Effect of cracks on the service life of RC structures exposed to chlorides

To move towards a more sustainable concrete, the enhancement of its durability is strongly encouraged and, dealing in particular with reinforced concrete (RC), this mainly means to prevent the damage due to environmental actions, e.g. due to chloride-induced corrosion. Therefore, there is the need of models aimed at designing durable structures. Usually the service life design models consider concrete in uncracked condition. In real structures, however, several phenomena can generate cracks on concrete surface, leading to an acceleration of the corrosion of steel rebar. A number of studies have been recently carried out in order to evaluate the influence of cracks on reinforced concrete durability in chloride-contaminated environment, however the knowledge of the effect of cracks on the initiation and propagation periods is still lacking. Furthermore, few studies have considered additional protection strategies, such as the use of stainless steel rebar. In this work, experimental results are presented concerning the influence of cracks on the service life of reinforced concrete structures in order to evaluate if cracks lead to an earlier corrosion initiation induced by chlorides. Prismatic specimens, reinforced with carbon steel and 304L stainless steel bars, were longitudinally cracked and exposed to ponding with 3.5% NaCl solution. The monitoring of corrosion behaviour showed that when cracks reached the steel surface corrosion initiated immediately

Photocatalytic activity of ZnO nanostructures grown by vapour and solution

Zinc oxide (ZnO) is one of the most studied functional materials in the last years because it matches the opportunity to be easily synthesized in nanocrystalline form (with different morphologies and by different growth techniques) with a very large number of possible applications in different fields (optoelectronics, photovoltaics, piezoelectric devices, gas-sensing and bio-sensing, photocatalysis, spintronics, nano power generators, cantilever production, etc.). In the present contribution we report on ZnO nanocrystalline structures, with the same wurtzite structure but different morphologies, synthesized by vapour-phase and by solution growth techniques. More in detail, ZnO nanotetrapods and nanopowders with different size have been obtained by a combination of metallic Zn thermal evaporation and controlled oxidation in a non-standard CVD (chemical vapour deposition) reactor where temperature have been set in the 450?C-650?C range. Other ZnO multi-branched nanostructures, resulting from aggregation or twinning of nanosized crystals, have been grown in aqueous solution of zinc salts and hexamine, in slightly alkaline medium below 100?C. Moreover, ZnO nanopowders have been obtained by thermal decomposition of a metallorganic gel precursor, resulting from dehydration of a zinc citrate solution. Different nanopowders samples have been prepared with different decomposition processes (time, temperature). ZnO nanostructures have been later on deposited on a photocatalysis-inert substrate (glass) from an alcoholic suspension at room temperature by forcing solvent evaporation and surface cleaning for a few minutes at 200?C in low vacuum. The obtained specimens are about 50 cm2 in size. All the ZnO nanostructure films are characterized by high porosity and high surface-to-volume ratios, which are generally basic requirements for the application in photocatalysis of gaseous species. The samples have been characterised by scanning electron microscopy and tested for photocatalytic degradation activity of airborne pollutant using a stirred flow photoreactor irradiated with UV-A. The measurements were carried out using ethylbenzene as organic target pollutant at concentration level typically found in ambient conditions. The samples demonstrated a good photocatalytic activity in the degradation of ethylbenzene in air

Photocatalytic activity of nanotubular TiO2films obtained by anodic oxidation: A comparison in gas and liquid phase

The availability of immobilized nanostructured photocatalysts is of great importance in the purification of both polluted air and liquids (e.g., industrial wastewaters). Metal-supported titanium dioxide films with nanotubular morphology and good photocatalytic efficiency in both environments can be produced by anodic oxidation, which avoids release of nanoscale materials in the environment. Here we evaluate the effect of different anodizing procedures on the photocatalytic activity of TiO2nanostructures in gas and liquid phases, in order to identify the most efficient and robust technique for the production of TiO2layers with different morphologies and high photocatalytic activity in both phases. Rhodamine B and toluene were used as model pollutants in the two media, respectively. It was found that the role of the anodizing electrolyte is particularly crucial, as it provides substantial differences in the oxide specific surface area: nanotubular structures show remarkably different activities, especially in gas phase degradation reactions, and within nanotubular structures, those produced by organic electrolytes lead to better photocatalytic activity in both conditions tested

Reactive Deep Eutectic Solvents (RDESs): A New Tool for Phospholipase D-Catalyzed Preparation of Phospholipids

The use of Reactive Deep Eutectic Solvents (RDESs) in the preparation of polar head modified phospholipids (PLs) with phospholipase D (PLD)-catalyzed biotransformations has been investigated. Natural phosphatidylcholine (PC) has been submitted to PLD-catalyzed transphosphatidylations using a new reaction medium composed by a mixture of RDES/buffer. Instead of exploiting deep eutectic solvents conventionally, just as the reaction media, these solvents have been designed here in order to contribute actively to the synthetic processes by participating as reagents. RDESs were prepared using choline chloride or trimethyl glycine as hydrogen-bond acceptors and glycerol or ethylene glycol, as hydrogen-bond donors as well as nucleophiles for choline substitution. Specifically designed RDES/buffer reaction media allowed the obtainment of PLs with optimized yields in the perspective of a sustainable process implementation

Towards a Complete Exploitation of Brewers’ Spent Grain from a Circular Economy Perspective

In the present work, brewers’ spent grain (BSG), which represents the major by-product of the brewing industry, was recovered from a regional brewery and fractionated in order to obtain a complete valorization. In particular, the whole process was divided in two main parts. A first pretreatment with hot water in an autoclave allowed the separation of a solution containing the soluble proteins and sugars, which accounted for 25% of the total starting biomass. This first step allowed the preparation of a medium that was successfully employed as a valuable growing medium for different microbial fermentations, leading to valuable fungal biomass as well as triglycerides with a high content of linear or branched fatty acids, depending on the microorganism used. The solid water-insoluble residue was then submitted to a lignocellulose deep eutectic solvent-mediated fractionation, which allowed the recovery of two important main fractions: BSG cellulose and BSG lignin. The latter product was tested as potential precursor for the development of cement water reducers with encouraging results. This combination of treatments of the waste biomass appeared to be a promising sustainable strategy for the development of the full exploitation of BSG from a circular economy perspective

Two-step fractionation of a model technical lignin by combined organic solvent extraction and membrane ultrafiltration

A fractionation method for technical lignin was developed, combining organic solvent extraction and membrane ultrafiltration of the solvent soluble component. This method was validated on a commercial wheat straw/Sarkanda grass lignin (Protobind 1000) using 2-butanone (MEK) as the solvent for both the extraction and the ultrafiltration operations. The parent lignin and the different obtained fractions were fully characterized in terms of chemical composition and physicochemical properties by gel permeation chromatography, gas chromatography/mass spectrometry (GC/MS), pyrolysis-GC/MS, total phenol contents, 31 P nuclear magnetic resonance ( 31 P NMR), thermogravimetric analysis, differential scanning calorimetry analysis, and Fourier-transform infrared spectroscopy. The results show that the proposed process allows a straightforward recovery of the different lignin fractions as well as a selective control over their molecular mass distribution and related dependent properties. Moreover, the operating flexibility of the Soxhlet/ultrafiltration process allows the treatment of lignins from different feedstocks using the same installation just by modulating the choice of the solvent and the membrane porosity with the best characteristics. This is one of the most important features of the proposed strategy, which represents a new fractionation approach with the potential to improve lignin valorization for materials science and preparative organic chemistry applications