Thermal and mechanical characterization of fly ash geopolymer with aluminium chloride and potassium hydroxide treated hemp shiv lightweight aggregate

Abstract

This research reports an experimental study on thermal and mechanical properties of Class C fly ash (FA) based geopolymer composited with hemp shiv, to develop as a sustainable building material. Hemp shiv, being applied as the lightweight aggregate, was treated by a new complex mineralizer, AlCl3 and KOH, prior to mixing with the FA. The treated hemp shiv to fly ash by mass ratio was 0.05, 0.10, 0.15 and 0.20 while the liquid alkaline (sodium hydroxide mixed with sodium silicate) to FA ratio used was 0.6. The result showed that the treatment product (aluminium chloride, Al(OH)3), formed on the hemp shiv surfaces, served as an effective moisture absorption barrier so the geopolymerization could satisfactorily occur. The SEM result revealed that the geopolymerization was retarded when the untreated hemp shiv was employed instead. Flexural strength of the geopolymer composites increased to around 3.55 MPa in the mixes with treated hemp shiv at the ratio of 0.05–0.15 (0.05 to 0.15 mix) before being degraded to the same level (2.42 MPa) of that of the reference (0 hemp shiv) in the 0.20 mix. Fracture toughness of the geopolymer composites had been improved steadily with an increasing amount of treated hemp shiv from 0.62 to 1.17 MPa∙m1/2. Thermal conductivity of the geopolymer composites was in the range of 0.36–0.25 W/m⋅K while thermal resistance was also acceptable until 200 °C. However, compressive strength and bulk density tended to decrease with an increasing amount of the treated hemp shiv, with those of 0.05, 0.10 and 0.15 mixes having met the requirements of the ASTM C129-99a: Standard specification for nonloadbearing concrete masonry units.