Influenza della porosità sulle proprietà dei materiali. Un approccio fenomenologico basato sulla geometria frattale

In this thesis, the correlation between microstructure and properties of porous materials is analysed using Fractal Geometry. In particular, the effect of pore size distribution in fluid transport, thermal conductivity and some mechanical properties is studied. Materials used in cultural heritage, contemporary architecture and industrial engineering such as limestone, earth based materials, traditional ceramics, advanced ceramics (zirconia and alumina) and binder have been examined. The porosimetry experimental data has been acquired by mercury intrusion technique. In this research, a model based on fractal of Sierpinski carpet is used. By mixing fractal units with different dimension and configuration, it was possible to create a microstructure of material similar to experimental. Some fractal analytical procedures have been developed to predict thermal conductivity, sorptivity, water vapour permeability and elastic modulus. The data obtained by fractal model has been compared with experimental data. The results obtained are quite close to experimental ones and it has been revealed that this procedure is more effective than other model proposed in the recent literature

Water Absorption Properties of Cement Pastes: Experimental and Modelling Inspections

An intermingled fractal units’ model is shown in order to simulate pore microstructures as pore fraction and pore size distribution. This model is aimed at predicting capillary water absorption coefficient and sorptivity values in cement pastes. The results obtained are in good agreement with the experimental ones. For validating this model, a comparison with other procedures has been shown. It is possible to establish that the newly proposed method matches better with the experimental results. That is probably due to the fact that pore size distribution has been considered as a whole. Moreover, even though the proposed model is based on fractal base units, it is able to simulate and predict different properties as well as nonfractal porous microstructure

Heat transfer in high porous alumina: Experimental data interpretation by different modelling approaches

Advanced porous ceramics are a remarkable class of materials with important applications in engineering fields. Porosity features have received wide attention for their capability to influence all properties. In this paper, the correlation between pore structure and heat transfer has been studied. Different analytical procedures found in literature as well as an Intermingled Fractal Units' model are proposed. Models predictions are compared with experimental data. It has been observed that IFU is particularly suitable to predict thermal conductivity values very close to experimental ones. This fact is related to its capability to replicate porous microstructures in terms of pore volume fraction, pore size range and pore size distribution

Determinazione della permeabilità di materiali lapidei nell’edilizia storica attraverso un modello frattale della microstruttura porosa

Per il calcolo della permeabilità di materiali porosi viene presentato un approccio basato sulla descrizione della microstruttura dei vuoti tramite la geometria frattale. Come materiali di riferimento sono stati considerati una calcarenite, rappresentativa di un litotipo poroso e largamente utilizzata nel settore dell’edilizia storica in diversi paesi del mediterraneo e alcuni sistemi caratterizzati da leganti moderni. È stata calcolata la dimensione frattale della microstruttura utilizzando dati porosimetrici ottenuti con la tecnica di intrusione forzata di mercurio, simulando successivamente le distribuzioni dimensionali dei pori sperimentali attraverso l’applicazione di un Intermingled Fractal Units model basato su unità tipo: tappeto di Sierpinski. Su questo modello viene studiata un’apposita espressione analitica della permeabilità dalla quale sono stati desunti valori che concordano in maniera soddisfacente con quelli ricavati dalle prove sperimentali

Porosity and pore size distribution influence on thermal conductivity of yttria-stabilized zirconia: Experimental findings and model predictions

Porous yittria-stabilized zirconia is an important advanced ceramic material for technological applications. One of the most important characteristics of this material is low thermal conductivity, which is greatly influenced by the presence of pores into the microstructure. In fact, air trapped in the pores represents a better thermal insulator. The role of the pore volume fraction on porous material characteristics has been extensively studied. On the other hand, the influence of the structure disorder, the pore size range and pore size distribution have been studied much less. In this study, an intermingled fractal model capable of relating thermal properties of ceramic materials and their pore microstructure has been proposed. Model predictions are found confirming the experimental data fairly well, even better than the others models available in the literature

Porous ceramic materials by pore-forming agent method: An intermingled fractal units analysis and procedure to predict thermal conductivity

Porous ceramic materials can be produced by different techniques. One of the most important is pore agent method. The pore fraction, size, shape and distribution are linked to the pore-forming agent. In these materials porosity has a great influence in their physical properties and one of them is thermal conductivity. The role of the pore size distribution has been studied much less than pore fraction, probably because it is very difficult to describe and to characterize it. For this reason, in this paper, an original intermingled fractal model to predict thermal conductivity (taking into account entirely pore size distribution) has been proposed. This model is capable to reproduce fractal or non-fractal microstructure. Calculated data are in good agreement with experimental ones. The model could be considered as a microstructure simulator to improve thermal performance of porous ceramic materials

Pore size distribution and porosity influence on Sorptivity of ceramic tiles: From experimental data to fractal modelling

The Sorptivity is a coefficient very important to characterize porous materials. It is associated to principal properties such as mechanical durability, thermal and electrical conductivity, etc. In this work, the Sorptivity coefficient of several systems of porous ceramics has been measured following the experimental procedure. In different situations, this very simple test could be not performed; in cultural heritage or during an optimised industrial process. Major reasons for this inability include that it would demand great quantitates of materials impossible to withdraw from the protected building, as well as the experimental test can last for several days, which reduces the possibility to correct/improve the industrial production process. In this regards, being very useful to have analytical formulas in order to calculate Sorptivity coefficient, an Intermingled Fractal Units model has been proposed. Starting from its capability to reproduce entirely the pore size distributions of porous materials, IFU is used to simulate water absorption process and to estimate the Sorptivity coefficient. The obtained results are in good agreement with experimental data and others two models predictions. This fact allows considering IFU model as a future tool for design materials and to predict their service life

Thermal behaviour of clay ceramics obtained by Spark Plasma Sintering: is fractal geometry a new possible road to design porous structures?

Porous clay ceramics represent an important class of construction materials. Their properties are strongly conditioned by microstructure features. In particular, a special attention has to be paid to porosity (pore fraction, pore shape, pore size, pore size distribution and topology distribution). In this work, thermal behaviour of porous ceramics has been studied comparing different modelling procedure. Fractal modelling, proposed in this paper, proves to be most reliable in predicting thermal behaviour of porous ceramics. For this reason, a design procedure for obtaining porous structures with specific thermal properties has been illustrated

Thermal conductivity of porous stones treated with UV light-cured hybrid organic-inorganic methacrylic-based coating. Experimental and fractal modeling procedure

This study presents an intermingled fractal model (IFU) capable of simulating the porous microstructure of natural calcareous stone substrate, typical of Apulia Region (Pietra Leccese, PL) used in historical buildings. The developed model is aimed at predicting, by an analytical approach, the thermal conductivity of these materials. To verify the actual ability of the proposed method to predict stone thermal conductivity, the intermingled fractal units model was applied to untreated natural stone, and to the same stone, treated with a novel UV-light curable O-I hybrid coating. The application of hydrophobic polymers to stone materials is, in fact, an effective way to preserve stone artifacts and protect cultural heritage from decay. To this aim, a novel experimental photopolymerizable organic-inorganic (O-I) hybrid protective coating, mainly intended for the protection of PL stone, was previously developed by some of the authors. The innovative hybrid product evidenced an extraordinary hydrophobicity, able to guarantee a very high preservation of the stone from water actions, as well as another important property required to a protective, i.e., a high traspirability of the stone substrate. Furthermore, the experimental product proposed was able to equal the performance of commercial available products, with the adjunctive advantage to be free-solvent