Search

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.

Alkali activated lightweight mortars, obtained by room temperature activation of coal fly ash, were studied as passive fire protection systems for steel elements. Physical, mechanical and thermal properties were investigated as a function of the compositional Si/Al molar ratio and of the amount of lightweight aggregate and foaming agent. Experimental findings were used as input data to assess their fire resistance by finite volume simulations. Results pointed out that the optimized alkali activated lightweight mortars are able to outperform alternative commercial cement-based mortars, thus representing a promising technology.

The aim of this work is to evaluate the cleanability performances of lapped porcelain stoneware surfaces with and without protective treatments. The knowledge of the material cleanability is an important selection parameter in buying tiles. However, an objective basis for testing and assessing this property still is lacking. In this study, standardized and laboratory tests to evaluate the cleanability performance of lapped porcelain stoneware products have been carried out and compared. Cleanability tests were performed by applying two different soiling suspensions, optimized for tile surfaces and reproducing chemical and mechanical actions simulating the working conditions and traditional cleaning operations. Surface characteristics (microstructure, topography, roughness) were analyzed before and after cleanability tests. The results showed a good correlation between different behavior in terms of cleanability and the microscopic and topographic characteristics of lapped tile. Respect to international standardized tests specific for ceramic tiles, such as stains resistance test, the laboratory procedures to evaluate the surface cleanability are able to better show cleanability improvements of lapped tiles with protective treatments.

The technological behavior of porcelain stoneware bodies during deposition and pressing of large slabs depends on the rheological properties of spray-dried powders and the way they affect compaction. Although the literature offers some insights into the characteristics of spray-dried powders for ceramic tiles, no data are available on bodies utilized by novel technologies for large slabs (>4 m2). In order to fill this gap, a systematic approach to properties and behavior of spray-dried powders for porcelain stoneware slabs was carried out. For this purpose, twenty industrially-manufactured spray-dried powders were characterized for intrinsic features (particle size and agglomerate size distribution; shape and moisture distribution in function of agglomerate size) and rheological properties (mass flow, static and dynamic angles of repose, poured and tap density, Hausner ratio). The effect of intrinsic characteristics on the flowability of powders was appraised, as the mutual relationships between the rheological parameters, in order to unveil the best parameters to be used in ceramic tile production. Two broad classes of spray-dried powders occur with a finer and a coarser agglomerate size distribution. Results reveal that ceramic powders are free-flowing, with rheological properties fluctuating in a rather narrow range of values, which makes hard to see significant relationships among the various methods (the only strict correlation is between mass flow rate and tap density). Flowability mainly depends on the occurrence of coarser aggregates, particularly those irregular in shape, stemming from coalescence of three or more individual agglomerates. A phenomenological description of how the spray-dried powders behave in the deposition on tape and the early stage of compaction is outlined.

A mild chelating agent treatment was performed on the residuals of the sorting processes of separately collected urban glass, which is currently landfilled. This fraction, that represents about the 10 wt% of the overall collected glass, has a very heterogeneous composition and contains relatively high amounts of lead and barium and consequently cannot be used to produce new glass containers. This contaminated material shows, when used as fine aggregate in Portland Cement based composites, an expansive behaviour due to the alkali silica reactions. The expansion can only be partially reduced by using finely ground soda lime glass, showing pozzolanic activity. However, after the chelating agent treatment, because of heavy atoms surface depletion, the synergic effect of pozzolan addition leads to a suppressed expansion, thus allowing the use of waste in the formulation of cement composites. Graphical Abstract: [Figure not available: see fulltext.].

Porcelain stoneware tiles are industrially processed by using high sintering temperatures and fast firing cycles that result in products characterized by an almost impervious surface layer surrounding a rather porous bulk material. Since mechanical properties are affected by porosity, the knowledge of the material stiffness is an important parameter to define the service behavior of tiles. In the present investigation, porcelain stoneware samples having different closed porosity were investigated in order to understand the influence of the porosity on the elastic constants of the materials. Based on the quantitative XRD phase composition, elastic constants have been calculated via Voigt-Reuss-Hill averaging, and the influence of porosity has been taken into account via power-law and exponential relations. It is shown that the effective elastic constants predicted by exponential and power-law relations are in agreement with experimental values. It may be concluded that for this class of materials, in the porosity range below 14–16%, both exponential and power-law relations are helpful tools to design tiles with controlled microstructure and tailored mechanical properties.

