Novel fiber-reinforced composite materials based on sustainable geopolymer matrix

Geopolymers are representing the most promising green and eco-friendly alternative to ordinary Portland cement and cementitious materials, thanks to their proven durability, mechanical and thermal properties. However, despite these features, the poor tensile and bending strengths usually exhibited by geopolymers due to their brittle and ceramic-like nature, can easily lead to catastrophic failure and represent the main drawback limiting the use of those materials in several applications. Fiber reinforced geopolymer composites may be considered a solution to improve flexural strength and fracture toughness. Different types of dispersed short fibers are here investigated as a reinforcing fraction for a geopolymer matrix based on an alkali-activated ladle-slag. It has been demonstrated that both organic and inorganic fibers can lead to a significant flexural strength enhancement. Moreover, the investigated geopolymers exhibit an increase in toughness, thus determining a switch from a brittle failure mode to a more ductile one

Electrodeposition of hydroxyapatite coatings for marble protection: Preliminary results

Surface coatings made of hydroxyapatite (HAP) have been proposed to protect marble artworks from dissolution in rain, originated by the aqueous solubility of calcite. However, HAP coatings formed by wet chemistry exhibit incomplete coverage of marble surface, which results in limited protective efficacy. In this study, electrodeposition was explored as a new route to possibly form continuous coatings over the marble surface, leaving no bare areas. Electrodeposition was performed by placing marble samples in poultices containing the electrolyte (an aqueous solution with calcium and phosphate precursors) and the electrodes. The influence of several parameters was investigated, namely the role of the working electrode (cathode or anode), the distance between the marble sample and the working electrode, the deposition conditions (potentiostatic or galvanostatic), the electrolyte composition and concentration, the applied voltage, and time. The coating morphology and composition were assessed by SEM/EDS and FT-IR. The protective ability of the most promising formulations was then evaluated, in all cases comparing electrodeposition with traditional wet synthesis methods. The results of the study suggest that electrodeposition is able to accelerate and improve formation of HAP coatings over the marble surface, even though the obtained protective efficacy is not complete yet

Nanostructured zirconia-based ceramics and composites in dentistry: A state-of-the-art review

The objective of this paper is to review the current knowledge on the development of nanostructured zirconia-based ceramics and composites suitable for application in dentistry. Isi Web of Science, Science Direct, Scientific.net databases, and Google were searched electronically for the period of 1980 to the present, matching the keywords \u201cnano\u201d with the keywords: \u201cZirconia, ZrO2, Y-TZP, and dental, dentistry\u201d. A total of 74 papers were found, with the majority coming from Asia, indicating a more active scientific interest on the topic in this geographic area, followed by Europe, South America, and North America. The research shows, even though the scientific activity on nanostructured ceramics was intense in the last fifteen years, the development of fully dense zirconia-based nanoceramics is yet at an initial stage, most of all from the point of view of the clinical applications. It has been demonstrated that nanostructured ceramics can show improved properties because of the reduction of the grain size to the nanoscale. This is also true for zirconia-based nanoceramics, where some improvements in mechanical, optical, as well as resistance in low-temperature degradation have been observed. Potential applications of this class of material in the dental field are discussed, summarizing the results of the latest scientific research

Preparation of low-cost nano and microcomposites from chicken eggshell, nano-silica and rice husk ash and their utilisations as additives for producing geopolymer cements

This work aims to prepare low-cost nanocomposite and microcomposite with lower molar ratio CaO/SiO2 (0.4). Nano-silica, rice husk ash and calcined chicken eggshell have been used as silica and calcium sources. Metakaolin has been separately replaced by 0, 10 and 20 wt% of each composite in order to study their behavior on the properties of geopolymers. The hardener used is sodium waterglass from rice husk ash. The surface area of nano-silica and rice husk ash was 54.40 and 4.08 m2/g, respectively. The cumulative volumes of the control geopolymer, the ones containing 10 wt% of microcomposite and nanocomposite are 119.71, 89.92 and 110.49 mm3/g, respectively. The compressive strength of the control specimen is around 64.02 MPa. The one using 10 wt% of microcomposite was 68.97 MPa. It drops to 42.88 MPa when metakaolin was replaced by 20 wt % of microcomposite. Whereas the one using 10 wt% of nanocomposite was 30.03 MPa and it decreases to 26.05 MPa when metakaolin was substituted by 20 wt% of nanocomposite. It can be concluded that 10 wt% of microcomposite could be mixed to metakaolin for strength development and nanocomposite does not recommend to use as an additive for producing high strength of geopolymer cements. © 2020, © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

