Synergistic dewatering of construction foundation sludge via tripartite strategy: high-efficiency flocculation and floc skeleton reinforcement mechanism

s In construction engineering, the disposal of waste slurries (particularly drilling-derived pile foundation sludge) poses significant environmental and resource challenges, necessitating efficient dewatering solutions. Conventional methods often prove inadequate for treating this inorganic-dominated sludge with poor natural separation capability. This study developed an amphoteric flocculant (PAAD) capable of auto-adapting to colloidal charges in sludge, coupled with a synergistic reagent combination strategy (PAAD/PAC/CaCl 2 : polyacrylamide/polyaluminum chloride/calcium chloride) to optimize dewatering performance. Systematic evaluation of key dewatering indicators including supernatant turbidity, specific resistance to filtration (SRF), sludge cake moisture content, floc settling velocity, and particle size distribution (d₅₀) demonstrated superior performance over conventional single-flocculant. The optimized system achieved remarkable metrics, turbidity: 6.5 NTU, SRF: 0.82×10¹¹ m·kg⁻¹, sludge cake moisture content: 30.28%, settling velocity: 0.54   cm/s, and particle size distribution (d₅₀): 70.77 μm. This tripartite strategy reduces chemical consumption by 66.7% compared to PAAD flocculant, offering sustainable sludge management for river channel engineering. Mechanism investigations revealed distinct roles of each component: PAAD dominated through charge neutralization and interparticle bridging, PAC enhanced charge neutralization via double-layer compression, while CaCl 2 exhibited multifunctional effects. Notably, CaCl 2 triggered pozzolanic reactions with inorganic constituents, generating high-density acicular solids that reinforced floc skeletons and created water-release channels. This tripartite synergy established a robust porous framework, significantly improving floc stability and dewatering efficiency.