Development Of Alkali-Excited Industrial And Agricultural Waste Based 3D Printed Geopolymer And Design For 3D Printer

As a kind of low-carbon building materials,geopolymer materials are widely used in the field of construction engineering.However,ordinary geopolymer materials have problems such as low printability,poor constructability,easy cracking and high density when used in 3D printing.In order to solve the above problems,research is mainly carried out from the perspectives of light,crack resistance,printability and constructability.Kenaf has widely cultivated throughout China,but it failed to get effective utilization.In this paper,kenaf fiber（KF）is intended to substitute the high-cost fiber to improve crack resistance of the 3D printed geopolymer material,while kenaf stalk core（KSC）is used to replace the limiting river sand providing skeletal support.In this way,alkali-excited industrial and agricultural waste based3D printed geopolymer（AIAW-3DPG）was developed.It can not only improve the shortcomings of common geopolymer materials,but also realize the large-scale and industrial utilization of kenaf straw,which reflects the important concept of complementary and sustainable development of industry and agriculture.In this paper,the effects of KSC dosage,KSC particle size and KF dosage on the working performance of AIAW-3DPG were analyzed through experiments.The KSC dosage,particle size and KF dosage that can be used for 3D printing were preliminarily determined.On this basis,the effects of KSC and KF on the printability,constructability,dry density and mechanical properties of AIAW-3DPG were further studied.Based on the experiment mixed with KSC and KF,the effects of alkali activator dosage（10 wt.%,15 wt.%,20 wt.%of the total mass of GGBFS and FA）and mass ratio of GGBFS to FA（15:85,20:80,25:75）on the working performance,microscopic properties,physical properties and mechanical properties of AIAW-3DPG materials under the same fluidity were analyzed.The main work and conclusions are as follows:（1）In order to study the AIAW-3DPG,this paper developed a low-cost 3D printer that is convenient for 3D printing materials development based on the operation characteristics and working principles of the commercial construction 3D printer.It has been continuously optimized in printing practice for many times,and has achieved good operation effect.（2）Research results of AIAW-3DPG mixed with KSC and KF simultaneously showed that as follows:Kenaf straw contained light KSC and high strength KF,which contributed to the working performance and crack resistance of it.After adding 1.5 wt.%KSC and 0.2 wt.%KF of the mass of slag and fly ash into the geopolymer material,the setting time can be shortened by 68%to achieve the effect of fast setting.Meanwhile,it is beneficial to reduce the apparent viscosity of geopolymer slurry in the extrusion stage and improve the viscosity recovery ability in the printing stage.The skeleton function of KSC in AIAW-3DPG and the bridging function of KF in shape retention and cracking resistance were revealed.The cooperation of KSC and KF significantly improves the constructability of continuous multilayer printing of AIAW-3DPG,and the thickness shape retention ratio six-layer continuous printing specimens is up to99.06%.（3）The optimization experiment results of the AIAW-3DPG show that as follows:The fluidity of AIAW-3DPG decreased slowly with the increase of alkali activator content,and the best printability and constructability can be obtained when the flow rate was controlled at 140～180 mm.AIAW-3DPG is lightweight with a maximum dry density of 1491.4 kg/m~3.When the content of alkali activator is low（10 wt.%）,there were a lot of unreacted“ball shaped”fly ash in AIAW-3DPG,and the structure is loose.Under the condition of high dosage of alkali activator（15 wt.%,20 wt.%）,the reaction degree of the system can be improved obviously by increasing the mass ratio of GGBFS to FA,and more gel can be formed,the compactness of the material can be improved.With the increase of alkali activator dosage and mass ratio of GGBFS to FA,the compressive strength and flexural strength of printed materials are increased.Taking printability,constructability,physical and mechanical properties and economic amount of alkali activator into consideration,it is recommended to use 15 wt.%alkali activator and25:75 of mass ratio of GGBFS to FA prepare AIAW-3DPG.In other words,the adopted technical route is to reduce the amount of alkali activator and increase mass ratio of GGBFS to FA.Compared with common cement-based materials,the CO₂ emission of the optimized AIAW-3DPG is lower,and the CO₂ emission reduction rate per unit volume（m~3）is 39.77%.The innovation of this paper is discussed as follows:（1）Proved the working mechanism of KSC and KF in 3D printing fly ash based geopolymer materials,revealed the skeleton function of KSC and the bridging function of KF,reflecting the important concept of complementary and sustainable development of industry and agriculture.（2）A kind of 3D printed material mixture ratio with excellent working performance and low cost was optimized by improving the mass ratio of GGBFS to FA and reducing the dosage of alkali activator.