Abstract The performance of masonry structures depends not only on the quality of blocks and mortars but also on their interactions. This study aims to evaluate the influence of unit and mortar characteristics on the compressive strength of masonry. Prisms were produced using concrete blocks with nominal strengths of 8 and 10 MPa, combined with mixed and industrialized mortars with lower, similar, and higher strengths compared to the blocks. Response surfaces and contour plots were generated to visualize the effects of unit and mortar properties on prism strength. Estimations were performed, and the failure mechanisms of prisms for various combinations of blocks and mortars were analyzed. The failure modes of the prisms were characterized by ductile failure (in weaker mortars), cohesive rupture of the assembly (in intermediate-strength mortars), and brittle failure (in stronger mortars), primarily due to lateral tensile forces acting on the blocks. The findings of this research contribute to the existing knowledge database in the field and can assist in the appropriate selection of blocks and mortars for structural masonry applications.

Resumo O bom desempenho da alvenaria depende não somente da qualidade dos blocos e argamassas, mas também das interações que se processam entre eles. Este trabalho teve como objetivo avaliar a influência das unidades e das argamassas na resistência à compressão da alvenaria. Prismas foram produzidos com blocos de concreto de resistências nominais de 8 e 10 MPa e argamassas mistas e industrializadas com resistências inferior, aproximada e superior à do bloco. Superfícies de resposta e gráficos de contorno foram desenvolvidos para mostrar o efeito das unidades e das propriedades das argamassas na resistência dos prismas. Estimativas foram realizadas e os mecanismos de ruptura dos prismas para diferentes combinações de bloco e argamassa foram analisados. Os prismas romperam de forma dúctil (argamassas mais fracas), pela ruptura do conjunto (argamassas intermediárias) e de forma frágil (argamassa mais fortes), principalmente pela tração nos blocos. Os resultados complementam as pesquisas da área já existentes e pode ser usado para selecionar corretamente blocos e argamassas para alvenaria estrutural.

Abstract The use of concrete block masonry for the construction of buildings is recurrent due to the economy and rationalization it provides to projects. However, the good performance of masonry depends not only on the quality of the materials used, but also on the interactions that take place between the unit and the mortar. In this research, we sought to analyze the characteristics of compressive strength and failure mode of concrete block prisms. Concrete blocks with nominal strengths of 8.0 MPa and 10.0 MPa were used, combined with six types of mortars (mixed and industrialized), of different strengths. In total, 36 prisms were built and tested. The experimental results indicate that the mortar prisms of lesser resistance failed in a ductile way, by crushing the mortar; intermediate mortar prisms gave the set rupture; while the mortar prisms more rigid than the block, broke frailly, mainly due to traction in the blocks. It is concluded that the specification of the mortars used in the execution of the masonry must be made not only according to their resistance, but also according to the type of block used, since the compatibility between these elements has a significant role in the performance of the set.

Resumo O uso de alvenaria de blocos de concreto para a construção de edifícios é recorrente em função da economia e racionalização que proporciona aos empreendimentos. No entanto, o bom desempenho da alvenaria depende não somente da qualidade dos materiais empregados, mas também das interações que se processam entre a unidade e a argamassa. Nesta pesquisa, procurou-se analisar as características de resistência à compressão e modo de ruptura de prismas de bloco de concreto. Foram utilizados blocos de concreto de resistências nominais de 8,0 MPa e 10,0 MPa, combinados com seis tipos de argamassas (mistas e industrializadas), de diferentes resistências. No total, 36 prismas foram construídos e ensaiados. Os resultados experimentais indicam que os prismas de argamassa de menor resistência romperam de forma dúctil, por esmagamento da argamassa; prismas de argamassa intermediária conferiram ruptura do conjunto; enquanto os prismas de argamassa mais rígida que o bloco, romperam de forma frágil, principalmente pela tração nos blocos. Conclui-se que a especificação das argamassas utilizadas na execução da alvenaria deve ser feita não somente em função da sua resistência, mas também de acordo com o do tipo de bloco empregado, visto que a compatibilidade entre esses elementos tem papel significativo no desempenho do conjunto.

ABSTRACT The technology of 3D printing has been studied by different researchers, due to the possibility of producing solid objects swiftly, time reduction, labor with fewer failures the construction process. One of the challenges to be overcome is related to the development of mixtures promising. Thus, research aimed at the technology of cementitious materials is necessary to develop extrudable and sustainable mixtures. This article aimed to investigate the potential use of (FA) and (MK) in cementitious materials for application in three-dimensional printing (3D) by checking the aspects of constructibility. In the first stage, tests of normal consistency and initial and final setting time were carried out on pastes, with calcium oxide 4% and addition of (FA) and (MK) in the percentages of 8%, 10% and 15% in relation to the cement mass, in order to establish an ideal water / cement ratio. In the second stage, given a pre-determined trace of 1: 1.5, in mass, the viscosity, yield stress, extrudability and verticality tests were carried out on the cementitious materials developed in the first stage. It was observed that for the aspects related to the normal cement consistency and initial and final setting time, the paste with 15% substitution (FA) presented a longer initial setting time when compared to pastes with (MK) added. yield stress, materials with 15% substitution (FA) and without superplasticizer additive showed favorable results in the relation of the initial and final yield stress, as the mixture of 15% (MK) with 0.4% superplasticizer additive. and, therefore, they were considered promising because they were subjected to extrudability and verticality tests. Thus, it is concluded that considering the constructibility applied to prototyping, cementitious materials with 15% substitution (FA) and (MK) in relation to the cement mass present results considered relevant for the application in 3D printing.

