Article

Microfabricated sol-gel relative humidity sensors for soil suction measurement during laboratory tests

Rafaela Cardoso,*^a Gabriele Sarapajevaite,^b Oleksandr Korsun,^b Susana Cardoso,^c Laura Ilharco^d

^aInstituto Superior Técnico (IST), Lisbon University, Lisbon, Portugal; Civil Engineering Research Innovation and Sustainability (CERIS), Institute of Construction, Structures and Territory of IST (ICIST), Lisbon, Portugal.

^bINESC-MN Microsystems and Nanotechnologies, Lisbon, Portugal.

^cInstituto Superior Técnico (IST), Lisbon University, Lisbon, Portugal; INESC-MN Microsystems and Nanotechnologies, Lisbon, Portugal.

^dInstituto Superior Técnico (IST), Lisbon University, Lisbon, Portugal; CQFM Centro de Química-Física Molecular, IST, Lisbon, Portugal.

Corresponding author: Rafaela Cardoso (email: rafaela@civil.ist.utl.pt).

*Present address: DECivil, IST, Av Rovisco Pais, 1, 1049-001 Lisbon, Portugal.

Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.

Published on the web 23 March 2017.

Received August 3, 2016. Accepted March 17, 2017.

Canadian Geotechnical Journal, 2017, 54(8): 1176-1183, https://doi.org/10.1139/cgj-2016-0419

Abstract

Currently there are no small sensors that can be incorporated inside soil samples for laboratory testing, to monitor water transport during loading. This is an important limitation to a better understanding of the hydromechanical coupled behaviour of soils. A sol-gel relative humidity sensor (11 mm × 11 mm), microfabricated in a clean room environment, was conceived to be incorporated in soil specimens during standard laboratory tests. The sensor operates based on changes in electrical resistivity detected by a cerium-doped silica–titania film deposited using a sol-gel technique over interdigitated aluminium electrodes spaced at 300 μm. To the best of the authors’ knowledge, sol-gel sensors for relative humidity measurement have never been used in soils; therefore, this is a novel application. The water retention curve of compacted kaolin was measured with the sensors and compared with the curve found using water dewpoint potentiometer WP4-C. The sensors were also tested incorporated in an oedometer cell, in which load was applied under vapour equilibrium. It was possible to detect the increment of the degree of saturation during compression. The use of the developed sensors incorporated in soils is considered acceptable for suction ranges between 1 and 10 MPa, which extends the suction interval covered by tensiometers, normally operating up to 2 MPa. Although the sensors require improvements in terms of sol-gel deposition and calibration protocol, the results confirm their scientific potential for being used in testing and characterization of unsaturated soils.

Keywords: microfabricated interdigitated electrodes, humidity sensors, suction, relative humidity, unsaturated soils, oedometric compression

