Spontaneous electrical effects in masonry affected by capillary water rise: The role of salts Elisa Franzoni ⇑ , Simone Bandini Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Università di Bologna, Via Terracini 28, 40131 Bologna, Italy highlights " One-brick-thick masonry model was built with fired clay bricks. " A steady-state capillary flux of water with chloride and sulphate was attained. " Moisture, salts and spontaneous potential were measured at different heights. " The role of salts was highlighted. " The results are consistent with the electrical double layer theory. article info Article history: Received 20 February 2012 Received in revised form 18 April 2012 Accepted 29 April 2012 Keywords: Soluble salts Efflorescence Rising damp Electrokinetic effects Spontaneous potential Brick masonry abstract The investigation of the electrical effects accompanying capillary water rise from ground in old masonries is of great practical interest, as such effects might be exploited for both measurement purposes (determi- nation of moisture and soluble salts) and for dehumidification purposes (techniques based on electroki- netic principles). In the present paper, the spontaneous dc voltages arising in a real-scale masonry model subject to a steady-state capillary flux of saline solutions (0.05 M sodium chloride and 0.05 M sodium sulphate in water) were measured. The resulting voltage depends on the amount and distribution of salts, rather than on moisture content in the masonry. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Capillary water rise is one of the main and most diffused prob- lems affecting old masonry walls [1], as it causes materials degra- dation [2], as well as hygienic and safety concerns for the building users [3]. The presence of moisture in historic structures is among the causes responsible for the emptying of old town centres and rural buildings, with great damage for local cultural identity. Thus, the investigation of capillary water rise in masonry walls, espe- cially in terms of degradation mechanisms, measurement tech- niques and remediation systems, is of paramount importance and still requires a strong research effort [4]. In particular, the current techniques for the dehumidification of old masonries are often not fully satisfactory due to several reasons (invasiveness, scarce effectiveness, poor long-term performance, bad aesthetic impact, etc.) and some promising results were shown by systems based on electrokinetic principles [5]. The occurrence of electrical effects in moist masonry walls is due to the electrical double layer arising at the water/solid interface in moist porous building materials [6]: when capillary water flux is present, e.g. from ground in the case of masonry, a spontaneous potential (streaming potential) takes place [7]. Nevertheless, the information on the electrokinetic phenomena occurring on site, in actual ma- sonry walls, are still very scarce [8] and a better knowledge of them could enhance the development of more reliable dehumidification systems and might also be exploited for on-site measurement of moisture and salts. For example, dehumidification systems based on electro-osmosis are usually applied to masonry without any preliminary investigation on the existing spontaneous potential and with no subsequent monitoring (except for the current con- sumed by the system, which however is not indicative of the actual dehumidification along the entire height of the wall), with strong prejudice for their real effectiveness. Moreover, the measurement of electrokinetic phenomena connected with rising moisture and salts might be a further tool for the smart monitoring of historic 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.04.098 ⇑ Corresponding author. E-mail address: elisa.franzoni@unibo.it (E. Franzoni). Construction and Building Materials 35 (2012) 642–646 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat