Papers by Keyword: Moisture

Abstract: The Sweating Slab Syndrome (SSS) was first mentioned in 2005 [3] and has further been discussed in [1], [2], [5], [6]. The condition is typically marked by the build-up of moisture in so-called big-box warehouse buildings on the top surface of concrete slab-on-ground construction which, when severe, can interfere with the routine operations of the facility, e.g. forklift traffic. The buildings are typically located in southern to southeastern regions of the United States and have non-climate controlled indoor environments. After drying, residues remain on the surface of the slab-on-ground, which have been identified as carbonation products of alkaline salts. Speculations as to the cause of this syndrome have included dew-point condensation, high vapor permeability of the slab, the troweling finishing process, bond breaker influence, unreacted silicates from integral or spray applied admixtures, and the absence of vapor retarder sheets under the slab. None of the speculated causes have been given supporting data or studied in detail, however. To determine the cause of the SSS, Wiss, Janney, Elstner, Associates, Inc. (WJE) applied a standard scientific methodology in 2019 consisting of three parts. The first part of this methodology was to collect data through observation, instrumentation, numerical simulation, and laboratory analysis. Second, a set of hypotheses was generated based on the data collection and logic. Finally, collected data was paired with one or multiple hypotheses in a logical way to disprove or support their validity. Results will be shown.

Abstract: Microbial growth often thrives in humid conditions, at high relative humidity. Moulds are complex organisms; many types of mould are able to survive strong variations in humidity and temperature, such as those on building façades. For some building materials a critical relative humidity is determined, which functions as a theoretical threshold; at this (or lower) relative humidity microbial growth will likely not occur. Hemp-lime is a building material that consists of hemp shiv (the woody core parts of the hemp stem) and building lime. It is a material that can be used for walls, and even though it has been used for more than 20 years, thusfar little is known about its critical moisture levels for microbial growth. The aim of this research was therefore to determine at what relative humidity microbial growth occurs on carbonated hemp-lime material, and to study if there is a protective influence of a carbonated lime binder on the hemp shiv. The objective was to study microbial growth on hemp shiv, hemp-lime and on hemp with a thin layer of lime at three relative humidity (75 %, 85 % and 95 %) and at two different temperatures (15°C and 23°C); conditions that could occur naturally in a hemp-lime façade exposed to high rain loads in a northern European climate. Hemp shiv seems to have a relatively low resistance to microbial growth, similar to that of wood. However, because the hemp is protected by lime it can withstand much higher relative humidity without microbial growth occurring on the material. The critical moisture level for hemp-lime seemed to occur between 75 and 85 % RH, while the material was completely without microbial growth at 75 % RH. The lime had a protective effect on the hemp and acted as a mould inhibitor, both over time and with varying temperature and humidity.

Abstract: This study investigated characteristics of moisture desorption for polylactic acid (PLA) filaments. The filaments tend to absorb moisture from humid air, led to moisten filaments. The absorption of even small amounts of moisture by filaments during storage and/or 3D printing, degraded the quality of final parts, and therefore, caused manufacturing problems. In this work, the filaments were subjected to humid conditions to achieve various moisture concentrations (0.75, 1.3 and 1.87 wt.%). Warm air-drying processes are used to reduce the moisture for different times (1, 2, 3, 4, 5 and 6 hours) and temperature (40, 50 and 60 °C). It was founded that the moisture from the polylactic acid (PLA) filaments can be discovered the moisture by use 60 degree of temperature in 5 hours warm air-drying process.

Abstract: Renovation processes of existing buildings, including historically protected ones, are most of the time focused on energy saving. Nonetheless these processes might affect the function of existing shallow foundations. This paper deals with the influence of soils moisture content onto the depth of freezing. The depth of freezing depends on the type of soil as well, not just the moisture content. The influence of water and soils composition are generally perceived to be substantial for depth of freezing. Sub-zero temperatures do significantly change the soils characteristics, which has an effect to the building structure. The purpose of the research done by the personnel of Brno University of Technology was to determine the effects of special measures against frost penetration of soil. These measures included the application of various materials and solutions over the terrain in winter to monitor frost depth of soil.

Abstract: The paper presents the results of laboratory studies of the influence of the physical properties of landfill soils on the stability of slopes, namely, the determination of mechanical properties – the angle of internal friction, specific adhesion, and the shear angle of experimental landslide blocks under conditions of different humidity, density and temperature; determination of physical properties – humidity, temperature and density on the fact of shear of the experimental blocks, taking into account the gradual increase in humidity. The results of laboratory tests are processed using the classical statistical method. This made it possible to confirm the reliability of the mathematical model, which includes the solution of individual tasks for assessing the physical properties of landfill soils, and the corresponding methodology developed on its basis for preventing emergencies associated with shear of landfill soils at potentially hazardous burial sites for solid domestic waste.

Abstract: Dielectric elastomer (DE) technology are used in several applications for example generator, sensor and actuator. One of the major factors that limits the DE performance is premature electrical breakdown. Compositing is the example that have been reported to increase the breakdown strength. In this study polydimethylsiloxane (PDMS) film will be incorporated with two different fillers which are titanium dioxide (TiO₂) and zinc oxide (ZnO). Both metal oxides will be calcined up to 300°C before they are added to the PDMS elastomer as fillers. The results show that the calcined TiO₂ and ZnO that incorporated in PDMS films show significant increase of breakdown strengths. Meanwhile, the calcined TiO₂ PDMS film give higher breakdown strength as comparison to the calcined ZnO counterpart.

Abstract: The process of silicon carbide producing (SiC) in a resistance furnace is accompanied by moisture movement in the batch. An important consideration is the accounting of moisture transfer in the preparation of the mathematical description of the process. The aim of the article is to improve the existing model of heat and mass transfer in SiC production.

Abstract: Bamboo powder drying machine plays a very important role in the production process of bamboo plywood. The function of the machine is drying bamboo powder to get the technical required appropriate moisture before pressing it into the standard bamboo boards. This article presents a design of bamboo powder drying machine with simple structure, long life, medium productivity and price suitable for medium and small scale production of Vietnam market. The first bamboo powder drying machine that was manufactured in Key Laboratory of Digital Control and System Engineering (DCSELAB) and its products are considered to respond the technical requirements of customers.

Abstract: In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for structural strengthening, and several researches have validated the effectiveness of SRP for masonry strengthening. Research has been carried out to study the bond behavior of SRP composites applied to a masonry substrate. However, how the moist and salt on masonry surface will affect bond, which is the weak link in real strengthening applications, is little known yet. This study aims at investigating the bond behavior of SRP composites applied to moist and salt-laden masonry blocks that were subjected to an artificial weathering protocol. Single-lap shear tests were conducted to determine the bond behavior, while ion chromatography provided the salts distribution of weathered specimens to interpret some results of the shear tests.

Abstract: Clay plasters have been used extensively in the past. Later, these plasters were replaced with more modern materials. In recent years, however, they have come back and are being used primarily for new constructions. The interest in ecological constructions and natural materials was significantly influenced not only by experts but also by ordinary users. A significant disadvantage of clay plasters is poor durability in the exterior environment and in contact with water in the liquid state where the part of the clay product is leached. The paper deals with the modification of clay plasters with silicate-based hydrophobic agents. The aim of this experiment is to improve the durability of these plasters and to extend their application both indoors and outdoors while maintaining typical advantageous properties.