Use of municipal solid waste incineration ash in 3D printable concrete

Concrete 3D printing is an application of 3D printing technology for the construction of concrete structural and non-structural elements. It is a rapid method of construction without the use of formwork, with minimum labor involvement and reduced material wastage. Curved walls and complex structures can be constructed by modifying the print path and controlling the rheological properties of concrete. The fusion of this technology with waste materials is necessary to reduce the problems associated with the recycling of wastes and to minimize CO2 emissions associated with the production of cement. In this study, two different municipal solid waste (MSW) incineration ashes (fly ash and bottom ash) were used to develop a concrete having rheological and hardened requirements of concrete used in 3D printing. Waste incinerator ashes were added as a substitute of ordinary Portland cement in concrete mix proportions. Flow table test and Gilmore needle test were used to measure the flow and setting time of concrete, respectively. Yield stress was measured by shear vane test. The buildability of ash containing printable concrete was simulated by comparing the vertical stresses due to the printing of concrete layers with the increase in the strength of the first stacked layer. Workability, open time, and buildability of the mix proportions were related to yield stress. The effect of adding waste incinerator ash upon the compressive strength was measured. The bond strength between layers at different printing time gaps was evaluated using bi-surface direct shear test. Experimental results showed that setting time promoting effect and initial yield stress enhancement by incinerated fly ash allows for a rapid construction speed with concrete 3D printing. This study concludes that incinerated fly ash can be successfully recycled in 3D printable concrete due to its favorable effects on rheology which are favorable for printing concrete.