Mussel shells powder as biogenic precursor of alkali activated binders for soil stabilisation

An experimental investigation on the mineralogical evolution and mechanical behaviour of Alkali Activated Binders (AABs) based on the activation of mussel shell powder (MSP) is developed. Two alkaline solutions of different chemical composition are considered for the activation (i.e., 12M NaOH solution and a mixture of 12M NaOH and Na2SiO3 solutions). Physical and mechanical behaviour of the binders are analysed by means of Ultrasonic Velocities (UV) measurements and Unconfined Compressive Strength (UCS) tests. The reactivity of the activated MSP is monitored over time using Thermogravimetric analysis (TGA). The mineralogical investigations are fundamental to support the interpretation of the mechanical performance of the binders. The alkaline environment induced by the activators affects the reactivity of MSP, promoting the precipitation of new crystalline carbonate hydrated phases. Moreover, the availability of silica species in the system favours the formation of silicate hydrated gels. From a macroscopic point of view, the binder activated with a mixture of NaOH and Na2SiO3 solution shows a relevant improvement of UCS consistent with the precipitation of stable cementitious compounds. An insight into the mechanical effects induced by AAB based on MSP on a dredged marine sediment is provided, highlighting the role of silicon availability on the effectiveness of the treatment.