High Temperature Damage Research Articles

Low-temperature sintering of silver-ammonia complex organic composite ink shows high conductivity for humidity sensors

The development of flexible electronic devices is faced with the challenge of difficult fabrication of complex functional structures on flexible substrates. In this paper, a high viscosity ink of silver-ammonia complex was developed based on the reductive ink principle. Using the electrohydrodynamic direct writing, composite fiber patterned printing was achieved on a flexible substrate. By low-temperature sintering of precursor fibers for reduction, a dense silver structure was formed on the surface, resulting in the formation of Ag/PEO conductive fibers. This approach avoided the high temperature damage to the flexible substrate and the adhesion of materials, while demonstrating good conductivity. The Ag/PEO conductive fibers exhibited different sensitivities to H2O molecules in low, medium, and high humidity environments, which were used to design a flexible Ag structure humidity sensor (ASHS) as a functional material. The ASHS showed a linear response relationship and a fast response speed in an environmental humidity range of 11 % to 75 %RH, enabling real-time monitoring of human respiration. This study demonstrates a promising application prospect of the silver-ammine complex ink in the field of flexible electronic devices.

Magnesium fertilization reduces high-temperature damages during anthesis in spring wheat (Triticum aestivum L.) by affecting pollen viability and seed weight.

Terminal heat during reproductive stages of wheat (Triticum aestivum L.) limits the productivity of the crop. Magnesium (Mg) is an essential macronutrient that is involved in many physiological and biochemical processes to affect photosynthesis and seed weight. The present study comparatively evaluated Mg applied to soil (80 kg MgSO4·7H2O ha-1) and to plant foliage (4% w/v) in improving wheat performance under terminal heat. Wheat crop was grown in two sets of treatments until the booting stage, and then one set of plants was shifted to a glasshouse (±5 °C) at the booting stage to grow until maturity in comparison to control plants kept under ambient warehouse condition. Heat stress reduced the pollen viability while foliar- and soil-applied Mg improved it by 3% and 6% under heat stress, respectively, compared to the control without Mg treatment. The 100-seed weight, spike length, and biological yield reduced by 39%, 19%, and 50% under heat stress; however, foliar and soil application increased 100-seed weight by 45% and 40%, spike length by 8% and 5%, and biological yield by 35% and 25% under heat stress, respectively. Soil Mg showed maximum SPAD chlorophyll values; however, response was statistically similar to that of foliar Mg as compared to the control without Mg supply. Membrane stability decreased (4%) due to heat stress while foliar and soil treatments improved membrane stability by 8% and 5% compared to that of the control, respectively. Thus, Mg application through soil or plant foliage can be an effective way to reduce negative impacts of terminal heat in wheat by improving pollen viability at anthesis and 100-seed weight that was attributed to increased chlorophyll contents during anthesis.

Research on Constitutive Model and Algorithm of High-Temperature-Load Coupling Damage Based on the Zienkiewicz–Pande Yield Criterion

The mechanical properties of rock can be weakened under the influence of high temperatures. To describe the mechanical behavior of rock under the action of high temperature more accurately, based on the Zienkiewicz–Pande yield criterion, the damage variable Dc which accounts for the coupling between high temperature and load is introduced. According to plastic potential theory and plastic flow law, the iterative incremental method for a high-temperature and load-coupled damage constitutive model in Flac3D is deduced in detail and compiled into the corresponding dynamic link library file (.dll file). By modifying the shape function to degenerate into the Mohr–Coulomb constitutive model, an elastic–plastic analysis of an ideal circular tunnel is performed, and a comparison is made between calculation results obtained from the built-in Mohr–Coulomb constitutive model in Flac3D, proving the correctness of the secondary development program. Finally, numerical simulations are conducted to study the effects of high-temperature damage using rock uniaxial compression tests, and the model’s validity is established by comparing it with previous experimental results.

