Hygroscopic Sorption Research Articles

Moisture Properties, Microstructural and Microbiological Characteristics of Flax and Hemp Shives Used in Construction Industry

ABSTRACT The construction industry is among the largest energy-consumer and waste-generating sectors, and it needs sustainable methods and materials to decrease its carbon footprint. One possible solution is to use secondary raw materials and crops as a basis for thermal insulation materials or passive buffers of moisture. This article presents the results of testing raw hemp and flax shives obtained from Polish crops for use in the construction industry. There are only a few works devoted to the parameters of the raw material itself, and no comparative studies are available on the shives themselves. Therefore, it is of utmost importance to compare the properties of shives obtained from these two fibrous plants, to understand their usability and possibilities. Our research focuses on measuring pore size distribution, hygroscopic sorption moisture, capillary rise, and contact angle. It was shown that both types of shives are characterized by similar porosity and hygroscopic sorption characteristics, but different pore size distribution and ability to absorb water through capillary action. Microbiological tests showed variations in the presence of fungi on the shives surfaces. The article also presents an example of the use of the tested materials as an internal wall covering and compares it to gypsum plaster.

Hygrothermal Performance of Lime-Based Thermal Insulation Mortars: Water Absorption, Hygroscopic Sorption, and Water Vapour Permeability

Lightweight mortars, which are able to capture carbon, offer moisture buffering and increase the thermal resistance of building elements could be useful for both new and renovated buildings. The hygrothermal properties of lime-based renovation and insulation mortars were studied and the possibilities of reducing water absorption was the main focus of the study. Water absorption coefficient, hygroscopic sorption, and water vapour transmission properties were studied according to EN 1015-18, ISO 12571 and ISO 12572. Hydrated lime was used as the main binder and volcanic sand as an aggregate, white cement and silane in two different concentrations acted as additives. Half of the specimens were kept in forced carbonation conditions (CO2 was added regularly). Drying and carbonation processes were monitored by weighing the specimens regularly. Silane had the ability to reduce water absorption and sorption. Forcing carbonation reduced water absorption and sorption and slightly increased water vapour permeability.

Experimental Characterisation of Different Ecological Substrates for Use in Green Roof Systems

Green roofs are made up of several components, including those belonging to the waterproofing and drainage layers, substrate, and vegetation. Of these, the substrate is undoubtedly one of the most important layers of a green roof, contributing not only to the healthy growth of vegetation but also to the water retention capacity and thermal behaviour of the whole solution. Although green roofs are widely recognized as sustainable solutions, it is possible to further improve their environmental performance by developing more ecological substrates that contain industrial by-products. Bearing this objective in mind, sixteen newly developed substrates were characterized in terms of thermal conductivity, specific heat, emissivity, water vapour transmission, hygroscopic sorption, and water retention/drainage capacity. These properties are extremely relevant when solving heat and mass transfer problems as well as for water management prediction. Two reference substrates were also studied for comparison purposes. The results showed that the new ecological substrates have properties that make them comparable to conventional substrates already available on the market. Additionally, the results showed that temperature, moisture content, and density play an important role in the behaviour of substrates of this kind and have a significant influence on many of the studied properties.

Hygrothermal simulation of building performance: data for Scottish masonry materials

Retrofitting thermal insulation to solid masonry walls alters their hygrothermal behaviour, which can be modelled by hygrothermal simulation software. However, such software needs values of key material properties to ensure satisfactory results and until now data has not been available for Scottish masonry buildings. This work aims to contribute to a Scotland-specific dataset of material properties for use by designers working on such buildings. Thermal conductivity, water vapour permeability, sorptivity, water absorption coefficient, hygroscopic sorption, density and porosity were all determined experimentally for selected historic and contemporary masonry materials. Within the range of materials tested three groups of materials properties emerge. Natural hydraulic lime mortars, hot-mixed quicklime mortar and earth mortar all show comparatively low density, high porosity, low thermal conductivity, high water vapour permeability and variable but generally high hygroscopic sorption. Craigleith, Hailes and Giffnock sandstones, no longer available but obtained from conservation works on historic buildings, and Locharbriggs and Hazeldean sandstones, obtained from current production, all show intermediate values of these properties. Crathes granodiorite and Scottish whinstone (from current production) show high density, low porosity, high thermal conductivity, low water vapour permeability and low hygroscopic sorption. It is shown that these materials are all relevant to Scottish buildings constructed in traditional masonry and this paper presents the first comprehensive set of hygrothermal property data for them.

