Acid-resistant clay bricks incorporating bottom ash and waste glass strengthened by mullite suppression and albite formation

This study reports a systematic investigation of vitrification-driven modification of fired clay ceramics through the co-utilization of lignite-derived bottom ash (BA) and post-consumer waste glass (WG). Clay bodies containing 2.5–10.0 wt% BA–WG (1:1 mass ratio) were fired at 900–1100 °C to evaluate their physical, mechanical, and chemical performance. The results reveal a competing mechanism within the clay matrix: at low additions (2.5–5.0 wt%), decomposition of BA-derived sulfate (SO 4 2- ) induces gas evolution and bloating, reducing bulk density. In contrast, at higher additions (7.5–10.0 wt%), the Na 2 O–CaO–SiO 2 -rich flux from WG dominates, promoting extensive vitrification and effective pore sealing. This vitrification-driven densification produces glass-rich matrices with reduced water absorption (∼7 %) and compressive strengths of 18–22 MPa, satisfying the minimum requirements of ASTM C62–17 for moderate-weathering clay bricks. Chemical durability is exceptional, with mass loss ≤ 0.02 % after acid immersion at pH 2 for 14 days. XRD and SEM analyses confirm that the high-flux BA–WG system fundamentally alters phase equilibria in the clay body, suppressing the formation of mullite—the typical reinforcement phase in clay and fly ash-based ceramics—and instead promoting a distinct strengthening mechanism: a continuous glassy matrix reinforced by crystalline albite (NaAlSi 3 O 8 ). This vitrification–albitization pathway, distinct from conventional crystalline-reinforcement routes, provides a clay-centered route for producing mechanically robust and acid-resistant fired ceramics while valorizing two industrial waste streams, bottom ash and waste glass. • First systematic study on BA–WG synergy in fired clay ceramic vitrification. • WG fluxes seal BA-induced pores, creating dense, glass-dominated microstructures. • BA–WG bricks achieve 18–22 MPa and high acid resistance (≤0.02% weight loss). • Mullite is suppressed; strength arises from an albite-reinforced glassy matrix. • Establishes a vitrification–albitization pathway turning BA/WG into durable ceramics.