Influence of in-situ polymerization on the performance of cement grouts with high recycled AAC powder content: A multi-technique hydration and mechanical modification study

Recycling of construction waste is essential for sustainable cement-based materials, yet the variable composition of recycled autoclaved aerated concrete (AAC) powder pose significant challenges when used in grouting applications. The synergistic effects of high-content recycled AAC powder combined with in-situ acrylamide (AM) polymerization remain unexplored exactly. This study addresses these gaps by systematically investigating the combined incorporation of recycled AAC powder (up to 45 wt%) and in-situ PAM polymerization (0–0.15 wt% AM) in cement-based grouts, hypothesizing that the pozzolanic reactivity of AAC and the polymer network formation would synergistically enhance toughness while requiring optimization to mitigate adverse effects on workability and hydration. Multi-scale characterizations were performed at different curing ages, including setting time, fluidity, mechaniacal strengths, water absorption, hydration heat, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, mercury intrusion porosimetry, 29Si MAS NMR. The pozzolanic activity of AAC powder promoted C-S-H gel formation, increased the Si/Ca ratio in C(-A)-S-H gel, and reduced ettringite and un-hydrated C2S contents. As a reasult, the early-age compressive strength of AAC- incorporated specimens increased from a high of 12.0 MPa to 19.2 MPa, which suggested the refinement function of AACP in early compressive strength. In contrast, in-situ PAM polymerization suppressed C-S-H and ettringite formation, elevated residual C2S, and lowered the Al/Ca ratio in C(-A)-S-H gel. The dual incorporation increased porosity and water absorption but enabled a PAM-C(-A)-S-H gel network that bridged microcracks, thereby enhancing material toughness. These findings demonstrate a viable pathway for developing eco-friendly, high-toughness grouting materials through waste valorization and polymer modification.