Residual performance of HPFRCC exposed to fire – Effects of matrix strength, synthetic fiber, and fire duration

2020 ◽  
Vol 241 ◽  
pp. 118038
Author(s):  
Doo-Yeol Yoo ◽  
Soonho Kim ◽  
Gi-Joon Park ◽  
Jung-Jun Park
Keyword(s):  
Fire Effects ◽  
Synthetic Fiber ◽  
Matrix Strength ◽  
Residual Performance

scholarly journals Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 445
Author(s):  
José Valdez Aguilar ◽  
César A. Juárez-Alvarado ◽  
José M. Mendoza-Rangel ◽  
Bernardo T. Terán-Torres
Keyword(s):  
Reinforced Concrete ◽  
Plain Concrete ◽  
Fiber Reinforced Concrete ◽  
Fiber Reinforced ◽  
Steel Fiber Reinforced Concrete ◽  
Cracking Behavior ◽  
Bending Tests ◽  
Depth Ratio ◽  
Residual Performance ◽  
Concrete Control

Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred.

scholarly journals A large database supports the use of simple models of post-fire tree mortality for thick-barked conifers, with less support for other species

Fire Ecology ◽  
2020 ◽  
Vol 16 (1) ◽  
Author(s):  
C. Alina Cansler ◽  
Sharon M. Hood ◽  
Phillip J. van Mantgem ◽  
J. Morgan Varner
Keyword(s):  
Tree Mortality ◽  
Characteristic Curve ◽  
Small Diameter ◽  
Fire Effects ◽  
Tree Level ◽  
Clear Understanding ◽  
Bark Thickness ◽  
Mortality Models ◽  
Species Specific ◽  
Stem Mortality

Abstract Background Predictive models of post-fire tree and stem mortality are vital for management planning and understanding fire effects. Post-fire tree and stem mortality have been traditionally modeled as a simple empirical function of tree defenses (e.g., bark thickness) and fire injury (e.g., crown scorch). We used the Fire and Tree Mortality database (FTM)—which includes observations of tree mortality in obligate seeders and stem mortality in basal resprouting species from across the USA—to evaluate the accuracy of post-fire mortality models used in the First Order Fire Effects Model (FOFEM) software system. The basic model in FOFEM, the Ryan and Amman (R-A) model, uses bark thickness and percentage of crown volume scorched to predict post-fire mortality and can be applied to any species for which bark thickness can be calculated (184 species-level coefficients are included in the program). FOFEM (v6.7) also includes 38 species-specific tree mortality models (26 for gymnosperms, 12 for angiosperms), with unique predictors and coefficients. We assessed accuracy of the R-A model for 44 tree species and accuracy of 24 species-specific models for 13 species, using data from 93 438 tree-level observations and 351 fires that occurred from 1981 to 2016. Results For each model, we calculated performance statistics and provided an assessment of the representativeness of the evaluation data. We identified probability thresholds for which the model performed best, and the best thresholds with either ≥80% sensitivity or specificity. Of the 68 models evaluated, 43 had Area Under the Receiver Operating Characteristic Curve (AUC) values ≥0.80, indicating excellent performance, and 14 had AUCs <0.7, indicating poor performance. The R-A model often over-predicted mortality for angiosperms; 5 of 11 angiosperms had AUCs <0.7. For conifers, R-A over-predicted mortality for thin-barked species and for small diameter trees. The species-specific models had significantly higher AUCs than the R-A models for 10 of the 22 models, and five additional species-specific models had more balanced errors than R-A models, even though their AUCs were not significantly different or were significantly lower. Conclusions Approximately 75% of models tested had acceptable, excellent, or outstanding predictive ability. The models that performed poorly were primarily models predicting stem mortality of angiosperms or tree mortality of thin-barked conifers. This suggests that different approaches—such as different model forms, better estimates of bark thickness, and additional predictors—may be warranted for these taxa. Future data collection and research should target the geographical and taxonomic data gaps and poorly performing models identified in this study. Our evaluation of post-fire tree mortality models is the most comprehensive effort to date and allows users to have a clear understanding of the expected accuracy in predicting tree death from fire for 44 species.

scholarly journals Factors Affecting Acoustic Properties of Natural-Fiber-Based Materials and Composites: A Review

Textiles ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 55-85
Author(s):  
Tufail Hassan ◽  
Hafsa Jamshaid ◽  
Rajesh Mishra ◽  
Muhammad Qamar Khan ◽  
Michal Petru ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Natural Fiber ◽  
Volume Fraction ◽  
Fiber Type ◽  
Alkali Treatment ◽  
Acoustic Properties ◽  
Synthetic Fiber ◽  
Sound Insulation ◽  
Factors Affecting ◽  
Wide Range

