*Article* **Utilization of Silicon Carbide Sludge as Metakaolin-Based Geopolymer Materials**

**Kae-Long Lin 1, Kang-Wei Lo 2,3,\*, Ta-Wui Cheng 3, Wei-Ting Lin 4 and Ya-Wen Lin 3**


Received: 10 August 2020; Accepted: 3 September 2020; Published: 7 September 2020

**Abstract:** The recycling of SiC sludge material is crucial for resource reutilization and environmental protection. In the current study, the effect of the mass ratio between the Na2SiO3 and sodium hydroxide (NaOH) solutions (NS/SS ratio) and the effect of SiC sludge on metakaolin geopolymers was comprehensively investigated to determine the underlying performance of the geopolymerization system. During thermal evolution, the second exothermic peak of 1.6NS10SCS (NS/SS ratio: 1.6, 10% SiC sludge) showed a heat evolution value of 990.6 W/g, which was the highest among other geopolymers. Additionally, the 1.6NS10SCS sample after 28 days of curing showed the highest flexural strength (6.42 MPa), compared to that of the others, and the DTA/TG (differential thermal analysis/thermogravimetry) results showed that the weight loss percentage increased to 14.62% from 400 to 750 ◦C. For the 29Si nuclear magnetic resonance deconvolution, 1.6NS10SCS exhibited high fractions of Q4(3Al) (33.63%), Q4(2Al) (23.92%), and Q4(1Al) (9.70%). Thus, the geopolymer with the optimal SiC-sludge replacement level and NS/SS ratio contained more macropores and geopolymer gels, which benefit structural development. The experimental results indicated that SiC-sludge can potentially serve as a partial replacement for metakaolin and exhibited favorable mechanic characteristics.

**Keywords:** utilization; SiC sludge; alkaline activator solutions; synergistic effect; geopolymer reaction