Atomistic simulations of geopolymer models: the impact of disorder on structure and mechanics

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

Expansion behavior of ground glass cullet used as aggregate or cement replacement

The possibility of exploiting revcycled glasses of different composition both as fine aggregates and as cement replacement in cementitious composites has been investigated. Experimental data so far collected on mortars show that some compositions generate highly expanding products that hinder their use also as fine fractions with possible pozzolan activit

Stress and Strain Profiles along the Cross-Section of Waste Tire Rubberized Concrete Plates for Airport Pavements

In this study, the results of an in-situ experimental program on the performance of concrete taxiways are presented. The experimental program has been undertaken at the Guglielmo Marconi airport of Bologna (Italy). It concerns two portions of the taxiway, one built with plain concrete and one with rubberized concrete. Each portion has been instrumented with strain gauges embedded in concrete for the acquisition of vertical strains. The results of the experimentation are discussed in view of possible applications to the computational analysis of the stress field induced into pavements by aircrafts

Rubberized Self-Compacting Concrete: Mechanical Performances and Durability

Rubberized self-compacting concrete (RSCC) is a new building material with ecosustainable characteristic due to the post-consumer tyres content in its concrete mix-design. Physical-mechanical properties and durability of RSCC must anyway be evaluated as they strongly depend on the concrete formulations. Fresh and hardened behavior as well as steel reinforced bar corrosion has been studied for RSCC, where fine aggregates have been partially replaced (up to 30 vol%) by post-consumer tyres. The reported results highlight a decrease in workability, compressive strength and elastic modulus with rubber content, whereas flexural strength seems less sensitive to rubber content. Corrosion activity, studied on steel reinforced RSCC over a period of about 8 months with drying and wetting cycle in water and NaCl 3% solution, is low and comparable to that of ordinary self-compacting concrete (SCC)

Ceramic Industry Air Quality. Emissions Into the Atmosphere From Ceramic Tile Processes

The subject of this chapter, air quality associated to the ceramic tile industry, represents a very interesting \u2018real scenario\u2019 in the framework of the whole volume. The reasons can be summarised in this way: (1) the ceramic tile technology includes several significant pollutant emissions into the atmosphere and (2) ceramic industry has generated \u2013 although many years ago and in rather small industrial areas, characterised by large concentrations of factories \u2013 some air quality problems. The Ceramic District of Sassuolo, Italy, can be considered as a significant example of such industrial areas and represents the main reference adopted in this chapter. Another \u2018ceramic district\u2019 is that of Castell\uf3n, Spain, which however is quite different as regards significant factors influencing air quality: factors such as territory, orography, climate, meteorological conditions, urban and industrial settlements and density, road system and traffic, etc. With reference to the Italian ceramic tile industry, this chapter deals with the description and quantification of emissions into the atmosphere from ceramic industries and aims to document the approach adopted, the resources used and the knowledge developed, to drastically reduce the environmental impact of these emissions on air quality. This objective has been successfully achieved, at the point that, in particular, the Italian ceramic tile sector is still working, in the framework of a continuous improvement approach, on its environmental performances, as well as on the exploitation of the results achieved as competitiveness factors

Experimental Evaluation of the Surface Alteration of Gasket Samples under Operative Conditions

This paper investigates the surface alteration of gasket samples commercialized by two alternative producers. These gaskets, in polymeric materials, are installed in process plants used for cleaning tires molds by a pioneering ultrasonic process. They are exposed to a combination of ultrasonic waves, temperature, humidity and acid attack causing several erosion phenomena. Their surface degradation under ordinary operative conditions was investigated using mechanical and tribological tests. The experimental characterization was performed by optical microscopy, scanning electron microscopy, thermograms, differential scanning calorimetry curves and infrared spectra aiming at defining the specific mechanics of wearing. As a conclusion, it was possible to state that even if samples exhibit similar chemical structures, their thermal and mechanical properties as well as their geometric dimensions are different. Such differences in the materials might cause various unexpected wear behaviors when gaskets are employed in the same working conditions