Recently, very rapid growth has been observed in the innovations and use of natural-fiber-based materials and composites for acoustic applications due to their environmentally friendly nature, low cost, and good acoustic absorption capability. However, there are still challenges for researchers to improve the mechanical and acoustic properties of natural fiber composites. In contrast, synthetic fiber-based composites have good mechanical properties and can be used in a wide range of structural and automotive applications. This review aims to provide a short overview of the different factors that affect the acoustic properties of natural-fiber-based materials and composites. The various factors that influence acoustic performance are fiber type, fineness, length, orientation, density, volume fraction in the composite, thickness, level of compression, and design. The details of various factors affecting the acoustic behavior of the fiber-based composites are described. Natural-fiber-based composites exhibit relatively good sound absorption capability due to their porous structure. Surface modification by alkali treatment can enhance the sound absorption performance. These materials can be used in buildings and interiors for efficient sound insulation.

scholarly journals Characterization of a new natural fiber extracted from Corypha taliera fruit

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Taslima Ahmed Tamanna ◽  
Shah Alimuzzaman Belal ◽  
Mohammad Abul Hasan Shibly ◽  
Ayub Nabi Khan
Keyword(s):  
Tensile Strength ◽  
Natural Fiber ◽  
Natural Fibers ◽  
Morphological Characteristics ◽  
Synthetic Fiber ◽  
X Ray Diffraction ◽  
Reinforced Composite ◽  
Potential Alternative

AbstractThis study deals with the determination of new natural fibers extracted from the Corypha taliera fruit (CTF) and its characteristics were reported for the potential alternative of harmful synthetic fiber. The physical, chemical, mechanical, thermal, and morphological characteristics were investigated for CTF fibers. X-ray diffraction and chemical composition characterization ensured a higher amount of cellulose (55.1 wt%) content and crystallinity (62.5%) in the CTF fiber. The FTIR analysis ensured the different functional groups of cellulose, hemicellulose, and lignin present in the fiber. The Scherrer’s equation was used to determine crystallite size 1.45 nm. The mean diameter, specific density, and linear density of the CTF fiber were found (average) 131 μm, 0.86 g/cc, and 43 Tex, respectively. The maximum tensile strength was obtained 53.55 MPa for GL 20 mm and Young’s modulus 572.21 MPa for GL 30 mm. The required energy at break was recorded during the tensile strength experiment from the tensile strength tester and the average values for GL 20 mm and GL 30 mm are 0.05381 J and 0.08968 J, respectively. The thermal analysis ensured the thermal sustainability of CTF fiber up to 230 °C. Entirely the aforementioned outcomes ensured that the new CTF fiber is the expected reinforcement to the fiber-reinforced composite materials.

Integrating fire effects on vegetation carbon cycling within an ecohydrologic model

2020 ◽  
Vol 416 ◽  
pp. 108880 ◽  
Author(s):  
Ryan R. Bart ◽  
Maureen C. Kennedy ◽  
Christina L. Tague ◽  
Donald McKenzie
Keyword(s):  
Carbon Cycling ◽  
Fire Effects ◽  
Vegetation Carbon

scholarly journals Predicting wildfire impacts on the prehistoric archaeological record of the Jemez Mountains, New Mexico, USA

Fire Ecology ◽  
2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Megan M. Friggens ◽  
Rachel A. Loehman ◽  
Connie I. Constan ◽  
Rebekah R. Kneifel
Keyword(s):  
New Mexico ◽  
Fire Severity ◽  
Fire Effects ◽  
Burn Severity ◽  
Fire Season ◽  
Archaeological Sites ◽  
Archaeological Record ◽  
Human Environment ◽  
Jemez Mountains ◽  
Archaeological Materials

Abstract Background Wildfires of uncharacteristic severity, a consequence of climate changes and accumulated fuels, can cause amplified or novel impacts to archaeological resources. The archaeological record includes physical features associated with human activity; these exist within ecological landscapes and provide a unique long-term perspective on human–environment interactions. The potential for fire-caused damage to archaeological materials is of major concern because these resources are irreplaceable and non-renewable, have social or religious significance for living peoples, and are protected by an extensive body of legislation. Although previous studies have modeled ecological burn severity as a function of environmental setting and climate, the fidelity of these variables as predictors of archaeological fire effects has not been evaluated. This study, focused on prehistoric archaeological sites in a fire-prone and archaeologically rich landscape in the Jemez Mountains of New Mexico, USA, identified the environmental and climate variables that best predict observed fire severity and fire effects to archaeological features and artifacts. Results Machine learning models (Random Forest) indicate that topography and variables related to pre-fire weather and fuel condition are important predictors of fire effects and severity at archaeological sites. Fire effects were more likely to be present when fire-season weather was warmer and drier than average and within sites located in sloped, treed settings. Topographic predictors were highly important for distinguishing unburned, moderate, and high site burn severity as classified in post-fire archaeological assessments. High-severity impacts were more likely at archaeological sites with southern orientation or on warmer, steeper, slopes with less accumulated surface moisture, likely associated with lower fuel moistures and high potential for spreading fire. Conclusions Models for predicting where and when fires may negatively affect the archaeological record can be used to prioritize fuel treatments, inform fire management plans, and guide post-fire rehabilitation efforts, thus aiding in cultural resource preservation.

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