Feasibility of waste foundry sand in high-strength self-compacting concrete and the effects of elevated temperatures

The disposal and recycling of waste foundry sand (WFS) as industrial solid waste can effectively solve potential environmental pollution problems. This paper conducted an experimental investigation on the effects of elevated temperatures on mechanical properties and microstructural characteristics of high-strength self-compacting concrete (HSSCC) incorporating WFS for substituting river sand with different contents (i.e., 0%, 25%, 50%, 75% and 100% by weight). The workability of fresh concrete including slump flow, J-ring, T500, and V-tunnel box tests were first measured. A series of tests including ultrasound pulse velocity (UPV), residual compressive strength and the behavior of capillary water absorption were conducted before and after different temperatures (100 °C, 200 °C, 300 °C, 400 °C) following an air-cooling time. Further, the thermal analysis and microstructural observation were conducted for the evaluation of high-temperature damage evolution by using thermogravimetry (TG), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The test results showed that the specimens obtained excellent self-compaction performance at 50% WFS replacement rate. The coupling effect of WFS substitution rate and temperature level has a large effect on the mechanical properties and thermal resistance. Compared with the control group, the 28-day compressive strength of HSSCC-WFS50 was increased by 8.2%. In addition, thermal analysis tests (TG/DTG/DSC) and SEM also elucidated the changes of HSSCC-WFS products and microstructures at high temperature from a fine microscopic perspective to reveal the deterioration mechanism of HSSCC-WFS durability after high temperature damage.

Experimental Research into the Repair of High Temperature Damage to Cement Mortar Samples Using Microbial Mineralization Technology

Experiments such as microbial activation culture, subculture selection, and fire damage repair of cement mortar specimens were conducted to investigate the repairing effect of Sporosarcina pasteurii as a repair agent for fire-damaged cracks in cement mortar specimens. In addition, multi-scale parameters such as compressive strength and chloride ion migration coefficient of cement mortar specimens before and after restoration were compared. The effect of microbial mineralization technology on the repair of fire-damaged cracks in cement mortar specimens was investigated, and the microstructure and mineral composition of the products were analyzed. The results showed that the strong alkaline environment in the cracks of the cement mortar specimens after a high temperature of 500 °C inhibited the activity of bacteria and weakened the mineralization effect; the compressive strength of the repaired cement mortar specimens was 22.8% higher than that of the unrepaired fire-damaged specimens; the compressive strength of the repaired cement mortar reached 78.2% of the strength of the original cement mortar specimen without high temperature; after restoration, the chloride ion penetration resistance of the cement mortar specimens decreased by about 16.9% compared with that before restoration.

Multi-factor coupling analysis and identification of tanks BLEVE

In a fire environment, liquid storage tanks are prone to integral cracking and eventually boiling liquid expanding vapor explosion (BLEVE), which a fireball, generates overpressure and ejected fragments with great impact on the safety of the tank area. Hence, it is important to reveal the influencing factors of the liquid storage tank failure process and the conditions that trigger integral cracking failure for the flammable liquid tank explosion accident prevention. This paper is aimed at the failure problem of metal storage tanks exposed to high temperature for a long time, through the fire experiment of small liquid tanks, taking the filling rate of tanks itself and the fire engulfment area as variables, the failure mechanism of tanks fire environment was explored from the aspects of pressure response, temperature response, failure form and tank deformation characteristics. A criterion was proposed to determine whether BLEVE will occur, which is based on the comprehensive analysis of the influence of tank internal pressure and high temperature damage of the material.

Hybrid fire collapse simulation of reinforced concrete structures under localized fires

The safety of extensive reinforced concrete (RC) buildings under sudden fire scenarios is of particular concern nowadays. Localized fires may bring serious damage and even collapse to the RC bearing structures, causing huge casualties and economic losses. However, due to the limitations of test facilities, technology, and high costs, etc., full-scale and even reduced-scale structural fire tests have been very limited. The recent development of numerical techniques instead of challenging physical tests has provided exciting prospects for refinement of structural fire behavior prediction. This paper is therefore focused on a hybrid fire collapse simulation method through performing damage analysis of the locally fire-heated components and collapse simulation of the remaining major structure. The damage and failure behavior of the fire-exposed substructure is simulated based on an energy-based elastoplastic damage model for concrete at elevated temperatures. While the resulting deformation and collapse of the rest main structure is modeled by conventional collapse analysis. The key to the hybrid simulation is the coordination of internal forces and deformations between the substructure and the main structure. The developed method allows for an integrated simulation of the whole process from high temperature damage of materials to fire destruction of local components and to the collapse of the entire RC structure.

