1,721,043 research outputs found
Coal fly ash geopolymer: study of weight variation and shrinkage as a function of relative humidity change
No full textIn the last twenty years a new class of materials known as geopolymers has rapidly grown in interest in order to reduce the CO2 emissions for cement and ceramic materials productions. Geopolymers are based on alkali activation of precursors able to consolidate at room or slightly higher temperatures. One of the main advantages of geopolymers is the possibility to use waste-based powders, such as coal fly ashes, thus promoting a circular economy approach. Nevertheless, the scope to classify geopolymers as a new binder for the construction sector can be obtained only by a good knowledge of both differences and similarities between this new class of materials and ordinary portland cement. As known, shrinkage is a critical aspect to take into account for a proper characterization of a new material in the construction industry. Indeed, shrinkage has a crucial importance for both durability aspects and structural long-term maintenance, due to possible cracks formation. At the present state, only a few researches on engineering properties and shrinkage of geopolymers have been made.
In this work, three different coal fly ash-based geopolymer mortars were studied with an attempt to investigate their drying shrinkage behavior (as opposed to chemical or autogenous). For comparison sake, an ordinary portland cement mortar was used as reference. Consistency at the fresh state and physical properties (i.e., bulk density, water absorption and total open porosity) of the mortars were determined. Then, two different behaviors were studied on specimens: 1) the first shrinkage during the first months of curing; 2) the dimensional variations related to humidity change after a long period of time. All tests have been made at a constant temperature and varying the relative humidity: weight change and shrinkage of all specimens were measured regularly.
Preliminary obtained results could be useful for the future set up of a predictive model for the shrinkage of geopolymer that at the present state does not exist
Gres porcellanato nelle pavimentazioni esterne: caratteristiche e posa
No full textLe piastrelle in gres porcellanato, prodotto industriale di altissima qualità, si qualificano come scelta ottimale anche per le pavimentazioni in esterno date le elevate prestazioni tecnico-funzionali. Nel contributo se ne analizzano le principali caratteristiche con riferimento anche ai sistemi di caratterizzazione delle piastrellature
Effect of the microstructure in the optimization of geopolymeric membrane supports for microfiltration of wastewaters
No full textAlkali activated materials and geopolymers have attracted a lot of research interests in the last 20 years
thanks to their excellent performances in terms of mechanical, thermal and durability properties. In
addition, these materials show promising properties in terms of sustainability when compared to
traditional binders commonly used in the building sector (i.e., ordinary Portland cement) and to
traditional and advanced ceramics (i.e., membranes, adsorbents, and catalysts). Sustainability in
geopolymers can be reached by using a broad variety of industrial by-products as raw materials and
by ambient or low temperatures (< 100 °C) consolidation.
The aim of the present study was the optimization of microstructural properties of one-part
geopolymers, based on flash-sintered metakaolin and anhydrous sodium silicate, for microfiltration
membrane support in wastewater treatments. Investigated geopolymers were shaped by uniaxial
pressing and cured at 70 °C for 24 h. Several parameters in terms of mix design optimization (i.e., alkali
concentration and water content) and pressing pressure were investigated to obtain a microstructure
suitable for the preparation of the support of flat asymmetric membranes. Assessment of the total
open porosity and the pore size distribution was carried out by mercury intrusion porosimetry, while
microstructural observations were performed by field emission gun-scanning electron microscopy
(FEG-SEM) coupled with energy dispersive spectroscopy (EDS). It was found that pressing is a
particularly suitable shaping method for one-part geopolymers thanks to the use of low water amount
for the activation of the mix. In addition, increasing the water content (up to 15 wt%) and pressing
pressure (up to 20 MPa) allowed the formation of a dense geopolymeric gel, while alkalis
concentration, ranging between Na/Al = 0.7 and 1.1, did not strongly influence the microstructure.
Finally, the optimized parameters for producing flat support for microfiltration membranes are a Na/Al
molar ratio equal to 1.0, 12 wt% water content and 2 MPa of pressing pressure. These conditions
allowed to obtain the same range of open porosity and pore size distribution characteristic of ceramic
membrane support used for the same purpose
Self-compacting concrete with recycled aggregates
No full textThis work investigates the state of the art on innovative and sustainable self-compacting concrete prepared with coarse and fine recycled concrete aggregates (up to 100% of total amount of aggregates). Fresh state behavior is presented and related to the hardened state and durability characteristics of the conglomerate.
Studies on this new research topic in the field of construction industry highlight that self-compacting properties can be maintained when recycled concrete aggregates are used and their good qualities enhance effective mechanical properties thus promoting its successfully use not only for non-structural elements, but also structural and highly reinforced structures which hinder the vibration procedures
Novel geopolymeric support for microfiltration membranes applied in wastewater treatment
No full textMicrofiltration membranes are widely used in wastewater treatment and are typically made of ceramic
or polymer materials. Despite the great durability of ceramic membranes, polymeric membranes are
very often preferred due to production costs. By using geopolymers, however, it is possible to obtain
microfiltration membranes with durability characteristics similar to those of ceramic materials, but
with considerably reduced production costs since geopolymers do not require a sintering treatment.
In this study, a geopolymer support for asymmetric microfiltration membranes is characterized in
terms of porosity and hydraulic permeability. The support was obtained by uniaxially pressing a dry
mixed powder consisting of metakaolin and anhydrous sodium silicate, sprayed with 12 wt% of water.
