Novel nano-particulate/polymer treatment systems for masonry enhancement and protection
Student thesis: Doctoral Thesis
Fundamental issues associated with addressing the UK housing shortage problem are climate change and the lack of usable building space. Conservation of old buildings, maintaining green land and a country filled with single walled older properties mean that the UK government has to retrofit existing older building stock. This would make a significant impact on reducing the carbon footprint of each household as well as to alleviate energy supply problems. The investigation of novel zinc oxide and titanium dioxide nanoparticulates in aqueous silane/siloxane oil-in-water (O/W) emulsions for practical exterior facade applications is presented. An initial emulsion was developed and optimised before further improvement through nanoparticulate incorporation was achieved. Nanoparticulates of zinc oxide and titanium dioxide were dispersed respectively using ultrasonication in n-isooctyltriethoxysilane before being incorporated into a base emulsion. Once formulations were optimised, applied studies and fundamental assessment of these emulsions were conducted. The aim of the work presented was to produce a practical facade emulsion that could be used in the retrofitting of existing building stock or for heritage remedial treatments. Initial research indicated that water was the governing factor in a diverse range of facade degradation mechanisms; improving water repellence, thermal envelope efficiency while reducing biofouling was recognised as being of key interest in this field. The study gives insight into aqueous water repellent emulsions, nanoparticulate integration by commercially practical means, and assessment of the attributes exhibited by such treatments. Rheological and morphological characterisation concluded that a gelled network structure is produced by the incorporation of the fabricated nanoparticulate colloids. The emulsions retained shear-thinning characteristics, ideal for deep treatment penetration to be achieved for porous silicate substrates. Accelerated ageing tests showed that the nanoparticulate emulsions were substantially more thermodynamically stable than the emulsion control while also being physically more stable due to surfactant-particulate stabilisation mechanisms of the polar phases. From further investigation it was also found that hydroxyl terminated siloxane could be integrated into these emulsions, helping to improve the ‘green credentials’ of such systems through the replacement of conventionally used trimethoxy terminated siloxanes, that release harmful methanol upon curing, thus substitution is preferential and in line with current European policy. Treatments improved thermal envelope efficiency of structures through the reduction of retained water in various forms including rising damp. Assessment was carried out using model houses exposed to various temperature and humidity scenarios under controlled heating. The findings showed that water was the root cause of heat loss and thus a key parameter when considering the improvement of a structures’ carbon footprint. These treatments allow water vapour to permeate out of a structure passively, reducing internal humidity issues including microbiological degradation and health related problems experienced by occupants. Investigation of bioreceptivity conducted though an 8 week algal culture streaming study concluded that treatments with <0.1wt% of the aforementioned nanoparticulates could reduce biofouling through photo-induced sanitisation. Furthermore, it was also found that while water repellence may vary at the facade interface due to the respective metal oxides photocatalytic nature, substrate interior water contact angles should remain high due to the absence of UV light. This is of key importance as it implies that simultaneous antifouling and rising damp remediation may be achieved by such treatments. One of the major advantages of the treatments presented is that they do not effectively alter the aesthetics of the substrate, unlike photo-induced ‘self-cleaning’ coatings that turn the facade white. In addition, these treatments are not susceptible to problems related to the cracking or chipping of coated surfaces, allowing them to provide better protection. From the above points it is clear that these treatments are the next paradigm in facade protection, complying with current social, ecological, political and industrial needs. This study presents the inception, development and investigation of key attributes and mechanisms of these novel treatments while showing critically that such emulsion treatments are practical with great potential to enhance the lives of UK residents.
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