References

Albrecht B, Benson C, Beuermann S. 2003. Polymer capacitance sensors for measuring soil gas humidity in drier soils. Geotechnical Testing Journal 26(1): 1-9 Crossref, Google Scholar.
ASTM. 2011. Standard practice for classification of soils for engineering purposes (Unified Soil Classification System). ASTM standard D2487. American Society for Testing and Materials, West Conshohocken, Pa. . Crossref, Google Scholar
Cardoso, R., Lima, A., Romero, E., and Ferrari, A. 2007. A comparative study of soil suction measurement using two different high-range psychrometers. In Experimental Unsaturated Soil Mechanics, Springer Proceedings in Physics. Springer Berlin Heidelberg. Vol. 112, pp. 79–94. Google Scholar
Cardoso, R., Sarapajevaite, G., Korsun, O., Cardoso, S., and Ilharco, L. 2017. Sol-gel relative humidity sensors: Impact of electrode geometry on performance in soil suction measurements. Journal of Sensor Technology. [In press.] Google Scholar
Decagon Devices, Inc. 2003. WP4-C Dew Point PotentiaMeter. Operator’s manual, version 1. Decagon Devices, Inc. Google Scholar
Fares A, Abbas F, Maria D, Mair A. 2011. Improved calibration functions of three capacitance probes for the measurement of soil moisture in tropical soils. Sensors 11: 4858-4874 Crossref, Medline, Google Scholar.
Fredlund, D.G., and Rahardjo, H. 1993. Soil mechanics for unsaturated soils. John Wiley and Sons, New York. Google Scholar
Jiang K, Fei T, Zhang T. 2014. Humidity sensor using a Li-loaded microporous organic polymer assembled by 1,3,5-trihydroxybenzene and terephthalic aldehydeitle. RSC Advances 4: 28451-28455 Crossref, Google Scholar.
Keyhani A. 2001. Development of mini-gypsum blocks for soil moisture measurement and their calibration to compensate for temperature. Journal of Agricultural Science and Technology 3: 141-145 Google Scholar.
Kizito F, Campbell C, Campbell G, Cobos D, Teare B, Carter B, Hopmans J. 2008. Frequency, electrical conductivity and temperature analysis of a low-cost capacitance soil moisture sensor. Journal of Hydrology 352(3–4): 367-378 Crossref, Google Scholar.
Kozhukharov S, Nenova Z, Nenov T, Nedev N, Machkova M. 2013. Elucidation of the contribution of modified titania films over the performance of thin film humidity sensors. Journal of Chemical Technology and Metallurgy 48(2): 142-146 Google Scholar.
Kozhukharov S, Nenova Z, Nenov T, Nedev N, Machkova M. 2015. Humidity sensing elements based on cerium doped titania-silica thin films prepared via a sol–gel method. Sensors and Actuators B: Chemical 210: 676-684 Crossref, Google Scholar.
Leong E-C, Tripathy S, Rahardjo H. 2003. Total suction measurement of unsaturated soils with a device using the chilled-mirror dew-point technique. Géotechnique 53(2): 173-182 Crossref, ISI, Google Scholar.
Lourenço S, Gallipoli D, Toll D, Augarde C, Evans F. 2011. Towards a tensiometer based suction control system for laboratory testing of unsaturated soils. Geotechnical Testing Journal 34: 1-10 Crossref, Google Scholar.
OIML. 1996. The scale of relative humidity of air certified against saturated salt solutions. International Recommendation OIML R 121: 1996. Organisation Internationale de Métrologie Légale (OIML). Grande Imprimerie de Troyes, Troyes, France. Google Scholar.
Rittersma ZM. 2002. Recent achievements in miniaturised humidity sensors – a review of transducer techniques. Sensor and Actuators A: Physical 96: 196-210 Crossref, Google Scholar.
Romero, E. 2001. Controlled suction techniques. In Proceedings of 4° Simpósio Brasileiro de Solos Não Saturados. pp. 535–542. Google Scholar
Romero E. 2013. A microstructural insight into compacted clayey soils and their hydraulic properties. Engineering Geology 165: 3-19 Crossref, ISI, Google Scholar.
Sukhyy KM, Gomza YP, Belyanovskaya EA, Klepko VV, Shilova OA, Sukhyy MP. 2015. Resistive humidity sensors based on proton-conducting organic-inorganic silicophosphates doped by polyionenes. Journal of Sol-Gel Science and Technology 74: 472-481 Crossref, Google Scholar.
Tarantino A, Mongiovì L. 2003. Calibration of tensiometer for direct measurement of matric suction. Géotechnique 53(1): 137-141 Crossref, Google Scholar.
Tarantino A, Gallipoli D, Augarde CE, De Gennaro V, Gomez R, Laloui L, Mancuso C, El Mountassir G, Munoz JJ, et al. 2011. Benchmark of experimental techniques for measuring and controlling suction. Geotechnique 61(4): 303-312 Crossref, Google Scholar.
Traversa E. 1995. Ceramic sensors for humidity detection: the state-of-the-art and future developments. Sensors and Actuators B: Chemical 23: 135-156 Crossref, Google Scholar.
Truong, H.V.P., and Holden, J.C. 1995. Soil suction measurement with transistor psychrometer. In Proceedings of the 1st International Conference on Unsaturated Soils (UNSAT 95), Paris. Edited by E.E. Alonso and P. Delage. A.A. Balkema, Rotterdam. Vol. 2, pp. 659–665. Google Scholar
Vaisala. 2004. HMT337: Vaisala HUMICAP humidity and temperature transmitter. Series HMT330. User’s guide. Vaisala. Google Scholar
van Genuchten MT. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal 44: 892-898 Crossref, ISI, Google Scholar.
Vanapalli SK, Fredlund DG, Pufahl DE. 1999. The influence of soil structure and stress history on the soil-water characteristics of a compacted till. Géotechnique 49(2): 143-159 Crossref, ISI, Google Scholar.
Vaz C, Jones S, Meding M, Tuller M. 2013. Evaluation of standard calibration functions for eight electromagnetic soil moisture sensors. Vadose Zone Journal 12(2) Crossref, Google Scholar.
Woodburn, J.A., and Lucas, B. 1995. New approaches to the laboratory and field measurement of soil suction. In Proceedings of the 1st International Conference on Unsaturated Soils (UNSAT 95), Paris. Edited by E.E. Alonso and P. Delage. A.A. Balkema, Rotterdam. Vol. 2, pp. 667–671. Google Scholar
Yuan Q, Li N, Geng W, Chi Y, Tu J, Li X, Shao C. 2011. Humidity sensing properties of mesoporous iron oxide/silica composite prepared via hydrothermal process. Sensors and Actuators B: Chemical 160: 334-340 Crossref, Google Scholar.