Curing was carried out at 70 °C for 24 hours and 6 more days at room temperature. The porosity of
samples pressed using 2 MPa (total open porosity of 39 % and a modal pore size of 23 μm) are
comparable to those of ceramic membranes for microfiltration [1]. The support permeability was
measured in a dead-end apparatus at a trans-membrane pressure varying from 0.2 to 0.5 bar, with
pure water and ethanol-water solutions. Hydraulic permeability of 30500 ± 3090 L/(h·m2·bar) was
obtained with 4 samples, whereas the use of 100 and 200 g/L ethanol-water solutions showed a
reduction in permeability to 26140 ± 2640 and 20820 ± 1430 L/(h·m2·bar) respectively. Further tests
performed on less porous samples obtained by pressing the powder at 5 MPa (total open porosity and
modal pore size of 27% and 15 μm, respectively) led to similar results. These initial characterizations
highlight the potential of this new material in the treatment of wastewater by membrane separation.
Future studies are ongoing to develop geopolymer selectives layer by dip coating to be applied on
geopolymer supports
A Study on Historic Mortars for Restorative Applications in Persepolis World Heritage Site: Curing in Site vs Laboratory
No full textTwo types of air lime mortars with inclusion of sesame cooking oil were synthesized. The behaviour of mortars in the site conditions and the laboratory can be distinct. Hence, the mortars were cured in two laboratory and natural climatic conditions of and Persepolis World Heritage Site. The mortars were monitored for two years under both conditions and the results demonstrated distinctions in characteristics of mortars, emanating from curing conditions. The air lime mortars cured in the site conditions exhibited increment in durability and hydric properties. In the natural outdoor conditions, some effects of addition of organics to mortars, such as retarding their setting time were less highlighted compared to laboratory curing mortars
A preliminary study on the characterization of Recycled Asphalt pavement (RAP)
No full textThe replacement of natural aggregates with recycled ones for concrete production is of vital importance in view of increasing the sustainability of construction materials in accordance with the Circular Economy. The use of crushed Recycled Asphalt Pavement (RAP) as aggregates for concrete will allow the production of more sustainable materials in the construction field. However, chemical, physical and mechanical characteristics of RAP aggregates shall be investigated to optimise their use for concrete production. This issue is one of the tasks of the research project “Sustainable concrete made with recycled asphalt pavement (RAP-CON)” granted by Fondazione Cariplo, currently ongoing.
This study reports the first results on the characterization of five types of RAP collected from different Italian Highways. Several properties of RAP as aggregates for concrete were investigated in terms of microstructure, dimensional stability and durability. In particular, morphological observation was carried out by optical and scanning electron microscopy, while open porosity and pore size distribution was evaluated by mercury intrusion porosimetry. Dimensional stability was assessed by preparing cementitious mortar and concrete samples, following the accelerating curing described in EN 1367-4. Lastly, durability was investigated in terms of resistance to freeze and thaw cycles performed in accordance with EN 1367 (parts 1 and 6) in presence of distilled water and salts (1 wt% NaCl solution), respectively. It was found that RAP is a suitable material for aggregates in concrete. Depending on the adhesion between the bituminous binder and the natural aggregates, different durability performances can be achieved. Finally, different results have been obtained as function of types of RAPs, indicating that their characterization before concrete preparation is an important step to ensure the performance of the final product
15 - TiO2 in the building sector
No full textThis chapter deals with innovative applications of photocatalytic TiO2 in different building materials, with particular reference to cement-based materials (concrete, mortars, and pavements) and tiles, which are omnipresent materials in constructions. The possibility of manufacturing materials with antipollution, self-cleaning, and antimicrobial surface is extremely attractive in buildings, while the use of embedded titania nanoparticles is expected to improve the mechanical strength of concrete, which is desirable for structural applications.
Two further applications of TiO2 are considered in the present chapter. The first one is in geopolymers, a new class of binders that received great attention in recent years, due to their much lower environmental impact and higher resistance to aggressive agents and high temperatures, compared to ordinary Portland cement. The second application is in the field of cultural heritage, where TiO2-based treatments may contribute to fight the chemical and biological deterioration processes threatening ancient building materials, thus helping one to preserve our national identities and economic prosperity
Sustainable Materials for Architectural Restoration in Developing Countries: from the New Historic Mixes for the Future
No full textIn this study, considerations for design and valorization of sustainable restorative materials for applications in the developing countries are investigated. The paper deals with several preliminary requisites leading to mortar design for conservation of built environment of these countries with numerous cultural heritage elements in need of conservation. Different forms of compatibility are discussed that does not exclude conceptual, physical, chemical, and aesthetical considerations. Where practicable, reversibility is a demanding property expected from such a restorative material. Moreover, sustainability of the restorative materials project is highly dependent on the environmental considerations. The suggested policies leads to significant reduction in use of materials with high carbon dioxide production and landfills. Economic considerations will also play an important role in the frame of conservation plan as their development potentially broadens the domain of conservation possibilities. This is an important value for developing countries with loads of historic buildings in need of restoration. The designation of waste-based strategy in design of restoration materials and their answer to requisites of the conservation plan are discussed. The conceptual suitability of low impact and waste-based restorative materials for treating the built environment in developing countries is justified and discussed. However, the sensetiveness of these countries in application of economic materials for restoration should be dealt with. An economic, high performance, and compatible restoration respects the feature of historic elements and is in-line with many historic material design strategies
Cleaner, sustainable, and safer: Green potential of alkali-activated materials in current building industry, radiological good practice, and a few tips
Full text linkAlkali-activated materials were prepared from four typical precursors (coal fly ash, granulated blast furnace slag, metakaolin, and brick waste powder) characterized for granulometry, elemental composition, and microstructure. High-resolution gamma-ray spectrometry was used to determine the activity concentration of Naturally Occurring Radioactive Materials (NORM) in all the materials to assess their radiological impact. All the investigated materials have been found to comply with the European dosimetric index (I) according to Directive 2013/59/Euratom. The results suggest the need for an accurate check of radioactivity throughout the mixing phases to prevent I exceedances. The productive chains were also evaluated by principal component analysis
- …
