Hygric Behaviour Research Articles

The hygric properties of cement mortar with salt spray deposition

Many buildings along the coast are exposed to the salt spray climate, but the hygric behavior of porous building materials under the influence of salt crystallization are unclear. In this study, an accelerated salt spray test was conducted on cement mortar. For samples with different salt spray cycles, chloride ion content was measured and saturated moisture content (wsat), open porosity (po) and apparent density (ρb) were obtained by a vacuum saturation test, while capillary absorption coefficient (Acap) and capillary moisture content (wcap) were determined from capillary absorption tests using innovative methods. Additionally, the pore characteristics and micromorphology of the samples were examined and analyzed using a mercury intrusion porosimeter (MIP) and a scanning electron microscope (SEM). The results indicate that a large amount of deposited salt crystals mainly clogs pores with a diameter of 0.02 to 0.12 μm, resulting in a 18.7 % decrease in po as well as a 30 % decrease in Acap and a 17.4 % decrease in wcap subjected to 35 salt spray cycles. This finding supports a deeper understanding of fluid moisture absorption and transfer in building envelope materials in coastal areas.

Effect of Applied Pressure on the Performance of Biodegradable Fiber Insulation Board Manufactured from Camphor Branches (Cinnamomum camphora)

Currently, the predominant thermal insulation materials in the construction industry are primarily derived from inorganic sources. While these materials demonstrate commendable thermal insulation capabilities, their widespread use raises significant environmental concerns. The utilization of wood fiber materials presents a promising solution to mitigate these drawbacks. This study focuses on the fabrication of biodegradable fiber insulation board (BFIB) using camphor branches. The manufacturing process avoids the use of chemical additives, employing a physical method that utilizes hot pressing and relies on the formation of intermolecular hydrogen and hydroxide bonds between the fibers. The study evaluates the influence of applied pressure on the properties of BFIB. SEM images reveal that, with an increase in applied pressure, the fibers exhibit a more regular pattern, subsequently enhancing the mechanical properties, hygric behavior, and fire resistance properties of BFIB. As an environmentally friendly and renewable material, BFIB holds the potential to substitute conventional insulation materials. It is particularly intriguing for energy-saving purposes when applied as building insulation for walls or ceilings.

Passively Maintained Closed Cavity Façade—Experimental Validation of the Mathematical Thermal Model

Although glass façades have been on the market for over a century, new improvements, following sustainable standards, are still being invented. An improvement of the actively maintained CCF has occurred in passive maintenance with natural ventilation of the cavity and insulation glass unit placed on the external side, which has served as a true motivation for further research. To develop the idea, a new type of CCF was invented, followed by the creation of the software, whose purpose is to determine optimal CCF façade components. During this research, an experimental and mathematical model was made regarding the thermal behavior, later validated by the measurements on-site in Rugvica, Croatia. Using simplified but unconventional methods, numerous formulae and variables, a simulation of climatic loads onto the CCF was conducted. Validations of the thermal model were made during winter and summer periods for southern and western façade orientation, explaining how heat transfers from the environment to close cavity façade elements. It was found from the analysis that air temperatures of the façade elements follow the outer air temperature, by constant air exchange with the outer space. The results showed great potential with up to 3 °C (5–10%) of difference in experimental and calculated results, thus creating a basis for further improvement of the software with the addition of structural and hygric behavior of the façade element, regarding climate conditions.

Simulation of moisture transport in fired-clay brick masonry structures accounting for interfacial phenomena

This paper presents a numerical study on moisture transport in brick masonry walls with a special focus on the simulation of their hygric performance as well as the hydraulic phenomena at the brick-mortar interface. A diffusivity model based on Fick's law is used to describe the moisture transport accounting for both liquid and water vapor movement. The necessary hygric parameters are obtained directly from experimental tests or determined by curve fitting. The proposed model is validated with respect to water absorption and drying tests. The good-fitness of the results is qualitatively assessed and an overall good agreement is found between the simulated and measured curves. It is demonstrated that the chosen liquid water diffusivity expression needs to be adjusted to represent drying processes; the necessary adjustment is made through a diffusivity factor implemented in the original analytical expression. The interface impact on water absorption is introduced as a hydraulic resistance. Moreover, it is hypothesized that the presence of successive interfaces entails an additive in-series effect. Conversely, the interfacial impact on drying is negligible. Finally, the proposed model is extended to different modeling approaches commonly used for mechanical studies of masonry. The necessary input data, modeling methodology, advantages and disadvantages associated with each modeling strategy are also discussed. The present study points out the need of studying water absorption in multi-layered structures made up of constituents with relatively similar hygric behavior. In such cases, the impact of imperfect contact at the interface between materials is not negligible.

