Ulrico Umberto Maria Sanna

Comparison between rheological models for portland cement pastes

Abstract Rheological properties of Portland cement pastes, measured with a rotating viscosimeter, have been correlated by means of different mathematical models. The best results are obtained with Eyrings equation, Herschel & Bulkleys equation and the parabolic equation, while Vom Bergs model only holds for low shears. The authors propose another equation derived from Eyrings but explicitly containing the term τo.

Use of granulated slag from lead and zinc processing in concrete technology

The possibility of using granulated slags resulting from the smelting of lead and zinc in partial, or total replacement of sand in mortars and concretes, has been examined. The major components of these vitreous slags are Ca, Si, Fe and Al compounds with lead concentration of a few percent. They have suitable particle sizes for use as sand and the slag mortars and concretes studied here yielded satisfactory mechanical strengths. The extraction of lead by acid eluants might however create some problems when concretes containing these slags have to be disposed off.

Mechanical properties of epoxy mortars with fly ash as filler

Abstract This paper is concerned with the use of fly ash filler in mortars containing epoxy resins as binders, as a replacement for quartz flour normally employed in such products which find application in pavings for industries, airports and heavily trafficked roads, as well as restoration and protection of concrete works. The stress/displacement curves of bending and compression tests are plotted for the systems tested. The results indicate that the specimens containing fly ash exhibit superior mechanical properties compared with the quartz-filler ones at the shorter curing times, while at longer curing time mechanical performance is comparable.

Dimensional variations, capillary absorption and freeze-thaw resistance of repair mortars admixed with polymers

The results are presented of an investigation aimed at determining the properties required by cement mortars admixed with polymers to be used as overlays in the repair of concrete structures. Tests were conducted using acrylic latex and epoxy resin as polymer admixtures. The adhesion of the modified mortars to different cement bases was tested under stresses induced by dimensional variations (ageing, thermal cycles), capillary absorption and freeze-thaw resistance.

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.

MECHANICAL AND THERMOHYGROMETRIC PROPERTIES OF ADHESION BETWEEN PCMS AND CEMENT SUPPORTS

Abstract A series of cement mortars admixed with either acrylic latex or epoxy resin has been characterized and used for repairing cement supports having different mechanical properties. The performance of the support/repair system under mechanical and thermohygrometric stresses was then assessed. The mortars containing acrylic latex proved particularly effective.

Pigments and materials across Sardinia’s walls: contribution on the Tomba dei Pesci e delle Spighe in Cagliari

Sardinia is an ancient island where it is possible to find signs and symbols, decorative engraved and colored traces of men and history. In 1997 an ancient tomb in Cagliari has been discovered: it is located in the necropolis of Tuvixeddu, an old and spread necropolis dating from Punic to Roman times now located in the urban texture. The tomb, consisting of only one chamber, is dated by archaeologists a few centuries A.D. The name, Tomba dei Pesci e delle Spighe, is related to the painted decorations that were clearly visible on the walls and roof of the burial chamber, not so easily distinguishable anymore because of natural decay processes. Wall paintings appear severely damaged owing to the darkening of some areas, the detachments of others and a widespread presence of superficial concretions on the roof surfaces. This contribution aims to characterize pigments and the painting technique used in this burial chamber and compare them to the roman tradition. The site is confined, with evident problems of conservation because of the critical microclimatic conditions. High humidity and degradation are compromising the legibility of the decorative schemes. Samples of constituting materials and concretions have been collected and analyzed using x-rays diffraction (XRD) and IR spectroscopy (µFTIR-ATR). Preparatory layers supporting the pictorial have inorganic nature: diffractograms showed the presence of gypsum and calcite. IR spectroscopy (µFTIR) and scanning electron microscopy coupled with an energy dispersive system (SEM-EDS) were used to investigate the nature of pigments. Samples of blue, red and yellow pigments have been investigated. Egyptian blue, cinnabar and earth pigments have been detected. Proteinaceous materials have been identified as possible binders for the pigments.

Crystallization of sodium sulphate in polymer impregnated plasters

Abstract The common occurrence and harmful effects of sodium sulphate make it a major cause of deterioration in plasters. The investigation conducted showed that a plaster composed of eminently hydraulic lime impregnated with water-repellent solutions (a perfluoropolyether or an oligomeric alkylalkoxysiloxane) or admixed with an acrylic latex is significantly more durable than plain plaster. In particular, the different modes of salt crystallization are discussed in relation to the microstructural properties conferred by the polymers, and to the thermohygrometric conditions of the system.

Properties of gas concretes containing high proportions of PFA

Abstract The rheological and mechanical properties of gas concretes prepared with ordinary Portland Cement (OPC) and up to 60% (by weight) pulverized fly ash (PFA) are studied. Working with lower water and high PFA contents, significant expansion is achieved only in the presence of plasticizing admixture, and in this case at hand an acrylic latex proved most suitable. The best mechanical properties were observed in the systems containing 40 and 60% PFA as OPC replacement, steam cured at 70 and 180°C respectively.

Long-term performance evaluation of an earthen grouting mortar: the Nuraghic complex of Genna Maria, Sardinia

Abstract This paper presents a critical assessment of the long-term performance of an earth-based material employed nine years ago in conservation work on a building of massive, Cyclopean-style construction at the Genna Maria Nuraghic complex in central-southern Sardinia (Italy). The material was used for filling the large gaps between stones in the masonry walls to create a barrier to ingress of water into the masonry walls. In situ observations and laboratory analyses were conducted on samples of the grouting material to assess its condition after nine years.