Characterisation of sustainable building walls made from rice straw bales

This study assesses the performance of sustainable building walls made from 80 kg/m3 and 100 kg/m3 straw bales. Experimental tests based on the procedures set out in conventional testing guidelines were designed to evaluate their hygrothermal and acoustic characteristics.First, experimental tests were performed to characterise intrinsic properties of rice straw fibres as loose material, such as specific heat capacity, hygroscopic sorption properties and biological resistance. Straw bales were then studied as a building material in terms of thermal conductivity, water vapour permeability and water absorption. The acoustic performance was also assessed by evaluating the airflow resistivity. Finally, different constructive solutions for walls that combined rice straw bales and a variety of coatings (lime mortar, gypsum plaster board and OSB) were studied in terms of thermal transmittance and thermal delay, and with respect to airborne sound insulation.Based on the experimental results presented herein, it can be concluded that rice straw bales can be used to build high performance sustainable building walls. These results also contribute to make the construction industry more confident that such an unconventional building solution can be safely used.

Thermo-hygrometric behavior of hempcrete walls for sustainable building construction in the Mediterranean area

Recent studies have demonstrated that the use of natural materials represents one of the pathways to achieve energy efficiency and environmental sustainability in buildings. In the framework of Circular Economy policies aimed at reducing the consumption of raw materials, shives, as an agricultural by-product of hemp cultivation, have gained a renovated life in the construction sector. Among all the building products made of hemp, hempcrete blocks are the most innovative, because they represent the solution to the needs of new and traditional buildings, offering a high energy saving, combined with the sustainability of materials and products, while remaining, in terms of shape and size, very close to the culture and the construction systems best known by professionals. In order to assess the potential benefits of hempcrete in the construction sector, its environmental performances were evaluated using the LCA methodology, following the international standard ISO 14044:2006+A1:2018 and in compliance with the European standard EN 15804:2012+A1:2013. To this purpose, four non-loadbearing walls were compared in the “cradle-to-gate” scenario, one made with hempcrete blocks and the others with more “traditional” materials. This research aims to be a basis for the development of future guidelines at national and international level in order to guarantee the maximum diffusion of this type of product also in the Mediterranean area. For this reason, it is important to identify the performance characteristics essential for hempcrete products studying their behavior not only as defined in the UNI EN ISO 12571, 2013 standard, but also in the Mediterranean climate. To achieve these objectives, some tests have been carried out to verify the thermo-hygrometric behavior. A 1 m2 of hempcrete wall was submitted to tests in a climatic chamber which simulated the environmental conditions typical of the south of Italy, in terms of temperature and moisture, in order to evaluate thermo-hygrometric behavior of hempcrete. Sensors and thermo-flowmeters for parameter analysis were applied on the wall. On the same material was carried out hygroscopic sorption tests as defined in the UNI_EN_ISO12571,2013 standard. The behavior detected by the experimental measurements on the masonry was compared with the simulated numerical behavior using WUFI software.

Thermal and moisture adsorption/desorption properties for a selection of vegetal insulation materials

Natural, or ‘green’ insulation materials, have become more popular for the ‘ecologisation’ of construction activities. The ecological aspects for such materials are being widely analysed, but experimental data about their physical properties when installed in building constructions remains lacking. In this study, pressed samples of three locally wild grown agricultural materials – rye, reed, and hemp – are analysed. Thermal conductivity measurements were carried out using the hot plate device. Comparison with widely used mineral insulation materials shows that thermal conductivity for simple pressed materials are roughly three times higher, and are comparable to plywood and cross-laminated timber insulation properties. Additional experiments regarding such materials include measurements of hygroscopic sorption properties (adsorption/desorption), determined using the dynamic gravimetric method at different temperatures and a wide, relative humidity range. The results obtained show that the difference in all studied materials appeared only at high humidity values; the rye straw and reed spikelets adsorbed more water than other materials, which is important for potential indoor air humidity assessment.

