Synthesis and performance evaluation of a superplasticizer prepared from coal-based humic acid

Superplasticizers (SPs) are indispensable in modern concrete technology. A novel, cost-effective method for synthesizing a high-performance SP using coal-based humic acid (CHA) derived from lignite is presented. Through oxidative depolymerization of lignite to prepare CHA, followed by sulfomethylation and condensation reactions, a CHA-based SP (called SP(CHA)) was successfully developed. Structural characterization confirmed the successful synthesis of CHA and its transformation into SP(CHA). Notably, the CHA demonstrated superior sulfomethylation reactivity compared with a commercially available sodium humate (NaA). Performance evaluations showed that the synthesized SP(CHA) outperformed both a commercial sulfonated naphthalene–formaldehyde condensate and SP(NaA) in terms of water-reduction efficiency, slump retention, and enhanced long-term compressive strength. Specifically, SP(CHA) achieved a water-reducing rate of 16.4% and a 28-day compressive strength improvement of 23.2%, exceeding the benchmarks for high-efficiency water reducers. By harnessing abundant and low-cost lignite resources, the approach holds substantial promise for advancing sustainable construction practices.