Changes in plaster microstructure by pre-stressing or by adding gypsum grains: microstructural and mechanical investigations

Gmouh, A.; Eve, S.; Samdi, A.; Moussa, Rédouane; Hamel, J.; Gomina, Moussa

doi:10.1016/s0921-5093(02)00938-3

Cited by 31 publications

(23 citation statements)

References 11 publications

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“…The 5% addition of VA/VL/VC caused the increase of the final setting time from 35.5 min to 82 min, while with the 10 % addition, the final setting time occurred in 106 min. The setting time process of gypsum can be divided into three steps: dissolution of the hemihydrate, nucleation of the gypsum crystals and growth of the CaSO 4 .2H 2 O crystals 16 . When mixed with water, the CaSO 4 .0.5H 2 O is quickly dissociated, forming Ca 2+ and SO 4…”

Section: Resultsmentioning

confidence: 99%

Mechanical and Microstructural Properties of Redispersible Polymer-Gypsum Composites

et al. 2019

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Studies on gypsum modified by polymers have been conducted to assess the potential of improvement in the mechanical performance, water resistance and increasing the setting time, facilitating its handling. Gypsum-based compounds made with different additions of redispersible polymers were studied, such as: ethylene-vinyl acetate (EVA), vinyl acetate terpolymer, vinyl laurate and vinyl chloride (VA/VL/VC), and vinyl acetate and vinyl versatate (VA/VeoVA). The influence on setting time, microstructural formation and on the bending performance was assessed, as well as and compression of the hardened gypsum. The composites were prepared using a polymer concentration of 5% and 10%, and water/gypsum ratio of 0.6. The addition of the polymer decreased the structural robustness and change in the microstructure. We concluded that the reduction in the amount of water through additives may allow a more complete and robust training of gypsum crystals and compounds with better mechanical performance.

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Section: Resultsmentioning

confidence: 99%

Mechanical and Microstructural Properties of Redispersible Polymer-Gypsum Composites

et al. 2019

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“…As shown in Figure (a), (b), short columnar crystals with length of 50μm were obtained by dihydrate gypsum crystals with length of 100μm while short columnar crystals with length of 100μm were obtained by dihydrate gypsum crystals with average length of 350μm. Crystals with large sizes are quite beneficial to products with good performance . Thus, dihydrate gypsum crystals with average length of 350μm are more suitable for the preparation of short columnar α‐hemihydrate gypsum.…”

Section: Resultsmentioning

confidence: 99%

Preparation of Whitening Dihydrate Gypsum and Short Columnar α‐Hemihydrate Gypsum with FGD Gypsum

Shao

Zhao

Gao

et al. 2017

Crystal Research and Technology

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Using FGD gypsum as the raw material, whitening and large prismatic dihydrate gypsum can be obtained by dissolution-crystallization and decoloring process with α-hemihydrate gypsum whiskers prepared in MgSO 4 -CaCl 2 -H 2 O solution, which can transform into whitening short columnar α-hemihydrate gypsum. The effects of aging temperature, pH, dosage of sodium dodecyl sulfonate (SDS), time on composition and morphology of products were investigated. The research shows that: whitening and large prismatic dihydrate gypsum with average length of 350μm and the whiteness of 82.57% can be obtained with 6g SDS (mass ratio of SDS/FGD gypsum was 1.2) addition and pH of 8 after 3.5h under 60°C. The effects of different morphologies of dihydrate gypsum on α-hemihydrate gypsum were discussed, which indicates that granularity and morphology of α-hemihydrate gypsum are directly related to dihydrate gypsum. And short columnar α-hemihydrate gypsum with the length of 100μm and the whiteness of 85.68% can be prepared by dihydrate gypsum obtained under optimum conditions mentioned above.the impurities sticking to the surface of FGD gypsum, but can't remove internal impurities, as a result, the whiteness of products is still low. So physical purification methods can't improve the whiteness of products dramatically.In acid or saline solution, dissolutionrecrystallization of FGD gypsum can release the impurities of internal crystals and obviously improve whiteness. Heiska P [5] invented a method to purify FGD gypsum in acid solution using magnetic separator. The whitening dihydrate gypsum purified can be used for coating or filler pigment for paper or board. Mao [6] found that CTAB can be used to achieve the control of crystal morphology in HCl solution by experimental and MD simulation. And needle-like crystals with high whiteness and good aspect ratios were obtained. Zhang [7] and Lu [8] studied the preparation of calcium sulfate whiskers with high whiteness in HCl-CaCl 2 -H 2 O and H 2 SO 4 -Ca-(OH) 2 -H 2 O respectively by physical method and chemical method. Although the whiteness of FGD gypsum can be improved obviously, acidation method is more suitable for α-calcium sulfate hemihydrate whiskers with large length-diameter ratios and short columnar crystals can't be obtained in acid solution due to fast growth rate along C-axis.Fu [9] and Shi [10] studied decoloring and whitening process of anhydrite or phosphogypsum by acid-leaching method. The material was firstly calcined under high temperature (>600°C) and then soaked in acid solution at a definite temperature, which can make the whiteness of anhydrous gypsum reach 90% or more. However, the process has many disadvantages, such as high energy consumption, serious equipment corrosion under strong acid and harsh reaction conditions. Zhang [11] researched the addition of anhydrous gypsum, high-strength gypsum and bleaching packing on the performance of compound gypsum and the whiteness of the products can be improved to 80.1%. Although the whiteness can be improved, different perfo...

