Claudio de Souza Kazmierczak

Revestimentos aplicados sobre substrato de blocos de cerâmica vermelha foram submetidos a carbonatação acelerada e a ciclos de envelhecimento acelerado por ciclagem de temperatura e choque térmico, sendo avaliadas as alterações de resistência de aderência e absorção de água, em macro escala, e do módulo de elasticidade, em micro escala. Observou-se que os revestimentos sofrem danos em função do envelhecimento acelerado, aumentando a porosidade e diminuindo seu módulo de elasticidade. A carbonatação isoladamente aumenta a aderência dos revestimentos, mas nestes o processo de envelhecimento acelerado gera mais microfissuras, igualando o comportamento de argamassas carbonatadas e não carbonatadas.

The scope of this work is the development of new composites with low environmental impact to act as radiological shielding in hospital environments. For this purpose, the radioprotection properties of cement pastes containing 20% ​​BaSO4, in addition to 10% fly ash and silica fume as SCM’s were investigated. The samples were characterized by consistency, apparent density and mechanical strength at 7 and 28 days of age. In addition, transmission measurements were performed for different sample thicknesses using a photon beam from a linear accelerator operating at 6 and 10 MV in a radiotherapy room. The barium pastes showed a reduction in sample thickness of approximately 10% compared to the reference paste (without barium) at the highest voltage analyzed to attenuate 90% of the incident radiation (according to current legislation). Among the SCM’s, silica fume stood out as the most suitable substitute when combined with barium in Portland cement matrices. Finally, the apparent density of the samples appears to be decisive for the performance of new materials in terms of radiological shielding.

The main mechanical properties that indicate the development of adhesion between mortars and substrates are tensile strength, shear strength, and bond length. However, most studies focus solely on tensile bond strength. This study proposes an alternative method for evaluating tensile and shear bond strength, which produces less variation in results, using a device specifically developed for this purpose. For the necessary validations, a 1:1:6 mortar mixture (by volume) consisting of cement, lime, and medium sand, along with a ceramic substrate, was used. Tensile and shear strengths were evaluated after wet curing at different ages. A new method for bond strength testing demonstrated promising results, reducing the variance of results by 39% using spatterdash and increasing the bond strength by 31% without spatterdash, at 28 days. This reduction in variability indicates that the new method mitigates the influence of external factors inherent to the testing process. The apparatus required for the alternative method was easy to produce and use, making it an efficient option for conducting adhesion tests on mortars in a laboratory environment.

This study aimed to identify the influence of replacing coarse natural aggregate with coarse recycled concrete aggregate on the thickness and volume of the cementitious paste under the variation of the water/cement ratio in the fresh and hardened properties of pervious concrete. The determined theoretical paste thickness was inefficient for pervious concrete dosage. However, it was found that the paste volume was the parameter that was best related to the mechanical and permeability properties of the studied material. Pervious concrete with natural aggregates showed higher compressive strength than concrete with recycled aggregates, although both met the regulations. All the concretes produced, except one with recycled aggregate of w/c ratio 0.25, reached the tensile strength in the minimum design bending. Pervious concrete with recycled aggregates showed more significant mass loss by abrasion and more porosity than concretes with natural aggregates. Finally, all pervious concretes presented permeability coefficients greater than the lower limit determined by the standard.

This study assesses the joint influence of capillary absorption and substrate roughness on the adhesive strength of a cementitious matrix on brick substrate. One cementitious rendering and two substrates with different water absorption and roughness were used. The capillary absorption coefficient and the roughness coefficient were determined in 1cm² test areas to then evaluate the matrix tensile bond strength and correlate it with the properties of the substrates. The results were validated by SEM and AFM analyses. Substrates with higher capillary absorption and lower roughness presented higher tensile bond strength. Micro and nanoscale analyses led us to conclude that, in the substrates used, the higher capillary absorption and the lower roughness generate a denser and less porous paste-substrate interface, suggesting a higher extent of contact between the hydrated paste and the substrate and, consequently, higher adhesive strength.

A anisotropia de superfície e as diferentes matérias-primas empregadas na produção de blocos cerâmicos têm influenciado, em coeficientes de variação altos, a resistência de aderência à tração em revestimentos. Dessa forma, o objetivo deste estudo é propor o método de microtração como alternativa de selecionar substratos cerâmicos que promovam menor coeficiente de variação na aderência para mesma dosagem de pastas cimentícias. Na metodologia, a aderência foi determinada empregado o ensaio de microtração. Foram utilizados cinco diferentes substratos cerâmicos e uma mesma pasta cimentícia. Os resultados demonstraram que substratos de diferentes olarias afetam de forma significativa a aderência de revestimentos cimentícios.

The method of measuring the roughness of ceramic substrates is not consensual, with unsuccessful attempts to associate roughness with the adhesion of coatings because the ceramic blocks have different areas of contact, shapes, and dimensions of the roughness as well as the extrusion process influences the mechanical anisotropy of the block. The goal of this work is a quantification and comparison of roughness data obtained by 2D and 3D methods, evaluating the variations of results between the measurement methods and formulating a critical analysis regarding the quality of the information obtained with each method. For this propose, four sets of ceramic blocks with different firing temperature were produced, in order to provide groups of blocks with different surface topographies in which the roughness was estimated. The roughness measurements were made in 4608 regions, resulting in 1536 values using 2D method and 3072 values using 3D method. In the 2D method for ceramic blocks, the measurement orientation strongly influences the result, depending on the measurement position and orientation. The 3D method generates a higher average value and allows to identify roughness variations typical of the ceramic block. The roughness estimation of a ceramic block surface must be done using the 3D method.