169,942 research outputs found
Environmentally Friendly La0.6Sr0.4Ga0.3Fe0.7O3 (LSGF)-Functionalized Fly-Ash Geopolymers for Pollutants Abatement in Industrial Processes
No full textAbstract: A ready-to use, highly sustainable solution for large scale exhausts catalytic abatement was developed: the active bricks. An environmentally-friendly composite was synthesized by depositing La0.6Sr0.4Ga0.3Fe0.7O3, by combustion synthesis, on a fly ash-based geopolymer improved to bear the high temperatures (> 900 °C) required for synthesis. The geopolymer was obtained using by-products and was synthesized at RT: its production is sustainable and cost efficient. Prepared composites have been tested for methane oxidation and show good, durable activity above 400 °C. Thermal stability was also proved. Composites are a good solution for oxidation of fuel residues in industrial processes. Graphic Abstract: [Figure not available: see fulltext.]
Unilateral amaurosis, extrinsic ocular motor paralysis and anterior cranial base fracture as complications of septoplasty
No full textFly ash geopolymers: effect of admixtures on fresh and hardened properties
No full textOne of the most important challenges for the cement industry is to find sustainable solutions to mitigate environmental footprint of its activities. Geopolymers are particularly attractive for this purpose; the use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for sustainable building products. The lack of information on effective admixtures is limiting the practical acceptance of geopolymer concrete. The purpose of this paper is to study the influence of different superplasticizers, commonly used in Portland cement concrete technology, on properties of fly-ash based geopolymers. First, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether, acrylic based superplasticizers) have been used for the preparation of pastes and mortars. Two different amounts of admixture were tested: 0.6wt% and 1.0wt% by mass of binder. Among the investigated admixtures, the polycarboxylic ether based superplasticizer is the most effective. With a dosage of 1.0wt % by mass of fly ash it can be achieved an increase in workability of both geopolymer pastes and mortars without compromising the final strength of hardened material
Acoustic emission study of heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars
No full textAlkali-activated fly ashes have been proposed for various applications where resistance against high temperatures is required, yet several details regarding the response of these materials to heat-exposure need to be clarified. In the present study, heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars was analyzed by in-situ acoustic emission (AE)detection during complete heating-cooling cycles (up to ∼1100 °C), augmented by thermogravimetry and ex-situ SEM and XRD analyses. The applicability of the lightweight mortars as passive fire protection coatings was assessed by recording temperature-time curves of mortar-coated steel plates. Cracking during heating was limited and associated exclusively with the dehydration of the materials in the temperature range ∼90–360 °C. However, samples heated to temperatures above ∼600 °C exhibited intense cracking on cooling. This was attributed to differential deformations caused by local sintering and partial melting at the glass transition temperature, and subsequent quenching on cooling
Assessing the suitability of fly ash geopolymer for strengthening existing reinforced concrete structure
No full textAbstract from the Young Researchers’ Forum, XIII AIMAT Congress and SIB Congress - Ischia, Italy, July 2016. Fiber-reinforced cementitious matrix (FRCM) composites have gained increasing interest as newly developed system for strengthening reinforced concrete structures. FRCM system provides for the embedding of high-strength fibers into an inorganic matrix. The possibility of using geopolymers instead of cementitious matrix is very attractive since this new class of inorganic material, synthetized through the alkali activation of an aluminosilicate precursor, showed competitive features when compared to cement based materials in both terms of performances and sustainability. However, research dealing with the use of geopolymer for strengthening and rehabilitation of reinforced concrete structures with externally-bonded composite materials are limited
C. Vinti, "La monnaie de l'absolu. Jean-Luc Godard, Du musée de l'imaginaire au musée du réel", Carabba, Lanciano 2017
No full textCompte-rendu du livre de Claudio Vinti, "La monnaie de l'absolu. Jean-Luc Godard, Du musée de l'imaginaire au musée du réel", Carabba, Lanciano 2017
High-temperature behaviour of alkali-activated composites based on fly ash and recycled refractory particles
No full textThis study aims to develop innovative and sustainable alkali-activated composites with enhanced performance at high temperatures. To reduce production costs and promote a circular economy model, coal fly ashes are selected as a precursor for the alkali activation and recycled refractory particles are used to develop products with high thermal dimensional stability. Matrices and composites are investigated as a function of two curing conditions (heat curing vs room temperature curing) and amounts of dispersed phase (recycled refractory particles) added to the matrix. Thermal stability is assessed based on thermal exposure in a muffle furnace at 800 and 1000 °C, heating microscope analysis, and dilatometry. In addition, mineralogical quantitative analyses are performed to obtain an insight into phase changing after thermal exposure. Results show that the recycled refractory particles do not hinder the alkali activation process, significantly reduce heat-induced cracking, increase the maximum temperature of dimensional stability of the composites up to 1240 °C, and improve the linear dimensional stability during heating. In addition, the heat curing does not significantly increase the temperature range of dimensional stability, whereas the room temperature curing generates a product less prone to cracking when exposed to high temperature, and therefore it can be preferred
Study of the influence of different admixtures on the properties of alkali-activated materials
No full textIn the last years many studies have been addressed on the development of new types of cement with the aim to find a sustainable alternative to traditional ordinary Portland cement. Alkali-activated materials (AAM) seem particularly attractive for this purpose, even if effective admixtures such as plasticizers still need to be designed limiting so far the diffusion of AAM for geopolymer concrete preparation.
AAM come from the alkali-activation of aluminosilicate powders with suitable amorphous content. Among all the suitable aluminosilicate precursors, great interest is nowadays focused on the possibility to activate industrial waste (e.g., slag or fly ash). The use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for green building products.
The purpose of this paper is to study the influence of different superplasticizers on the AAM properties. In particular, first, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether-, and acrylic based superplasticizers) have been used for the preparation of carbon fly ash pastes and mortars in order to improve their physical and mechanical properties at the fresh and hardened state. Different amounts were tested with the aim to determine the best concentration. The results are then compared with those of reference AAM prepared without any admixture addition.
Among the investigated admixtures, the mix with the polycarboxylic ether based plasticizer has the best behavior in terms of both fresh and hardened state properties. The optimum amount of SP corresponds to a dosage of 1% by mass of fly ash. Test results show an increase in terms of workability of both geopolymeric pastes and mortars in comparison with AAM samples without any admixture addition. Moreover the use of polycarboxylic ether based superplasticizer does not compromise the final strength of hardened material
Mode-I fracture testing of alkali activated materials
No full textIn an attempt to reduce the CO2 emissions related to the production of cement and ceramic materials, a new class of materials known as alkali activated materials (AAMs) has rapidly grown in interest in the last two decades. One of the main advantages of AAMs is the possibility of using waste-based powders thus promoting a circular economy approach. In this work, three different coal fly ash-based alkali activated mortars were studied in order to investigate their fracture properties. The fracture energy depended on the type of aggregate employed and its values were consistent with those of similar cement-based mortars. Similarly, the size of the fracture process zone compared well with similar cement-based mortars
- …
