We report here, for the first time in the literature, a method to synthesize hydrophobic and superhydrophobic concrete. Concrete is normally a hydrophilic material, which significantly reduces the durability of concrete structures and pavements. To synthesize water-repellent concrete, hydrophobic emulsions were fabricated and applied on portland cement mortar tiles. The emulsion was enriched with the polymethyl-hydrogen siloxane oil hydrophobic agent as well as metakaolin (MK) or silica fume (SF) to induce the microroughness and polyvinyl alcohol (PVA) fibers to create hierarchical surfaces. Various emulsion types were investigated by using different mixing procedures, and single-and double-layer hydrophobic coatings were applied. The emulsions and coatings were characterized with optical microscope and scanning electron microscope (SEM), and their wetting properties, including the water contact angle (CA) and roll-off angle, were measured. A theoretical model for coated and non-coated concrete, which can be generalized for other types of materials, was developed to predict the effect of surface roughness and composition on the CA. An optimized distance between the aggregates was found where the CA has the highest value. The maximal CA measured was 156°for the specimen with PVA fibers treated with MK based emulsion. Since water penetration is the main factor leading to concrete deterioration, hydrophobic waterrepellent concretes have much longer durability then regular concretes and can have a broad range of applications in civil and materials engineering.

Abstract:Tribology involves the study of friction, wear, lubrication, and adhesion, including biomimetic superhydrophobic and icephobic surfaces. The three aspects of icephobicity are the low ice adhesion, repulsion of incoming water droplets prior to freezing, and delayed frost formation. Although superhydrophobic surfaces are not always icephobic, the theoretical mechanisms behind icephobicity are similar to the entropically driven hydrophobic interactions. The growth of ice crystals in saturated vapor is partially governed by entropically driven diffusion of water molecules to definite locations similarly to hydrophobic interactions. The ice crystal formation can be compared to protein folding controlled by hydrophobic forces. Surface topography and surface energy can affect both the icephobicity and hydrophobicity. By controlling these properties, micro/nanostructured icephobic concrete was developed. The concrete showed ice adhesion strength one order of magnitude lower than regular concrete and could repel incoming water droplets at´5˝C. The icephobic performance of the concrete can be optimized by controlling the sand and polyvinyl alcohol fiber content.

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Hydrophobic and self-cleaning photocatalytic ceramics and concrete with potential for the superhydrophobicity are promising novel materials for civil engineering applications including buildings, bridges, road pavements, and airport runways. Due to embedded liquid-repellent properties, such materials have low water and salt absorption and, therefore, enhanced durability. However, in applications requiring high traction (e.g., tire and pavement), there is a concern that reduced adhesion may compromise the friction. This paper reports on wetting, dry friction, and roughness properties of TiO2 coated (hydrophilic) and polymethyl hydrogen siloxane (PMHS) coated (hydrophobic) self-cleaning ceramic tiles. The coefficient of friction values of the tile–rubber interface do not change significantly with the applications of the coatings up to 0.67 for hydrophilic TiO2 based and up to 0.46 for hydrophobic TiO2 + PMHS coatings versus 0.45 for uncoated reference. Friction has adhesion and roughness-related components and this response can be attributed to the roughness component of friction due to TiO2 coating. The challenges related to hydrophobic coatings, including the durability and future research, are also discussed.

This research focuses on an evaluation of mineral phase and structure transformations in Class F fly ash-based geopolymer systems. The research also studies the strength response of geopolymers when exposed to temperatures between 25 and 800 °C. The purpose of this research is to understand the processes that occur in alkali-activated systems within a wide range of high-working temperatures. The XRD, SEM, and DTA/TG analyses performed for the alkali-activated compositions after exposure to different temperatures confirmed a direct correlation of structural transformations with strength performance. The detrimental effect of sodium hydrocarbonate Na3(HCO3)(CO3) 2H2O or trona contained in one of the fly ash products was observed for the corresponding alkali-activated composite under high-temperature exposure between 600 and 800 °C. It was also detected that a high-temperature interval of 400–800 °C created favorable conditions that helped to form nanosized nepheline crystals and an additional vitreous substance that also contributed to a denser alkali-activated matrix.

Coal power plants represent the large source of environmental pollution in soils, ground and surface water by leaching out toxic compounds from open landfilled and impounded coal combustion residuals (CCR) such as fly ash. The use of fly ash as a main component in geopolymer binder (GB) systems is one of the effective methods of CCR beneficial utilization. The toxicity assessment as well as leachability of harden geopolymers were tested in aqueous media where oat seeds were used as affected test objects. Bio-resistance of the developed geopolymers was evaluated by the resistance to mold fungi growth. The developed geopolymers demonstrated a very low toxicity and leachability to the biota based on the low effect to germinating ability and growth retardation of the exposed oat seeds. Therefore, the studied fly ash products were proved to be environmentally safe when used in GB systems. The absence of fungi growth observed on the surface of geopolymer samples demonstrates high bio-resistance.

Nowadays geopolymer is promising and relevant material that can be effectively used in wide range of application areas. It is possible because of there are a lot of potential sources of raw materials for geopolymer synthesis. Raw components are the one of the key parameters that effect on geopolymer performance. On the other hands, the technological stages of geopolymer synthesis is no less important factor. The purpose of this study was to determine effect of technological parameters of geopolymer synthesis such as component composition of solid state phase, alkaline activator preparation and its introduction onto geopolymer paste as well as curing temperature on performance characteristics of geopolymer. Fly-ash based geopolymer samples were prepared with adding of different mineral components: Portland cement (PC), kaolin, metakaolin; different curing temperature conditions: ambient temperature and temperature treatment at 70 °C in oven during 24 hours; different methods of preparation and application of alkaline activator: using of fresh alkaline solution and using alkaline solution after 24 hours of cooling. The results show that efficiency of curing temperature conditions strongly depend on component composition of geopolymer paste. Samples, containing PC and metakaolin demonstrate better characteristics after curing under ambient temperature. Samples, containing kaolin and reference composition (fly ash only) the temperature treatment in oven is the best curing method (increasing in compressive strength up to 13 times). Using alkaline solution of NaOH after 24 hours of cooling gives a good effect on geopolymerization process and provides increasing in compressive strength value from 13 to 84 % for all experimental geopolymer pastes. However, average density for all compositions is varied slightly.