Banca de DEFESA: LEONARDO DE SOUZA DIAS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : LEONARDO DE SOUZA DIAS
DATE: 15/02/2022
TIME: 15:00
LOCAL: meet.google.com/hxy-nxfi-kxf
TITLE:

MIX DESIGN METHODOLOGY BASED ON BASIC CONSTITUENT RELATIONSHIPS OF MIXTURES FOR 3D CONCRETE PRINTING (3DCP)

KEY WORDS:

3DCP, printability, squeezze-flow testing, constitutive mixture variations, hardened state.

PAGES: 95
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Construção Civil
SPECIALTY: Materiais e Componentes de Construção
SUMMARY:

3D printing using cementitious materials has gained prominence in recent research, however there are still many gaps in the parameters required for dosing the mixtures with printability, because these parameters depend on the interaction of the printing system (printer type, pumping, extrusion, printing speed, etc.) with the intrinsic properties of cementitious mixtures, such as particle size of the materials, cement types and mineral additions, volumetric water/binder ratios (Vw/Vb), paste/aggregate volume (Vp/Vs), paste volume (Vp), water volume (Vw) and sand/total solids ratio (S/total solids). This paper analyzed six mixtures for printing with variations in the cement: sand (by mass) ratios, keeping constant the water/dry materials (Vw/Md) ratio, evaluating the printing capacity of these mixtures in a gantry-type 3D printer with mechanized movement in its axes, possessing a material deposition extruder nozzle. The evaluation of the printing capacity was carried out taking into account the visual aspects, pumpability, and filament integrity. The mixtures were then submitted to mini-slump tests, spreading on a consistency table, squezze-flow and deformation under load of the printed filaments at printing intervals of 0, 15 and 30 min, and then the ideal ranges of constitutive ratios of the mixtures (Vp, Vp/Vs, Vw/Vb, Vw, S/solids) compatible with printing were determined. The properties in the hardened state, flexural and compressive strength, adhesion between layers, specific mass and voids index were determined for specimens extracted from printed pieces with cuts in sizes as specified in standards for each test. The results showed that for the printing system used there is an ideal range for these constitutive relations, and that the mixtures even presenting different viscous flow, measured according to squeeze flow, can be printable, as long as they meet the ideal ranges for the determined relations. With respect to the interface of the printed layers, these are critical points of fragility possibly due to factors such as the formation of regions with voids and loss of surface moisture, which favors the reduction of mechanical performance of the parts especially with the increase of deposition time. On the other hand, the increase of time provided a positive effect on the stability and deformation of the filaments, since it favors the stiffness of the substrate offering greater support to the later printed segment.

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