Development of a separation process for gypsum-contaminated concrete aggregates

Title: Development of a separation process for gypsum-contaminated concrete aggregates
Author(s): T. Schnellert, K. Kehr and A. Müller
Paper category : conference
Book title: 2nd International RILEM Conference on Progress of Recycling in the Built Environment
Editor(s): V.M. John, E. Vazquez, S.C. Angulo, C. Ulsen
e-ISBN: 978-2-35158-122-3
Publisher: RILEM Publications SARL
Publication year: 2011
Pages: 477 - 482
Total Pages: 6
Nb references: 11
Language: English

Abstract: Gypsum is a finishing building material. The gypsum building materials are easily workable and light. Besides a comparatively low energy is required for the production, which leads to ecological and economic advantages. These aspects contribute to the fact that the production of gypsum materials around years has been higher than any other building materials [1]. Gypsum content in building materials increased for 3% in the year 2000, much higher than 1% of the year 1985 [2]. The gypsum amount referred to the produced concrete amount has increased for decades.

Moreover, apart from the expected increase of the gypsum amount in construction materials, a substantial portion of gypsum was used to build sanitary room walls and anhydrite gypsum into floor in 2.15 million apartments of precast concrete buildings (slab method) in the area of the new Federal states in Germany. In the end life, the entire buildings were demolished resulting a gypsum contaminated concrete aggregates, without possible reuse. The content of leachable sulfate found was higher than that permitted for the use in road or earthworks.

In construction & demolition (C&D) sites or C&D recycling plants, a process capable to separate the gypsum materials of the other materials is necessary for reuse or use of C&D aggregates. The available process is to abort the contaminated C&D waste masses in recycling process, redirecting probably for a landfill that is an illogical solution in terms of economic and environmental aspects. In future, the increase of gypsum amount in C&D materials will clearly become a problem for the usual recycling process.

So, the separation from gypsum from the remaining building materials represents a challenge at the recycling technology. In the wet gravity separation criterion, the density variation of the individual materials due to water absorptivity must be considered. When the effective densities of particles are similar, the separation is not efficient anymore requiring a modified set technology that uses asymmetrical strokes [11]. In this contribution the separation between concrete and gypsum materials is demonstrated by the use of the modified set technology.

Online publication: 2012-02-08
Publication type : full_text
Public price (Euros): 0.00