Influence of salt (NaCl) on hydric and hygric dilatation of clay-rich rocks

• Hydric (liquid water) dilatation decreases with increasing salinity of pore water. • Salt contamination reverses hygric (water vapour) dilatation phases of clay-rich rocks. • Crystallisation of NaCl develops higher strain than hydration of clay interlayers. • Changes in volume occur more frequently once clay-rich rocks are exposed to salts. • Salt weathering of clay-rich rocks produces granular disintegration and scaling. The mechanisms through which crystallisation of salts and hydration of swelling clays cause deterioration of rocks are generally understood. However, how these two decay mechanisms operate synergistically is less clear. In this study, we investigated the impact of a salt (NaCl) on the deterioration of clay-rich basaltic scoria from which the churches forming the UNESCO World Heritage Site of Lalibela in Ethiopia are hewn. The basaltic scoria is rich in smectite (swelling clay) and zeolitic minerals which have micropores and an affinity for efficient water absorption. Hydric and hygric swelling experiments were carried out on 50 mm cube quarry samples and continuous measurements were taken with Linear Variable Displacement Transformers (LVDT). Hydric (liquid water) tests involved partially submerging the samples in deionised and saline solutions. Hygric (water vapour) tests were done in an environmental cabinet where the RH fluctuated between 60% to 90% RH with salt-free and salt-contaminated samples. The results showed that contamination with salts alters both hydric and hygric behaviour. Hydric swelling was reduced in most samples when contaminated with salt, while the expansion and contraction phases in hygric tests were reversed after contamination with NaCl. Continuous measurement of dilatation allowed us to quantify the strain developed during the phase transition of NaCl. Due to the crystallisation pressure, hygric dilatation increased significantly in salt-contaminated samples. Salt-contaminated samples also showed frequent episodic changes in volume that corresponded both with the hydration/dehydration of clay interlayers and crystallisation/dissolution of NaCl. These volume changes correspond with the damage profile on the surface of the samples, i.e., contour scaling and granular disintegration. The results indicate that the mechanism through which salt contamination accelerates the decay of clay-rich rocks is via an increase in the frequency and degree of hygric dilatation.

Experimental Characterization of Raw Earth Properties for Modeling Their Hygrothermal Behavior

Raw earth is one of the oldest building materials of mankind. Almost a third of the world’s population is living in an earth-based house. However, their use remains low compared to conventional materials such as concrete, steel, and wood. Although these geosourced materials are abundant, recyclable, and have a low environmental footprint, their use is very limited in the construction sector. This can be explained by the lack of data regarding their hygrothermal behavior. In this context, the present work aims to highlight the properties of cob construction material with straw addition. An experimental characterization of hygrothermal and microstructural properties has been carried out. Thermal conductivity, specific heat, sorption isotherms, moisture storage capacity, moisture buffer value (MBV), and water vapor permeability are obtained experimentally. Then, the collected data are used as input parameters of a numerical prediction model to numerically assess the thermal and hygric behavior. Cob is then compared to other more commonly used materials to highlight the benefits of its use within the context of the energetic and environmental transition. Our results will allow better understanding of the behavior of the new geosourced material thanks to experimental and numerical investigation.

Drying characteristics of two capillary porous building materials: Calcium silicate and ceramic brick

The wetting and drying ability of porous building materials plays a significant role in moisture transfer in the building envelope and thus influences the durability and energy efficiency of buildings. The drying characteristics of the material provide insight into the moisture transport feature over a wide moisture content range, and hence, the drying process can assist in improving the accuracy of moisture transport modelling for the heat, air and moisture (HAM) simulation and in comprehending the hygric behavior of buildings responding to environmental change.In this paper, the drying behaviors of calcium silicate and ceramic brick were experimentally and numerically investigated. The approaches to determine the drying rates of the first and second drying durations were first evaluated and proposed. The influence of the surface air flow velocity and sample dimension on the drying process was analyzed. The descriptive parameters to assess the drying rate were further discussed. The drying coefficient was shown to be able to describe the drying ability of porous building materials. Numerical simulation was conducted and compared with the measurement for a better understanding of the coupled heat and moisture transfer phenomena during the drying process.

