Earthen plasters stabilized through sustainable additives: An experimental campaign

The earthen architecture widely spread in many countries of Europe, America, Asia, Africa, testifies to a particular material and immaterial culture. Nevertheless, it is a fragile heritage, which needs continuous maintenance. To encourage the preservation of such evidence of building techniques, an experimental campaign aimed at the development and evaluation of the performances of protective earthen plasters was undertaken. The durability of the plasters was improved through the addition of different additives, some of them traditional (such as lime and gypsum) and others innovative (geopolymers, enzymes), and resulting from industrial wastes (cement kiln dust). These additives have been selected considering low production costs and a reduced environmental impact, to improve the sustainability of the interventions. The performances of the earthen plasters in terms of efficacy (resistance to water erosion, water absorption, drilling, thermo-hygrometric cycles) and compatibility (changes in color and water vapor permeability) have been evaluated. Good performances were obtained by the different mixtures and, in particular, by those stabilized with gypsum. The results of this experimentation could find a useful application in the preservation of both ancient and new earthen built heritage

Mechano-chemical activation: an ecological safety process in the production of materials to stone conservation

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Stabilization of earthen plasters: Exchange of knowledge and experiences between Italy and Morocco

The preservation of earthen architectural heritage and earthen contemporary architecture asks for the experimentation and the development of proper materials and intervention techniques in order to prevent decays which may compromise the conservation of earthen heritage over time. This research program, thanks to a bilateral cooperation between the CNRST-UCA and CNR-ICVBC, aims to design and test earth-based plasters stabilized with traditional products (gypsum or lime), in order to acquire information necessary to develop more durable earthen mixtures to be applied both on existing and new buildings. The experimental campaign intends to assess the capacity of these stabilized plasters to guarantee an appropriate protection of earthen walls. The plasters have been tested at first in laboratory, then they have been applied on an earthen building in the outskirts of Marrakesh. The performances of the on site plasters are still under study and will not be presented in this paper

From the historical sugar refinery of Chichaoua (Morocco) to the lab: A reverse engineering experimentation on the hydration of earthen materials stabilized with lime

In order to explain the good state of conservation and good mechanical characteristics of the lime-stabilized earth of the sugar refinery near Chichaoua (Morocco, XVIth A.C.) XRD, SEM-EDX, TG-DSC, FT-IR analyses were performed on collected samples. Moreover laboratory earth samples were prepared with selected clay minerals (presence of attapulgite) and lime, involving a reverse engineering process in order to investigate the reaction products during curing . The same analyses performed on the historical samples were carried out on lab samples. Moreover, compressive strength was assessed. The results were compared to the ones obtained on the historical samples. The maturation of lime-stabilized rammed earth was due to lime carbonation and to earth drying and consolidation. Furthermore, the formation of mixed CSH phases was evidenced, possibly because of a slow pozzolanic reaction between lime and clays, that took place in long times both in lab and in historical samples.In order to explain the good state of conservation and good mechanical characteristics of the lime-stabilized earth of the sugar refinery near Chichaoua (Morocco, XVIth A.C.) XRD, SEM-EDX, TG-DSC, FT-IR analyses were performed on collected samples. Moreover laboratory earth samples were prepared with selected clay minerals (presence of attapulgite) and lime, involving a reverse engineering process in order to investigate the reaction products during curing . The same analyses performed on the historical samples were carried out on lab samples. Moreover, compressive strength was assessed. The results were compared to the ones obtained on the historical samples. The maturation of lime-stabilized rammed earth was due to lime carbonation and to earth drying and consolidation. Furthermore, the formation of mixed CSH phases was evidenced, possibly because of a slow pozzolanic reaction between lime and clays, that took place in long times both in lab and in historical samples

Porosities of building limestones: using the solid density to assess data quality

A good knowledge of the volume-fraction porosity is essential in any technical work on porous materials. In construction materials the porosity is commonly measured by the Archimedes buoyancy method, from which the bulk density of the test specimen is also obtained. The porosity and the bulk density together fix the solid density of the specimen, as only two of the three quantities are independent. The solid density, although rarely discussed, is determined by the mineralogy of the specimen, and therefore can provide a valuable check on the accuracy of porosity and bulk density measurements. Our analysis of published data on calcitic limestones shows that the solid density is generally close to the ideal crystallographic density of calcite. Small deviations can often be traced to variations in mineral composition. However some published porosity–density data are inconsistent with the known mineralogy. Deviations which cannot be ascribed to composition may be assumed to arise from measurement errors. We show the value of using the solid density as a quality check on the measured porosity. We recommend that the solid density should always be calculated for this purpose when the Archimedes method is used. This check can be useful also when porosities are measured by helium pycnometry or by mercury intrusion porosimetry

Influence of solvent granularity on the effective interaction between charged colloidal suspensions

We study the effect of solvent granularity on the effective force between two charged colloidal particles by computer simulations of the primitive model of strongly asymmetric electrolytes with an explicitly added hard sphere solvent. Apart from molecular oscillating forces for nearly touching colloids which arise from solvent and counterion layering, the counterions are attracted towards the colloidal surfaces by solvent depletion providing a simple statistical description of hydration. This, in turn, has an important influence on the effective forces for larger distances which are considerably reduced as compared to the prediction based on the primitive model. When these forces are repulsive, the long-distance behaviour can be described by an effective Yukawa pair potential with a solvent-renormalized charge. As a function of colloidal volume fraction and added salt concentration, this solvent-renormalized charge behaves qualitatively similar to that obtained via the Poisson-Boltzmann cell model but there are quantitative differences. For divalent counterions and nano-sized colloids, on the other hand, the hydration may lead to overscreened colloids with mutual attraction while the primitive model yields repulsive forces. All these new effects can be accounted for through a solvent-averaged primitive model (SPM) which is obtained from the full model by integrating out the solvent degrees of freedom. The SPM was used to access larger colloidal particles without simulating the solvent explicitly.Comment: 14 pages, 16 craphic

Serpentinite and ophicalcite in the architecture of eastern Liguria and as decoration of Tuscan religious buildings

The serpentinite is a metamorphic rock with a particular texture and colour ranging from light to dark green that was used in the Middle Ages architecture of Eastern Liguria and Central Tuscany as an element of embellishment of high value. This value was in relation to its aesthetic aspect but also to the high processing cost due to its hardness, requiring specialized workers. This research aims at broadening the knowledge related to the use of serpentinite together with that of a reddish brecciate variety of this lithotype, an ophicalcite traditionally called “Rosso di Levanto”. Conservation issues of these two materials, which are affected mainly by physical phenomena, will be highlighted

Influence of added salt on the surface induced ordering of nanoparticles with discretely distributed charges

The formation of an electric double layer composed of spherical nanoparticles is analyzed by means of a generalized Poisson-Boltzmann model and Monte Carlo simulations. We study a solution of symmetric and asymmetric mixtures of spherical particles that reside between two planar like-charged surfaces. Each spherical particle carries two elementary charges that are attached at its poles. The electrolyte solution also contains monovalent point-like salt ions. Our theoretical model properly accounts for intra-particle correlations - that is correlations between the spatially separated charges belonging to a single multivalent spherical particle. Correlations between different spherical particles are neglected. It is shown that added salt decreases the number density close to the charged surface and influences the orientation of spherical particles. Increasing salt concentration decreases the order parameter of the spherical particles. Generalized Poisson-Boltzmann results, obtained by solving an integral differential equation, and predictions from Monte Carlo (MC) simulations are in excellent agreement

Bridging like-charged macroions through longdivalent rod-like ions

Bridging like-charged macroions through longdivalent rod-like ion