Search

Abstract: Limestones used as building material are especially prone to weathering in coastal environments due to interactions between sea mist and the carbonate stone. Subtle variations of the commercial surface finishing may lead to differences in decay patterns and aesthetic properties due to salt crystallization. To explore this potentially contrasting behavior, tablets of rough and polished low-porous limestone were aged in a sea-salt spray corrosion chamber to simulate their exposure in a coastal environment. Different crystallization morphologies and relative proportions of soluble (halite) and less soluble (gypsum) salts were observed in the aged rough and polished surface samples. These morphologies are ascribed to the microtextural characteristics and the surface pore systems of the diverse (rough and polished) substrates that in turn influence fluid (saline solution) transport toward their interior, as well as the different salt solubilities interacting with the substrates. Polished surfaces exhibit little evidence of damage after the ageing test in contrast to the rough samples but do have conspicuous gypsum on the surface together with halite. The scarcity of gypsum on the rough surfaces, in addition to a more severe change in the porosity system, suggests that salts penetrate deeper when the stone surface is not polished. Potential decay induced by salt crystallization pressure is therefore minimized when the stone surface is polished. However, polished surfaces show more significant changes in luminosity and chroma after the ageing test, and so are less attractive from an aesthetic point of view. Surface finishing is thus an important feature that needs to be characterized for a better understanding of the weathering behavior of building stones used in coastal environments. [Copyright &y& Elsevier]

The changes in brick porosity upon firing (700 up to 1100 °C) and its relation to the mineralogical composition are examined. Two types of raw clay with a composition representative of that used in brick-making industry were selected to manufacture the bricks: one contains notable amounts of carbonates, with a grain size of under 1 mm, and the other is predominantly quartzitic and lacking in carbonates. We demonstrate that the presence or absence of carbonates strongly influences the porosity development and, therefore, the brick texture and physical-mechanical properties. The carbonates in the raw clay promote the formation of fissures and of pores under 1 μm in size when the bricks are fired between 800 and 1000 °C. The absence of carbonates results in a continuous reduction in porosity and a significant increase in the pore fraction with a radius (r)>1 μm as the firing temperature rises and smaller pores coalesce. Porosity and pore size distribution results obtained from the combined use of hydric tests (HT), mercury intrusion porosimetry (MIP) and digital image analysis (DIA) of scanning electron microscopy photomicrographs are compared. A clear correlation between the water absorption and drying behaviour of the bricks and the porosity plus pore size distribution is observed. DIA discloses the evolution of size, shape and connectivity of macropores (r> 1 μm) and evidences that MIP results underestimate the macropore content. Conversely, MIP gives a good estimate of the open porosity and of the distribution of pores with r<1 μm. It is concluded that the combined use of these complementary techniques helps to fully characterise the pore system of bricks. These results as well as the study of the evolution of the speed of ultrasound waves vs. time yield useful information to evaluate the bricks physical–mechanical behaviour and durability. The relevance of these findings in the conservation of historic buildings is discussed. [Copyright &y& Elsevier]

This research examines fired clay bricks made with waste pomace from the wine industry as an additive in brick production. To this end, we analyse and discuss the chemical, mineralogical, textural and physical-mechanical behaviour of fired bricks made with three concentrations of wine pomace (2.5, 5 and 10 wt%) and at three different firing temperatures (800, 950 and 1100 °C) and evaluate their durability to salt crystallization. Variations in colour were also examined. The firing process resulted in the decomposition of phyllosilicates and carbonates, the crystallization of Fe oxides and the appearance of high-temperature Ca- (and Mg-) silicates phases such as gehlenite, wollastonite, anorthite and diopside. The bricks made with added wine pomace had very similar mineralogy to the control samples made without it. The bricks made with added wine pomace were lighter than the control samples and underwent less linear shrinkage during the drying process. Particles in the wine pomace were consumed during firing, leading to the appearance of voids. The bricks made with this additive had higher levels of water absorption and poorer mechanical strength. The greatest colour differences were detected after increasing the amount of waste, which generally resulted in yellower bricks. The increase in firing temperature resulted in an improvement in mechanical resistance regardless of the composition of the bricks. However, bricks fired at 1100 °C made without additive are more resistant to damage caused by salts than those made with wine pomace. [Display omitted] • The reuse of wine pomace reduces the quantity of clayey material in the production of bricks. • The addition of wine pomace augments the size and number of pores in the bricks. • Bricks with wine pomace are suitable for use as lightweight materials in the construction industry. • The addition of wine pomace modifies the lightness and chromatism of bricks, not the mineralogy. [ABSTRACT FROM AUTHOR]