Scale-up experiments of expanded perlite-geopolymer composite block with special regard to the effect of water

Abstract

Water is essential for improving the workability of lightweight geopolymer composites and the formation of the sodium aluminosilicate hydrate (N-A-S-H) gel. On the one hand, this study presents a technology for producing scaled-up composites with ultra-high lightweight aggregate content, highlighting the importance of the correct mixing sequence of components and spraying technique. On the other hand, it also reports and discusses the properties of a lightweight geopolymer composite with ultrahigh lightweight aggregate content with special regard to the effect of water on the mechanical properties and microstructure of the composites. Composite panels were prepared using expanded perlite (EP) as lightweight aggregate and mechanically activated fly ash-based geopolymer (GP). The composite was characterised in terms of uniaxial compressive strength, flexural strength, density, microstructure, water absorption, and thermal conductivity. The thermal conductivity of the lightweight geopolymer composite was 0.107 W/m K. The maximum compressive strength of the composite was 527 kPa with an average density of 228 kg/m 3 . The flexural strength reached its maximum of 437 kPa. Based on the results of compressive strength tests in two different water saturation states, direct contact with water had a slightly negative effect on the compressive strength. However, in the air-dry state, the strength of the composite regains 83–96 % of the reference value. The Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) results proved the formation of the main geopolymerisation reaction products in the composite matrix. Being in contact with water weakened the strength of the N-A-S-H gel and caused the formation of sodium carbonate crystals in the matrix as a result of the reaction of free alkali ions and CO 2 absorbed from the atmosphere. Based on the results, using fly ash-based geopolymer as a binder and expanded perlite in large proportions, a lightweight composite can be produced that has suitable mechanical properties and thermal conductivity properties for thermal insulation. • The developed technology made it possible to produce composites with ultra-high lightweight aggregate content. • The long-term properties and the effect of water on the properties of the EP-GP composite were studied. • Lightweight geopolymer composites with excellent mechanical properties and good durability were formulated. • The water helped to transport the unreacted Na + to the surface of the composite, which appeared there in the form of NaHCO 3 . • Water causes a small loss in the strength of the EP-GP composite.

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