Water Vapor Adsorption in Porous Building Materials: Experimental Measurement and Theoretical Analysis

Electron microscopy approach to the wetting dynamics of single organosilanized mesopores

Columnar mesoporous silicon (PSi) with hydrophobic vs. hydrophilic chemistries was chosen as a model for the local (pore-by-pore) study of water-pore interactions. Tomographic reconstructions provided a 3D view of the ramified pore structure. An in situ study of PSi wetting was conducted for categorized pore diameters by environmental scanning TEM. An appropriate setting of the contrast allows for the normalization of the gray scale in the images as a function of relative humidity (RH). This allows constructing an isotherm for each single pore and a subsequent averaging provides an isotherm for each pore size range. The isotherms systematically point to an initial adsorption through the formation of water adlayers, followed by a capillary filling process at higher RH. The local isotherms correlate with (global) gravimetric determination of wetting. Our results point at the validation of a technique for the study of aging and stability of single-pore nanoscale devices.

Paper-Based Humidity Sensors as Promising Flexible Devices: State of the Art: Part 1. General Consideration

In the first part of the review article "General considerations" we give information about conventional flexible platforms and consider the advantages and disadvantages of paper when used in humidity sensors, both as a substrate and as a humidity-sensitive material. This consideration shows that paper, especially nanopaper, is a very promising material for the development of low-cost flexible humidity sensors suitable for a wide range of applications. Various humidity-sensitive materials suitable for use in paper-based sensors are analyzed and the humidity-sensitive characteristics of paper and other humidity-sensitive materials are compared. Various configurations of humidity sensors that can be developed on the basis of paper are considered, and a description of the mechanisms of their operation is given. Next, we discuss the manufacturing features of paper-based humidity sensors. The main attention is paid to the consideration of such problems as patterning and electrode formation. It is shown that printing technologies are the most suitable for mass production of paper-based flexible humidity sensors. At the same time, these technologies are effective both in the formation of a humidity-sensitive layer and in the manufacture of electrodes.

Discussion on effect of material on UV reflection and its disinfection with focus on Japanese Stucco for interior wall

Research has previously shown that ultraviolet light C (UV-C) can inactivate unexpected infection. However, this type of potential disinfection is dramatically reduced for the shadow area such as under desk or medical equipment. Because the UV-C reflectance ratio is low on the general wall surfaces. We compared Stucco against the other materials to investigate whether we could improve disinfection for the shadow area. The reflectance ratios of UV-C irradiation of each material were examined, with particular attention to the rates for the author’s Modified Stucco. To evaluate the disinfection effects of the UV-C reflective lighting, colonies of E. coli and of Staphylococcus hominis were cultured in an agar media and counted over a certain time period after applying UV-C irradiation from a sterilizing lamp onto the investigation materials. The author’s Modified Stucco, produced reflectance ratios that was 11 times that of white wallpaper. This demonstrated that the UV-C reflected on the Stucco wall having optimum components and their compositions inhibited the number of E. coli and S. hominis, resulting in significantly disinfection effects on white wallpapers. The space with Modified Stucco and then irradiated by a UV-C may give a strong disinfection effect.

Experimental and Modeling Investigations on the Water Sorption Behaviors of Autoclaved Aerated Concrete

The thermal and moisture properties of building envelope materials determine their performance over many years of use. Moisture has a particularly negative impact, impairing all the technical parameters and adversely affecting the microclimatic conditions inside the building. This article presents research and analysis on the moisture behavior of partitions made of autoclaved aerated concrete. Autoclaved aerated concrete is a very popular material for building external walls because of its relatively good thermal insulation and sufficient strength, if it is not subjected to increased moisture. This study investigated how the moisture content of this material changes with the change in relative air humidity. The four most popular density classes were studied. The sorption isotherms were determined by the static gravimetric method throughout the whole hygroscopic range. Moreover, the applicability of various models to describe sorption isotherms of this material group has been extensively evaluated. The tested models (Peleg, Redlich, Chen, Oswin, Henderson, Lewicki, Caurie, and GAB) all provided a very good fit with the experimental results for the tested material group (R² ranged from 0.9599 to 0.9978). This paper indicates that the use of two additional approximation parameters (SSE and RMSE) allows a more precise assessment of the quality of individual models.

Lightweight Vapor-Permeable Plasters for Building Repair Detailed Experimental Analysis of the Functional Properties

Three types of lightweight plasters for building repair were prepared and tested. The composition of plasters was designed in respect to their compatibility with materials used in the past in historical masonry. For the hardened plasters, detailed testing of microstructural and macrostructural parameters was realized together with the broad experimental campaign focused on the assessment of mechanical, hygric, and thermal properties. As the researched plasters should find use in salt-laden masonry, specific attention was paid to the testing of their durability against salt crystallization. The mechanical resistance, porosity, water vapor transmission properties, and water transport parameters of all the researched plasters safely met criteria of WTA directive 2-9-04/D and standard EN 998-1 imposed on repair mortars. Moreover, the tested materials were ranked as lightweight plasters and due to their low thermal conductivity they can be used for the improvement of thermal performance of repaired masonry. The salt crystallization test caused little or no damage of the plasters, which was due to their high porosity that provided free space for salt crystallization. The developed plasters can be recommended for application in repair of damp and salt masonry and due to their compatible composition also in historical, culture heritage buildings. The added value of plasters is also their good thermal insulation performance.