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“…As micrografias das amostras dos compósitos ajudam a explicar alguns dos resultados obtidos. Na Figura 6a, compósito referência, podem ser verificados cristais de gipsita alongados, prismáticos e em formato de agulhas, corroborando o relato de Gmouh et al [30], que estudaram mudanças na microestrutura de gesso avaliando as potencialidades de reutilização dos resíduos de gesso que já foram empregados em obras de construção civil.…”

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Desempenho físico-mecânico de compósitos à base de gesso reforçados com embalagens multicamadas trituradas

et al. 2020

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RESUMO As embalagens multicamadas são utilizadas por um período de tempo bastante curto gerando um volume de descarte elevado. Por serem formadas por diferentes materiais devido suas diversas camadas, sua reciclagem é dificultada. Sendo assim, são importantes novas aplicações para essas embalagens pós-consumo, como por exemplo o seu reaproveitamento em compósitos. Neste contexto, o objetivo deste trabalho foi desenvolver e caracterizar compósitos à base de gesso reforçados com embalagens multicamadas trituradas. As proporções utilizadas para a incorporação dos reforços foram de 0%, 7,5%, 15%, 22,5% e 30% em substituição ao gesso. Foram produzidos corpos de prova (três repetições por tratamento) para avaliação das propriedades de absorção de água, umidade, massa específica aparente, compressão e flexão estática, os quais foram confeccionados com dimensões de 40 x 40 x 160 mm. Para o ensaio térmico, as dimensões foram de 200 x 200 x 20 mm. Os reforços adicionados levaram a um aumento em umidade e absorção de água, enquanto que, para massa específica aparente, condutividade térmica, resistência à flexão, resistência à compressão e rigidez na compressão houve decréscimo. A incorporação de embalagens multicamadas em compósitos de gesso mostrou ser uma alternativa viável, visto que, além de aplicar a logística reversa reutilizando estas embalagens que muitas vezes são descartadas no meio ambiente de maneira inadequada, gerando diversos impactos, ainda melhorou a propriedade térmica dos compósitos e diminuiu a densidade destes. Ademais, todas as porcentagens atenderam a normatização para resistência à flexão, e para a resistência à compressão, apenas a substituição de 30% não atendeu a normativa.

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Changes in plaster microstructure by pre-stressing or by adding gypsum grains: microstructural and mechanical investigations

Cited by 31 publications

References 11 publications

Mechanical and Microstructural Properties of Redispersible Polymer-Gypsum Composites

Mechanical and Microstructural Properties of Redispersible Polymer-Gypsum Composites

Preparation of Whitening Dihydrate Gypsum and Short Columnar α‐Hemihydrate Gypsum with FGD Gypsum

Desempenho físico-mecânico de compósitos à base de gesso reforçados com embalagens multicamadas trituradas

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