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Construction products prepared from autoclave hardened fines from C&DW



Title: Construction products prepared from autoclave hardened fines from C&DW
Author(s): F. Hlawatsch, F. Schlütter, M. Berger and J. Kropp
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: 469 - 476
Total Pages: 8
Nb references: 7
Language: English


Abstract: Construction and demolition wastes represent a huge volume of mineral compounds such as debris of natural stone from claddings, masonry units and mortars from buildings as well as concrete from roads, buildings and infrastructure. The demolition process itself as well as the further treatment by crushing and classification of the debris result in granular materials with a significant share of fines. While recycling options exist for the coarser fractions, fines with grain sizes less than 2 to 4 mm are usually discarded because of their deleterious effects on the mechanical properties and durability of the recycling product.

An experimental investigation into the chemical reactivity of the fines has shown, however, that due to the prevailing composition of the mineral phases, i.e. clay minerals, calcium and silicious compounds, a hydrothermal hardening mechanism can be initiated at elevated temperatures, in most cases without any addition of further binders such as cement. Strength and deformation properties of the resulting products were tested and the observed results indicate potentials for the recycling product in masonry applications.

In the research project, the phase composition of the recycled fines, the grain size distribution, the compaction as well as the parameters of the hydrothermal hardening, i.e. the maximum temperature and duration of hardening have been varied, and strength, porosity characteristics as well as shrinkage behaviour after hardening were measured.

In pilot tests fines from crushed concrete, crushed clay bricks, calcium silicate bricks, autoclaved aerated lightweight concrete and slags from thermal power plant were evaluated for their hardening potential, and compressive strengths up to 18 N/mm2 were observed. In further studies which concentrated on crushed concrete fines, the mechanisms of hardening and the underlying phases transformations were investigated. The results show that the hydrothermal reactions are comparable to the hardening of calcium silicate bricks and the same technology can be used for the production of construction products out of fines from demolition waste.


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