The topic of sustainability of reinforced concrete structures is strictly related with their durability in aggressive environments. In particular, at equal environmental impact, the higher the durability of construction materials, the higher the sustainability. The present review deals with the possible strategies aimed at producing sustainable and durable reinforced concrete structures in different environments. It focuses on the design methodologies as well as the use of unconventional corrosion-resistant reinforcements, alternative binders to Portland cement, and innovative or traditional solutions for reinforced concrete protection and prevention against rebars corrosion such as corrosion inhibitors, coatings, self-healing techniques, and waterproofing aggregates. Analysis of the scientific literature highlights that there is no preferential way for the production of “green” concrete but that the sustainability of the building materials can only be achieved by implementing simultaneous multiple strategies aimed at reducing environmental impact and improving both durability and performances.

Geopolymers are a new class of binders based on alkali activation of natural and by-products raw materials. Their properties and eco-compatibility highly depends on the reaction system. The (Na,K)₂O-Al₂O₃-SiO₂-H₂O system shows a distinguishing pseudo-zeolitic network structure, but reaction requires a high amount of activators. The aim of this work is to investigate how the use of forest biomass ash (FBA), as partial replacement material in the production of metakaolin (MK) based geopolymeric mortar, and affect its properties. FBA is a by-product of the combustion process of forest biomass in thermal power plants. Mortars with a FBA content of 0%, 10%, 20%, and 30% wt have been tested for workability, flexural, and compressive strength. Capillary absorption, micro-morphological features, thermal, and shrinkage behavior have been investigated. The addition of FBA allowed for a decrease in the use of alkaline activator up to 20%, while preserving the characteristic broad hump centered at approximately 28° 2θ Mechanical properties of the geopolymeric mortars decrease proportionally with metakaolin replacement, even if a compression strength of more than 35 MPa is still obtained with a FBA content of 30% wt. After thermal cycles of up to 700 °C, all of the mortars still retain their cohesiveness, with an overall loss of mechanical strength of about 80% of the initial value that can be attributed to the formation of microcracks as a consequence of the network strain and distortion due to dehydration and shrinkage.

The aim of this project is to investigate the behaviour of several special types plasters specifically designed to degrade the most common pollutants which are present in the atmosphere. In particular, specific additives have been added to these plasters, in order to obtain a broad spectrum of active and synergic response, each of which have peculiar functions: - microporous materials, such as clinoptilolite, a natural zeolite, that promotes the adsorption of air pollutants thanks to its porous nature; - nano-fillers, such as carbon nanotubes, that behave both as reinforcing agents as well as adsorbent materials; - photochemical agents, such as titanium oxide, that degrade air pollutants, previously adsorbed on carbon nanotubes and zeolites, thanks to the action of light that activates photodegradation reactions. All the samples were also characterized in terms of mechanical properties, adhesion to supports and water absorption. Furthermore, photodegradation tests were carried out by exposing plaster surfaces, wetted with a Rodamine solution, to Ultraviolet rays (UV) for different times. Plasters photodegradative capacity was evaluated and the results highlighted the fact that the designed admixtures showed an important photodegradative action, strictly dependent on the types and specific ratios of the selected additives.

The present work concerns the characterization of trimetallic nickel catalysts, NiMoRe (Nickel/Molybdenum/Rhenium), NiMoCu (Nickel/Molybdenum/Copper) and NiMoCo (Nickel/Molybdenum/Cobalt), supported on gadolinia-doped ceria and the evaluation of their catalytic performance in the auto-thermal reforming of ethanol to hydrogen. Catalysts have been prepared by wet impregnation and characterized by XRD, SEM-EDX, TG-DSC, TEM, CHNS, H₂-TPR and micro-Raman spectroscopy. The resistance of Ni-alloy catalysts to the carbon deposition and sulfur poisoning has been studied. All catalysts show a similar behavior in the auto-thermal reforming reaction: 100% of ethanol conversion and high selectivity to syngas products, up to 77 vol.%. At 800 °C the coke deposition is very low (less than 0.34 wt%). Sulfur content affects the selectivity and the activity of the catalysts, especially towards the coke formation: high sulfur content promotes the ethylene formation, therefore the amount of coke deposited on spent catalyst increases. NiMoCu seems to be the trimetallic catalyst less sensitive to this aspect.

Fabric-reinforced cementitious composites are a recent family of commercial products devoted to the external retrofitting and strengthening of masonry and concrete structures. In the present work, the authors investigate the possibility of using, as matrix, a mortar based on alkali-activated materials. Basalt textile was selected as reinforcement because it is an effective, low-cost and environmentally friendly reinforcement. The matrix was prepared using by-products of industrial processes. Mortar was characterized by measuring its drying shrinkage, capillary water absorption, compressive and flexural strengths and analyzed using X-Ray diffractometry, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The mechanical behavior of the composites was investigated through tensile and direct shear tests. The basalt fabric-reinforced alkali-activated matrix composite showed, under tension, a tri-linear response curve, mainly governed by cracks development and widening. The measured ultimate stress, ultimate strain and tensile modulus of elasticity in region III were 434 MPa (CoV 14.2%), 2.192% (CoV 4.1%) and 39 GPa (CoV 11.3%), respectively. The load–global slip response curves of the composite show an average peak load around 1148 N (CoV 23.0%) and an exploitation ratio versus the textile and the tensile of 0.40 and 0.86, respectively. Even if the preliminary results are encouraging, the performance of FRAAM composites would be positively affected by an increase of the dimensional stability of the matrix.

In recent decades, relevant environmental and economic reasons have driven an increasing interest in using a large amount of recycled aggregate in replacement of natural ones to produce mortar and concrete. The present study aims to investigate the effect of substituting 100% of natural sand with recycled aggregate on fresh properties, mechanical properties, and the durability of a thixotropic and a self-leveling mortar. Recycled aggregate was characterized using X-ray diffractometry and energy-dispersive X-ray spectroscopy. Its morphology was investigated using scanning electron microscopy and automated morphological imaging. Recycled aggregate mortars showed a moderate decline in initial workability, as well as higher shrinkage and porosity than the control ones. The compressive strength of self-leveling mortars produced with recycled aggregate was only 6% lower than mortars produced with natural sand. The gap increased to 40% in the case of thixotropic mortars. The self-leveling recycled aggregate mortar showed equivalent resistance to freeze–thaw cycles and better sulfate resistance than the control one. The thixotropic recycled aggregate mortar showed comparable sulphate resistance and only slightly lower resistance to freeze–thaw cycles than the control one. Their capacity to relief stresses, due to hydraulic pressures and the formation of expansive products, arises from their higher porosity. Thermal stability of the prepared mortars, after a curing period of 90 days, up to 700 °C, was also investigated. A significant decrease in ultrasonic pulse velocity is observed in the 200–400 °C interval for all the mortars, due to the dehydration–dehydroxylation of calcium silicate hydrate. The overall decline in the strength of both the recycled aggregate mortars was comparable to the control ones. The results reported in the present investigation suggest that the selection of high-quality recycled aggregate helps to obtain good-quality mortars when a large amount of natural sand is replaced.