Toward high-performance green building: Influence of geopolymer and straw fiber on mechanical and thermal performance

Abstract

Raw earth bricks were stabilized with a kaolin-based geopolymer binder activated by an alkaline solution, then reinforced with straw fibers to improve their mechanical and thermal performance. Formulations were prepared with a geopolymer content ranging from 0 % to 6 % by weight. The optimum 6 % formulation was combined with straw fiber contents ranging from 0 % to 1.5 % by weight. Samples were characterized for density, thermal conductivity, thermal diffusivity, mass heat capacity, volumetric heat capacity, thermal effusivity, compressive strength, and tensile strength. Incorporating the geopolymer significantly improved mechanical properties, with increased compressive strength from 0.892 MPa to 3.076 MPa and tensile strength from 0.114 MPa to 0.624 MPa. In parallel, a slight increase in thermal conductivity was observed, reaching 0.629 W/m.K for sample G6. Adding straw fibers to formulations containing 6 % geopolymer enabled a progressive reduction in thermal conductivity, reaching a minimum value of 0.316 W/m.K for 1.5 % fibers (G6F6). The volumetric heat capacity increased significantly to 3.0013 × 10⁶ J/m³ .K. At the same time, the thermal effusivity reached 973.12 W.s ¹ ᐟ²/m².K. Mechanically, tensile strength continued to grow with the addition of fiber, reaching 0.923 MPa. In contrast, compressive strength peaked at 5.217 MPa at 0.75 % fiber (G6F3) before decreasing at higher contents. These results show that an optimum compromise between thermal and mechanical performance is obtained for a straw fiber content of 0.75 % and 1 % by weight.