Resumen Este estudio tiene como objetivo analizar el desempeño de dos composiciones de hormigón con adición de esporas de B. sutilis con relación a su capacidad de relleno de fisuras durante el periodo de cura, evaluando la influencia de la adición en la resistencia a compresión. Para ello han sido estudiadas seis composiciones de hormigón, divididas en dos dosificaciones: 1:1:2 y 1:2:3 (cemento: árido fino: grava) en peso, con relación a/c de 0,33 y 0,45. Para cada una de las mezclas se utilizaran concentraciones de 0, 0.3x108 or 1.2x108 de esporas de B. sutilis/mL. Los resultados obtenidos han demostrado que todas las muestras con adición de esporas presentaron precipitación de cristales, posiblemente carbonato de calcio, que fue visualizado en las fisuras. Más estudios microestructurales deberán ser realizados para comprobar que de hecho ocurrió el relleno de las fisuras. La resistencia a compresión presentó resultados satisfactorios, pues no hubo diferencias significativas en relación al hormigón de referencia, a nivel de 5% de probabilidad.

Abstract This study aimed to analyze the performance of two concrete mixtures with the addition of B. subtilis spores regarding their capacity of filling cracks during the curing time, evaluating whether the addition can influence the compressive strength of the concrete. For so, six concrete mixtures were studied divided in two mix compositions: 1:1:2 and 1:2:3 (cement: sand: gravel) with w/c of 0.33 and 0.45, respectively. For each composition were added concentrations of 0, 0.3x108 or 1.2x108 of B. subtilis spores/mL. The results showed that all the samples with spores addition presented crystals precipitation, possibly calcium carbonate, that visually filled the cracks. However, more studies of microstructural analysis should be conducted to prove that the cracks were closed. The compressive strength presented satisfactory results, because the addition of 1.2x108 spores/mL did not present significant differences in compressive strength at probability level of 5%, when compared to the reference concrete.

RESUMO A incorporação de nanossílica vem sendo estudada como uma alternativa para melhorar as características dos materiais cimentícios, pois tende a aumentar as reações pozolânicas e preencher os espaços intersticiais, diminuindo a porosidade e melhorando a resistência mecânica. Neste contexto, o presente estudo teve como objetivo avaliar o comportamento mecânico e as características microestruturais de três compósitos cimentícios: um de referência e dois contendo diferentes teores de nanossílica dispersas em policarboxilato (NDP), de 0,2 e 0,4%, em relação à massa do cimento. O comportamento mecânico foi avaliado mediante o ensaio de resistência à compressão e resistência à tração por compressão diametral. Além disso, foram realizados ensaios de absorção de água e análise microestrutural em Microscópio Eletrônico de Varredura (MEV). A partir da análise dos resultados, verificou-se que a adição de NDP melhorou as propriedades mecânicas e as características microestruturais dos compósitos cimentícios. Sendo que o compósito contendo o maior teor de NDP (0,4%) obteve melhores resultados aos 28 dias, apresentando um aumento de 55% na resistência à compressão, 79% na resistência à tração por compressão diametral e diminuindo em 40% a absorção de água, em relação à referência, possivelmente pela atuação da NDP. Porém, ao analisar a incorporação dos dois teores de NDP (0,2 e 0,4%), se verificou que ao dobrar o teor não houve uma melhora significativa da resistência à compressão, pois a incorporação de 0,2% de NDP aumentou a resistência à compressão em 53% em relação à referência. Quanto à análise microestrutural em MEV, verificou-se um refinamento da microestrutura a partir da incorporação de NDP, mas não foram visualizadas diferenças entre os dois teores incorporados.

ABSTRACT The incorporation of the nanosilica has been studied as an alternative to improve the characteristics of cementitious materials because tends to increase the pozzolanic reactions and fill the interstitial spaces, decreasing the porosity and improving the compressive strength. In this context, the present study has the goal to evaluate the mechanical behavior and the microstructural characteristics of three cementitious composites: the reference e two with different levels of nanosilica dispersed in polycarboxylate (NDP), 0.2 and 0.4%, in relation to the cement mass. The mechanical behavior was evaluated through the compressive strength test and tensile test (Brazilian denomination). Furthermore, were done water absorption tests and microstructural analysis by Scanning Electron Microscope (SEM). From the analysis of the results, it was verified that the addition of NDP improved the mechanical properties and the microstructural characteristics of cementitious composites. The NDP content (0.4%) showed better results at 28 days, presenting a 55% increase in compressive strength, 79% tensile test and a 40% decrease in the absorption of water, in relation to the reference, possibly through the NDPs performance. However, when analyzing the incorporation of the two NDP contents, it was verified that when the content was doubled there was no significant improvement in the compressive strength, since the incorporation of 0.2% of NDP increased the compressive strength in 53% in relation to the reference. As for the microstructural analysis, a refinement of the structure was verified from the incorporation of NDP but no differences between the two incorporation was visualized.