This work investigates the effects of the structure, the bulk chemical composition and amount of the aluminosilicate fines on the strength development, pore refinement, water permeability, moisture control capacity and the microstructure of inorganic polymer concretes (IPC). The amorphous fines, one from pumice and another from recycled glass, presented sponge-like microstructure with tortuous pore network that maintained the presence of fine capillary pores while semi-crystalline feldspar sludge, the third type of fine aggregates used for this study, showed more dense and compact microstructure that explain the higher strength enhancement. Both amorphous and semicrystalline fines contributed to decrease the porosity, improve the strength and microstructure. However, based on the moisture control capacity and the durability indicators, the fine aggregate derived from semicrystalline feldspar was found to be more appropriate and efficient for the development of IPC at short time scale of curing. Pumice fine aggregate was found to be effective only with a long term curing. (C) 2015 Elsevier Ltd. All rights reserved.

Geopolymers are hydrated aluminosilicates with excellent binding properties. Geopolymers appeal to the construction sector as a more sustainable alternative to traditional cements, but their exploitation is limited by a poor understanding of the linkage between chemical composition and macroscopic properties. Molecular simulations can help clarify this linkage, but existing models based on amorphous or crystalline aluminosilicate structures provide only a partial explanation of experimental data on the nanoscale. This paper presents a new model for the molecular structure of geopolymers, in particular for nanoscale interfacial zones between crystalline and amorphous nanodomains, which are crucial for the overall mechanical properties of the material. For a range of Si–Al molar ratios and water contents, the proposed structures are analyzed in terms of skeletal density, ring structure, pore structure, bond-angle distribution, bond length distribution, X-ray diffraction, X-ray pair distribution function, elastic moduli, and large-strain mechanics. Results are compared with experimental data and with other simulation results for amorphous and crystalline molecular models, showing that the newly proposed structures better capture important structural features with an impact on mechanical properties. This offers a new starting point for the multiscale modeling of geopolymers.

Recent work on the elastic constants of plagioclase feldspars is reviewed. Based on the 21 elastic constants (stiffnesses) reported in the literature for triclinic plagioclase monocrystals of different composition, the effective elastic constants of dense, single-phase, polycrystalline plagioclase aggregates with isotropic microstructure are calculated via standard Voigt- Reuss-Hill averaging. Master curves show the good agreement of the constants obtained via the two approaches (experiment and simulation) and recall the fact that values reported in the older literature have been underestimated. Fit relations are given for the calculation of Young's modulus, shear modulus, bulk modulus, Poisson ratio and density in dependence of the composition. These fit relations may serve as handy tools for obtaining relevant input information for the calculation of effective elastic constants of multiphase ceramics produced with Ca and Na containing raw materials.

This research investigates different kinds of waste as possible new binder components for the production of cement based mortar and concrete. Waste types have been selected on the basis of availability in the Emilia Romagna Region. In particular, three different wastes (i.e., waste from rectified porcelain gres tile, sea shell fragments and eggshell waste from agri-food industry) are explored as a possible substitution of a certain fraction of cement in order to evaluate their effect. Chemical properties and physical behavior of the waste are studied, and the activity index of the waste is investigated. A series of mortar specimens with normalized silica sand and a binder compositional ratio of cement (CEM I) at 75 wt.% and waste at 25 wt.% is prepared. The physical and mechanical behavior of the mortar is investigated at different curing time (i.e., 2, 7, 28 and 90 days). This research shows first preliminary results of the MATER-SOS Project, funded by the Emilia Romagna Region, Italy (POR FESR 2014-2020), aimed at implementing circular economy processes in the constructions industry.