Abstract
The feasibility of substitute building materials (SBMs) in engineering applications was investigated within the project. A geogrid-reinforced soil structure (GRSS) was built using SBM as the fill material as well as vegetated soil for facing and on top of the construction. Four different SBMs were used as fill material, namely blast furnace slag (BFS), electric furnace slag (EFS), track ballast (TB), and recycled concrete (RC). For the vegetated soil facing, a mixture of either recycled brick (RB) material or crushed lightweight concrete (LC) mixed with organic soil was used. The soil mechanical and chemical parameters for all materials were determined and assessed. In the next step, a GRSS was built as a pilot application consisting of three geogrid layers with a total height of 1.5 m and a slope angle of 60°. The results of the soil mechanical tests indicate that the used fill materials are similar or even better than primary materials, such as gravel. The results of the chemical tests show that some materials are qualified to be used in engineering constructions without or with minor restrictions. Other materials need a special sealing layer to prevent the material from leakage. The vegetation on the mixed SBM material grew successfully. Several ruderal and pioneer plants could be found even in the first year of the construction. The porous material (RB and LC) provide additional water storage capacity for plants especially during summer and/or heat periods. With regard to the results of the chemical analyses of the greening layers, they are usable under restricted conditions. Here special treatment is necessary. Finally, it can be stated that SBMs are feasible in GRSS, particularly as fill material but also as a mixture for the greenable soil.
Highlights
Mineral waste, and especially construction and demolition waste (CDW) as well as soil material, will be the largest waste stream in terms of volume once a certain level of urbanization has been reached
The substitute building materials (SBMs) materials used in the study are recycled brick material (RB), crushed lightweight concrete material (LC), blast furnace slag (BFS) electric furnace slag (EFS), track ballast (TB), and recycled concrete material (RC)
The materials used in the pilot application for facing and greening purposes consist either of crushed brick material (RB) or crushed lightweight concrete (LC) which was mixed with organic soil with a mixture rate of two parts SBM and one part organic soil (Figure 2)
Summary
Especially construction and demolition waste (CDW) as well as soil material, will be the largest waste stream in terms of volume once a certain level of urbanization has been reached. While the majority of CDW is reused [2], other materials are often used for low-value purposes, such as landfill cover materials or for backfilling of open-cast mines [3] This kind of use is considered a downcycling process. Ashes, and CDW which are reused in the construction process are considered so-called substitute building materials (SBMs) in Germany. Used examples for GI in civil engineering are green roofs, vegetated gabions, or vegetated reinforced soil constructions While these constructions are well established, the simultaneous use of SBMs in these constructions has rarely been carried out. No applications of materials such as slag or track ballast to be used in RSS are published yet This paper fills this gap as soil mechanics tests were carried out. Cost–benefit analyses as a comparison between conventional materials and SBM as well as life-cycle assessment were not within the scope of this work and will be subjects of future studies
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