Void Structure and Strength of Foam Geopolymer Concrete: Impact of Using Different Binder and Filler Types

A study has been undertaken to investigate the effect of using different types of binder by changing the source materials (fly ash and metakaolin individually or in combination) on the void structure and strength of geopolymer foam concrete made at a density of 1,000 kg/m3. For a given binder type, the effect of using different types and fineness of filler (natural fine sand and silica sand) was examined as well. Nine mixes made with different binding mediums and fine aggregate types were designed by adopting an absolute volumes method and produced with preformed foam technique at a density of 1,000 kg/m3. The results show that the pore merging is more evident in foam concrete mix (FC) rather than geopolymer foam concrete mixes (FGC). The irregularity of voids for FGC was less than that of FC, indicating that the void merging is greater in foam concrete mix. The reduction in pore diameter (D50 and D90) is clearly linked to the increase in compressive strength, implying that the effect of geopolymer medium type was significant. The finer pore size distribution was for the foam geopolymer mix produced with 75% metakaolin and 25% fly ash (type C) as binder paste, which gained the highest strength of 7.4 MPa (125% of conventional foam concrete). In terms of fine aggregate type, use of silica sand increased the compressive strength by approximately 28%–30% for foam fly ash or metakaolin based geopolymer mixes compared to the corresponding mixes made with the natural fine sand.