Abstract
This manuscript investigates the degradation of the properties of recycled plaster‐mixed aluminate cement (RAP) and analyzes its degradation mechanism by DSC/TG and SEM. The results showed that the setting time of RAP was shortened due to the fast formation of recycled ettringite (AFt) and its strength was decreased relative to the pure recycled plaster (RP) in the absence of aluminate cement. Different from the properties of RP and RAP, the hydration of commercial plaster was slowed down by the addition of aluminate cement for its low hydration rate, and its strength was increased with respect to the pure commercial plaster (CP) without aluminate cement. Therefore, the properties of RP and RAP could be seen to decrease in relation to CP and commercial plaster mixed aluminate cement (CAP). The SEM and DSC/TG analyses confirm the presence of cluster and fine crystals and noncementing AH3 in RAP, which demonstrates its degradation of properties.
Highlights
At present, commercial gypsum is one of the most commonly used materials in ceramic mold [1, 2] and general construction work [3, 4] because of its characteristics of light weight, stable volume, heat insulation, sound insulation, good fire resistance, and humidity adjustment [5]
Materials. e original gypsum (OG) comes from Yuhuan gypsum factory in Yingcheng, Hubei, China. e aluminate cement is produced by Guizhou Xifeng Rendu Building Materials Co., Ltd., CA-50. eir chemical compositions were measured by X-ray fluorescence (XRF)
When the aluminate cement was not added in the commercial plaster (CP), recycled plaster (RP), hardened CP, and hardened RP were obtained following the same steps as before, and the water to plaster ratio of CP and RP were 0.63 and 0.85, respectively. e properties tests were conducted based on the Chinese standard GB 9776-2008 [25]. e test methods for w/p, setting time, and strength have been described in our previous research [24]. e sample dimensions for mechanical properties determination was 40 mm × 40 mm × 160 mm
Summary
Commercial gypsum is one of the most commonly used materials in ceramic mold [1, 2] and general construction work [3, 4] because of its characteristics of light weight, stable volume, heat insulation, sound insulation, good fire resistance, and humidity adjustment [5]. According to Suarez et al, the amount of waste gypsum produced each year is as high as 80 million tons, of which about 15 million tons are landfilled [6]. It takes up a large amount of arable land and pollutes the environment, and produces hydrogen sulfide gas when it is mixed with organic matter, which is harmful to humans [7, 8]. E flexural strength and compressive strength were 1.66 MPa and 2.94 MPa, respectively, and the extended hydration and degraded strength of pure recycled plaster could be found in relative to commercial plaster. Zhu et al [16] analyzed the degradation mechanisms of pure recycled plaster mechanical performance and attributed it to the increased porosity and larger pore size of recycled plaster
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