Banca de DEFESA: CARLOS FERNANDO GOMES DO NASCIMENTO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : CARLOS FERNANDO GOMES DO NASCIMENTO
DATE: 17/06/2022
TIME: 14:30
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

Cement-based Composites with Pure Graphene Multilayer Addition: Investigation, of Effects on Structural, Morphological, Chemical and Mechanical Properties

KEY WORDS:

cement; mortars; composites; graphene; mechanical properties.

PAGES: 221
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

Cementitious composites are materials widely employed in the construction industry and have efficient physical-mechanical properties. In order to develop high performance cement-based materials, nanotechnology has been undergoing an evolutionary process during the last years, associating itself to the design of nanomaterials applied to cement-based materials. An interesting nanomaterial that has been the target of study in the construction sector is the pure graphene, since it has a high specific surface area and specific properties for being lightweight, rigid, and waterproof. The main goal of this work was to investigate the physical, chemical and microstructural efficiency of mortar composites with different contents of pure graphene in relation to the mass of the binder at 7, 14, 21 and 28 days. In this sense, prismatic (4 cm x 4 cm x 16 cm) and cylindrical (5 cm x 10 cm) specimens were prepared by using 6 (six) mixtures: a reference (REF) and other 5 (five) with 0.03%, 0.06%, 0.09%, 0.12% and 0.15% pure graphene (GRAPH). The prismatic (CP's) were used to analyze the flexural tensile strength and the cylindrical ones to evaluate the axial compressive strength, water absorption by capillarity and immersion, mass density, ultrasonic wave propagation and modulus of elasticity. Mineralogical analyses were performed on the precursor materials: cement, pure graphene and fine aggregate (sand) through X-ray diffraction test (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In addition, thermal analyses (TGA/DTA) were performed for the cementitious composites after the hydration process. The results revealed that the fine aggregate particles (sand) have a specific mass of 2.985 g/cm³. The pure graphene nanoparticles have dimensions of approximately 50 μm, interplanar distance of 3.340 Å and easy agglomeration process because they are hydrophobic. Portland cement showed 64.6% calcium oxide (CaO) and 18.81% silicon dioxide (SiO2). Regarding the results of (XRD), it was possible to note that the cement-based composites have the formation of tricalcium silicate (C3S), dicalcium silicate (C2S) and tricalcium aluminate (C3A). As for the (XRF) results, the presence of (SiO2) and (CaO) in larger proportions was evidenced. The (SEM) test with secondary electrons (SE), evidenced that the pure graphene nanoparticles have more than 75% of carbon in its composition. For the mortar composites, it was observed the formation of crystals of calcium silicate hydrate (C – S – H), voids/interstitials, portlandite (CaOH2) and ettringite (AFt). It was noted by (SEM) with backscattered electron detection (EDS) that the higher the content of pure graphene nanoparticles, the higher the percentage of carbon. For the (FTIR) results it was noted that most of the absorption bands were shifted through asymmetric bending, where for the cementitious composites the formation of alite belonging to the functional group (Si – O), (C – O) belonging to the carbonaceous group of calcites (CO3)2– and (O–H) group present in water molecules were identified. The (TGA/DTA) results showed that the decomposition of (C – S – H) occurs between 150 ºC and 200 ºC, (C – H) between 430 ºC and 520 ºC and of calcium carbonate (CaCO3) between 700 ºC and 800 ºC. Dehydration of monosulfate (C4AS.H18) and ettringite Ca6Al2(SO4)3(OH)12 occurred between 91 ºC and 160 ºC. The decomposition of the silicates occurs at temperatures above 600 ºC. As for the results, the mixtures with 0.06% of (GRAPH) showed axial compressive strength 15% higher when compared to mortars with (REF), being this considered an "optimum" value, besides having a significant sample correlation of (R² = 0.979). On the other hand, the flexural tensile strength test revealed that the mixture with 0.03% and 0.06% of (GRAPH) had significant improvements of 8.5% and 18%, respectively. The results of water absorption by capillarity showed that the mortar composites containing 0.15% of nanoparticles of (GRAPH), had a water rise of approximately 0.70 g/cm², i.e., 33% lower when compared to the reference mixtures. The mixtures containing 0.15% of (GRAPH), had 6.8% water absorption per immersion, i.e., 51% lower when compared to the reference cementitious composites. It was observed that the mass density of the mixtures containing 0.06% of (GRAPH), had similar behavior to the mixtures with 0.03% of (GRAPH). As for the composites containing 0.15% (GRAPH) nanoparticles, they had a mass density of approximately 2.25 kg/m³. The data were analyzed through the Pareto diagram, where it was noticed that the particle dimensions and the void index directly influence the results of specific mass. The results corresponding to the analysis of ultrasonic wave propagation and modulus of elasticity were more evident in the mixtures containing different graphene contents. The cementitious composites with 0.15% of (GRAPH) presented 4458 m/s and 69.40 GPa. The pozzolanic activity index (PAI) in the mixtures containing 0.06% of (GRAPH) was not so evident presenting a result of 85%, i.e., below the established by the standard, which is 90%. Finally, studies aimed at the use of nanomaterials in cementitious composites can be carried out to promote improvement in physical, chemical and mineralogical performance of materials in the construction industry.

BANKING MEMBERS:
Externo à Instituição - ELIANA CRISTINA BARRETO MONTEIRO - UPE
Externo à Instituição - FELIPE MENDES DA CRUZ - UPE
Presidente - 3100969 - NATHALIA BEZERRA DE LIMA