Banca de QUALIFICAÇÃO: HUGO ALESSANDRO ALMEIDA DINIZ

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : HUGO ALESSANDRO ALMEIDA DINIZ
DATE: 21/09/2022
TIME: 09:00
LOCAL: Remota
TITLE:

Synergistic effects of sand, water and metakaolin incorporation on the properties of 3D printing concretes by experimental mix design

KEY WORDS:

3DCP; extrudability; buildability; metakaolin; mixture planning.

PAGES: 120
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Materiais Conjugados Não-Metálicos
SUMMARY:

The three-dimensional concrete printing (3DCP) is a construction technique that emerged to innovate and insert the construction industry in the context of revolution 4.0. It consists of laying successive layers of a cementitious composite without the need for formwork and with the possibility of making multiple geometric shapes. This enables the execution to occur faster, more accurately, and with less waste. However, for 3DCP to be applied, it is necessary that the composite used allows continuous flow through a printing nozzle (extrusion capability) and, after printing, presents a low deformation, in the fresh state, even after the weight exerted by the successive layers printed above. Coupled with this, high levels of cement are commonly used to achieve these abilities, making this practice damaging to the environment. In this study several tests were performed in order to understand the influence of sand, of metakaolin and of water in the extrudability and buildability in composites for 3D printing. The analysis was based on a statistical experimental planning of mixtures to measure and understand the relationships between the variables: cement replacement content by metakaolin, sand/ binder ratio and water/ binder ratio. To measure extrusion an experimental flow rate test was developed and also by correlation with the spreading (mini slump-flow). To understand the buildability, the maximum number of printed layers, the section deformation index, layer thickness compliance, and squareness variation in printed blocks were analyzed. The squeeze-flow was performed to understand the thixotropy along with complementary tests of characterization of the dry mixtures and in the fresh state. To understand the applicability of the material, the strengths of the mixtures and the printed blocks were measured. The water/ binder factor had a preponderant influence on the extrusion capacity, which was expected, because water is the component responsible for the fluidization of dry materials. However, it can be observed that the granulometry and proportioning of the mix can also have a positive effect on extrusion when there is not a good packaging between the particles of sand and binder, generating internal voids that increase the internal mobility. The sand had a positive effect until the proportion of 1:1.5, however, after 30 minutes, this effect becomes very small. The metakaolin presented the advantage of maintaining a good fluidity over time, due to a slower setting. In buildability, the increase of sand and reduction of water were advantageous to reduce deformation and increase the maximum number of internal layers. The incorporation of metakaolin was negative, increasing the deformation of the section and the layers. The yield stress in squeeze-flow was directly related to the flow rate, validating the experimental methodology created. It was also observed that the printing process, as well as the deformations that occurred, influenced in the final strength of the printed block. Traces that contained higher axial compressive strength of the material, in the prismatic samples, did not correspond directly to a higher compressive strength of the printed block. Strokes that contained a higher strength of the material did not correspond directly to a higher strength of the printed part. For a satisfactory 3D printing process of concrete, sand promoted a higher resistance to deformation and better buildability; the metakaolin up to the percentage of 20% shows positive for maintaining fluidity over the printing time, besides a small reduction in the weight of the structure; and, in the range between 0.37 and 0.43 of water/binder ratio, mixtures with good printing abilities were obtained.

COMMITTEE MEMBERS:
Presidente - 1298936 - ANTONIO EDUARDO MARTINELLI
Externa ao Programa - 2621720 - ANA CECILIA VIEIRA DA NOBREGA - UFRNExterno à Instituição - KLEBER CAVALCANTI CABRAL - UFERSA