{"id":19687,"date":"2025-12-08T14:36:28","date_gmt":"2025-12-08T13:36:28","guid":{"rendered":"https:\/\/www.darda.de\/?page_id=19687"},"modified":"2025-12-08T14:36:28","modified_gmt":"2025-12-08T13:36:28","slug":"concrete-rebound-losses","status":"publish","type":"page","link":"https:\/\/www.darda.de\/en\/knowledge\/concrete-rebound-losses","title":{"rendered":"Concrete rebound losses"},"content":{"rendered":"
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Rebound losses<\/em> occur primarily during the application of shotcrete: part of the material applied to the surface bounces off, falls to the ground, and can usually no longer be incorporated into the structure. This affects material consumption, quality, and occupational safety and later influences deconstruction. In application areas such as concrete demolition and special demolition<\/strong> as well as rock excavation and tunnel construction<\/strong>, understanding rebound losses is essential for properly planning methods, work sequences, and tools\u2014such as concrete pulverizer<\/strong> or rock wedge splitter and concrete splitter<\/a><\/strong>.<\/p>\n

Definition: What is meant by concrete rebound losses<\/h2>\n

\u201cConcrete rebound losses\u201d refers to the portion of shotcrete (cement paste, sand, aggregates) that, upon impact on the substrate, rebounds and falls to the ground as loose rebound material. Causes include the high impact velocity of the particles, impact angle, aggregate gradation, moisture content, and the geometry and roughness of the substrate. Rebound affects the composition of the applied layer (e.g., binder enrichment at the surface) and thus the adhesion, density, durability, and the subsequent removal behavior during deconstruction.<\/p>\n

Causes, key figures, and measurement of rebound losses<\/h2>\n

Rebound losses occur to varying degrees depending on the process (dry- or wet-mix shotcrete), nozzle pressure, nozzle distance, application angle, aggregate (size, shape, gradation), admixtures (e.g., accelerators), layer thickness, position (overhead, wall, floor), and workforce qualification. Typical rebound rates range\u2014depending on boundary conditions\u2014from single-digit to mid double-digit percentages and can be determined by weighing (input quantity vs. net built-in amount) or by accompanying tests (layer thickness, density, sampling and sieving of rebound material). Lower rebound rates mean more efficient material use, less rework, and more homogeneous layers\u2014advantages that are noticeable later in special demolition<\/em>.<\/p>\n

Formation and influencing factors in shotcrete<\/h2>\n

The rebound mechanism is physically governed by the momentum of the aggregate. If the particle strikes without sufficient embedding in plastic cement paste, it leaves the surface again. In the dry-mix process, higher air content, rough particle characteristics, and unfavorable nozzle handling promote rebound; in the wet-mix process, appropriately adjusted consistency often achieves lower rebound fractions.<\/p>\n

Typical influencing factors in practice<\/h3>\n