Mechanical properties of recycled materials in non-load bearing wall structure, Master´s Thesis Anssi Luoma

The use of recycled materials is the key component of sustainable development in the construction industry. This study examines the suitability of recycled materials obtained from the Turku region for non-load bearing wall structure using both rammed earth and casting methods.

The traditional method of rammed earth involves methodically compacting damp natural soil inside a mould. The mould may be removed immediately after compacting the soil, leaving behind wellstructured compacted earth. Casting technique was specifically studied focusing on precast interlocking concrete blocks. With these it is possible to create interlocking blocks that allow convenient and efficient construction. Using both techniques, the objective was to create an environmentally friendly construction material from recycled materials. The compressive strength is the most important property for both construction methods and the created construction material. The materials used as binders in this research were bio-based fly ash and bottom ash, blast furnace slag and CEM III/B. Crushed concrete and quarry fines have been used as aggregates. Nominal quantities of cement have been utilized solely as an activator in the masses, constituting between
3,33-5,00% by weight of the dry mass.

Laboratory tests were conducted to assess the properties and suitability of recycled materials for specific construction methods. The study focused on the compressive strength of the materials, employing ultrasonic pulse velocity and unconfined compression tests. Freeze-thaw cycles were also examined for their impact on material properties. Six samples were tested for each set, with three undergoing freeze-thaw cycles and three undergoing immediate unconfined compression testing. The rammed earth method exhibited higher compressive strengths compared to the casting technique when utilizing recycled materials. After 28 days of curing, rammed earth samples achieved 3,1-18,1 MPa compressive strengths, while casting method samples varied from 0,8-11,2 MPa. Freeze-thaw cycles had minimal impact on rammed earth samples, and using Stora Enso fly ash as a binder increased the maximum compressive strength after freeze-thaw cycles. Conversely, casting method samples experienced an average 37% decrease in compressive strength when exposed to freeze-thaw cycles.

Using recycled materials, both precast and rammed earth methods are best suited to simple, nonload bearing structures that do not require high structural properties such as high compressive, tensile or shear strength. The main advantage of using recycled materials is the low carbon footprint compared to for example using traditional concrete.