Effects of Chemical Parameters on the Fresh State Properties of CDW-Based Geopolymer Systems

The fresh properties of construction and demolition wastes (CDW)-based geopolymer pastes depend on various factors such as the contents of aluminosilicates in precursors, the combination of precursor powders and the contents of alkaline solutions and water. In order to quantify the effects of the aforementioned factors on the fresh properties of CDW-based geopolymer compositions, an algorithmic mix design method was employed based on precursors contents, liquid/solid (L/S) and synthesis chemical oxide values. This study presents the influence of SiO₂/Al₂O₃ (Si/Al) and Na₂O/SiO₂ (Na/Si) molar ratios and precursors contents on the flowability and setting behavior of mono and binary geopolymer systems prepared with red clay brick waste (RCBW), ceramic tile waste (CTW) and concrete waste (CW). Binary systems were adjusted to include precursors contents between 20 and 80%. The results confirmed a high correlation between the oxide ratios and the followability and setting times of geopolymers, though the same L/S ratio was used for all compositions. Overall, increasing Si/Al and Na/Si ratios resulted in increased flowability. In addition, increased ratio of Si/Al resulted in increased setting times; while increased Na/Si caused the setting times to reduce. It was determined that Si/Al was more influential than Na/Si on the flowability of geopolymer pastes. However, the effect of Na/Si was more dominant on setting times compared to Si/Al ratio.