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3.4. Effect of Declining Alkali Equivalent Given the simplified process for producing alkali-activated cementitious materials and the convenience of storing and transporting raw materials, only sodium silicate powder was used to prepare alkali activators in this study. Therefore, the silicate modulus (Ms) of alkali activators was a constant value and the ingredient of alkali activators could only be adjusted by AE. Considering the pulp waste proportion, the compressive strength, and the optimization of slurry texture, three kinds of slurries were selected as the samples to investigate the most suitable value of AE. Based on the results of the BFS substitution with waste mixtures in papermaking, the lime mud significantly improved the compressive strength of the slurry. Moreover, two SPW test groups and one PWM test group were used for AE adjustment. The waste substitutions were S7L3, S8L2, and PWM3-4. The content of AE in the activator decreased from 10% to 2%. The effects of AE on the compressive strengths are shown in Figure 10. When the content of AE exceeded 6%, the compressive strength increased as the AE decreased. The reason was the presence of excessive hydroxyl ions in the slurry, which could form carbonate on the sample surface by evaporation of water [19]. In addition, this reaction led to the destruction of the colloidal structure. With 6% of AE, the compressive strength reached its peak. This result is consistent with the best AE interval in a previous study [30]. However, S8L2 and PWM3-4 failed to harden after 24 h and could not be de-molded. This result suggested that the alkalinity of the activator was not sufficient to fully stimulate the activity of the BFS and lime mud, resulting in a dramatic decrease in compressive strength. Since the AE was 6%, the compressive strength could approach more than 65 MPa after 28 days of curing. 10 of 12 strength. Since the AE was 6%, the compressive strength could approach more than 65 MPa after 28 days of curing.
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Figure 10. The effect of different AE on the compressive strength. Figure10. The effect of different AE on the compressive strength. 4. Conclusions
4. Conclusions This study evaluated the potential of various wastes in papermaking to be alkali- activated as cementitious materials in terms of mechanical properties, flexibility, and sam- ple texture. The results expanded the knowledge boundary of paper waste reuse and demonstrated the potential advantages of using papermaking wastes as building materi- als (e.g., toughness enhancement and wood texture). Some experimental data (e.g., 6% AE, 20% waste addition) can also be used as a reference for the actual transformation of wastes in papermaking. However, the experimental findings have limitations in terms of This study evaluated the potential of various wastes in papermaking to be alkali- activated as cementitious materials in terms of mechanical properties, flexibility, and sample texture. The results expanded the knowledge boundary of paper waste reuse
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