Recent Development on Self‐Cleaning Cementitious Coatings

Abstract

One of the ways that surfaces can be self-cleaning is by repelling water so effectively that water-borne contaminants cannot attach-by being superhydrophobic. This is demonstrated particularly well by the Indian Lotus, Nelumbo nucifera, which has leaves that remain clean in muddy water. The leaves can be cleaned of most things by drops of water, an effect that has been patented and used in technical systems [1]. 1.1 Superhydrophobicity 1.1.1 Introducing Superhydrophobicity Superhydrophobicity is where a surface repels water more effectively than any flat surface, including one of PTFE (Teflon R). This is possible if the surface of a hydrophobic solid is roughened; the liquid/solid interfacial area is increased and the surface energy cost increases. If the roughness is made very large, water drops bounce off the surface and it can become self-cleaning when it is periodically wetted. To understand more about this type of self-cleaning it is necessary to consider how normal surfaces become wetted and become dirty. The effect has been a focus of much recent research and has been reviewed recently [2-7]. A good mathematical explanation can be found in a recent book chapter by Extrand [8].

TiO2-based Photocatalytic Cementitious Composites: Materials, Properties, Influential Parameters, and Assessment Techniques

“…The basic heterogeneous photocatalytic process is the activation of a semiconductor photocatalyst by irradiation [25]. TiO 2 , ZnO, and CdS are widely used semiconductor materials [26]. Semiconductors contain a filled conduction band and an empty valence band, which are separated by a band gap of energy (E g ).…”

“…Among all the transition metal oxides, TiO 2 is the most studied photocatalyst for self-cleaning cementitious materials because of its low cost, chemical stability and human safety, non-toxicity, and efficient photocatalytic activity [11,26,30]. Under ambient conditions, TiO 2 has three main crystal structures including anatase (distorted tetragonal crystal structure), rutile (also tetragonal), and brookite (orthorhombic crystal structure), in which only rutile and anatase are attractive for practical applications since they are wide band gap semiconductors [17,21,25,31].…”

“…As Zhong and Haghighat [40] revealed, scientists have developed their own testing methods to assess the depolluting effect of a variety of photocatalytic materials [40], and yet there is no agreement on the most appropriate evaluation method [199]. Similarly, there is no worldwide standard to evaluate the self-cleaning property; however other available standards, which are strictly related to this property, are often used by researchers [26]. For photocatalytic cementitious materials, several test methods have been developed based on (i) type of pollutants (e.g., NO x , organics, etc.)…”

Green maintainability design criteria for nanostructured titanium dioxide (TiO2) façade coatings

“…Midtdal and Jelle (2013) report that TiO 2 coating requires less maintenance than ordinary façade coatings, resulting in time and cost savings, due to its strong adhesion characteristics (Rudic et al, 2015). Enea (2013) affirms that in the last two decades, nanotechnology and photocatalysis have created technologies focusing on external building envelope, reducing maintenance costs and improving durability.…”

“…This pressing global issue has moved the building and construction industry towards environmentally friendly approaches. The pursuit for sustainability has transformed the whole product-delivery process of design and construction, thereby advancing the maintainability of buildings (Enea, 2013). This highlights the importance of considering maintainability issues right from the design stage, where cost savings on maintenance are of the highest priority.…”