism: The flat surface 2 D case , 2008 .

[31]  N. Neithalath,et al.  An electrical impedance investigation into the chloride ion transport resistance of alkali silicate powder activated slag concretes , 2013 .

[32]  Diego González-Aguilera,et al.  Automatic mapping of moisture affectation in exposed concrete structures by fusing different wavelength remote sensors , 2016 .

[33]  Isidro Sánchez,et al.  Impedance spectroscopy study of hardened Portland cement paste , 2002 .

[34]  Jianqiao Ye,et al.  Hybrid graphene/geopolymeric cement as a superionic conductor for structural health monitoring applications , 2016 .

[35]  Mauricio Sánchez-Silva,et al.  Non-destructive methods for measuring chloride ingress into concrete: State-of-the-art and future challenges , 2014 .

[36]  Richa Srivastava,et al.  Moisture sensor based on ZnO nanomaterial synthesized through oxalate route , 2008 .

[37]  Nemkumar Banthia,et al.  Carbon-fiber reinforced cement based sensors , 2007 .

[38]  T. L. Yeo,et al.  Optical fiber sensors for monitoring ingress of moisture in structural concrete , 2006 .

[39]  Jian He,et al.  Geopolymer-Based Smart Adhesives for Infrastructure Health Monitoring: Concept and Feasibility , 2011 .

[40]  Prinya Chindaprasirt,et al.  Electrical conductivity and dielectric property of fly ash geopolymer pastes , 2011 .

[42]  J. Provis.  Geopolymers and other alkali activated materials: why, how, and what? , 2014 .

[43]  M. Maslehuddin,et al.  Effect of moisture, chloride and sulphate contamination on the electrical resistivity of Portland cement concrete , 1996 .

[44]  Kristina Norling Mjörnell.  Self-desiccation in concrete , 1994 .

[45]  Gwo-Bin Lee,et al.  Humidity Sensors: A Review , 2005 .

[46]  F. Berkemeier,et al.  On the physical interpretation of constant phase elements , 2009 .

[47]  Branko Glisic,et al.  Sensing sheets: Optimal arrangement of dense array of sensors for an improved probability of damage detection , 2015 .