Strength and network evolution of waste glass powder activated by rice husk ash-derived sodium silicate

Under the condition of an approximately constant NaO equivalent, with waste glass powder as the sole precursor, rice husk ash-based sodium silicate combined with NaOH was used to prepare rice husk ash-based sodium silicate-activated glass powder cementitious materials (RAGP) with moduli of 1.0, 1.5, and 2.0. Compressive strength, XRD, FTIR, and XPS analyses were performed to characterize the strength development and silicon-oxygen network evolution at 7 d and 28 d. The results show that the 7 d compressive strength decreased from 31.4 MPa to 29.6 MPa as the modulus increased; at 28 d, RAGP-1.5 achieved the highest compressive strength of 39.6 MPa, corresponding to an increase of 31.1%. Compared with the raw glass powder, the centroid of the amorphous diffuse peak of the hardened RAGP shifted toward higher angles by 2.13°–2.33°, while the centroid difference among the different mix proportions did not exceed 0.19°, indicating that alkali activation altered the amorphous scattering environment of the glass powder without inducing a resolvable crystalline phase transformation. The main Si-O-T band of all specimens was located at 973–981 cm and did not exhibit a consistent shift with curing age. In addition, the bridging oxygen ratio at 7 d decreased from 55.38% to 50.40% as the modulus increased; at 28 d, the bridging oxygen ratio of RAGP-1.5 reached 63.25%, an increase of 10.47% relative to 7 d, consistent with the ranking of compressive strength. A higher NaOH proportion was favorable for early-age depolymerization of the glass network, whereas the later-age strength depended on the balance between continued glass dissolution and polycondensation of soluble silicon; within the present mix design range, the activator composition with a modulus of 1.5 yielded the highest 28 d compressive strength and the largest increment in bridging oxygen.