Resumo Este estudo tem como objetivo avaliar a influência da adição de esporos de B. subtilis AP91 nas propriedades mecânicas de argamassas. Para tanto, a bactéria B. subtilis AP91 isolada de folhas de arroz da variedade agulha precoce foi utilizada na concentração de 105 esporos/mL em argamassas com traço de 1:3 (em massa) e relação água/cimento (a/c) de 0,63. Os esporos bacterianos foram adicionados de duas diferentes formas: na água de amassamento e por imersão em solução contendo os esporos. A análise por Microscopia Eletrônica de Varredura (MEV) com Sistema de Energia Dispersiva (EDS) mostrou cristais com picos de cálcio, o que possivelmente indica a presença de carbonato de cálcio bioprecipitado. Os resultados obtidos a partir da análise mecânica mostraram que a bioprecipitação de CaCO3 pela bactéria B. subtilis AP91 foi satisfatória, particularmente quando os esporos foram adicionados à água de amassamento, aumentando a resistência à compressão em até 31%. Portanto, conclui-se que a adição de esporos de B. subtilis AP91 na água de amassamento das argamassas induziu a biocimentação, que aumentou a resistência à compressão. A bioprecipitação de carbonato de cálcio pode ter outras consequências benéficas, como o fechamento de poros e fissuras em materiais cimentícios, que poderiam melhorar a durabilidade, embora mais pesquisas neste aspecto ainda sejam necessárias.

Abstract This study aims to evaluate the influence of B. subtilis AP91 spores addition on the mechanical properties of mortars. B. subtilis strain AP91, isolated from rice leaves of the needle variety, which has an early cycle of production, was used at the concentration of 105 spores/mL in mortars with cement-to-sand ratio of 1:3 (by weight) and water-to-cement ratio (w/c) of 0.63. These spores were added in two different ways: in the mixing water and by immersion in a solution containing bacterial spores. Scanning Electron Microscope (SEM) analysis showed crystals with calcium peaks on the EDS, which possibly indicates the presence of bioprecipitated calcium carbonate. The results obtained in the mechanical analysis showed that the bioprecipitation of CaCO3 by B. subtilis strain AP91 was satisfactory, particularly when the spores were added in the mixing water, increasing the compressive strength up to 31%. Thus, it was concluded that the addition of B. subtilis AP91 spores in the mixing water of cement mortars induced biocementation, which increased the compressive strength. This bioprecipitation of calcium carbonate may very well have other advantageous consequences, such as the closure of pores and cracks in cementitious materials that could improve durability properties, although more research is still needed on this matter.

In this work we used the Photoacoustic Spectroscopy (PAS) to evaluate the crosslinking of the copolymer from ethylene vinyl trimethoxysilane (EVS) and the grafted vinyl trimethoxysilane (VTS) on low density polyethylene (LDPE). PAS is used for sounding the overtone bands and stretching frequencies combinations of the groupings -Si-OH, =CH2, -CH3 and -CH2 -CH3, in the near and medium infrared range. The samples were typically prepared with 3%, 5% and 7% of catalyst and crosslinked in the temperatures of 70, 80 and 90ºC. Using the overtone bands of -OH groups the PAS shows the optimum combination, pointing a better crosslinking effect for 80ºC and in the range 5% to 7% of catalyst, typically.