A Master of Science thesis in Civil Engineering by Aktham S. Alchaar entitled, “Evaluation of 3D Concrete Printing in the United Arab Emirates”, submitted in February 2020. Thesis advisor is Adil Al-Tamimi. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).
3D concrete printing has been recently studied as a new scheme of construction. The automated nature of such technique allows for reductions in waste generation, less manpower requirements, and fabrication of complex geometries. However, the use of concrete for this application is challenging. The material shall be flowable for ease of extrusion. Printed layers shall preserve their shape and rapidly attain strength to bear their own weight and the subsequent layers. However, there is a lack of guidance on the design of 3D printing concrete mixes. In addition, the change in performance of 3D printing concrete under different environmental conditions is still generic. The aim of this research is to develop a concrete mix using local materials, and to evaluate it in two environmental conditions: ambient and site conditions. The experimental program addressed fresh state properties through flow table, open time, extrudability, and shape stability. Compressive strength, flexural strength, and interlayer bond shear strength have been evaluated as mechanical properties in this research by testing a total of 61 specimens. A novel test setup was designed for bond strength evaluation at different printing time intervals. 19 trial mixes were performed, and one mix was chosen as the optimum based on extrudability and shape stability/quality. It was observed that inclusion of fibers enhances shape stability, but higher dosages of superplasticizer become required. It was found that flow table and open time of site conditions decreased by 9% and 16% respectively, compared to ambient flow table (86%) and open time (7.2 minutes) on average. This was owing to accelerated loss of flowability. Shape retention index (ambient) was 0.94-0.96 for different lengths and number of layers, and dropped by 2-8.5% under site conditions. Compressive strength was evaluated to be 47 MPa in control cubes. Results from compression and bond tests indicated accelerated water evaporation and surface dehydration in site conditions, and that the presence of joints in printed parts is detrimental to such strength parameters. Finally, flexural strength was increased in site conditions compared to control and ambient specimens by 21% and 18% respectively. Flexural strength results demonstrated that fibers are better oriented through print process, and can be further improved in hot mixes due to lower viscosities.