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

Irreversible dilation of NaCl contaminated lime-cement mortar due to crystallization cycles

The mechanism of damage occurring in NaCl contaminated materials has not been clarified yet. Apart from crystn. pressure, other hypotheses have been proposed to explain the cause of decay. Irreversible dilation has been obsd. in a few cases but has never been studied in a more systematic way. The aim of the research is to contribute to the modeling of this phenomenon. In the present paper the effect of NaCl on the hydric and hygric behavior of a lime-cement mortar is extensively studied. The results indicate that NaCl influences the hydric and hygric dilation behavior of the material. The material contaminated with NaCl shrinks during dissoln. and dilates during crystn. of the salt. This dilation is irreversible and sufficient to damage the material after few dissoln./crystn. cycles. This behavior is not restricted to NaCl, but is obsd. in the presence of other salts as well (NaNO3 and KCl). Outcomes of electron microscopy studies suggest that salts causing irreversible dilation tend to crystallize as layers on the pore wall

Salt transport and crystallization in plaster layers : a nuclear magnetic resonance study

The durability and performance of specially developed restoration plasters or renders, are not always as good as expected. Salt crystallization is one of the causes of the observed degradation processes. To understand these processes in more detail, we investigated whether transport in the plasters depends on the masonry material. The transport of salt and moisture during drying of some plaster/strate systems is followed with a Nuclear Magnetic Resonance technique. The observed differences in drying behaviour can be related to differences in pore structure between the plaster and substrate. For a good performance of the plaster a proper matching of its pore-size distribution with that of the masonry is required

Natural and synthetic consolidants for earth heritage: a review

Since ancient times, natural products have been used to preserve earthen structures. Old recipes with cactus resin, bee wax, or linseed oil, have passed through generations and, in some countries, are still used nowadays. On the other hand, 20th and 21st centuries brought synthetic products as a solution to restore and conserve historical buildings. Although these synthetic products were extensively studied for stone-based monuments, they are also being used in earth heritage. The act of consolidating a degraded surface is, in conservation field, one of the most sensitive points, since the options available do not offer reliable solutions. Most of the times, the product applied, specifically in earth heritage, do not embrace two of the most important aspects in any conservation procedure: compatibility and reversibility. This paper aims to review the main consolidants (natural and synthetic) commonly used in earth heritage conservation, and also to draw the attention for the importance of a solid diagnosis of the initial state of conservation. With this review, it was possible to understand a lack of homogeneity in the identification of decay phenomena, as well as in recognizing its mechanisms of occurrence, and consequently in choosing the proper consolidant or treatment.The support from grant PD/BD/114411/2016 is acknowledged. This work was partly financed by FEDER funds through the Operational Programme Competitiveness Factors (COMPETE 2020) and by national funds through the Foundation for Science and Technology (FCT) within the scope of project SafEarth PTDC/ECM-EST/2777/2014 (POCI-01- 0145-FEDER-016737)

Characterization of a hybrid nano-silica waterborne polyurethane coating for clay bricks

A transparent hybrid organic-inorganic waterborne coating was evaluated for the protection of clay bricks. The nanocomposite film was prepared by combining an environmentally friendly process based on UV-curing of water-based acrylic resins and a mild thermal treatment to form nanosilica in situ from alkoxysilane precursors. Coated and uncoated facing bricks were compared by scanning electron microscopy, surface profilometry, water wettability, and capillary rise tests. The hybrid coatings act as a moderate water repellent; interestingly, no appreciable alteration of the aesthetic properties of the brick was observed, in particular no gloss or color change appeared after the treatmen