Hydrophobic Coating

Diagnostics and Testing Methods

An important factor relating to any new technology is to check its effectiveness and efficiency in terms of actual on-site performance. Similarly, facades using photocatalytic coatings need to be tested for its performance. This section briefly introduces test methods found in reviewed literature.

A study conducted in Texas [25], USA used scanning electron microscope (SCM) with energy dispersive spectroscopy (EDS) of specimens for TiO₂ infused concrete elements which were weathered near high-traffic road conditions. However, this method required core samples from the concrete which made it an intrusive study which makes it unfavourable to be used in the field.

[26] laboratory tested white cement products having titanium dioxide using aerograph technique. They used yellow dye (phenantroquinone) under simulated sun light conditions and measured reflectance of surface and found that in only 8 hours’ complete recovery of colour of cement samples were obtained.

[27] developed a self-cleaning test using red dye (rhodamine B) on different photocatalytic surfaces. Under UV lights at one-meter distance the dye was subjected to a photo-degradation process on the samples. Colorimetric measurements were taken in this experiment based on the colorimetric parameter a* from colour system CIE L*a*b*(Commission Internationale de l’Eclairage). Authors found that in 24 hours 65% of the colour was recovered under UV light.

Dienemann (as cited in, [10] also studied self-cleaning ability of concrete cubes with TiO2 using brush-impregnated rhodamine B under a day light lamp. The study found colour was recovered between 75-95% after 24 hours depending on the different mix specimens.

[28] used red wine as an organic dye in a similar study. In this case complete colour recovery of cement plates were observed after 48 hours under UV lights.

Red wine stains discolouration on TiO2/SiO2/Eternit plates as a function of irradiation time

(Source: Yuranova et al., 2007)

[29] studied the colour change of the façade of a Roman church with self-cleaning finishes using a Miniscan XE colorimeter. This study also used the CIE L*a*b* colour system and estimated the difference of colour (ΔE) against time relative to initial conditions. Therefore, this was noted as a better analysis of colour change over time to model the performance of a self-cleaning technology.  The author defined human perception of colour as a function of difference of colour as given in Table 2.4.

Human perception of the colour change based on ΔE values (Source: Zhang, 2008)

[30] followed a similar methodology studying a public complex in France. Colorimetric measurements were taken using a portable colorimeter and analysed using the CIE lab colour system. The human perception of colour changes of the façade was categorized between obvious, very slight and not visible; depending on the calculated ΔE from the colorimetric measurements.