Assessing influences of different factors on the compressive strength of geopolymer-stabilised compacted earth

Building with earth is an ancient technique which has been the object of numerous studies during the last decade, due to sustainable properties of the material. To improve the mechanical properties and the durability of earthen material, hydraulic binders are usually added (e.g. cement or lime). Other binders with lower carbon footprint are investigated to reduce the environmental impact of stabilised earth material. The present paper investigated a geopolymer-stabilised compacted earth (GSCE). The geopolymer was obtained by using fly ash and an alkaline activator solution (a mixture of Na 2 SiO 3 and NaOH). First, a parametric study was performed to identify the important factors to be investigated. Then, 360 specimens were manufactured and tested under uniaxial compression, to investigate influences of different factors on the compressive strength: Na 2 SiO 3 /NaOH ratio (1, 1.5 and 2); the mixing procedure; curing temperature (ambient, 60 and 90 °C) and evolution of compressive strength as a function of time (7, 14, 28, 56, 90 and 180 days). The scanning electron microscopy, X-ray diffraction and Fourier-transform infrared spectroscopy techniques were applied to investigate the microstructure of GSCE specimens. The geopolymerisation in the specimens was verified by using these techniques. It was shown that the chemical bond C-H (a product of reactions between the activator and CO 2 in the air) influenced the evolution of the compressive strength in function of time. The results showed, that after 28 days, the compressive strength of GSCE continued to increase 20–25% until 56 days. The unstabilised and cement-stabilised specimens were also tested and compared with GSCE specimens.