Developing a novel mix design technology for ‘rammed Earth’ using pulp mill fly ash as cementitious material

Rammed earth (RE) is a traditional soil-based building material made by compressing a mixture of natural earth and binder ingredients in temporary frameworks. The modern RE uses 5 to 10% cement as a binder to meet the strength and durability requirements. Due to the CO₂ footprints associated with cement production, this research aimed to develop and assess innovative waste-to-product technologies and strategies for the transformation and effective utilization of pulp mill residues in the construction sector as a partial replacement for conventional Portland cement. For the experimental study, the as-received pulp mill fly ash (PFA) and a fly ash-based geopolymer synthesized by alkali-silicate activation method, were incorporated as cement substitutes in the RE mixtures. Initially, the local soil was collected and characterized by important index and engineering properties. The fly ash was procured from a local pulp mill, and its physico-chemical, mineralogical, and morphological characterization, as well as environmental impact, was identified. Further, the various mix designs of RE material incorporating local soil and different proportions of Portland cement, pulp mill fly ash, calcium bentonite, and alkali-silicate activator (a mixture of sodium silicate and sodium hydroxide solutions) were developed. The compacted RE specimens were cured and tested for 7-day and 28-day unconfined compressive strength (UCS) variations. The PFA and calcium bentonite-treated samples, as well as samples that were stabilized by the alkali-silicate activator, exhibited significant strength improvement. Further, the cured RE specimens were subjected to a standard freeze-thaw durability test to evaluate their frost resilience properties as a sustainable construction technique under extreme climatic conditions. The alkali-silicate activator-treated samples were highly unstable under extreme weathering conditions. On the other hand, the specimens treated with calcium bentonite and PFA retained their full strength under the freeze-thaw cycles. As a result, it was concluded that even though the alkali-silicate activation of PFA improved the compressive strength of RE samples, this method is not durable in hard weathering conditions. Furthermore, treating RE specimens with PFA and bentonite was beneficial for the improvement of mechanical and durability properties of RE samples and can be a practical step towards the utilization of waste by-products.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat