Rice-husk-based superplasticizer to increase performance of fly ash geopolymer concrete

Workability is a major drawback of fly-ash-based geopolymers due to high viscosity. In this research, a new type of superplasticizer is developed to overcome this workability issue. Due to the high viscosity of geopolymeric binder structures, none of conventional superplasticizers was found effective in maintaining the viscosity of the mixture. The novel hybrid superplasticizer was developed by utilizing agrowaste – that is, rice husk – and an alkaline activator. Characterization studies [by X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscope] of the material indicated that the amorphous silica from rice husk reacts with the alkaline activator – that is, sodium hydroxide – and results in the in situ synthesis of sodium silicate and lignin. The developed superplasticizer was used in different percentages in fly-ash-based geopolymeric systems to study its engineering properties. The workability of the fresh geopolymer concrete was measured using the slump cone test method as per IS 1199-1959, while the compressive strength was evaluated as per IS 516-1959, and it is reported that the workability of the geopolymer concrete was improved significantly compared to that of conventional geopolymeric systems. In the present work, an attempt has also been made to establish a working mechanism for the developed superplasticizer with geopolymeric systems, which indicated its compatibility with [–Si–O–Al–O–]_n networks.