Investigating sorption and specific surface area of manufactured fillers on fresh properties of filler-modified cement pastes

Fines are known to influence the rheology of cementitious materials, yet the specific role of adsorption characteristics and differences in specific surface area (SSA) among various manufactured aggregates remains insufficiently explored. Moreover, traditional absorption methods, such as the EN 1097-6 sand cone test, have limitations when applied to fine particles, underscoring the need for more reliable alternatives. This study addresses these challenges by systematically evaluating the water absorption, vapour sorption capacity, and SSA of manufactured sand fillers from diverse geological sources and relating these properties to the workability of filler-modified cement pastes. Water sorption was measured through both submersion and vapour adsorption at 100% relative humidity (RH), while Brunauer–Emmett–Teller (BET) SSA and pore structure were determined from N₂ and water vapour adsorption isotherms over 0–100% RH. Results indicate that water vapour adsorption generally provides higher SSA values than nitrogen, reflecting its ability to access finer pores. Moreover, vapour sorption at 100% RH shows a strong correlation with aggregate surface area, offering a more reliable alternative to traditional absorption tests. The incorporation of air content in the calculations enhances the predictive accuracy of the slump flow based on packing. These findings highlight the importance of adsorption properties in optimising filler selection to achieve the desired rheological performance of cement pastes. By combining nitrogen and water vapour adsorption with EN 1097-6 absorption, this study provides a systematic evaluation of manufactured fillers and establishes direct links to rheological performance — an approach that has rarely been pursued in previous research. This can provide new insight for more consistent mix design and advanced applications where precise rheological control and binder reduction are critical.