Banca de DEFESA: Jayme de Melo Ribeiro

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Jayme de Melo Ribeiro
DATE: 18/08/2022
TIME: 14:00
LOCAL: PECC
TITLE:

MICROSTRUCTURAL ANALYSIS OF TERNARY CEMENT PASTES WITH NANOSILICA AND METAKAOLIN AT EARLY AGES

KEY WORDS:

Metakaolin, nanosilica, early ages, ternary mixtures, synergistic effect, Portland cement

PAGES: 110
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Construção Civil
SPECIALTY: Materiais e Componentes de Construção
SUMMARY:

The growing need for high performance cementitious composites, as well as the environmental issues linked to the intense production of Portland cement, favored the advent of the use of supplementary cementitious materials (SCM) with high reactivity, such as metakaolin, as well as the development of new materials with potential application in cementitious matrices, such as nanosilica. Although there are already studies that address the interaction of metakaolin (MK) and nanosilica (NS), there is still a lack of knowledge regarding the understanding of the synergistic effect of these two materials at early hydration ages. Thus, this work aimed to carry out an evaluation of the microstructural changes of ternary Portland cement mixtures using metakaolin and nanosilica at the initial hydration ages of 1, 3 and 7 days. For this, four mixtures were produced, one reference (REF), two binary (2% nanosilica, 2NS, and 15% metakaolin, 15MK) and one ternary (13% metakaolin and 2% nanosilica, 13MK2NS). The pastes were evaluated from compressive strength tests and microstructural tests. From the results of compressive strength, it was found that although the 13MK2NS mixture replaced 15% of clinker, at all ages tested it presented mechanical strength equivalent to the 2NS mixture, which presented the highest result among the mixtures produced. Furthermore, it was also observed a tendency of strength growth of the 13MK2NS mixture after 7 days, while the 2NS mixture tends to stabilize at the same age. When monitoring the heat of hydration of the pastes from the isothermal calorimetry test, it was found that the C-S-H peak occurred more quickly in the 2NS mixture, however the 13MK2NS mixture presented higher heat flux at this peak. Qualitative, semi-quantitative and quantitative analyzes made from X-ray diffraction, infrared spectroscopy (FTIR) and thermogravimetry (TG/DTG), respectively, showed high consumption of calcium hydroxide (CH) by the 13MK2NS mixture through the pozzolanic reaction, reflecting the synergistic action between MK and NS. It was also verified that, from the results of nuclear magnetic resonance (29Si NMR), in the 13MK2NS mixture there was a greater incorporation of aluminum in the structure of C-A-S-H, which led to a greater average chain length of these hydrates at ages 1.3 and 7 days. In general, it was observed that the synergistic interaction between MK and NS occurs from 1 day and favors the alteration of several microstructural parameters during the hydration of the cementitious composite.

BANKING MEMBERS:
Presidente - 1734221 - JOAO HENRIQUE DA SILVA REGO
Interna - 1573495 - VALDIRENE MARIA SILVA CAPUZZO
Externo à Instituição - OSCAR AURELIO MENDOZA REALES - UFRJ