Recycled concrete powder (RCP) utilization as an auxiliary cementitious material absorbs construction waste and promotes low-carbon transition in construction by replacing high-carbon materials. This study optimized RCP’s particle size and amorphous SiO₂ content through physical activation, systematically investigating its effects on alkali-activated cementitious materials (AACMs). The results demonstrated that 20% activated RCP enhanced compressive strength by 9% (34.2 MPa), only 12.7% lower than that of the reference samples. Hydration analysis revealed activated RCP delayed exothermic peaks but increased total heat via active particles. Life-cycle assessment showed substituting 20% ground granulated blast-furnace slag (GGBS)/fly ash (FA) with RCP reduced carbon emissions from 169.3 to 165.9 kg CO₂-e/ton (−2.1%). Although activation slightly raised emissions to 166.6 kg CO₂-e/ton, RCP’s carbon contribution remained at 9% versus GGBS’s 83% dominance. Crucially, the activation’s 0.7 kg CO₂-e/ton increase was offset by 4.7 kg CO₂-e/ton reductions from material substitution and waste recycling benefits, confirming its net carbon-neutral potential.

This study addresses the recycling of construction waste wood and the development of thermal insulation materials by developing a high-belite sulfoaluminate cement-based recycled wood powder thermal insulation mortar (HRTM). High-belite sulfoaluminate cement (HBSC) and building gypsum (GY) were used as hydraulic binders, and recycled wood powder (RWP) was used as a full substitute for natural fine aggregate. The effects of the RWP-to-binder ratio (R/B) and GY replacement ratio on workability, mechanical properties, thermal insulation performance, water resistance, and drying shrinkage behavior were systematically investigated. The hydration products, pore structure, and microstructural evolution were characterized by thermogravimetry-differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and low-field nuclear magnetic resonance. Increasing R/B reduced dry density and thermal conductivity while improving water retention. The maximum water retention rate was 99.22% at R/B = 1/6 and 15% GY. The mechanical properties and drying shrinkage behaviour varied across the GY series and were influenced by GY replacement, water content, and PCE dosage. At R/B = 1/9 with 10% GY, HRTM exhibited a dry density of 992.19 kg/m³, a thermal conductivity of 0.253 W/(m·K), and a 28 d compressive strength of 23.8 MPa. The microstructural results showed corresponding changes in water-bearing hydration products, matrix continuity, and the RWP–matrix interface. These findings support the use of recycled wood powder in lightweight thermal insulation mortar.