RESUMEN
This paper explores the impact of steel-PVA hybrid fibers (S-PVA HF) on the flexural performance of panel concrete via three-point bending tests. Crack development in the concrete is analyzed through Digital Image Correlation (DIC) and Scanning Electron Microscope (SEM) experiments, unveiling the underlying mechanisms. The evolution of cracks in concrete is quantitatively analyzed based on fractal theory, and a predictive model for flexural strength (PMFS) is established. The results show that the S-PVA HF exhibits a synergistic effect in enhancing and toughening the concrete at multi-scale. The crack area of steel-PVA hybrid fiber concrete (S-PVA HFRC) is linearly correlated with deflection (δ), and it further reduces the crack development rate and crack area compared to steel fiber-reinforced concrete (SFRC). The S-PVA HF improves the proportional ultimate strength (fL) and residual flexural strength (fR,j) of concrete, and the optimal flexural performance of concrete is achieved when the steel fiber dosage is 1.0% and the PVA fiber dosage is 0.2%. The established PMFS of hybrid fiber-reinforced concrete (HFRC) can effectively predict the flexural strength of concrete.
RESUMEN
This paper investigates the effects of steel fiber and PVA fiber hybrid blending on the compressive strength (fcc), splitting tensile strength (fts), compression energy (W1.0), and shrinkage properties of concrete. It also establishes a multi-factor crack resistance index evaluation model based on the Analytic Hierarchy Process (AHP) to comprehensively evaluate the crack resistance of concrete. The results show that the steel-PVA hybrid fiber (S-PVA HF) further enhances fcc, fts, the compression energy, and the shrinkage suppression properties of the concrete. The crack resistance of the steel-PVA hybrid fiber concrete (S-PVA HFRC) is the best when the proportion of steel fiber is 1.0% and that of the PVA fiber is 0.2%, and it increases up to 143% compared to the baseline concrete. The established concrete crack resistance evaluation model has a certain reliability.
RESUMEN
Neonatal Sprague-Dawley rats were randomly divided into normal control, mild hypoxia-ischemia (HI), and severe HI groups (N = 10 in each group at each time) on postnatal day 7 (P7) to study the effect of mild and severe HI on anxiety-like behavior and the expression of tyrosine hydroxylase (TH) in the substantia nigra (SN). The mild and severe HI groups were exposed to hypoxia (8 percent O2/92 percent N2) for 90 and 150 min, respectively. The elevated plus-maze (EPM) test was performed to assess anxiety-like behavior by measuring time spent in the open arms (OAT) and OAT percent, and immunohistochemistry was used to determine the expression of TH in the SN at P14, P21, and P28. OAT and OAT percent in the EPM were significantly increased in both the mild (1.88-, 1.99-, and 2.04-fold, and 1.94-, 1.51-, and 1.46-fold) and severe HI groups (1.69-, 1.68-, and 1.87-fold, and 1.83-, 1.43-, and 1.39-fold, respectively; P < 0.05). The percent of TH-positive cells occupying the SN area was significantly and similarly decreased in both the mild (17.7, 40.2, and 47.2 percent) and severe HI groups (16.3, 32.2, and 43.8 percent, respectively; P < 0.05). The decrease in the number of TH-positive cells in the SN and the level of protein expression were closely associated (Pearson correlation analysis: r = 0.991, P = 0.000 in the mild HI group and r = 0.974, P = 0.000 in the severe HI group) with the impaired anxiety-like behaviors. We conclude that neonatal HI results in decreased anxiety-like behavior during the juvenile period of Sprague-Dawley rats, which is associated with the decreased activity of TH in the SN. The impairment of anxiety and the expression of TH are not likely to be dependent on the severity of HI.