Effects of Three Exogenous Substances on Heat Tolerance of Peony Seedlings

In this study, one-year-old seedlings of Paeonia ostii ‘Fengdan’ were used as materials. The method of spraying exogenous salicylic acid (SA), calcium chloride (CaCl2) and abscisic acid (ABA) was used. The effects of different concentrations of SA, CaCl2 and ABA on the heat tolerance of peony seedlings under high temperature stress were studied. The optimum concentration and mechanism of SA-, CaCl2- and ABA-induced heat tolerance of peony seedlings under high temperature stress were discussed. The results showed that 100 μmol/L SA, 40 mmol/L CaCl2 and 40 mg/L ABA had the best induction effect on the heat tolerance of peony. The effects of three exogenous substances on the heat resistance of peony seedlings were ranked as SA > CaCl2 > ABA. The three exogenous substances mainly alleviated high temperature damage by alleviating the degradation of chlorophyll (Chl), relative electrical conductivity (Rec) content, increasing superoxide dismutase (SOD) activity, soluble proteins (SPs), free proline (Pro) and soluble sugars (SSs) content, and reducing SSs content under high temperature stress. The five indices had the most significant effect on the three exogenous substances in improving the heat resistance of peony seedlings. These could be used as an index to identify the heat resistance.

An Inverse Optimization Method for the Parameter Determination of the High-Temperature Damage Model and High-Temperature Damage Graph of Ti6Al4V Alloy.

Ti6AL4V alloy is widely used in the biomedical and energy vehicle industries, among others. Ti6Al4V alloy cannot be fabricated at ambient temperatures; hence, it requires hot forming. However, this method is susceptible to crack defects. The crack defect problem of Ti6AL4V alloy in the hot-forming process cannot be ignored, so we must develop a precise hot-forming damage prediction model. In this study, three high-temperature damage models of Ti6Al4V alloy were developed, considering the temperature and strain rate. These models were derived from the normalized Cockcroft and Latham (NCL), Oyane, and Rice and Tracey (RT) damage models. The damage parameters of the models were identified using a genetic algorithm combined with finite element simulation. The force accumulation error of the Ti6AL4V alloy specimen, which was obtained from a simulated thermal tensile test and an actual test, was used as an optimization target function. Then, the damage parameters were optimized using the genetic algorithm until the target function reached the minimum value. Finally, the optimal damage model parameter was obtained. Through program development, the three high-temperature damage models established in this paper were embedded into Forge® NxT 2.1 finite element software. The simulated thermal tensile test of Ti6AL4V alloy was performed at a temperature of 800-1000 °C and a strain rate of 0.01-5 s-1. The simulated and actual fracture displacements of the tensile specimens were compared. The correlation coefficients (R) were calculated, which were 0.997, 0.951, and 0.912. Of the high-temperature damage models, the normalized Cockcroft and Latham high-temperature damage model had higher accuracy in predicting crack defects of Ti6Al4V alloy during the hot-forming process. Finally, a fracture strain graph and a high-temperature damage graph of Ti6Al4V alloy were constructed. The Ti6Al4V alloy damage evolution and thermal formability were analyzed in relation to the temperature and strain rate.