Hygric Behavior of Viticulture By-Product Composites for Building Insulation.

One possible approach to reducing the environmental impacts associated with the building sector is the development and use of bio-based building materials. The objective of this study is to determine the water properties of bio-based insulation materials, derived from winegrowing co-products, which promote energy efficiency. The water performance of these new bio-based materials is based on the measurement of the moisture buffer value, the sorption isotherm, and the water vapor permeability. Four by-products are analyzed: stalks, grape pomace, crushed stalks, and skins; they are combined with a potato starch binder. The performance of these composites is compared to two other bio-based composites (hemp/starch and beet pulp/starch). The stalk/starch composite can be classified as a hygroscopic and breathable material with excellent moisture retention capacity.

Hygric Properties of Machine-Made, Historic Clay Bricks from North-Eastern Poland (Former East Prussia): Characterization and Specification for Replacement Materials.

This paper deals with the hygric characterization of early 20th century machine-made clay bricks, representative of great number of historical buildings in north-eastern Poland. Heritage buildings have a high potential for adaptive reuse, which is strictly connected with an urge for knowledge about the properties of these existing building envelopes. To better understand the hygric behavior of historic buildings, various experimental laboratory tests, including density, water absorption, compressive strength and freeze-thaw resistance, were conducted. In order to assess the microstructural characteristics of the tested bricks, mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) tests were performed. These tests were conducted on clay bricks from historic buildings, as well as on those that are currently being produced, in order to identify the relationship between the materials used in the past and the replacements produced presently. This paper addresses the lack of systematic application of existing standards for evaluating the state of the conservation of historic bricks and for establishing the specifications for replacement bricks. The results of conducted study and further research will be the basis for creating a historic materials database. It would be a useful tool for selecting bricks that correspond with the historically used materials and help to maintain homogenous structure of the restored buildings.

Water absorption characterisation of historic plasters. Comparison of different methodologies in a case study in Tyrol, Austria.

Balancing conservation of historic buildings and improvement of their energy performance is a challenging task that involves multiple factors. Prescriptive standards for interventions of internal insulation in modern materials are not compatible with conservation of historic plasters and thus a more detailed and sympathetic approach must be used. Knowing the hygric behaviour of historic plasters is a prerequisite in the assessment of any intervention of internal insulation. In this paper, four different methods for the quantification of the water absorption coefficient, laboratory and onsite based, are presented and applied to an outstanding case study in Tyrol (AT). The variability observed, between methods but also between the different layers of plasters found onsite and even between measurements, highlighted the need for robust guidelines for the application and interpretation of the results. This study summarises the numerous factors influencing the result of the water absorption measurement and shows a first investigation into one of these aspects (heterogeneity of the wall). Numerical simulation has proven to be an effective tool to use in combination with experimental results in testing the effect of the different parameters affecting the water absorption characterisation of historic plasters.

Experimental characterization of moisture transport in brick masonry with natural hydraulic lime mortar

This article presents an experimental study on the hygric performance of brick masonry with a special focus on the hydraulic characterization of the brick-mortar interface. The hygric behavior was studied at the level of the constituent materials as well as at the composite scale. An extruded fired-clay brick and two types of mortar –Portland cement mortar and natural hydraulic lime mortar– were chosen as target materials. The hygric properties were determined following prescribed experimental procedures. The experimental program included vacuum saturation tests, static gravimetric tests for adsorption/desorption isotherms, dry/wet cup tests, capillary absorption tests, and isothermal one-dimensional drying. The results allowed for a comprehensive identification of the main hygric features of the target materials. Fired-clay brick and lime mortar revealed low hygroscopicity and a strong capillary-active behavior with negligible hysteresis, whereas cement mortar showed activity in both hygroscopic and capillary ranges with a distinct moisture storage hysteresis. Different curing conditions led to dissimilar properties between the lime mortar prepared in molds and the same mortar cured in masonry bed joints. Water absorption in fired-clay bricks showed a marked anisotropic behavior, likely derived from the extrusion process. The existence of an imperfect hydraulic contact at the brick-mortar interface was demonstrated for water absorption. Conversely, the interfacial effect on drying kinetics was not evident.

