In this study, geopolymers were reinforced with artificial aggregates, and the effect of the coating of the aggregates with various solutions on the strength of the composites was analyzed. The applied alkaline coating solutions were sodium silicate and NaOH. The composites made with coated aggregates had a higher compressive strength than specimens made with pure aggregates, regardless of kinds of coating solutions. That was possible because the geopolymers paste kept their fluidity during the forming process; thus, the coating layer of the aggregates prevented the aggregates from absorbing water. In addition, a high concentration of NaOH in the vicinity of the boundary between the matrix and the aggregates enhanced the geopolymeric reaction, which in turn increased the compressive strength of the composites. In particular, when the geopolymer was combined with aggregates coated with NaOH of 16 M, the resulting composite had a compressive strength of 32.2MPa, which is about six times higher than that of composites with pure aggregates. With the advantage of light weight, the composites fabricated in this study can be used in various fields, such as insulation boards, sound proofing materials, fire protecting materials, and chemically resistant materials.

Keywords: Aggregate, Coating, Geopolymer, Coal Ash.