Rheology of binary nanomodified self‐compacting geopolymer concrete based on response surface methodology

Geopolymer concrete offers lower carbon emissions than Portland cement concrete, yet incorporating nanomaterials may alter the rheology of fresh self‐compacting geopolymer concrete (SCGC). This study used response surface methodology (Box–Behnken design, 29 mixes) to quantify the effects of alkali content (N/B), water‐binder ratio (W/B), nano‐silica (NS), and nano‐calcium carbonate (NC) (0–0.4 wt%) on static/dynamic yield stress and plastic viscosity. The results show that balanced additions of NS and NC minimize static yield stress, whereas strongly unbalanced dosages (one <0.15% and the other >0.30%) markedly increase static yield stress, indicating a pronounced interaction between the two nanomaterials. Quantitatively, increasing NS from 0 to 0.4 wt% raises the static yield stress by about 39% in NC‐free mixtures, whereas at 0.4 wt% NC the same NS increase reduces the static yield stress by approximately 27%. Increasing W/B above 0.53 improves flowability and reduces yield stresses and plastic viscosity, while higher N/B increases both dynamic yield stress and plastic viscosity, reflecting its viscosity‐compensation effect associated with accelerated geopolymerization. In addition, plastic viscosity decreases by ~20% with NC addition (0–0.4 wt%) and by 65%–70% when W/B increases from 0.50 to 0.60. These findings establish quantitative rheology‐composition relationships for nanomodified SCGC and provide guidance for mixture optimization to achieve both self‐compacting performance and fresh‐state stability.