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Organisationseinheit der BAM
Stress is a normal part of life for fungi, which can survive in environments considered inhospitable or hostile for other organisms. Due to the ability of fungi to respond to, survive in, and transform the environment, even under severe stresses, many researchers are exploring the mechanisms that enable fungi to adapt to stress. The International Symposium on Fungal Stress (ISFUS) brings together leading scientists from around the world who research fungal stress. This article discusses presentations given at the third ISFUS, held in Sao Jose dos Campos, Sao Paulo, Brazil in 2019, thereby summarizing the state-of-the-art knowledge on fungal stress, a field that includes microbiology, agriculture, ecology, biotechnology, medicine, and astrobiology.
Volumetric changes follow Portland cement hydration reactions: aluminates' hydration is generally expansive, whereas silicates' reaction leads to shrinkage. Determining the volumetric variation at very early ages (i.e., first minutes/hours) presents operational challenges; most standards prescribe the measurement on specimens that are already hardened, while measurements from the fresh state are not standardized. This article reports the first attempt to use in-situ X-ray diffraction (XRD) to measure the early-age volumetric variation of a cementitious paste. For this purpose, a C3A + gypsum paste was assessed for 36 h, measuring its vertical displacement over time through XRD. The results showed that the expansion increased in the first ∼13 h, in line with the ettringite formed up to ∼11 h. In addition, the volumetric expansion agreed well with the heat release in calorimetry. It is concluded that the volumetric variation measurement of cementitious pastes through in-situ XRD is a promising technique, but further studies are needed to make this technique consolidated.
This study investigated the effect of incorporating three types of nanosilica (NS), two powders, and one colloidal suspension on the hydration, strength, and microstructure of calcium sulfoaluminate (CSA) cement pastes prepared with and without a superplasticizer (SP). X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and compressive strength tests were performed after 2, 5, and 28 days of hydration. The results showed that both NS powders delayed cement hydration at an early age, which was attributed to particle agglomeration (confirmed by dynamic light scattering). Whereas well-dispersed colloidal NS did not significantly affect the hydration of CSA at the investigated ages. SP incorporation improved the dispersion of CSA cement particles, resulting in a 10% increase in the degree of hydration of ye’elimite at 28 days for the system without NS. Conversely, when the SP was incorporated in NS-containing mixtures, it hindered cement hydration of the systems with powdered NS, but did not significantly affect the cement hydration of the system containing colloidal NS. The SEM images suggested that the SP changed the ettringite morphology, thereby negatively affecting the mechanical strength of the CSA pastes.