Modelling and Experimental Study of Moisture Transport in Wood, Taking into Account Diffusion and the Accompanying Adsorption of Water Vapour by Cell Walls

The paper presents a model of moisture transport in wood taking into account diffusion and the accompanying adsorption of water vapour through the skeleton. A two-parameter form of the source term was proposed, depending on the distance of the current moisture content (MC) from the equilibrium state. The tests on cubic samples with a side of 2 cm were carried out which allowed to determine the coefficients of the proposed model on the basis of the reverse method. The tests were performed for pine, larch, oak and ash in all directions of orthotropy. Tests on thin samples were also performed to verify the source term.

Physico-Mechanical and Hygro-Thermal Properties of Compressed Earth Blocks Stabilized with Industrial and Agro By-Product Binders

This study investigated the engineering properties of compressed earth blocks (CEBs) stabilized with by-product binders: calcium carbide residue (CCR) and rice husk ash (RHA). The dry mixtures were prepared using the earthen material and 0-25 wt% CCR, firstly, and 20 wt% CCR partially substituted by the RHA (CCR:RHA in 20:0-12:8 ratios), secondly. The appropriate amount of water was thoroughly mixed with the dry mixtures. The moistened mixtures were manually compressed into CEBs, cured, dried, and tested. The stabilization of CEBs with CCR increased the dry compressive strength (CS) from 1.1 MPa with 0% CCR to 4.3 MPa with 10% CCR and above; decreased the bulk density (ρ_b:1800-1475 kg/m³) and increased the total porosity (TP:35-45%). This resulted in the improvement of the coefficient of structural efficiency (CSE: 610-3050 Pa∙m³/kg). It also improved the thermal efficiency given the decrease of the thermal conductivity (λ: 1.02-0.69 W/m∙K), thermal diffusivity (a: 6.3 × 10^-7 to 4.7 × 10^-7 m²/s) and thermal penetration depth (δp: 0.13-0.11 m). The RHA further improved the CS up to 7 MPa, reaching the optimum with 16:4 CCR:RHA (ρ_b: 1575 kg/m³ and TP: 40%). The latter reached higher CSE (4460 Pa∙m³/kg) than cement stabilized CEBs (3540 Pa∙m³/kg). It reached lower λ (0.64 w/m∙K), a (4.1 × 10^-7 m²/s) and δp (0.11 m) than cement CEBs (1.01 w/m∙K, 6.8 × 10^-7 m²/s, and 0.14 m). Additionally, the stabilization of CEBs with by-products improved the moisture sorption capacity. The improvement of the structural and thermal efficiency of CEBs by the stabilization with by-product binders is beneficial for load-bearing capacity and thermal performances in multi-storey buildings.

Experimental investigation on water adsorption and desorption isotherms of the Longmaxi shale in the Sichuan Basin, China

The understanding of water adsorption and desorption behavior in the shale rocks is of great significance in the reserve estimation, wellbore stability and hydrocarbon extraction in the shale gas reservoirs. However, the water sorption behavior in the shales remains unclear. In this study, water vapor adsorption/desorption isotherms of the Longmaxi shale in the Sichuan Basin, China were conducted at various temperatures (30 °C, 60 °C) and a relative pressure up to 0.97 to understand the water sorption behavior. Then the effects of temperature and shale properties were analyzed, and the water adsorption, hysteresis, saturation and capillary pressure were discussed. The results indicate that water adsorption isotherms of the Longmaxi shale exhibit the type II characteristics. The water molecules initially adsorb on the shale particle/pore surfaces at low relative pressure while the capillary condensation dominates at high relative pressure. Temperature favors the water sorption in the shales at high relative pressure, and the GAB isotherm model is found to be suitable for describe the water adsorption/desorption behavior. The high organic carbon and full bedding are beneficial to water adsorption in the shales while the calcite inhibits the behavior. There exists the hysteresis between water adsorption and desorption at the whole relative pressure, which suggests that the depletion of condensed water from smaller capillary pores is more difficult than that from larger pores, and the chemical interaction contributes to the hysteresis loop for water sorption. The capillary pressure in the shales can be up to the order of several hundreds of MPa, and thus the desorption of water from the shales may not be as easy as the water adsorption due to the high capillary pressure, which results in water retention behavior in the shale gas reservoirs. These results can provide insights into a better understanding of water sorption behavior in the shale so as to optimize extraction conditions and predict gas productivity in the shale gas reservoirs.

Effect of Hygrothermal Aging on Hydrophobic Treatments Applied to Building Exterior Claddings

Hydrophobic materials are among the most commonly used coatings for building exterior cladding. In fact, these products are easily applied to an existing surface, significantly reduce water absorption and have a minimal impact on the aesthetic properties. On the other hand, although these products have a proven effectiveness, their long-term durability to weathering has not yet been systematically studied and completely understood. For these reasons, this study aims to correlate the effect of artificial aging on the moisture transport properties of hydrophobic treatments when applied on building exterior claddings. Three hydrophobic products (an SiO2-TiO2 nanostructured dispersion; a silane/oligomeric siloxane; and a siloxane) were applied on samples of limestone and of a cement-based mortar. The moisture transport properties (water absorption, drying, water vapor permeability) of untreated and treated specimens were characterized. Furthermore, the long-term durability of the specimens was evaluated by artificial aging, that is, hygrothermal cycles (freeze–thaw and hot–cold). All treatments have significant hydrophobic effectiveness and improve the long term-durability of the treated specimens. However, the results showed that the three hydrophobic products have different effectiveness and durability, with the SiO2-TiO2 nanostructured dispersion being the most durable treatment on limestone, and the siloxane the most suitable for cementitious mortar.