Banca de DEFESA: HENRIQUE ALMEIDA SANTANA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : HENRIQUE ALMEIDA SANTANA
DATE: 27/02/2023
TIME: 08:00
LOCAL: Ambiente virtual
TITLE:

Durability of vegetable fibers in alkali-activated cementitious matrices: effects of matrix dosage and exposure to the elements

KEY WORDS:

Alkali-activated binders, dosage, vegetable fibers, alkaline hydrolysis, durability.

PAGES: 142
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Construção Civil
SPECIALTY: Materiais e Componentes de Construção
SUMMARY:

Alcali-activated binders (LAA) have mechanical properties equivalent to Portland cement (CP). However, as in CP, the fragile behavior of the LAA demands the use of reinforcements capable of making them suitable for applications involving dynamic cargo or tensile tensions. Vegetable fibers (FV) have the potential to improve the mechanical properties of fragile construction materials, acting especially to improve toughness and post-phissing resistance. However, little is known about the durability of FV when used as tenacification elements in LAA. In this sense, this work aims to evaluate the effect of fiber treatments (alkaline and hornification), alkaline activator (NO and K), matrix aggressiveness and composite aging in FV durability. To this end, the statistical design of experiments with mixtures for characterization and control of LAA aggressiveness produced with metacaulim, treated asbest cement residue and alkaline solutions was used. The matrix/fiber interaction was evaluated by pullout tests, direct exposure of the fibers in the matrix and aging of composites by 120 days. The dosage method made it possible to control the aggressiveness of the matrix through the electrical conductivity of a leached solution, which varied between 7.26 and 41.10 ms/cm for sodium -based activated mixtures and between 6.42 and 33.50 ms /cm for potassium -based activated mixtures. Through the pullout test, the intense loss of adhesion resistance to the fibers exposed in the most alkalinity matrices was noted, indicating the degradation of lignin and hemicellulose. With the direct exposure test, the effect of the most aggressive matrix on the retention of fiber traction resistance was also observed, pointing out cellulose degradation. The mechanical evaluation of composites after aging showed that matrix optimization
It provided the maintenance of composite traction and toughness resistance, a result that converges with the higher thermal stability and better microstructural integrity of fibers extracted from composites. In this sense, it is found that matrix optimization is the main tool to enable the production of composites to LAA and FV.

COMMITTEE MEMBERS:
Interno - ***.925.915-** - PAULO ROBERTO LOPES LIMA - UEFS
Interno - 2315713 - MARCELO STROZI CILLA
Interno - 2137887 - CLEBER MARCOS RIBEIRO DIAS
Externo à Instituição - ROMILDO DIAS TOLEDO FILHO - UFRJ
Externo à Instituição - HOLMER SAVASTANO JUNIOR - USP
Externo à Instituição - BRANT WALKLEY