Impact of surface waterproofing on the performance of brick masonry through the moisture exposure life-cycle

Moisture is one of the major causes of damage to building systems, affecting the hygrothermal performance and durability of building systems. Surface treatment products are available in the market that can influence the hygric performance of masonry facades under water exposure. These are of a wide range of chemical compositions, and they claim to waterproof the masonry surfaces while not diminishing vapour transmissibility. This paper presents and discusses the findings from a series of benchtests carried out to measure hydrophobicity, water absorption and water vapour transmission following the relevant codes for an appraisal of the hygric behaviour change in brick masonry induced by waterproofing through three distinct phases of the life-cycle of moisture exposure, i.e. first contact with water, wetting and drying. To this end, 4 waterproofing products including silane/siloxane blend liquid and cream, and acrylic and stearate-based liquids were selected for testing, along with 3 brick types common in the 50s and 60s to be representative of the majority of the UK building stock. The findings show that the treatment products indeed enhance the surface hydrophobicity and reduce water absorption while allowing water vapour transmission to differing degrees: silane/siloxane blend cream overall was found the most effective throughout the moisture-exposure life-cycle, with an average of ~96% reduction in water absorption and 18% of increase in water vapour resistance in comparison to the untreated case, followed by the stearate-based liquid with 57% reduction in water absorption and 12% increase in water vapour resistance. The acrylic-based product demonstrated good performance in hydrophobicity and water vapour transmission tests, however led to a comparatively higher water absorption capacity than the other treatment products with only ~40% reduction in comparison to the base-case. Finally, silane/siloxane blend liquid was found to lead to the lowest contact angle, demonstrating a lower-than-others capacity to developing surface hydrophobicity, and led to 35% reduction in water absorption and 28% increase in water vapour resistance, making it the poorest product in the dataset to lead to watertight and vapour open systems under water exposure. Based on the test results it was also deemed beneficial to use masonry specimens to account for its composite nature, rather than using results obtained from brick and mortar separately to infer the wall response under exposure.

Energy performance and climate control in mechanically ventilated greenhouses: A dynamic modelling-based assessment and investigation

Controlled environment agriculture in greenhouse is a promising solution for meeting the increasing food demand of world population. The accurate control of the indoor environmental conditions proper of greenhouses enhances high crop productivity but, contemporarily, it entails considerable energy consumption due to the adoption of mechanical systems. This work presents a new modelling approach for estimating the energy consumption for climate control of mechanically ventilated greenhouses. The novelty of the proposed energy model lies in its integrated approach in simulating the greenhouse dynamics, considering the dynamic thermal and hygric behaviour of the building and the dynamic response of the cultivated crops to the variation of the solar radiation. The presented model simulates the operation of the systems and the energy performance, considering also the variable angular speed fans that are a new promising energy-efficient technology for this productive sector. The main outputs of the model are the hourly thermal and electrical energy use for climate control and the main indoor environmental conditions. The presented modelling approach was validated against a dataset acquired in a case study of a new fully mechanically controlled greenhouse during a long-term monitoring campaign. The present work contributes to increase the knowledge about the dynamics and the energy consumption of greenhouses, and it can be a valuable decision support tool for industry, farmers, and researchers to properly address an energy efficiency optimisation in mechanically ventilated greenhouses to reach the overall objective of decreasing the rising energy consumption of the agricultural sector.

Hygrothermal behavior of wood fiber insulation, numerical and experimental approach

