Experimental Study on the Explosive Spalling in High-Performance Concrete: Role of Aggregate and Fiber Types

A complete description of the mechanical behavior of High-Performance Concrete in fire still requires further efforts to fully understand the tricky phenomenon of spalling, whose complexity comes from the interaction among different phenomena, namely: the microstructural changes occurring in concrete at high temperature, the pressure rising in the pores, and the stress induced by both thermal gradients and external loads. To what extent these different aspects influence each other is still not completely clear, and within this context a comprehensive experimental campaign has been launched at the Politecnico di Milano, focusing on the role played by concrete grade, aggregate type, and fiber type and content. Eleven concrete mixes are investigated considering three grades (fc ≥ 40, 60 and 90 MPa), three aggregate types (silico-calcareous, basalt and calcareous aggregates) and different fiber types and contents (steel and monofilament or fibrillated polypropylene fibers)

A nature‐inspired nrf2 activator protects retinal explants from oxidative stress and neurodegeneration

Oxidative stress (OS) plays a key role in retinal dysfunctions and acts as a major trigger of inflammatory and neurodegenerative processes in several retinal diseases. To prevent OS‐induced retinal damage, approaches based on the use of natural compounds are actively investigated. Recently, structural features from curcumin and diallyl sulfide have been combined in a nature‐inspired hybrid (NIH1), which has been described to activate transcription nuclear factor erythroid‐ 2‐related factor‐2 (Nrf2), the master regulator of the antioxidant response, in different cell lines. We tested the antioxidant properties of NIH1 in mouse retinal explants. NIH1 increased Nrf2 nuclear translocation, Nrf2 expression, and both antioxidant enzyme expression and protein levels after 24 h or six days of incubation. Possible toxic effects of NIH1 were excluded since it did not alter the expression of apoptotic or gliotic markers. In OS‐treated retinal explants, NIH1 strengthened the antioxidant response inducing a massive and persistent expression of antioxidant enzymes up to six days of incubation. These effects resulted in prevention of the accumulation of reactive oxygen species, of apoptotic cell death, and of gliotic reactivity. Together, these data indicate that a strategy based on NIH1 to counteract OS could be effective for the treatment of retinal diseases

Toward the renal vesicle: Ultrastructural investigation of the cap mesenchyme splitting process in the developing kidney

Background: A complex sequence of morphogenetic events leads to the development of the adult mouse kidney. In the present study, we investigated the morphological events that characterize the early stages of the mesenchymal-to-epithelial transition of cap mesenchymal cells, analyzing in depth the relationship between cap mesenchymal induction and ureteric bud (UB) branching. Design and methods: Normal kidneys of newborn non-obese diabetic (NOD) mice were excised and prepared for light and electron microscopic examination. Results: Nephrogenesis was evident in the outer portion of the renal cortex of all examined samples. This process was mainly due to the interaction of two primordial derivatives, the ureteric bud and the metanephric mesenchyme. Early renal developmental stages were initially characterized by the formation of a continuous layer of condensed mesenchymal cells around the tips of the ureteric buds. These caps of mesenchymal cells affected the epithelial cells of the underlying ureteric bud, possibly inducing their growth and branching. Conclusions: The present study provides morphological evidence of the reciprocal induction between the ureteric bud and the metanephric mesenchyme showing that the ureteric buds convert mesenchyme to epithelium that in turn stimulates the growth and the branching of the ureteric bud

Spalling Test on Concrete Slabs Under Biaxial Membrane Loading

Concrete spalling is a rather complex phenomenon ensuing from the interaction of different aspects – often hard to be monitored – namely, temperature, pressure in the pores and stress. It is, in fact, commonly agreed that spalling is triggered by the mutual influence of hygro-thermal and thermo-mechanical processes. Aimed at investigating these two critical issues, an ad hoc test setup was developed at the Politecnico di Milano, based on in plane-loaded slabs. Concrete specimens of dimensions 800x800x100 mm were subjected to the Standard Fire at the intrados, while a constant biaxial compressive load was applied. Pore pressure and temperature at 6 different depths, as well as the flexural behaviour, were continuously monitored during the test. Taking advantage of this facility, an experimental campaign was carried out on one High-Performance Concrete (fc ≥ 60 MPa with silico-calcareous aggregate), without or with one among 3 different fibre types (steel fibre, monofilament or fibrillated polypropylene fibre). So far, tests on concrete without and with polypropylene fibre were carried out. Explosive spalling was observed in plain concrete only, with a remarkably homogeneous spalled layer. In all cases, the mechanical response was characterized by sagging deflection due to thermal strain followed by hogging deformation due to creep and plastic strain