Characterization of alkali bonded expanded perlite

The thermal and mechanical properties of a lightweight alkali bonded material were investigated in correlation with the microstructure and porosity. The material was produced using fine granules of expanded perlite as raw powder and potassium di-silicate aqueous solution as alkaline activator, instead of the commonly used sodium silicate, to improve thermal performances. After consolidation, the material was subjected to microstructural analyses, as well as to thermo-physical and mechanical tests. Density was 467 40 kg(-1)m(-3), the total porosity 80 vol%, the average pore size 0.24m and compressive strength was 1.5 0.5 MPa. It was observed that, besides the action of potassium di-silicate as an alkali binder, expanded perlite granules reacted on the surface forming geopolymer nano-precipitates. Laser Flash Method was employed to evaluate the whole thermal behavior within the temperature range 25-550 degrees C: thermal conductivity was 0.084 m(-1)K(-1) at 25 degrees C and 0.121 Wm(-1)K(-1) at 550 degrees C. At high temperature, the thermal conductivity resulted similar or even lower when compared with commercial perlite - sodium silicate materials with lower densities in the range 180-260 kg/m(3). Results show that lightweight alkali bonded expanded perlite materials can be produced with improved thermal properties by exploiting potassium silicate and overcoming the poor temperature resistance of organic binders. (C) 2018 Elsevier Ltd. All rights reserved.