Characterization of sewage sludge ash and its effect on moisture physics of mortar

A study was carried out to investigate the potential use of ash obtained as an incinerated by-product in sewage sludge treatment, as a possible supplementary cementitious material. Chemical parameters and granulometry of the sewage sludge ash and selected physical and hygroscopic properties of cement-ash-based mortar are presented and compared with results from previous studies. The effect of different ratios of cement substitution and two pre-treatment methods for ash, i.e. ash grinding and water washing, on the physical properties of mortar were investigated by using density, porosity and compressive strength as elemental indicators of the mortar quality. The hygroscopic sorption properties of the individual constituents alone and the resulting mortar samples were described by sorption isotherms for water vapour and by a capillary water absorption test. Results showed that the SSAs typically consisted of larger particles compared to the cement particles. Incorporation of ash resulted in more porous mortar structures compared to cement-based mortar, which affected the material's mechanical properties such as the compressive strength. 28-day compressive strength decreased with increasing ash content and porosity. Cement conveyed the greatest ability to adsorb and react with water and there were clear differences between the different ashes. Despite the differences in sorption properties between the different constituents, the effect of ash content on mortar sorption isotherms was negligible.

Deterioration of volcanic tuff rocks from Armenia: constraints on salt crystallization and hydric expansion

Volcanic tuffs are widely used in the Armenian architecture and represent building stones of the country’s most precious cultural heritage sites. For the very first time, extensive investigations regarding their chemical and mineralogical composition as well as the influence of petrophysical properties on their weathering behavior were realized. Different groups of tuff rocks could be identified, which differ greatly in their chroma, texture, their chemical and mineralogical composition, as well as their weathering behavior. At 30% porosity and 25% micropores, the tuff rocks show a sharp limit of changing water transport and retention behavior. Swellable clay minerals, the amount of micropores and the hygroscopic sorption value show a direct relation with the hydric expansion and proved to be reliable parameters for its estimation. Zeolite minerals proved to drastically increase the sorption values of the tuff rocks and are discussed as a cause for potential disjoining pressure. Furthermore, the application of the salt bursting test by European standard on these glass-rich volcanic tuff rocks is questioned, due to considerable different mineralogy and fabric in comparison to classic ash-rich tuffs.

Survey of dilution or adsorption enthalpies of a series of hygroscopic sorption materials

Abstract In order to assess the thermal behavior of water based sorption systems, isothermal titration calorimetry (ITC) experiments were done to measure the integral dilution enthalpies (ΔHD) of concentrated salt solutions via stepwise addition of water. Moreover the adsorption enthalpy (ΔHA) of different solids were measured with ITC as well. The data showing values of ΔHD in the range from 14 kJ/kg (KNO3) to −415 kJ/kg (NaOH) and ΔHA values from around 0.3 kJ/kg (MIL-53-AL) to −1380 kJ/kg (Zeolite XBF 13). Furthermore the titration results of the solid materials enable the possibility to calculate the adsorption capacity of these substances.

Micro-porosity and minero-petrographic features influences on decay: Experimental data from four dimension stones

Sedimentary stones have been used since long as dimension stones, constituting the primary building material of several monumental structures all over the world. The understanding of their behaviour when exposed to weathering factors is crucial for preservation, replacement and restoration intervention. Although not directly involved with decay mechanisms, micro-pores (i.e. open pores with radius <0.1 µm) and their interconnection to the wider ones are important for air and water flow inside rocks. In fact, micro-pores are not directly the site of ice or salt crystallization, nor of oil and gas entrapment, but are the main pathway for fluids during both adsorption and evaporation processes. The study of narrow pores is therefore crucial to predict e.g. stone durability and physical properties. This study presents the study on four different sedimentary lithotypes vastly employed as dimension or ornamental stones in Italy, both sound and artificially weathered. In particular, coupled MIP and hygroscopic sorption based micro-porosimetry were used to uncover liability to relative humidity variation, in association with a thorough mineralogical characterization. The MIP intrusion pattern attained pore shapes and typology description for the different rock types; but only the hygroscopic sorption helped deciphering the on-going processes. Moreover, the coupling of petrography and petro-physical analyses (i.e. MIP and hygroscopic sorption based micro-porosimetry) pointed out that phyllosilicates have a role in decay processes of rocks due to swelling and/or suturing of the adjacent voids.

Effects of MDI content on properties of thermally treated oriented strand board (OSB)

The paper discusses the influence of methylene diphenyl diisocyanate (MDI) content on mechanical properties of thermally post-treated single-layered oriented strand boards (OSB). The OSB differed in adhesive content (3, 4 and 5%) and the high temperature (HT) level of the thermal modification (TM) (untreated, 160, 175 °C). To characterise the mechanical behaviour of the OSB, the modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond (IB) of dry and boiled specimens were determined. In addition, the adsorption and desorption isotherms were investigated. The hygroscopic sorption isotherms were calculated according to the Hailwood-Horrobin equation. It was observed that the MOR and the IB of the post-treated OSB are significantly increased with higher MDI content. An increase of the MDI content from 3% up to 5% is not sufficient to compensate the loss of strength caused by TM. However, an increase of MDI-content of about 1% compensates the significant loss of IB of dry and boiled specimens. The MOE is not influenced by TM. With increased adhesive content, thermally treated and untreated specimens show slightly higher values. The thermal post-treatment of OSB alters the wood-water-interaction. The hygroscopicity is reduced. The higher the HT level, the lower is the sorption behaviour. It was also detected that a higher MDI content does not influence the hygroscopicity.

