Gypsum Plates Research Articles

Light timber framed wall under fire: Effect of the load and cladding

Light Timber Frame Walls are made of solid timber elements and are usually protected by cladding materials (gypsum). This investigation finds the effect of different load levels and cladding systems on the fire resistance. The timber frame structure is made with three studs and two rails, and will be analysed with two different protection levels. The computational model includes the thermal analysis under standard fire and a sequential mechanical analysis with time increments. Both, thermal and thermo-mechanical models are validated against experimental results developed in the reduced scale and full scale. The timber frame structure is deemed to have failed when it is no longer supporting the test load. The results are also compared with the failure criteria used for the experimental tests. The timber frame is deformed and all simulated models attained the global bucking instability mode, with studs moving to the outside of the furnace, due to the effect of load and charred layer. The fire resistance of a double-layered light timber frame wall is higher than a single-layered, and both decrease with the load level. This ability is reduced by 46%, on average for all load levels, when using only one gypsum layer. A new formula is proposed to determine the fire resistance, based on the load level and cladding systems. The fire resistance of the specimens with two layers of gypsum plates decreases faster than the specimens with one layer of gypsum, with respect to the increase of the load level.

Fracture of quasi-brittle geomaterials with a circular hole under compression

The new nonlocal fracture criteria are proposed, which are the extension of the average stress criterion and the point stress criterion, and which contain a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material microstructure, but also ductile properties of the material, geometry of the specimen, and its loading conditions. The formulas are obtained for the critical pressure in the problem of tensile fracture initiation in the specimens of geomaterials containing a circular hole and subjected to uniformly or nonuniformly distributed compression. The results of the calculations are in good agreement with the experimental data on failure of gypsum plates with a hole.

Fast Method for Testing the Photocatalytic Performance of Modified Gypsum

The measurement of the photocatalytic activity of building materials is quite time-consuming. Up until now, researchers have mainly used the equipment described in ISO 22197-1 to ISO 22197-4 for the determination of air purification activity, although other apparatus such as colorimeters, UV-Vis/DR spectroscopes and equipment for contact angle measurements have also been used. Usually, photocatalytic activity measurements take from one hour up to several hours. In this study, we present a very fast method for the measurement of the photocatalytic activity of gypsum. A specially designed printer with a modified bubblejet cartridge was used to apply a special ink on the surface of gypsum plates. Then the surface was irradiated by UV-A light and every 3 s a picture of the surface was taken. The results showed that the discoloration of the dye occurs after a few seconds of irradiation and the time depends on the amount of photocatalyst used as well as the number of printed ink layers. It was concluded that it is possible to use this method for a quick comparison of the photocatalytic activity of different types of modified gypsum materials.

Yellowing of laser-cleaned artworks: Formation of residual hydrocarbon compounds after Nd:YAG laser cleaning of gypsum plates covered by lamp black

Abstract The removal of black crusts decaying the surface of artworks is an important concern for the conservation of cultural heritage. Nd:YAG laser cleaning of encrusted stones and plasters at 1064 nm is widely recognized as an effective restoration technique, but induces a noticeable yellowing of the treated surface. Several researches carried out on the effects of laser cleaning have been focused on the induced yellowing and how to visually mitigate this phenomenon. To this end, UV-B radiations were successfully used to lessen the laser-induced yellowing due to the removal of lamp black particles on gypsum. The mechanism at play for both the formation of the compounds yellowing the surface and their disappearance upon UV-B exposure remains, however, poorly understood. Within the frame of this research, we apply surface-sensitive characterization techniques to analyze the yellowed surface produced after Nd:YAG Q-Switched laser cleaning of lamp black deposit on a gypsum plate, and the same surface after UV-B exposure. A combination of X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy has been used to identify the residual carbon compounds responsible for the yellow coloration of the substrate. A nanoscale structural description of the ejected particles collected during the laser cleaning was finally performed with transmission electron microscopy. We found that the yellowing is due to partially oxidized hydrocarbons compounds deposited at the surface of the gypsum substrate. We propose that they form by reactions between carbon species emitted by the vaporization of the carbon particles, with hydrogen and oxygen produced by the dissociation of water molecules coming together from dehydration of the gypsum surface and from the water sprayed by the operator during cleaning.

Ductile-Brittle Transition in Geomaterials, Caused by Tensile Stress Concentration

The possibility of using known nonlocal and stress gradient fracture criteria to describe brittle, quasi-brittle, and ductile fracture of materials with openings is analyzed. A common property of these criteria is the introduction of intrinsic material length characterizing its structure, which allows one to describe the size effect in conditions of stress concentration. At the same time, the scope of application of nonlocal criteria is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone. To expand the scope of application, new fracture criteria are proposed, which are the development of the average stress criterion, and the stress gradient criterion, and which contain a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material structure, but also plastic properties of the material, geometry of the sample, and its loading conditions. Expressions are obtained for the critical pressure in the problem of the formation of tensile cracks under compression in the samples of geomaterials with a circular hole. The calculation results are in good agreement with the experimental data on the fracture of drilled gypsum plates.

Influence of irradiation on stability and effectiveness of TiO 2 /N,C photocatalysts

The gypsum building material was enriched with photocatalytic properties for indoor air purification. The photocatalytic additive to gypsum was TiO2 modified with carbon from various sources. The photocatalytic activity of gypsum plates was performed towards NO x removal. Carbon doping into TiO2 improved not only total degradation of NO x on corresponding gypsum plates but also NO2 selectivity was changed, limiting the production of toxic NO2. The exhibition of photocatalysts on the visible and ultraviolet irradiation has been also carried out to examine their durability. First, the stability of modifying element – carbon in TiO2 structure was analysed, indicating on the gradual reduction of carbon content with irradiation time, especially when the carbon source was cyclic hydrocarbon. Second, the photocatalytic activity of the gypsum plates was performed at each stage of the ageing process. Based on this insight, the correlation between carbon content in modified photocatalysts loaded to gypsum plates and photocatalytic activity of them was described in detail.

Nonlocal Criteria for Brittle and Quasi-Brittle Fracture of Geomaterials and Rocks

Nonlocal criteria are used for prediction materials and rock mass failure near stress concentrations (pores, faults, openings, excavations). A common property of nonlocal fracture criteria is the introduction of the intrinsic material length characterizing its microstructure, which allows one to describe the size effect in conditions of stress concentration. At the same time the scope of their application is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone. To expand the scope of the criteria for cases of fracture with a developed fracture process zone, it is proposed to abandon the hypothesis of the size of this zone as a material constant, associated only with the material structure. New fracture criteria are proposed, which are the development of the average stress criterion, and point stress criterion, and which contain a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material structure, but also plastic properties of the material, geometry of the sample, and its loading conditions. Expressions are obtained for the critical pressure in the problem of the formation of tensile cracks under compression in the samples of geomaterials with a circular hole. The calculation results are in good agreement with the experimental data on the fracture of drilled gypsum plates.

NOx photocatalytic degradation on gypsum plates modified by TiO2-N,C photocatalysts

Abstract In presented studies the photocatalytic decomposition of NOx on gypsum plates modified by TiO2-N,Cphotocatalysts were presented. The gypsum plates were obtained by addition of 10 or 20 wt.% of different types of titanium dioxide, such as: pure TiO2 and carbon and nitrogen co-modified TiO2 (TiO2-N,C) to gypsum. TiO2-N,C photocatalysts were obtained by heating up the starting TiO2 (Grupa Azoty Zakłady Chemiczne Police S.A) in the atmosphere of ammonia and carbon at the temperature: 100, 300 i 600ºC. Photocatalyst were characterized by FTIR/DRS, UVVis/DR, BET and XRD methods. Moreover the compressive strength tests of modified gypsum were also done. Photocatalytic activity of gypsum plates was done during NOx decomposition. The highest photocatalytic activity has gypsum with 20 wt.% addition of TiO2-N,C obtained at 300ºC.

Visualization of Microwave Energy Distribution in a Multimode Microwave Cavity Using CoCl2 on Gypsum Plates

This study provides a facile method to map the microwave field distribution in a multimode microwave cavity. Anhydrous calcium sulfate powder was used to make the gypsum plates that were used as the carrying medium. Cobalt chloride hexahydrate, whose color changes when losing part or all of its crystal waters, was selected as an indicator of the energy absorption. The cobalt chloride aqueous solution at a concentration of 1.6% was absorbed by the dried gypsum plates. After introducing the plates into a microwave field, those areas that receive more microwave energy were preferably heated, resulting in the release of the moisture and consequently the loss of crystal water from the cobalt chloride hexahydrate. The color change on the plate formed a color map indicating the microwave field distribution. This method was used to investigate the energy distribution of a microwave oven by placing single or multiple plates in horizontal or vertical positions at different locations in the cavity.

Mechanical strength and thermal conductivity of low-porosity gypsum plates

The thermal conductivity and mechanical strength of gypsum and gypsum-cellulose plates made from commercial plaster by a new process have been measured. The gypsum parts made by the new process, 'novogesso', have high mechanical strength and low porosity. The gypsum strength derives from both the high aspect ratio of the gypsum crystals and the strong adhesion among them by nano-flat layers of confined water, which behaves as supercooled water. Another contribution to the strength comes from the nano-flatness of the lateral surfaces of the gypsum single crystals. The bending and compression strengths, σB and σc, of gypsum plates prepared by this new technique can be as high as 30 and 100 MPa, respectively. The way gypsum plates have been assembled as well as their low thermal conductivity allowed for the construction of a low-cost experimental house with thermal and acoustic comfort.

Monitoring Analysis for the Velocity of Crack Propagation

The crack gauge sensor and pencil core sensor are two kinds of elements commonly used to monitor the crack propagation velocity; both of them have the advantage of easy operation, low price, etc. However, they also have the disadvantage, namely, bigger measuring error. In this paper, the work principles of these two sensors are introduced, next, these two sensors are used to measure the crack propagation velocity in the fracture mechanics experiment of gypsum plates, then according to the experimental results, the measuring errors are analyzed and the correcting methods are suggested; at last, the crack propagation velocity are discussed, and the conclusion that the starting velocity of propagation is a variable and related to the dynamic process and the restrained conditions is pointed out.

Emanation of radon from fly-ash and gypsum

The emanation of radon from fly-ash and gypsum can be estimated from a simple model. The cases of a fly-ash dump and a room panelled with gypsum plates are considered.

Estimates of the resistance to chemical transport posed by the deep‐sea boundary layer1,2

A strategy has been developed to permit the in situ calibration of measurements made with benthic chambers of chemical fluxes across the sediment‐water interface. The resistance to chemical transport posed by the boundary layer is estimated using chemical transport techniques in benthic flux chamber mock‐ups and on the sea floor. Dissolution from gypsum (alabaster) plates is measured both inside and outside the flux chambers. CaCO3 dissolution and radioisotope uptake techniques are suitable for laboratory and deep‐sea calibration of benthic fluxes. Broadly concordant resistance estimates have been achieved within flux chambers with these three quite different approaches. An estimate of 470 µ for the equivalent stagnant boundary film thickness has been made by the alabaster method on the sea floor at MANOP site H in the eastern Pacific. The transport of Mn2+ from the bottom waters to site H nodules, if controlled by diffusion through a film of this thickness, would be sufficient to explain their growth rates.