Quick nozzle mixing technology for 3D printing foam concrete

Foam concrete has begun to be combined with 3D printing technology considering multiple advantages, including fire resistance, thermal insulation, sound absorption, and environmental friendliness. However, the traditional production and pumping processes could be challenging. This study attempted to simplify the foaming process using the Quick Nozzle Mixing technology (QNM) with Sodium dodecyl sulfate (SDS) as a foaming agent. First, the surface tension of mixing water with varying dosages of SDS was evaluated. Secondly, the effects of mixing methods on the wet density, flowability, foaming efficiency, and compressive strength of concrete with SDS were investigated. Results show that QNM is a feasible approach directly to producting and printing foam concrete with a low wet density of 1500 kg/m(3) and printed compressive strength of 3.5 MPa. Regardless of mixing methods, the critical micelle concentration of SDS dominated the development of flowability, wet density and compressive strength. When the SDS dosage was beyond the critical value, these properties notably changed with increasing SDS dosages. Regarding the Quick Mixing Method, the mixing duration regulated the foaming effect of SDS in concrete. The compressive strength decreased with mixing duration; this effect became more pronounced by increasing SDS dosages. Finally, a relationship was found between compressive strength and wet density that held regardless of mixing method and SDS concentration.