Many new insulation materials are being developed and thermally tested aiming at understanding and improving their insulation characteristics in order to improve the energy performance of new and existing buildings. Bio-sourced materials appear among the new insulation solutions presenting the advantage of being able to save energy on one hand and having a low environmental impact on the other. The wood fiber material is one of the most successful natural insulation materials being recently used in building constructions. It presents many advantages besides its insulation performance; due to its density, it stores moisture thereby improving the indoor air quality; it is also an excellent acoustic insulator because it has a natural tendency to absorb and reduce sounds. In order to evaluate its effectiveness in building applications, this study analyzes the hygrothermal modelling and performance of the wood fiber insulation in building applications by adopting two approaches: A numerical approach using a mathematical model that describes heat and mass transfer within the wood fiber material being considered as porous media. The hygrothermal characteristics of the wood fiber material are first determined experimentally for this purpose, namely the thermal conductivity, the heat capacity, and the isotherms of sorption and desorption. An experimental approach is carried out in controlled and uncontrolled ambiance conditions in order to validate the numerical model. A 50 cm × 50 cm wood fiber sample having an 8 cm thickness is tested for this purpose. A very high accordance is observed between the measured and modelled results for both the temperature and the relative humidity evolutions within the sample at x = 2 cm and x = 4 cm with a mean difference \( \overline{\Delta \mathrm{T}} \) of 0,21 °C at x = 4 cm and 1 °C at x = 2 cm. The maximum recorded differences for the relative humidity are: 5,5% and 4,5% at x = 2 cm and 4 cm respectively. The ability to predict the thermal and the hygric behavior of the wood fiber insulation will thus allow a better understanding of the efficiency of natural insulation materials.

Determination of the hygric properties of the heritage stone of the Cathedral of Cuenca through the water absorption by capillarity test

Abstract This work analyses the characterization of the hygric behaviour of a stone heritage material by solving the inverse problem using experimental data obtained from a water absorption by capillarity test (EN 15801). This common test is undemanding and requires relatively simple equipment as compared to other hygric characterization tests. For the solution of the direct problem of transient flow in partially saturated porous media, a computational module was developed in COMSOL Multiphysics that includes the conceptual model from the standard EN 15026. The selected material was the heritage stone of the Cuenca Cathedral, differentiating between two characteristic lithotypes: one with greater porosity and another that is more resistant, with more reduced porosity. Based on the experimental results, the intrinsic permeability and the parameters of the moisture storage function are estimated for the two lithotypes. Similarly, contrast tests were conducted to quantify the estimation error. A stochastic analysis was performed to assess if the estimated hygric parameters satisfactorily characterize the behaviour of the studied stone.

Modeling the similarity and the potential of toluene and moisture buffering capacities of hemp concrete on IAQ and thermal comfort

Controlling and understanding indoor humidity and pollutants can help reduce the risk of health concerns. The experimental results suggested that there is a similarity relationship between water vapor and Volatile Organic Compounds (VOC) in diffusion through porous media. In this paper, the similarity between the moisture and pollutant transport and storage coefficients of porous building materials has been clearly established and explained. In addition, two similarity coefficients have been defined for VOC storage and diffusion to estimate the VOC properties from the moisture properties of the same material. A coupled hygric-pollutant (VOC) model which can be used to simulate VOC and hygric behavior of building materials under dynamic conditions is presented. The model which is implemented in the environment SPARK (Simulation Problem Analysis and Research Kernel) suited to complex problems using finite difference technique with an implicit scheme, has been validated with the experimental data. It is then applied to study the effect of toluene and moisture buffering capacities of a hemp concrete wall on indoor toluene concentration and relative humidity (RH). Hemp concrete was chosen in this study because it is an environmentally-friendly material that is used more and more in building construction. The toluene (TOL, selected VOC for this study) transport and storage properties obtained from hygrique properties of hemp concrete based on the assumption of the similarity between toluene and moisture transport have been modelled and investigated. At the room level, the results obtained show that taking into account the sorption capacity toward moisture and toluene has a significant effect on indoor RH and IAQ because hemp concrete contributes to dampen indoor RH and toluene variations. The numerical model presented is very useful for the building design optimization and can be used for a fast estimation of indoor pollution and hygrothermal conditions in building.

A User-Friendly Tool to Characterize the Moisture Transfer in Porous Building Materials: FLoW1D

This paper presents a user-friendly tool—FLoW1D (One-Dimensional Water Flow)—for the estimation of parameters that characterize the unsaturated moisture transfer in porous building materials. FLoW1D has been developed in Visual Basic for Applications and implemented as a function of the well-known Microsoft Excel© spreadsheet application. The aim of our work is to provide a simple and useful tool to improve the analysis and interpretation of conventional tests for the characterization of the hygric behavior of porous building materials. FLoW1D embraces the conceptual model described in EN 15026 for moisture transfer in building elements, and its implementation has been verified and validated correctly. In order to show the scope of the code, an example of an application has been presented. The hygric characterization of the limestone that is mostly employed in the Cathedral of Santa Maria and San Julian in Cuenca (Spain) was conducted based on an analysis of the conventional water absorption by capillarity tests (EN 15801).