Hydration properties of briquetted wheat straw biomass feedstock

Biomass densification elevates the bulk density of the biomass, providing assistance in biomass handling, transportation, and storage. However, the density and the chemical/physical properties of the lignocellulosic biomass are affected. This study examined the changes introduced by a briquetting process with the aim of subsequent processing for 2nd generation bioethanol production. The hydration properties of the unprocessed and briquetted wheat straw were characterized for water absorption via low field nuclear magnetic resonance and sorption balance measurements. The water was absorbed more rapidly and was more constrained in the briquetted straw compared to the unprocessed straw, potentially due to the smaller fiber size and less intracellular air of the briquetted straw. However, for the unprocessed and briquetted wheat straw there was no difference between the hygroscopic sorption isotherms, which showed that the amount of cell wall water was not affected by the briquetting process and that the sugar yield was similar after a combined hydrothermal pretreatment and enzymatic hydrolysis. The factors which offset the benefits introduced by the briquetting process need to be further examined to optimize the processing parameters and enzyme recipe for better use of the wheat straw biomass feedstock.

Determination of hygrothermal performance of clay-sand plaster: influence of covering on sorption and water vapour permeability

Indoor finishing materials considerably influence indoor climate because of their moisture buffering ability occurring due to the sorption and diffusion properties of materials. Hygroscopic sorption properties were determined in accordance with the standard EVS-EN ISO 12571 and the principles given in the standard EVS-EN 1015-19:2005 were followed when determining water vapour permeability properties. The same specimens (thickness 2.4 cm) were used for both tests. To describe the dynamics during the first hours, the specimens were weighted at 1, 2, 3, 6, 12, 24, 48, 72 hours after changing the humidity level. Moisture uptake (kg/m2) and moisture uptake rate kg/(m2h) within the very first hours at 0-30, 30-50 and 50-80%; moisture content at RH level of 30%, 50% and 80%; points (30, 50 and 80%) at sorption curve were monitored. Six different covering materials were used: fine finishing mortar with cellulose, fine finishing mortar without cellulose, casein paint, cellulose base coat, lime paint, casein base coat, clay plaster not covered. The rate of moisture uptake was highest within the first hour after a sudden change in moisture level. Water vapour diffusion equivalent air layer thickness Sd=0.11-0.13 m was recorded.

Hygrothermal Behaviour of Three Internal Retrofit Prototype Solutions

Although the application of internal insulation to existing perimeter walls poses significant challenges in terms of building physics and loss of habitable space, it is sometimes an inevitable choice because of practical or legislative constraints. Innovative solutions are then required to deliver satisfying performances and reduce nuisance to inhabitants of residential buildings in case they are going to remain in their flats during the retrofit works.Three systems for inner thermal retrofitting purposes have been designed and produced as prototypes. Two of them are composed by silica aerogel containing fibrous material: the first one is a rigid flat laminated panel, the second one is a rollable solution with a fabric finishing layer. The third insulating system is a perlite based board with a hydrophobic layer. All the materials composing the retrofit solutions have been characterized by means of laboratory tests in order to measure their main hygrothermal properties. In fact, some parameters are fundamental for determining the hygrothermal performance of the composite systems: thermal conductivity, at dry and wet state (moisture dependant), water vapour diffusion resistance factor, hygroscopic sorption at isotherm condition and water absorption coefficient. All those measured data were necessary for optimizing the solutions, guaranteeing energy efficiency and vapour open layers to systems that are intended for installation on existing walls.

