Pre-treatment and utilization of recycled fine glass dust for 3D Concrete Printing

Abstract

The first part of this thesis investigated different pre-treatment methods of the fine glass dust in order to increase the reactivity when it was used as a cement replacement in cementitious mixtures. The results showed that the optimal pre-treatment for the fine glass dust was a heat-treatment at 600∘C for 1 hour combined with a grinding treatment of 1 hour. The heat-treatment was efficient in removing the organic compounds from the fine glass dust and the grinding treatment was efficient in reducing the particle size of the fine glass dust. The second part of this thesis investigated the influence of different cement replacement percentages by pre-treated fine glass dust in cementitious mixtures. Results showed that higher FGD percentages resulted in a reduction in compressive strength. However at longer curing ages (between 28 and 90 days) a small increase in strength development was observed. This could be attributed to the pozzolanic activity of the fine glass dust, which caused secondary strength development at later curing ages. It was also shown that significant amounts of secondary products were formed in the mixture with 25% FGD, which caused volume instability of the mixture. For the mixture with 10% FGD no volume instability was observed. The third part of this thesis investigated the suitability of pre-treated fine glass dust for 3D Concrete Printing using the set-on-demand printing technique. For the mixture with 50% FGD in the cementitious mixtures it was found that a superplasticizer (SP) dosage of 0.4% was sufficient to develop a pumpable cementitious mixture. For the mixture with 20% FGD, this SP dosage was found to be 0.35%. As a combination of cementitious mixture with an accelerator slurry with 10% and 8% CaCl2, Mix FGD50- SP0.35-Acc10% and FGD20-SP0.35-Acc8% provided promising results in terms of fast stiffness and strength development. Due to volume instability of the FGD50 mixture, only mix FGD20-SP0.35-Acc8% was tested on printability. This mixture proved to be printable with a nozzle moving speed of 3600 mm/min and a time interval between layers of 18.8 seconds. Therefore a 20% replacement of Portland cement with fine glass dust could be used to develop a printable cementitious mixture for 3DCP. The fourth part of this thesis discussed the applicability of the developed mixture in practice. A concrete bus shelter was used as a case study and it was shown that the mixture developed enough strength to withstand the stresses of the designed structure. The developed mixture FGD20-SP0.35- Acc8% was promising for implementation in 3DCP in terms of sustainable development of the concrete industry and as a new utilization of a byproduct from the glass recycling industry