Effects of mussel shell aggregates on hygric behaviour of air lime mortar at different ages

Mussel shells, composed of calcium carbonate (>95%) and organic matter, are suitable alternatives to conventional sand in mortar. In addition, the use of lime instead of cement as a binder has also been considered for sustainable construction materials as well as in restorative applications.This study aims to contribute to the knowledge of air lime mortar through the analysis of the water transport properties of air lime mortar produced with mussel shell aggregates at different ages. Four mortar groups were obtained from the reference mortar by replacing limestone sand with mussel shell sand at substitution rates of 25%, 50%, and 75%. Water absorption, capillary uptake, weight variation, and drying from the fresh state up till one and two years were determined. The organic matter content and flaky seashell shape are responsible for the main differences observed between the mussel mortars and reference mortar. These two characteristics promote transport tortuosity paths and hydrophobic behaviour leading to reduced capillary uptake and increased drying resistance index. Furthermore, they enhance water retention, which increases the carbonation rate.

Hygric behavior of hydrophobized brick and mortar samples

Moisture that penetrates into porous building materials is a major reason for their deterioration and the subsequent failure of the whole structure. Water repellency treatment could prevent serious damages to materials and components. Hydrophobization is a method with a long tradition for protecting buildings from wind-driven-rain-induced moisture absorption. Nonetheless, it remains an ambiguous practice. To understand the nature of water repellency it is important to examine how hydrophobization works, how the existing products differ from one another, and how the hygric response of the substrate changes after treatment. The aim of this article is to characterize the impact of water repellent agents on the properties of building materials mostly used in old facades: clay brick and lime mortar.The resulting open porosity and pore size distribution, determined with vacuum saturation and mercury intrusion testing respectively, reveal only minimal change in the overall pore structure after impregnation. Our findings also show that hydrophobic treatment is nearly impermeable to liquid water, by evaluating the samples with capillary absorption tests, but still permeable to water vapour, by testing the samples with cup tests. Moreover, the water impermeability grows after exposure to water. In addition, the water repellent agent appears to spread progressively in the material for a long time after the hydrophobic treatment, yielding high final impregnation depths. These findings confirm that water repellent agents successfully hydrophobize the tested materials, with a water-tight but vapour-open hydrophobic layer that goes deep into the material, without notably changing its pore size distribution though.

Hygric Behavior of Cement Composites Elaborated with Flax Shives, a Byproduct of the Linen Industry

The reuse of flax shives, an agricultural waste, in the elaboration of cement composites offers an interesting alternative to meet the challenge of their elimination and solve an environmental problem. The composites studied are developed by adding flax shives to Portland cement and water. Due to their honeycomb structure the flax shives are used as lightweight aggregates and provide insulating properties to the composites. However they are hygroscopic and can release water-soluble molecules responsible for setting retardation, large dimensional variations and low mechanical strengths. In previous works these drawbacks have been reduced by the development of coating processes using lime, linseed oil and paraffin as coating substances. When coated shives are used the composites exhibited compressive strength 8 to 27-fold higher, drying shrinkage two to threefold lower compared to the raw shives composite, and belong to the insulating class of the lightweight concrete. The thermal conductivity of the composites may be negatively affected by environment humidity, so their hygric behavior must be determined. The establishment of the sorption isotherms and the evaluation of the water vapor transport allow the assessment of the hygric behavior. The treatment of the flax shives involves a decrease in the moisture adsorption capacity of the composites up to 48% for a paraffin coating. The composites can be ranked in descending order of hygroscopicity: raw, lime-coated, linseed oil-coated and paraffin-coated shive composites. Only the water vapor permeability and resistance factor of the paraffin-coated shive composite are significantly lower (46%) and higher (73%) compared to those of the raw shive composite. The analytical models (GAB, Janssen and Roels) adjust the experimental results and the influence of flax shives treatment on the composites hygric behavior is demonstrated.