Alessandra Etuko Feuzicana de Souza Almeida

Thermogravimetric analyses and mineralogical study of polymer modified mortar with silica fume

Mineral and organic additions are often used in mortars to improve their properties. Microstructural investigation concerning the effects of styrene acrylic polymer and silica fume on the mineralogical composition of high-early-strength portland cement pastes after 28 days of hydration are presented in this paper. Thermogravimetry and derivative thermogravimetry were used to study the interaction between polymers and cement, as well as the extent of pozzolanic reaction of the mortars with silica fume. Differential scanning calorimetry and X ray diffraction were used to investigate the cement hydration and the effect of the additions. The results showed that the addition of silica fume and polymer reduces the portlandite formation due to delaying of Portland cement hydration and pozzolanic reaction.

Carbonatação acelerada efetuada nas primeiras idades em compósitos cimentícios reforçados com polpas celulósicas

O objetivo deste trabalho foi avaliar o efeito carbonatacao acelerada nas propriedades fisicas e desempenho mecânico de compositos cimenticios reforcados com altos teores de polpas celulosicas. Os compositos foram moldados em laboratorio pelo processo de succao a vacuo do excesso de agua e posterior prensagem, e a carbonatacao acelerada foi realizada em diferentes estagios de cura. O estudo das propriedades microestruturais foi realizado por microscopia eletronica de varredura ambiental e difracao de raios X. Os resultados obtidos mostraram que a carbonatacao acelerada nos primeiros dias de cura resultou em maiores resultados de propriedades mecânicas e melhora na interface fibra-matriz. A carbonatacao acelerada reduziu o conteudo de portlandita [Ca(OH) 2 ] e aumentou o teor de calcita [CaCO 3 ] que e o principal composto resultante da carbonatacao. Consequentemente, ocorreu a reducao da alcalinidade na matriz cimenticia, o que pode favorecer a durabilidade das fibras celulosicas que se destacam como alternativas as fibras minerais e sinteticas, e podem contribuir para o desenvolvimento sustentavel na tecnologia dos materiais de construcao.

Study of the adherence between polymer-modified mortars and porcelain stoneware tiles

Despite the excellent characteristics of porcelain tiles, their application on building facades requires special attention, since this material differs from conventional ceramics and because facades are exposed to weathering that can damage ceramic revetments. The combination of polymer and silica fume to produce mortars results in excellent properties, which are ideal for repairs and revetments requiring high performance. Such improvements justify its study for the installation of porcelain tiles. This article presents bond strength results for mortars containing different amounts of polymer and silica indicating the applicability of these mortars as a construction material. To complement this study, the interface between the porcelain and the mortars was analyzed by scanning electron microscopy (SEM).

Bamboo cellulosic pulp produced by the ethanol/water process for reinforcement applications

A polpacao organossolve e o processo quimico limpo que utiliza solventes orgânicos para remocao de lignina e hemicelulose de materias-primas lignocelulosicas. Esse metodo proporciona a facilidade de recuperacao do solvente no final do processo. Neste trabalho foi produzida polpa celulosica de bambu pelo processo organossolve, avaliando diferentes temperaturas e tempos de reacao, e as polpas foram analisadas visando a futura aplicacao para reforco de compositos. A producao de polpa de bambu pelo processo organossolve foi estudado variando as condicoes de cozimento de 1, 2 e 3 h a 150, 170 e 190° C, a fim de alcancar as condicoes ideais de rendimento e caracteristicas quimicas e fisicas da polpa para a potencial aplicacao em reforco de compositos. Os melhores resultados para a deslignificacao (numero de kappa 38), com a degradacao da fibra relativamente baixa (viscosidade de 625 cm3 g-1), razao de aspecto de 40,4 e o indice zero span de 204 Nm g-1, foram obtidos pelo processo de polpacao a 190°C durante 2h. Essa condicao de polpacao pode ser considerada como a mais adequada em relacao aos demais intervalos de tempo estudados no presente trabalho. A maior resistencia mecânica e menor incidencia de defeitos morfologicos na fibra (6,0% de curls e de 10,6% de kinks) podem demonstrar o potencial da polpa organossolve bambu como elemento de reforco.

POLPA CELULÓSICA DE BAMBU PRODUZIDA PELO PROCESSO ETANOL/ÁGUA PARA APLICAÇÕES DE REFORÇO

Organosolv pulping is the clean chemical process of using organic solvents to aid in the removal of lignin and hemicellulose from lignocellulosic raw materials. This method provides facility for solvent recovery at the end of the process. In this work, it was to produce bamboo cellulosic pulp by the organosolv process evaluating different temperatures and reaction times, and the pulps were analyzed aiming their future application in the reinforcement of composites. The production of bamboo pulp by the organosolv process was studied varying the cooking conditions at 1, 2 and 3 h and 150, 170 and 190 o C of temperature, in order to achieve the ideal conditions of yield, chemical and morphological characteristics of the pulp for its potential application in the reinforcement of composites. The best results for delignification (kappa number of 38), with relatively lower fiber degradation (viscosity of 625 cm 3 g -1 ), aspect ratio of 40.4 and the index zero-span of 204 Nm g -1 , were achieved for the pulping process at 190 o C for 2 h. These pulping conditions can be considered as the more appropriate in the range of time intervals evaluated in this work. The higher mechanical strength and the lower incidence of morphological defects in the fiber (6.0% of curls and 10.6% of kinks) can demonstrate the potential of organosolv bamboo pulp as a reinforcing element.

Potential Use of Colloidal Silica in Cement Based Composites: Evaluation of the Mechanical Properties

The properties of cement based composites depend not only on the properties of their individual components but also on their interfacial characteristics and transition zone between fiber and matrix. There has been a renewed interest in the use of cellulosic pulp as micro-fiber reinforcement in cement based composites. The addition of nanoparticles, such as colloidal silica, to fiber-cement could allow a better control of its microstructure and the enhancement of the matrix/fiber interface. The objective of this work is to evaluate the effects of colloidal silica on the microstructure and mechanical performance of cementitious matrices and fiber-cement composites. These cementitious materials were prepared with 0%, 1.5%, 3%, 5% and 10% w/w colloidal silica suspension content. Cementitious matrices without fibers were produced by vibration. Fiber-cement composites with unbleached Eucalyptus kraft pulp as a micro-fiber reinforcement were produced by the slurry dewatering technique followed by pressing. All composite materials were cured by water immersion. A splitting (Brazilian) test was carried out to determine the tensile strength of cementitious matrices. Mechanical behavior of the fiber-cement composites was evaluated via modulus of rupture and fracture toughness based on load-displacement curves (L-d curves) under continuous loading and 3-point bending arrangement. The energy of fracture was measured through a stable crack propagation test with SENB (single-edge notched bending) configuration also under a 3-point bending arrangement. The matrix with highest content of colloidal silica suspension (10% w/w) presented high values of water absorption and consequently presented the lowest splitting tensile strength. The average values of modulus of rupture and fracture toughness of fiber-cement tend to decrease with increasing colloidal silica content. However, the pullout mechanism increased significantly in the fiber-cement composites with additions between 3% and 10% w/w of colloidal silica suspension as compared to that without any addition, noted by degree of improvement in the energy of fracture and by scanning electron microscopy micrographs (SEM). These findings show the potential use of colloidal silica to improve the transition zone between the cellulosic fiber and the cementitious matrix. The results of this study show an important way to engineer and control the fracture process of the composites.