MODELLING AND OPTIMIZATION OF FRESH AND MECHANICAL PROPERTIES OF FIBER REINFORCED GEOPOLYMER MORTARS FOR UTILIZING IN 3D CONCRETE PRINTING TECHNOLOGY

Abstract

The purpose of the thesis is to develop carbon fibre reinforced geopolymer mixtures for 3D printing. The effects of alkaline activators (NaOH and Na2SiO3 solutions) and carbon fibre on fresh and hardened properties were investigated experimentally. Various fresh properties, including setting time, workability, extrudability, open time, shape retention, and rheological characteristics such as shear stress and apparent viscosity were examined. For hardened state testing, the specimens produced through 3D printing and mould casting. They were subjected to mechanical (compressive strength, flexural strength, splitting tensile strength) and durability related testing (UPV, water absorption, sorptivity, chloride penetration) procedures. Various combinations and molarities of NaOH and Na2SiO3 were employed to activate a mixture of ground granulated blast furnace slag (GGBFS) and fly ash (FA). The molarities of NaOH were used as 8, 10, and 12 M. The Na2SiO3 / NaOH ratios were selected as 1 and 2, while the carbon fibre volume fractions were employed at 0, 0.3, and 0.6%. The incorporation of carbon fibres has been observed to improve the rheological characteristics, specifically in terms of shape retention. Nevertheless, incorporation of carbon fibre led to a decrease in the workability of mortars and had an adverse impact on the extrudability qualities of geopolymers. Furthermore, the addition of carbon fibre also led to a slight decrease in compressive strength. The findings of the study also indicated that the enhancement of the molarity of NaOH had a positive impact on many fresh properties of the mixes, including shape retention, apparent viscosity, shear strength, and compressive strength. The results indicated that the strength and durability properties of 3D printed samples were less than those of mold-cast due to weak interfaces between layers. Meanwhile, the incorporation of carbon fibres has been observed to improve flexural and tensile strength. Moreover, the examination of the microstructure by scanning electron microscopy (SEM) demonstrated a satisfactory level of density and appropriate interconnection at the microstructural level among the components forming the geopolymer matrix. The thesis also includes a Response Surface Method based optimization study to determine performance based optimum mix parameters of the geopolymer mortar to be used for 3D printing purpose.