Recycling of expired cement and aged supplementary cementitious materials based on close packing theory and space filling effect

To reduce the pressure of energy crisis and greenhouse effect from cement manufacturing, this paper proposes a technique on recycling of expired cement by blending with aged silica fume and slag through particle close packing design. To verify the accessibility of optimal packing arrangement, several porous structure measurements are conducted, including mercury intrusion porosimetry, nitrogen adsorption, scanning electron microscopy, nuclear magnetic resonance and hardened strength development with thermal gravimetric analysis. The obtained results manifest that the porous structure of hardened paste is mainly divided into three ranges as <11 nm, 11–50 nm and around 80 μm diameters; while attributed to the filling effect of aged silica fume on pores below 12.2 nm and slag filling effect on over 12.2 nm, the optimal mixture presents obviously better pore distribution than pastes without close packing design; moreover the scanning photography factually verifies the fine particle and hydration products filling effect in air pore spaces, and the liquid magnetic signal intensity further displays the microstructure density modification especially after 28days. As a whole, the close packing design is proved as an efficient method to reutilize the expired cement with aged silica fume and slag, and this proposition will significantly turn three unqualified construction wastes into useful material on eco-friendly consideration.