Feasibility of treated recycled materials for rammed earth structures, Master´s Thesis Otso Laurila

Rammed earth is a construction method in which moist soil or similar granular material is compacted into moulds. It offers the potential to reduce the carbon footprint of certain structures that nowadays are constructed using concrete. Such structures include non-load bearing walls such as noise walls, but also blocks that could be stacked to form partition walls or to support and stabilize slopes.

The use of recycled materials in the construction industry is advocated due to increasing regulations on CO2-emissions and preservation of exhaustive natural resources. In this thesis, low emission composites were developed for application in stabilized rammed earth construction. The emissions of the composites in this thesis are lowered by exploring the use of local municipal wastes, namely crushed concrete aggregate, incineration slag and utilizing a low-cement binder. The first section involves a forensic study on an existing rammed earth structure that has been exposed to Nordic conditions for 2,5 years. Based on the forensic analysis on these rammed earth composite samples, strength and moisture-based durability issues are recognized to be pitfalls in visible deterioration of the existing structures. To further improve the performance of these composite (considering strength and durability), new recipes of binder-stabilized rammed earth were explored. Incineration slag was treated with a hydrophobizing agent. This was done to potentially eliminate the degradation caused by the expansion of absorbed water during freezing. The samples were tested to determine their properties after 28 days of curing. These properties included uniaxial compressive strength (including after freeze-thaw cycles), propensity to capillary suction and other analytical inspections. Calorimetric measurements were done on some samples to study the hydration in stabilized rammed earth.

Uniaxial compressive strength values between 2,03 – 20,06 MPa were reached. Freeze-thaw durability of the samples was observed to be good after 15 freeze-thaw cycles, especially in the hydrophobized samples. A significant decrease in the capillary water absorption was observed in the hydrophobized samples, hinting to a possibility of using hydrophobized materials as way of mitigating freeze-thaw damages in rammed earth. Long-term performance of the hydrophobic agent was not studied, but the results indicate that the hydrophobicity is diminished when the samples are subjected to freeze-thaw cycles.