Low-cost lightweight geopolymer mortars based on Ground Granulated blast-furnace slag, calcium carbonate, and silica sand flour were investigated as lightweight building material. The effect of two chemical foaming agents such as hydrogen peroxide (H2O2) and sodium perborate tetrahydrate (NaBO3.4H2O) on bulk density, porosity, and compressive strength was studied. FTIR, XRD, XRF, and SEM were used to investigate the raw materials and selected samples of prepared lightweight geopolymers. The use of grinding calcium carbonate and silica sand flour enhanced the compressive strength, workability, and homogeneity of the geopolymer.

The lightweight geopolymer given about 3.30 - 17.60 and 1.70 - 6 MPa of compressive strengths at 28 days of curing with bulk densities from 584 to 1340 kg/m3 and 745 to 1770 kg/m3 in the case of hydrogen peroxide and sodium perborate mixes, respectively. The images of morphology and microstructure results indicate that the porosity and pore size increase with the increase of the foaming agent due to the release of oxygen gas upon its decomposition. According to the results of bulk density MC-H1, MC-H1.25, and MC-B2.5 mixes can be considered ultra-lightweight geopolymers with proper compressive strength. The results show that hydrogen peroxide mixes have better performance in the physico-chemical and mechanical properties than sodium perborate mixes.