Valorization of sugar beet waste as a foaming agent for metakaolin geopolymer activated with phosphoric acid: Fid-Bau Portal

Valorization of sugar beet waste as a foaming agent for metakaolin geopolymer activated with phosphoric acid

Rashad, Alaa M. / Gharieb, Mahmoud / Shoukry, H. / Mokhtar, M.M.

Highlights • It is possible to recycle carbonated lime residue as a foaming agent for MK-geopolymer. • The incorporation of CR reduced density, compressive strength and thermal conductivity. • The incorporation of CR increased water absorption and porosity. • The optimum ratio of CR was 6% which produced the lowest thermal conductivity (0.8 W/mK) • Specimens containing CR showed higher resistance against wetting/drying cycles.

Abstract This study is the first attempt to investigate the possibility of recycling carbonated lime residue (CR) (a by-product from the sugar beet-making industry) as a foaming agent. For this purpose, phosphoric acid (H3PO4) was used as an activator for metakaolin (MK) to obtain MK geopolymer pastes. Subsequently, the MK was partially replaced by CR at ratios oscillated from 2 wt% to 6 wt% with a step of 2 wt%. After suitable curing, the bulk density, compressive strength, water absorption, total porosity, and thermal conductivity were determined. Furthermore, the durability of this new type of foamed geopolymer was determined by the test of accelerated aging depending on wetting/drying cycling. The X-ray diffraction (XRD), thermogravimetric analysis/its derivative (TGA/DTG), scanning electron microscopy (SEM), and energy dispersive X-ray spectra (EDS) were used to analyze the results. The results confirmed that it is possible to use CR as a renewable foaming agent which can produce porous microstructure. The incorporation of 6 wt% CR showed the lowest thermal conductivity (0.08 W/mK), the lowest bulk density (631.5 kg/m³), the lowest compressive strength (2 MPa), the highest water absorption (35%), and the highest total porosity (61.2%). In addition, the specimens containing CR foaming agent showed superior durability as estimated from accelerating aging due to their porous microstructure which helped in facilitating water vapor mobility in and out of the geopolymer hardened skeleton.