Gypsum Plaster Waste Recycling: Analysis of Calcination Time

Abstract:

The gypsum plaster is a material widely used in constructions around the world. It is a material with high versatility that can be applied from wall coverings to decorative ornaments. However, during its application in buildings, large amounts of waste materials are generated. The average values of waste during its application are higher than 45% of the gypsum amount used. A series of tests were conducted to develop a feasible methodology to reuse this waste material. The results collected at this stage indicated that it is possible to obtain a recycled product with low energy consumption. It was noted that after a certain number of procedures in which gypsum was subjected to recycling, there was a loss of workability; however, it did not present relevant changes in mechanical properties. This lack of workability avoids the recycled material maintain its properties in the fresh state as it is subjected to recycling. This work evaluates the calcination time of gypsum plaster waste for the production of a gypsum plaster with binder properties for using as components. The temperature of calcination was kept constant (150 °C), but the residence time in the stationary kiln was modified. The properties in the powder state (bulk density, fineness modulus, specific mass and sieve analysis), fresh state (mini-slump, setting times and kinetics of temperature) and in the hardened state (compressive strength and hardness) were analysed in order to have some answers about the performance of the recycled gypsum. In the fresh state, the recycled material showed good results for precast components. The initial setting times were good for all residence times and the final setting times for the material calcined in periods of 5 and 6 hours. In the hardened state, the best compressive strength results were obtained for all residence times, and hardness for calcination for 3, 4, 5 and 6 hours. All these results were satisfactory when compared to the commercial plaster took as reference. On the other hand, there was a lack of workability in those pastes indicating that an admixture is needed to adjust this property of the recycled material.

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