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

Pore Size Distribution Influence on Suction Properties of Calcareous Stones in Cultural Heritage: Experimental Data and Model Predictions

Water sorptivity symbolises an important property associated with the preservation of porous construction materials. The water movement into the microstructure is responsible for deterioration of different types of materials and consequently for the indoor comfort worsening. In this context, experimental sorptivity tests are incompatible, because they require large quantities of materials in order to statistically validate the results. Owing to these reasons, the development of analytical procedure for indirect sorptivity valuation from MIP data would be highly beneficial. In this work, an Intermingled Fractal Units' model has been proposed to evaluate sorptivity coefficient of calcareous stones, mostly used in historical buildings of Cagliari, Sardinia. The results are compared with experimental data as well as with other two models found in the literature. IFU model better fits experimental data than the other two models, and it represents an important tool for estimating service life of porous building materials

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

Coating's influence on wind erosion of porous stones used in the Cultural Heritage of Southern Italy: Surface characterisation and resistance

Wind erosion (or aeolian corrosion) is one of the most relevant causes of weathering and degradation which has affected building surfaces in Cultural Heritage. The effect depends on the wind strength, the impact of particles transported and their size and the characteristics of surfaces affected. This aspect is very important for historical buildings constructed by using limestone as Lecce stone (LS). LS has an extraordinary ability to be shaped, but is very sensitive to decay. Exfoliation, wind erosion, absorption of water by capillary from the soil, are its main degradation causes. For such a reason, the application of effective products able to act as “sacrifice film” became necessary in order to minimise the degradation rate by preserving the limestone substrate against serious weathering agents. In this work, the effects of aeolian corrosion, simulated by means the accelerated test with sandblasting method, were studied. In particular, the effectiveness of two specific commercial coatings, such as an innovative free-solvent hybrid organic-inorganic coating (HYBRID) and a solvent-based coating (AS), was assessed relating to their capability to preserve Lecce stone from the aeolian corrosion phenomenon. The protective efficacy was guaranteed by both the commercial coatings even after accelerated wind erosion test, by confirming a high hydrophobicity, low capillary water absorption and an adequate depth of penetration inside the stone able to assure durability

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

Bending strength of porous ceramics tiles: Bounds and estimates of effective properties of an Intermingled Fractal Units' model

In this work, a semi-analytical model for the determination of effective mechanical properties of porous ceramic tiles obtained by pore forming agent is proposed. MIP tests allow measuring porosity and pore size distribution of experimental systems. These data are used for developing an Intermingled Fractal Units' model (IFU) as approximant of porous microstructures. IFU model is then combined with classical structural mechanics theory for the analytical computation of the bending strength of brittle ceramic beams. Bounds and estimates are given in full form and the detailed algorithm can be easily implemented in a numerical package. A preliminary comparison with experimental data shows the capability of the proposed model to reproduce the effective mechanical behaviour of ceramic tiles

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

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