Papers by Keyword: Gypsum

Abstract: Accurate prediction of the soil shear strength parameters is essential in the reliable geotechnical design of civil engineering structures. This recent paper investigates the effect of the dry testing condition on the shear strength parameters of the sandy soil using the direct shear apparatus and compared with the saturated condition tests in previous researches on the same soil. The dry soil, usually above the water table, is the principal condition of the Al-Najaf city soil in Iraq. Samples are selected from the site of the University of Kufa, which represents the sandy soil of the city. For reliability purposes, the soil is exposed to different pre-soaking durations (one, two, and four weeks) then air-dried for shear tests. The main results revealed that the angle of internal friction (Φ) tested as a dry sample decreases about -6% up to two-weeks soaking then recovered upon four-week soaking about +6%. Compared to the saturated testing, there are increases in F between 6%-17% from saturated tests. Finally, it is recommended to aware in the selection of testing conditions for calculations of the angle of internal friction.

Abstract: This paper presents the research method of hardening process of gypsum binders and composites, based on them, using the ultrasonic method. Modern construction composites, based on higher water resistance gupsym, contain the coarse aggregate particles, giving them heat and sound insulating properties. One of the frequent purposes, designing such composites, is the slowdown of the processes of setting, so it allows the builders to work with the material for a sufficiently long period. The use of standard control penetration methods of the setting processes for the considered composites becomes difficult because of the presence of course particles in the binder paste. The ultrasonic method is proposed to use alternatively to study the process of setting. For its implementation, the technique has been developed, based on the use of ultrasound systems for quality control of concrete products. The transit time of ultrasonic signals through the layer of hardening binder paste with the fixed thickness was measured in a regular intervals until completely setting. On the basis of the obtained data, the ultrasound velocity was calculated and the setting time was determined. For this purpose, a differential curve of the time of ultrasound transmission was plotted, and the period was considered, at which the transition to the steady-state condition was carried out, it is equivalent to the end of the setting. The initial setting was determined by the first trip of the measuring equipment, corresponding moment of the formation of the primary crystal structure of the composite, which has sound-transmission properties. To verify the values of the setting time, the simultaneous measurement of the plastic strength of the model system was used. The moments of the beginning and the end of the setting, as well as the ultrasound velocities which were typical for these moments, were determined with the plastic strength. The obtained velocity values allowed to find the setting times of other composites. The actual setting time is estimated based on the values, obtained by all the available methods. The model, based on percolation theory, has been proposed for analyzing the physicochemical phenomena during the setting.

Abstract: Gypsum, or sulphate, binders are inorganic powder binders, which are among the so-called aerial mortars. These, after mixing with water, form a material that is well-workable for a certain time, which solidifies, hardens and is stable only in the air. Gypsum as a building material is formed by heating a raw material called plaster stone - CaSO₄·2H₂O and can acquire various properties depending on how it is produced. Its resulting properties can be affected to some extent by the source from which the raw material for its production is obtained, whether it is plaster stone or whether it the source is a secondary product from industrial production. [1] Production and use result from the ability of the original raw material to release crystalline-bound water under elevated temperatures and to bind it again after it has been added thus recreating a solid structure.

Abstract: The Development of new materials for building industry is a necessary issue to promote sustainability. Gypsum is an important low cost material very abundant in the northeast region of Brazil. Its physical properties make it an interesting material to form composite materials. This work presents a study of gypsum reinforced with Caroá (neoglasiovia variegate) natural fibers, where different amounts of fibers (1, 2, and 3%) were added into gypsum matrix. Three different fiber sizes (5, 10, and 20mm) were used to evaluate the effect of fiber size on the properties. PVAc was added in order to enhance the interactions between matrix and fibers. Mechanical strength was characterized by compression and bending tests. The addition of 1% mass Caroá fibers leads to a slightly increase on the mechanical strength independently of fiber size.

Abstract: This work aims to characterize the post-consumption plaster and compare it with virgin plaster. Burrs from plaster frames manufacturing were collected at the manufacturer. These samples were dried in a drying oven. Then, they were milled in a ball mill, until forming a fine and homogeneous powder. The samples were returned to the drying oven at three different temperatures, 100, 150 and 200°C, to define the best drying temperature, because the water removed in this process changes the structure of the semi-hydrated calcium sulfate gypsum into bihydrated. Then, vibrational Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were performed to characterize the virgin plaster and the reused plaster, making it possible to know the structure and the groups present in the components.

Abstract: In current work unique hexagonal microparticles of silicon oxide (phytolite), isolated from the red algae Tichocarpus crinitus, which grows in the Sea of Japan described. The structures of poytolites are characterized by the methods of optical microscopy and scanning electron microscopy. The role of these formations in plant life and the mechanism of their synthesis remains unclear.

Abstract: The main components of polymer carboxyl group are introduced.The effects of macromolecular carboxyl groups on the limestone-gypsum wet flue gas desulfurization (FGD) system of coal-fired power plants in China were studied by test method. The results showed that the macromolecular carboxyl groups can accelerate the chemical absorption of SO₂ under the action of active agents and crystallization agents, improve the desulfurization efficiency of about 2%, and shorten the limestone ablation time of more than 40%, catalytic calcium sulfite oxidation of calcium sulfate.

Abstract: This paper deals with the verification of the possibility of preparing synthetic ettringite in a way of direct addition of aluminum sulfate and calcium hydroxide as an alternative to the hydration of yeelimite. The stability of the resulting system was studied using the X-ray diffraction (XRD) and differential thermal analysis (DTA) in two different environments, namely in a laboratory environment and the environment of saturated water vapour. The evaluations of X-ray diffraction analysis and thermal analysis show that in the ettringite sample stored in the laboratory environment, evaporation of molecular water and subsequent transformation of ettringite into metaettringite or monosulfate can occur over time. Conversely, exposition of saturated water vapour environment can lead to saturation of the system by free calcium ions due to the slow dissociation of calcium carbonate, and thereby increase the amount of ettringite at the expense of gypsum and aluminum amorphous phase. To verify the above, it is recommended long-term monitoring of samples exposed in monitored environments.

Abstract: There is experience of the production and use of low density autoclaved aerated concrete. It is shown that fly-ash from Reftinskaya State District Power Plant efficiently substitutes the quartz sand aerated concrete technology. Its use opens up additional opportunities for AAC with the density of 300-400 kg/m³. In order to optimize the structure and properties it has been suggested to introduce the gypsum aerated concrete additive into the autoclave in the amount of 3-5% by weight of the dry components. The introduction of gypsum ensures the creation of a uniform homogeneous structure, resulting in the increased strength properties and reduced drying shrinkage. The resulting aerated concrete has thermal conductivity of 0.075-0.100 W/m·K, it allows using and creating single-layer fencing structures without additional insulation. The low-density gas-ash concrete production allows extending the scope of cellular concrete application and increasing its competitive advantages over other walls and insulating materials.

Abstract: The technology of wood waste processing to obtain a construction material is presented. Thermo-modified ground bark as a filler and gypsum as a binder were used in the composite. The experimental studies to determine the strength and water absorption of the composite material of the filler concentration and the fractional composition were presented. The analysis of the results was conducted.