Water and Chloride Transport Properties of Renovation Plasters Developed for Historical Masonry (original) (raw)
Related papers
Water Vapour Storage Capacity of Masonry Renovation Plasters Contaminated with Chlorides
Materials Science, 2018
The effect of sodium chloride presence on the water vapour storage capacity was studied for six types of plasters designed for application in masonry restoration. Sorption isotherms were measured using a static climate chamber method. The researched materials were characterised by their bulk density, matrix density, and total open porosity. For the studied materials, measurement of chloride binding isotherms by an adsorption method was done in order to reveal their capacity to accumulate salts and relate the adsorbed water vapour to the amount of contained salt. The experimental sorption data measured for salt contaminated samples were analysed using relation expressing the dependence of the mass equilibrium moisture content (EMC) of plasters saturated with salt solution of given molality on relative humidity of the environment. For relative humidity up to 70 %, good agreement between measured and calculated data was obtained. For higher relative humidity, the water vapour adsorption capacity of studied materials was not fully exploited especially for lower chloride concentrations. The type of binder together with physical parameters of examined materials was found to have a decisive role in chloride binding. One of the tested materials can be possibly classified as WTA renovation plaster, considering its total open porosity, bulk density and high binding capacity for chlorides. On the other hand, one must take into account its hygroscopicity, especially in case of a higher salt contamination.
Transport and Crystallisation of Salts in Masonry and Plasters
2004
For the understanding of the salt crystallisation mechanism in restoration plasters, insight in the mechanism of moisture transport is essential, as well as in the influence of salts on that mechanism. More specifically the drying behaviour, i.e. the moisture / salt transport and distribution during drying, is important. For a number of damage cases the salt and moisture distribution is analysed and, for some of the cases, the development of the damage over time is shown. The same is done for damage development in laboratory experiments. Recent experiments with NMR make it possible to understand better the moisture transport and the drying of porous materials. On the basis of the discussed examples, hypotheses are proposed on factors determining the salt damage mechanism.
Experimental analysis of coupled water and chloride transport in cement mortar
Cement and Concrete Composites, 2004
Coupled water and chloride transport in cement mortar is analyzed experimentally in the paper. Samples with initial moisture content corresponding to 45% relative humidity are subjected to one-sided sodium chloride-in-water solution uptake, and moisture profiles and chloride concentration profiles are determined in three chosen time intervals. In the evaluation of measured moisture profiles and chloride concentration profiles, diffusion model is employed. Moisture diffusivity is determined as function of moisture content and chloride diffusion coefficient as function of chloride concentration using two methods commonly used for analysis of moisture profiles, namely the double integration method and the Matano method. The highest values of both coefficients are obtained by Matano method for the curves corresponding to 24 h exposure to the solution, the lowest values by Matano method for 168 h, the results obtained by double integration method are in between. The complementary experiments with distilled water as penetrating liquid performed for the sake of comparison do not show this feature. It is observed that water transport in the initial time period is for the chloride solution faster and in later times slower than for distilled water. Therefore, the observed differences in the calculated apparent values of moisture diffusivity and chloride concentration coefficients are attributed to the fact that Cl À and Na þ ions are adsorbed on the pore walls faster than water molecules. This effect should be included into the mathematical models using ion binding isotherms.
Characterisation of the progression of salts in walls of earthen architecture heritage
Mineralogical Magazine, 2022
Two hundred years (1750-1950) of earthen architecture represents an important period of construction in the central region of Portugal. Earthen architecture is usually built close to the coast or to rivers and placed in sandy ground. The impact of rising damp is a general problem and efflorescences are a common cause of damage decay. This problem was studied in a building with two types of earthen construction, adobe masonry walls and formed masonry walls. The aim of this research was to characterise the conditions for the appearance and phase transitions of thénardite and mirabilite, and determine how to prevent progression of salt effects in the two types of wall to support future conservation measures. Laboratory capillarity and porosimetry tests with dolomitic air lime mortar and hygrothermal monitoring were pursued along with in situ tests. Visual assessment showed that the progression of salts depends on the composition of the earthen materials. To understand these differences, all crystalline solid phases were analysed by powder X-ray diffraction, and building interior hygrothermal conditions were monitored. An investigation into the influence of surface lime water painting and sacrificial mortar application on the crystallisation of sodium sulfates concluded that these also depend on the wall's composition. Data allowed us to conclude that inside the building the temperature and humidity [relative humidity (RH = 100 p w /p°w > 70)] conditions led to the adobe breakdown by the fast conversion from thénardite to mirabilite. Therefore, contact with wet atmospheres should be avoided and interior hygrothermal conditions should be controlled. Laboratory and in situ tests showed that the environmental conditions of the spaces had effects on the results. The results contribute to understanding of the salt progression and pattern of decay, as well as supporting future recommendations for building conservation, based on the identification of environmental conditions proper to their occurrence.
2020
All forms of solid historical structures – whether natural stone or brick masonry – are typically subject to the problem of rising damp and the concomitant crystallisation of soluble salts it transports. Some buildings are particularly susceptible, for example former stable buildings that are contaminated with nitrates leaching from animal faeces. Nitrates are the most critical group of harmful salts, which also includes sulphates and chlorides, as they are more readily soluble and can therefore rise to higher wall areas. Even slight fluctuations in air humidity can cause a change of aggregate state from solid to liquid and vice versa. When salts crystallise, they increase in volume. When this occurs within the pores of a material, it loosens the structure from within, causing it to disintegrate at the surface in particular. Depending on the pore structure, firmness and evaporation capacity of the materials, this can affect the bricks, the mortar or both.
Chloride profiles in surface-treated mortar specimens
Construction and Building Materials, 2000
Mortar specimens coated with six different surface treatments were immersed in 1 M NaCl solution for almost a year and then chloride profiles were measured. The interfacial chloride content C between the surface treatment layer and the substrate and i the pseudo diffusion coefficient D were calculated by fitting the error function solution of Fick's 2nd law to the profiles in the ps substrate. All of the surface treatments reduced C to below the surface chloride content of the untreated control specimen, i indicating that chloride diffusion into the substrate was restricted by the surface treatments. The effect of surface treatments on D varied. The experimental data are compared with a numerical model of chloride diffusion and discrepancies are discussed in ps terms of factors not included in the model. ᮊ
Carbonation and chloride ingress are the two main causes of corrosion in reinforced concrete structures. Despite the combined action of these mechanisms being a reality, there is little research on the effect of carbonation on the chloride diffusion in concrete. This work intends to study the influence of carbonation on chloride diffusion of mortar specimens. Cubic mortar specimens were cast with 0.55 of water-cement ratio. After curing, the specimens were subjected to 56 days of wetting and drying cycles. Half the samples were immersed for a day in a 3.5% NaCl solution and then placed for 6 days in a carbonation chamber (4%CO 2 ); the other half were also kept a day in 3.5% NaCl, but after were kept during 6 days in laboratory environment. Afterwards, the depth of chlorides and CO 2 penetration was evaluated. Complementary tests were also carried out, such as rapid chloride migration coefficient and water capillary absorption. The results show that carbonation has a direct influence on chloride penetration, decreasing it. The noncarbonated samples showed a profile with higher amount of chloride than carbonated ones. This fact can be related to the refinement of the mortar pores caused by carbonation and observed in water absorption tests.