Manufacturing and durability of alkali-activated composites with bamboo fibres

Alkali-activated materials (AAM) represent a new class of materials that has rapidly grown in interest in the last twenty years in order to reduce the CO2 emissions for cement and ceramic materials productions. They are based on alkali-activation of precursors able to consolidate at room or slightly higher temperatures. The possibility of using waste-based powders such as for example coal fly ashes is one of the main advantages of AAM, thus promoting a circular economy approach. Even if characterized by a lower environmental impact, AAM suffer from some drawbacks, mainly the extreme brittleness and the low dimensional stability. One of the main solutions to overcome these problems can be the use of fibres, such as steel, basalt, or polypropylene ones. Moreover, the addition of natural fibres with the scope to obtain a similar improvement could provide a huge environmental benefit. The overall effect of bamboo fibres on the properties of mortars formulated with fly ashes activated by alkaline solutions has been here investigated. The length of the fibres was varied in order to obtain the best properties of the composite materials. A reference mortar without fibres and with the same liquid/binder and binder/sand ratio has been prepared for comparison. No heat curing has been used in all the mortars. The consistency at the fresh state, as well as the microstructural, physical and mechanical properties at the hardened state of the obtained materials have been studied. Finally, the durability of the investigated composite materials has been investigated by means of both freeze-thaw and temperature-humidity cycles. Obtained results show a good resistance to temperature-humidity changes and freeze-thaw stresses of the reinforced mortars, thus fostering the use of natural fibres to improve the performance of low carbon footprint building materials such as alkali-activated composites in the civil engineering applications.