Conventional Gypsum Research Articles

Investigation of properties of fluorogypsum-slag composite binders – Hydration, strength and microstructure

A composite binder of high strength and low water absorption has been developed using industrial by-products fluorogypsum, granulated blast furnace slag and Portland cement. The development of strength in the binder at an early age is attributed to the conversion of anhydrite into gypsum and at later age is due to the formation of ettringite and tobermorite, as a reaction of slag with lime produced during the hydration of cement. These cementitious phases fill in pores and voids of the hydrating gypsum crystals to form a dense and compact structure of low porosity and low pore volume. The reaction products formed during the hydration period were confirmed by scanning electron microscopy and X-ray diffraction. The reduction in porosity and low pore volume of binders, as studied by mercury intrusion porosimetry, are responsible for attainment of high strength and better stability towards water in composite binders than the conventional gypsum plaster.

Comparison of Energy Dissipation, Stiffness, and Damage of Structural Oriented Strand Board (OSB), Conventional Gypsum, and Viscoelastic Gypsum Shearwalls Subjected to Cyclic Loads

A key element in the seismic load resisting system of a wood framed structure is the shear wall which is typically sheathed on one side with plywood or oriented strand board (OSB) and gypsum on the other. The shear capacity of gypsum sheathed shear walls is typically neglected in high seismic areas due to the susceptibility of conventional drywall screw connections to damage caused by earthquakes. The earthquake resistance of an innovative viscoelastic (VE) gypsum shearwall is evaluated and compared to conventional structural and non-structural walls. Ten 8 ft × 8 ft wood framed wall specimens of three configurations [nailed-OSB, screw-gypsum, and VE polymer-gypsum] were subjected to a cyclic test protocol. The energy dissipation, stiffness, and damage characteristics of all shearwalls are reported herein. Testing results indicate the VE-gypsum walls can dissipate more energy than the OSB structural panels and 500% more energy that the conventional gypsum sheathed walls and contains a constant source of energy dissipation not seen in the structural and non-structural walls. The wall stiffness of the OSB wall degrades at a far greater rate that the VE gypsum wall and at continued cycling degrades below the VE wall stiffness. Unlike both of the conventional wall types, the VE wall showed no visible or audible signs of damage when subjected to shear displacements up to 1.

Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity

The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, “green” gypsum wallboard, and “green” carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The “green” materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K ma) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in “green” wallboard and “green” carpet. At the same relative humidity level, the “green” wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings. Implications: Based on the results of this study, the sink effects of these commonly used materials (conventional and “green” gypsum wallboards, “green” carpet) on indoor formaldehyde concentration could be estimated. The effects of relative humidity on the diffusion and partition coefficients of formaldehyde were found to differ for materials and for different humidity levels, indicating the need for further investigation of the mechanisms through which humidity effects take place.

Energy-saving effect of a factory ceiling incorporating microencapsulated Phase Change Materials

The enhancement of thermal-insulation capability of rooftop and exterior wall are key issues in energy conservation for buildings. The objective of this study is to provide insights into thermal-insulation alternatives that will improve the thermal performance of rooftop constructions. In doing so, experiments have been performed for investigating the energy-saving effect of adding microencapsulated Phase Change Materials (mPCM) to a conventional factory ceiling (gypsum board). The average energy-saving effect at the entire heat absorption stage of a mPCM gypsum board compared with a conventional gypsum board is 31.7 per cent.

Fabricação de chapas de partículas aglomeradas usando gesso como material cimentante.

Neste trabalho, foram confeccionadas chapas aglomeradas, utilizando gesso como material cimentante e papel reciclável dissociado (jornal e offset) e partículas de madeira de pinus como reforços. Em todos os tratamentos, a razão madeira (ou fibras) para gesso foi mantida em 0,25 (base seca) e duas dosagens de água (w) foram empregadas: 0,4 e 0,8, correspondendo à razão água:gesso. As chapas foram prensadas a frio em prensa de laboratório, em um processo similar à produção de chapas aglomeradas convencionais. Após condicionadas em câmara climatizada, as chapas foram testadas em flexão estática, dureza, arrancamento de parafusos, absorção d'água e inchamento em espessura. Em geral, a adição de fibras causou melhoria nas propriedades das chapas. Diferenças estatísticas significativas em relação à testemunha (gesso puro) foram encontradas para resistência à flexão estática (MOR), dureza e arrancamento de parafusos em relação a alguns dos tratamentos estudados. Já a inclusão de fibras de papel reciclável, com w = 0,4, não apresentou diferenças significativas em relação à testemunha para absorção d'água e inchamento em espessura. Os melhores resultados foram encontrados com papel jornal, com um coeficiente w = 0,4.

Structural and thermal behavior of coal combustion and gasification byproducts: SEM, FTIR, DSC, and DTA measurements

Structural and thermal behavior of coal combustion and gasification byproducts: SEM, FTIR, DSC, and DTA measurements

Dimensional and formation analysis of a restorative ceramic and how it works

In-Ceram ceramic appears to use conventional powder/liquid processing techniques to form the coping substructure; however, the process results in a near net-shape restoration with minimal sintering shrinkage. Scanning electron microscopy, Brunauer-Emmett-Teller analysis, particle size classification, and linear dimensional changes during sintering were used to analyze In-Ceram ceramic. In-Ceram ceramic had a minimal linear shrinkage of 0.21% after the sintering of the alumina powder. This shrinkage can be readily compensated for by the expansion of conventional gypsum products and should result in acceptable clinical fits for In-Ceram ceramic restorations. Theories and explanations were described to account for the near net-shape and high strength of In-Ceram. Continuous interpenetrating phase composite technologies were used to create a substantial increase in strength. Future applications of this technology are encouraging.

Obtaining an energy storing building material by direct incorporation of an organic phase change material in gypsum wallboard

A laboratory scale energy storage gypsum wallboard was produced by the direct incorporation of 21%–22% commercial grade butyl stearate (BS) at the mixing stage of conventional gypsum board production. The incorporation of BS was strongly facilitated by the presence and type of small amounts of dispersing agents. The physico-mechanical properties of the laboratory-produced thermal storage wallboard compare quite well with values obtained for standard gypsum board. The energy storing board has a ten-fold increase in capacity for the storage and discharge of heat when compared with gypsum wallboard alone.