Optimizing a hybrid mortar for an alkali-activated material by papermaking process wastes and blast furnace slag utilizing Taguchi–Grey relational analysis method

Different types of papermaking process wastes (PPWs) are generated in the paper industry. The compositions of the waste materials vary significantly depending on the source of the waste materials. To date, a standard methodology for the comprehensive assessment of the recovery potential of the waste materials generated has not been established. This research adopted the Taguchi–Grey relational analysis method to evaluate and efficiently recycle and reuse these wastes systematically. With regard to the development of the PPW- blast furnace slag (BFS) hybrid system, four types of PPWs, namely lime mud (LM), primary sludge (PS), fly ash (FA), and bottom ash (BA), were systematically utilized. Herein, the setting time, compressive strength, flexural strength, and shrinkage of the mortars that were based on the PPW-BFS hybrid system are analyzed. The results revealed that different factors affected different mortar properties. The setting time was primarily affected by the PS content, the BA content significantly influenced the compressive and flexural strengths, and the BA and LM contents exerted effects on the degree of shrinkage of the materials. The optimal PPW–BFS mortar composition was determined (LM: 5%; PS: 5%; FA: 30%; BA: 10%). It was observed that the optimal mortar composition attained a strength grade of M30, with successful mitigation of premature stiffening and volume shrinkage in the hybrid system.