• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.221-224
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• 2003

Polyvinyl chloride (PVC)/gypsum Polymer blend materials were prepared by melt blending of PVC with gypsum and additives. Effect of gypsum content on the properties of PVC/gypsum Polymer blend material was studied by investigating physico-mechanical properties, thermal properties and morphology development. It was found that the replacement of gypsum for methylene-butadiene-sarene (MBS) component in PVC/gypsum polymer blend material enhanced the tensile strength, but gradually decreased its impact strength. Besides, with the increase of gypsum content, the elongation at break of material gradually decreased. The Presence of the different gypsum contents made a shift of g1ass transition temperature and increased the thermal stability as well as the processing temperature range of polymer blends. The observation of morphology, the results of the physico-mechanical properties and thermal properties proved simultaneously that PVC/gypsum Polymer blend material with the gypsum content of 22.56 wt.% reached the optimum results among five kinds of PVC/gypsum Polymer blend materials investigated.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.134-137
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• 2000

A study on the development of material for a light weight partition wall using material of gypsum and waste paper is be considered to improve workability, setting time, properties of strength by use of $\beta$-Gypsum for controling setting time. According th the experiments, as quantity of gypsum in binder increase, workability and strength of specimens deteriorate. Appropriate quantity of $\beta$-Gypsum was 3~6% of binder and When it was used more than 10%, setting time was so fast. When additive quantity of waste paper has increased to 1%, flexural strength decreased to some 8~12% and density decreased abort 3% in comparison with otherwise specimen.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.342-348
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• 2001

This study was conducted to obtain granular crystalline gypsum that can be used as raw material for plaster boards or cements from waste Plaster board. We could disintegrate preferentially gypsum to gypsum needle in 10${\mu}{\textrm}{m}$ or less size among the contents of waste plaster board (gypsum, paper, fiber, and inorganic material .etc.) by hydration afterwards the dehydration of crushed waste plaster board. In this case, the optimum conditions for minimizing the size of gypsum were dehydration rate of 75%~ 85%, hydration concentration of 10~20%, agitation speed of 250~400rpm, crushing size of 2cm or less. Gypsum of 98.21% grade was recovered with 99.0% yield from under screenings of 325mesh wet screening which followed by the dehydration-hydration process performed in the conditions of dehydration rate of 80%, hydration concentration of 15%, agitation speed of 300rpm, crushing size of 2cm or less. Subsequently, Plate-like Crystalline gypsum of is 151${\mu}{\textrm}{m}$ size and the grade of 99.49% with the Yield of 98.0% from the upper screenings of 270mesh wet screening carried out after the re-crystallization of the recovered gypsum needle slurry.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.102-105
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• 2001

Gypsum has been known as a prominent material for improving alkali soil, and this material can be supplied easily in large scale by recycling waste gypsum plasterboard from construction and demolition sites in advanced countries. In April 2000, in the part of western Jilin Province in China, where alkali soil spread vastly, we conducted a cultivating experiment of corn and rice after treating with granule recycled waste gypsum at six alkali soil fields which total area were 14000$m^2$. We confirmed that pH of soil decreased in a short period and alkali soil changed soft a desirable condition for farm work, and furthermore, gypsum caused to accelerate the growth of a plant, both corn and rice.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.3
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• pp.47-54
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• 2012

As a large construction such as highway, dam, reclaimed land etc. increase in number more and more, large amount of fill materials are required. It is needed to utilize a gypsum which is a by-product yielded from chemical plants, as fill materials. Though some studies have been conducted to know a engineering characteristic of gypsum, it is not certain that water contents were checked at $45^{\circ}C$ dry oven. This study proposed that water contents must be measured at $45^{\circ}C$ dry condition because gypsum is changed to other types as a dry temperature. As the results obtained by compaction tests, it is found that moisture of gypsum in compaction must be within -5.0~2.5 % O.M.C (optimal moisture content).

• Resources Recycling
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• v.14 no.2
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• pp.10-18
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• 2005

The manufacture property of anhydrous calcium sulfate (anhydrite Ⅱ) from flue gas desulfurization (FGD) gypsum discharged from domestic thermoelectric power plants to apply as an auxiliary material of cement and concrete by high temperature treatment were investigated. The FGD gypsum was completely converted to anhydrite Ⅱ at the temperature of 700$^{\circ}C$ and the retention time of 1 hr. In the phase transformation process, particle size was also changed. The chemical composition, particle size and heat property of anhydrite Ⅱ made from the FGD gypsum were similar to them of natural gypsum. In the leaching test of sulfate ion (SO$_4^{2-}$) at the temperature of 90$^{\circ}C$ and the retention time of 1 hr, the amount of leached SO$_4^{2-}$ for the anhydrite Ⅱ that was sintered at 700$^{\circ}C$ for 1 hr was about 50 wt.% based on that of natural gypsum. In addition, the amount of leached SO$_4^{2-}$ for the anhydrite Ⅱ by adding the slaked lime of 3 wt.% decreased about 70 wt.% comparing with that of natural gypsum. In the application test, the compressive strength of cement and concrete manufactured by using the anhydrite Ⅱ as an auxiliary material were similar or superior compared with them of cement and concrete done by natural gypsum as an auxiliary material.

