The effect of mixing method on tricalcium silicate-based cement.

AIM: To evaluate the effect of three methods of mixing on the physical and chemical properties of tricalcium silicate-based cements. METHODOLOGY: The materials evaluated were MTA Angelus and Portland cement with 20% zirconium oxide (PC-20-Zr). The cements were mixed using a 3 : 1 powder-to-liquid ratio. The mixing methods were manual (m), trituration (tr) and ultrasonic (us) activation. The materials were characterized by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy. Flowability was analysed according to ANSI/ADA 57/2012. Initial and final setting times were assessed following ASTM C266/08. Volume change was evaluated using a micro-CT volumetric method. Solubility was analysed according to ADA 57/2012. pH and calcium ion release were measured after 3, 24, 72 and 168 h. Statistical analysis was performed using two-way analysis of variance. The level of significance was set at P = 0.05. RESULTS: The SEM analysis revealed that ultrasonic activation was associated with a homogeneous distribution of particles. Flowability, volume change and initial setting time were not influenced by the mixing method (P > 0.05). Solubility was influenced by the mixing method (P < 0.05). For pH, at 168 h, significant differences were found between MTA-m and PC-20-Zr-m (P < 0.05). For calcium ion release, PC-20-Zr-tr had higher values than MTA-m at 3 h, and MTA-tr had higher values than PC-20-Zr-m at 168 h (P < 0.05). CONCLUSIONS: The ultrasonic and trituration methods led to higher calcium ion release and pH compared with manual mixing for all cements, whilst the ultrasonic method produced smaller particles for the PC-20-Zr cement. Flow, setting times and volume change were not influenced by the mixing method used; however, it did have an impact on solubility.

Environmental changes and human work in the region of the Upper Paraná River floodplain: processes and interactions.

The environment and society constitute a complex of elements and interactions. Thus, an understanding of the processes in which the environment and psychosocial elements are involved may not be gained from knowledge of just one isolated variable. Based on such premises, the present paper, which summarizes the results of a series of studies, adopts work relationships as its main focus, but in addition, it has two complementary objectives. One is to present some analyses on the interaction between human actions and the environmental changes that have been taking place in the region of the Upper Paraná River floodplain and in its boundaries. A secondary aim is to show how those two factors have been changing people's working and living conditions and the identity configuration of some of the human groups that live at that site.

Environmental changes and human work in the region of the Upper Paraná River floodplain: processes and interactions / Mudanças ambientais e trabalho humano na região da planície de inundação do Alto Rio Paraná: processos e interações

The environment and society constitute a complex of elements and interactions. Thus, an understanding of the processes in which the environment and psychosocial elements are involved may not be gained from knowledge of just one isolated variable. Based on such premises, the present paper, which summarizes the results of a series of studies, adopts work relationships as its main focus, but in addition, it has two complementary objectives. One is to present some analyses on the interaction between human actions and the environmental changes that have been taking place in the region of the Upper Paraná River floodplain and in its boundaries. A secondary aim is to show how those two factors have been changing people's working and living conditions and the identity configuration of some of the human groups that live at that site.

O ambiente e a sociedade são conjuntos complexos de elementos e de interações. Por isto, a compreensão de processos em que estejam envolvidos tanto elementos ambientais quanto psicossociais não pode ser feito a partir do conhecimento de uma ou outra variável isolada. Partindo destas premissas, este texto adota como eixo principal as relações de trabalho e tem dois objetivos complementares. Um deles é o de apresentar algumas análises sobre a interação entre as ações humanas e as transformações ambientais que vêm ocorrendo na região da planície de inundação do Alto Rio e em seus entornos. O outro é o de mostrar como aqueles dois fatores têm alterado as condições de trabalho, de vida e até mesmo a configuração da identidade dos participantes de alguns dos grupos humanos que ali residem.