Abstract
This paper presents the hardened properties of a high-performance fibre-reinforced fine-aggregate concrete extruded through a 9mm diameter nozzle to build layer-by-layer structural components in a printing process. The printing process is a digitally controlled additive method capable of manufacturing architectural and structural components without formwork, unlike conventional concrete construction methods. The effects of the layering process on density, compressive strength, flexural strength, tensile bond strength and drying shrinkage are presented together with the implication for mix proportions. A control concrete (mould-cast specimens) had a density of approximately 2250kg/m3, high strength (107MPa in compression, 11MPa in flexure) and 3MPa in direct tension, together with a relatively low drying shrinkage of 175μm (cured in water) and 855μm (cured in a chamber at 20°C and 60% relative humidity) at 184days. In contrast well printed concrete had a density of 2350kg/m3, compressive strength of 75–102MPa, flexural strength of 6–17MPa depending on testing direction, and tensile bond strength between layers varying from 2.3 to 0.7MPa, reducing as the printing time gap between layers increased. The well printed concrete had significantly fewer voids greater than 0.2mm diameter (1.0%) when compared with the mould-cast control (3.8%), whilst samples of poorly printed material had more voids (4.8%) mainly formed in the interstices between filaments. The additive extrusion process was thus shown to retain the intrinsic high performance of the material.
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