• Journal of Technologic Dentistry
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• v.38 no.4
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• pp.255-262
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• 2016

Purpose: This study examined the effect of wettability of gypsum materials and rubber impression material on the marginal fitness of zirconia copings. Methods: Three commercially available gypsum materials(Fugirock EP, Snow Rock, Tuff Rock) and three zirconia blocks(iJAM Emerald, LUXEN Smile block, ICE Zirkon transluzent) were studied. The zirconia copings were fabricated by using dental CAD/CAM system. Contact angles on the impression materials were measured with contact angle measuring device. Silicone replica method was used to measure the marginal fitness and cutting was performed on the bucco-lingual and mesio-distal sides. It were observed with a stereomicroscope at °ø40 magnification. The data were statistically analyzed with One-way ANOVA. Results: Mean values of contact angles were $58.3{\pm}0.7^{\circ}$ for Tuff Rock, $77.5{\pm}0.5^{\circ}$ for Fugirock EP and $87.8{\pm}0.5^{\circ}$ for Snow Rock and the difference between them was statistically significant(p<0.05). The smallest values of marginal fitness for the JF groups were $30.7{\pm}3.0{\mu}m$ for bucco-lingual direction, $29.3{\pm}3.0{\mu}m$ for mesio-distal direction. One-way ANOVA showed statistically significant difference between groups for marginal fitness(p<0.05). Conclusion: Tuff rock gypsum material had superior wettability to others. The mean marginal fitness of the Tuff rock gypsum material group were significantly better than other groups. Thus they can be also expected to show clinically satisfactory marginal fitness.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.351-354
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• 2000

In recent years, the world development of alternative construction materials is associated with disposal problems of waste materials as a result of industrial activities. Technologies of refining gypsum to several gypsum modifications ($\alpha$ and $\beta$-hemihydrate) which can be used as construction material in a large scale do actually exist or are under development. This paper provides a technical and economic perspective of the waste gypsum treatment. Especially, several applications particularly of $\alpha$-hemihydrate will be presented, e.g. artificial gypsum aggregate and light-weight masonry units.

• Journal of the Korea Institute of Building Construction
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• v.8 no.1
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• pp.57-62
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• 2008

Twelve mortars were mixed and tested to explore the effect of gypsum on the compressive strength development and shrinkage strain of alkali-activated mortars. Powder typed sodium silicate and ground granulated blast-furnace slag were employed as alkaline activator and source material, respectively, to produce cementless mortar. The main variables investigated were alkali quality coefficient combining the concentration of activator and main compositions in source material, and the adding amount of gypsum ranged between 1 and 5% with respect to the weight of binder. Initial flow, compressive strength development, modulus of rupture, and shrinkage strain behavior of mortar specimens were measured. In addition, the hydration production of alkali-activated pastes with gypsum was traced using X-ray diffraction and energy-dispersive X-ray analysis combined with scanning electron microscope image. Test results showed that the initial flow of slag-based alkali-activated mortar was little influenced by the adding amount of gypsum. On the other hand, the effect of gypsum on the compressive strength of mortar specimens was dependent on the alkali quality coefficient, indicating that the compressive strength increased with the increase of the adding amount of gypsum until a certain limit, beyond which the strength decreased slowly. Shrinkage strain of mortar tested was little influenced by the adding amount of gypsum because no ettringite as hydration product was generated. However, the adding of gypsum had a beneficial effect on reducing the microcrack in the alkali-activated mortar.

• Resources Recycling
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• v.10 no.6
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• pp.43-52
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• 2001

This study was conducted to obtain granular crystalline gypsum that can be used as raw material for Plaster boards or cements from waste Plaster board. Gypsum could be Preferentially disintegrated to gypsum needle in $10\mu\textrm{m}$ or less size by hydration after the dehydration of crushed waste Plaster board. The finer the gypsum needle, it is easier to remove coarse impurities and to recover the gypsum needle. The optimum conditions for obtain the finer gypsum size were dehydration rate of 75~85%, solid concentration at hydration of 10~15%, agitation speed of 250~400 rpm, crushing size before dehydration of 2 cm or less. Gypsum of 98.21% grade was recovered with 99.0% yield as the undersize of 325 mesh wet screening followed by the dehydration-hydration process performed at the conditions of dehydration rate of 80%, solid concentration at hydration of 15%, agitation speed of 300 rpm, crushing size before dehydration of 2 cm or less. After the recrystallization of recovered gypsum, Plate-like gypsum of $151\mu\textrm{m}$ size with 99.49% grade was obtained as the oversize of 270 mesh in a wet screening.