Compressive strength of high strength class C fly ash-based geopolymers with reactive granulated blast furnace slag aggregates designed by Taguchi method

•Geopolymers were produced by class C fly ash and granulated blast furnace slag.•Taguchi method for evaluating more influencing factors with fewer experiments.•High performance specimens with the strength more than 70 MPa were achieved.

Compressive strength of geopolymeric specimens produced by class C fly ash and granulated blast furnace slag aggregates has been studied. Four different independent factors comprising of aggregate content, sodium hydroxide concentration, curing time and curing temperature were considered as the variables. To attain the maximum possible accurate responses by means of the smallest amount of examinations, Taguchi design of experiment method was followed. By taking into account three levels for each factor, 9 series of experiments were conducted on the specimens at 2 and 7 days of water curing regime. For both considered regimes, a specimen with 30 weight percent of aggregate and sodium hydroxide concentration of 12 M cured at 90 °C for 16 h had the highest compressive strength. On account of reactivity between aggregates and the fly ash, the compressive strength was reached to 69.3 ± 5.3 MPa and 76.2 ± 3.6 MPa at 2 and 7 days of water curing, respectively. Fracture surface of specimens with the highest and the lowest strengths as well as effect of each considered factor on the compressive strength of the specimens were studied.