A comparative study of compressed lateritic earth bricks stabilized with natural pozzolan-based geopolymer binders synthesized in acidic and alkaline conditions

Abstract

Two geopolymer binder systems made under alkaline and acidic conditions have been evaluated for the stabilization of compressed lateritic earth bricks (CEBs) using natural pozzolan as aluminosilicate precursor. The preparation of alkaline and acidic activators involved the combination of sodium silicate and 10 mol/L sodium hydroxide solutions, as well as 10 mol/L phosphoric acid solutions, respectively. CEBs were prepared to comprise different proportions of natural pozzolan of 5, 10, 15, and 20 %. The physico-mechanical and mineralogical properties of compressed earth bricks were studied using the compressive strength, the dry and wet bulk density, the water absorption rate, Fourier transform infrared spectroscopy (FTIR), powder X-Ray Diffraction (PXRD) and optical microscopy (OM).The results showed that in the acid environment, the mechanical performance increased considerably with the pozzolan content and slightly with the curing time, whereas in the alkaline environment these performance decrease for the sample with 0 to 10 % of pozzolan and remain constant for the sample with 15 to 20 % of pozzolan after 14 days of curing. The utilization of acid-activated geopolymer binder in the production of laterite-based compressed earth bricks has been shown to be more effective compared to the utilization of an alkali-activated geopolymer binder. The high performance of acid-stabilized CEBs is related to the best reactivity of natural pozzolan in acid medium allowing the formation of Al-O-P bonds.