Utilization of agricultural wastes as fiber, binder and aggregates of geopolymer mortars: Application of taguchi method for strength and durability optimization

Abstract

The present study deals with the compressive strength, flexural strength, capillary water absorption, dry shrinkage, resistance to freeze-thaw cycles, and high temperature resistance of geopolymer mixtures based on agricultural wastes. For the construction of geopolymer mixtures, rice husk ash was used as binder, corn stalk was used as aggregates, and wheat straw, barley straw, and sugarcane straw were used as fibers. Since geopolymer mixtures might be influenced by many factors, the present study used the Taguchi method to design experiments, to optimize factors, and to predict properties so as to avoid the relevant full-fledged experimental works. The present study took into account the factors of curing method (heat curing and ambient curing), concentration of sodium hydroxide solution (6, 9, and 12 M), mass ratio of sodium silicate to sodium hydroxide (2, 2.5, and 3), mass ratio of alkaline activator to binder (0.3, 0.4, and 0.5), mass ratio of aggregate to binder (1, 2, and 3), type of fiber (wheat straw, barley straw, and sugarcane straw), and fiber volume (0, 4, and 8% in terms of the binder weight) as inputs for Taguchi analysis. Given the number and levels of considered factors, 18 mix designs were examined on the basis of the L18(63×12) orthogonal array proposed by Taguchi. The results indicated that the optimal levels of the factors of curing method, concentration of sodium hydroxide solution, mass ratio of alkaline activator to binder, and mass ratio of sodium silicate to sodium hydroxide for almost all tests were respectively equal to heat curing, 12, 0.5, and 3, while the optimal levels of other factors were variable depending on the type of test.