Effect of nano clay and PCE on the buildability of ultra-fine dredged sand-based 3D printing materials

Abstract

The use of ultra-fine dredged sand instead of natural sand in construction 3D printing materials can significantly reduce the cost. However, ultra-fine dredged sand has fine particles and high angular morphology, which can hinder the buildability and continuous printability of construction 3D printing materials. The addition of polycarboxylate superplasticizer (PCE) can effectively solve this problem. Considering that the change of PCE (content of 0, 0.1%, 0.2%, 0.3%) content has a great influence on the printing performance of mortar, in order to make up for this deficiency, nano clay (content of 0,1%) is added to the mortar. The experimental results showed that the addition of nano clay can significantly reduce the negative effects of PCE on the yield stress and apparent viscosity of 3D printing materials (3DPM). When the content of PCE is 0.2%, the addition of 1% NAC could increase the static yield stress and viscosity growth rate of 3DPM by 111.8% and 115.3% respectively. In addition, unconfined compressive strength test, isothermal calorimetry, Mercury invasion porosity method and thermogravimetric analysis were used to characterize the hardening properties of 3DPM. The results of heat of hydration showed that the addition of nano clay reduced the hydration exothermic peak of 3DPM, but increased the total heat release. The results of pore structure analysis showed that the addition of nano clay reduced the macropore (>1000 nm) of 3DPM from 19.31% to 18.82%. Thermogravimetric analysis showed that the addition of nano clay increased the hydration products. Therefore, the compressive strength of 3DPM was kept within an acceptable range. Finally, the laboratory’s printing results indicated that the 3DPM can print up to 20 layers continuously.