Optimisation of hybrid alkaline binder with a high glass powder content

There is a growing interest in utilising waste glass in cement and concrete production to reduce the environmental impact. This paper studies the feasibility of incorporating a very high volume of glass powder (≥65 %) in a hybrid alkaline binder (HAB) activated by sodium carbonate and sodium citrate. The HAB was optimised in two stages to achieve optimal performance in terms of flowability, strength, cost-effectiveness, and carbon footprint: the first stage focused on the optimisation of the ternary binder consisting of 5-20 % slag, 10-25 % ordinary Portland cement (OPC), and 65-80 % glass powder; and the second stage optimised the contents of activators (sodium carbonate and sodium citrate) and superplasticisers. The prepared pastes were tested for flowability and compressive strength. Meanwhile, microstructural analyses were conducted to characterise the morphology and structure of the paste samples. The optimal HAB comprising 65 % glass powder, 25 % OPC, and 10 % slag was suggested based on a multi-criteria decision-making approach. This mix achieved very good flowability (210 mm flow diameter) when activated by 4.75 % sodium carbonate and 1 % sodium citrate. Meanwhile, a very high compressive strength of up to 63.0 MPa was achieved at 28 days. The optimised HAB also exhibited very good hydrolytic stability and high early strength. Compared with the OPC counterpart, the optimised HAB is approximately 33 % more cost-effective and emits 53 % less greenhouse gases.