Recycling and utilization assessment of steel slag in metakaolin based geopolymer from steel slag by-product to green geopolymer

This paper presents an experimental study that aimed to recycle steel slag waste as a supplementary material in metakaolin based geopolymer, resulting in a new type of geopolymer composites. The mechanical properties and microstructure analysis of geopolymer composites were carried out. The metakaolin based geopolymer composite (MGC) was prepared by a three-key parameter (the mole ratios of SiO2/Al2O3, Na2O/SiO2, and H2O/ Al2O3) composition design method. The flexural strength and compressive strength test results show that the strength increment of MGC after 3 days is very limited. MGC exhibits the typical early strength property on compressive strength. Then, the steel slag powder (SS) was added to replace metakaolin to synthesize the steel slag-metakaolin based geopolymer composite (SSMGC) with the determined mix proportion. The strength test results indicate that the incorporation of SS contributes to the strength increment at a later age than MGC. The XRD patterns, SEM images, and EDS line scanning analysis indicate that SSMGC undergoes hydration in alkaline solution and accumulates hydrated calcium silicate gel with curing age besides the silica-alumina gel generated during geopolymerization. Due to the low content and low activity of steel slag active components, the degree of hydration and the amount of calcium silicate gel are inferior to the geopolymerization and silica-alumina gel caused by metakaolin, and ultimately lead to the relatively lower strength of SSMGC than that of MGC. However, the negative effect of adding SS to MGC on the mechanical strength becomes very small with curing age.

Automated summary

This paper presents an experimental study on recycling steel slag waste as a supplementary material in metakaolin based geopolymer to create a new type of composite material. By analyzing the strength and microstructure of two different composites, it was found that the incorporation of steel slag into the geopolymer resulted in lower strength compared to the geopolymer without steel slag at early ages, but the negative effect decreased with curing age.