Laboratory testing of non-standard original historic building materials and related implications for conservation

For an assessment or an analysis of a historic building, determination of the material properties is always crucial. However, this is usually a challenging issue because material extraction from a historic building for standard laboratory testing is usually not allowed or the amount of material available for testing is very limited. Lack of comprehensive standards for testing irregularly shaped and non-standard-size specimens, taken from historic buildings, unfortunately compounds the uncertainty. This paper offers a discussion of such issues by using the case study of Odda’s Chapel in Gloucestershire, UK, and describing the systematic examination of a total of six lime mortar and Blue Lias stone samples extracted from this Grade I listed building. The programme of testing and the results obtained are compared with the latest European standards relating to sampling and testing of material of cultural properties. Internal microstructure, hygroscopic sorption and water absorption characteristics, and the density and mechanical properties of the materials are documented and alternative testing techniques are compared. Identification of some of the above-mentioned material properties shows that the agreement between results obtained from the various test methods is considered satisfactory, depending on the testing approach and material heterogeneity.

Sorption and Thermal Properties of Insulating Mortars with Expanded and Vitrified Small Ball

Abstract Expanded vitrified small hollow ball (EVSB), made from a special type of perlite mineral is one of the recently developed materials in China. It is widely used as a cementitious thermal insulating mortar for building envelope construction in hot-humid areas of southern China. However, EVSB is a porous material sensitive to environmental moisture. The thermal insulating property of the EVSB mortar is dependent on its moisture transport and storage characteristics. In this study, hygroscopic sorption properties of EVSB mortars have been investigated in comparison with those of normal expanded perlite particle (NEPP) mortars. The Brunauer, Emmett and Teller specific surface area and the Barrett, Joyner and Halenda pore size distribution, as well as the scanning electron microscope micromorphologies of the mortars were assessed. It was observed that EVSB mortars had lower moisture sorption capacity than NEPP mortars when the relative humidity (RH) was higher than 70 % because of its lower total pore volume. The addition of water-repellent admixtures in the mortar decreased the moisture sorption capacity of EVSB mortars but still maintains the same physisorption isothermal characteristics. It is also evident that the thermal conductivity values of both NEPP and EVSB mortars increased rapidly when RH is above 90 %. However, the increased rate of thermal conductivity of NEPP mortars was apparently higher than that of EVSB mortars. It is hoped that finding from this study will help to develop a better understanding of the in situ thermal performance of the EVSB mortar used for the building envelope construction in hot and humid areas of southern China.

Hygroscopic Moisture Sorption Kinetics Modeling of Corn Stover and its Fractions

Corn stover, a major crop-based lignocellulosic biomass feedstock, is required to be at an optimum moisture content for efficient bioconversion processes. Environmental conditions surrounding corn stover, as in storage facilities, affect its moisture due to hygroscopic sorption or desorption. The measurement and modeling of sorption characteristics of corn stover and its leaf, husk, and stalk fractions are useful from utilization and storage standpoints, hence investigated in this article. A benchtop low-temperature humidity chamber provided the test environments of 20°C, 30°C, and 40°C at a constant 95% relative humidity. Measured sorption characteristics with three replications for each fraction were obtained from instantaneous sample masses and initial moisture contents. Observed sorption characteristics were fitted using exponential, Page, and Peleg models. Corn stover fractions displayed a rapid initial moisture uptake followed by a slower sorption rates and eventually becoming almost asymptotic after 25 h. Sorption characteristics of all corn stover fractions were significantly different (P 0.05) on these fractions. The initial 30 min of sorption was found to be critical due to peak rates of sorption from storage, handling, and processing standpoints. The Page and Peleg models had comparable performance fitting the sorption curves (R2 = 0.995), however the exponential model (R2 = 0.91) was not found suitable because of patterned residuals. The Arrhenius type relationship (P < 0.05; R2 = 0.80) explained the temperature variation of the fitted sorption model parameters. The Peleg model fitted constants, among the sorption models studied, had the best fit (R2 = 0.93) with the Arrhenius relationship. A developed method of mass proportion, involving individual corn stover fraction dry matter ratios, predicted the whole corn stover sorption characteristics from that of its individual fractions. Sorption characteristics models of individual corn stover fractions and predicted whole corn stover including a nomogram can be used for direct and quick estimation. Developed sorption characteristics find application in several fields of corn stover biomass processing, handling, and transport.

Operational properties of a heat-insulation composite with expanded polystyrene crumbs

The operational properties (strength, heat conductivity, hygroscopic sorption, vapor permeability, and frost resistance) of a heat-insulation composite of density 150–350 kg/m3 are investigated. The matrix consists of an aerated concrete substance and a disperse filler of expanded polystyrene crumbs obtained by crushing the household polystyrene package waste. The macro-and microstructure of the composite are considered. It is found that the operational properties of the material directly depend on its density, determined by the amount of the cementing substance in the matrix.