Ultra low-temperature fabrication of hollow glass microspheres and polysilazane coating for enhanced thermal protection of carbon/epoxy composites

This investigation was aimed to develop high-temperature resistant coatings suitable for carbon fiber-reinforced epoxy composites at ultra low preparation temperatures. In the organic-inorganic coating, hollow glass microspheres were chosen as the filling phase, and polysilazane was selected as the film-forming material. Fourier transforms infrared spectra showed that polysilazane can be cross-linked and solidified at low temperatures, which provided the possibility for protecting the substrate from high-temperature damage. By modifying the surface of hollow glass microspheres, the coating dispersions were able to maintain good stability within 120 min. The coating exhibited good thermal vibration resistance and could stand at 220 °C for 30 min after 6 cycles without obvious cracking and peeling. After the static thermal test, the coated composites still maintained a flexural strength of 603.7±19.2 MPa (retention rate can reach 86.6%) at 250 °C, which was higher than that (593.3±14.8 MPa) of uncoated samples at 190 °C. The results indicated that the coating has the advantage of low curing temperature, convenient operation, and excellent thermal protection performance, which could further expand the potential application of carbon fiber-reinforced epoxy composites in firefighting unmanned aerial vehicles, hypersonic missiles, and other fields.

Insights into oxidation and nitridation of alumina-forming FeCrAl alloy after supercritical water exposure: Effect of pre-corrosion on high-temperature damage behavior

This work investigated the corrosion characteristics of FeCrAl alloy in supercritical water (SCW), and focused on the effect of SCW pre-corrosion on the alloy oxidation and nitridation at 900 °C. FeCrAl alloy formed outer Fe-rich oxides (mainly Fe2O3) and inner Fe-Cr-Al oxides during SCW exposure. SCW pre-corrosion made FeCrAl alloy exhibit different morphologies and phase compositions in the same medium. SCW pre-corrosion promoted the deposition of Ni and Mo elements from the autoclave, filling the gaps in flaky oxides by forming Ni- and/or Mo-rich products in air and N2. Moreover, SCW pre-corrosion avoided the appearance of accelerated nitridation zones in N2. However, pre-corrosion caused the preferential diffusion of N2 and air. Outward-diffused Cr ions during SCW exposure reacted with O impurities in N2 to form Cr2O3 that easily dissociated N2, leading to the development of nitridation towards the alloy interior.

A non-specific lipid transfer protein, NtLTPI.38, positively mediates heat tolerance by regulating photosynthetic ability and antioxidant capacity in tobacco

Non-specific lipid transfer proteins (nsLTPs) play an important role in plant growth and stress resistance; however, their function in tobacco remains poorly understood. Therefore, to explore the function of NtLTP in response to high temperature, we identified an NtLTPI.38 from tobacco, obtained its overexpression and knockout transgenic plants, and further studied their response to heat stress (42 °C). The results showed that NtLTPI.38 overexpression in tobacco reduced chlorophyll degradation, alleviated the high temperature damage to photosynthetic organs, and enhanced the photosynthetic capacity of tobacco under heat stress. NtLTPI.38 overexpression in heat-stressed tobacco increased the contents of soluble sugar and protein, proline, and flavonoid substances, reduced the relative conductivity, and decreased H2O2, O2•−, and MDA accumulation, and increased the enzymatic antioxidant activities, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), compared to wild type (WT) and knockout mutant plants. RT-PCR confirmed that the expression levels of antioxidant enzymes and thermal stress-related genes were significantly upregulated under thermal stress in overexpression plants. Therefore, NtLTPI.38 enhanced heat tolerance in tobacco by mitigating photosynthetic damage and improving osmoregulation and antioxidant capacity. These results provided the theoretical basis and a potential resource for further breeding projects to improve heat tolerance in plants.

Investigation of the correlation between molecular structures with high-temperature and salt resistance for acrylamides polymer in drilling fluid

Deep oil and gas are essential alternative resources for future energy sources, but the lack of high temperature and high salt resistance mechanisms and agents significantly limits their development. Copolymers of six commonly used high-temperature and salt resistance monomers and acrylamide with similar molecular weights were prepared to improve oil recovery in deep reservoirs. The effects of different functional groups on the high-temperature and salt resistance of polymers were revealed by the drilling fluid and elemental analysis, TOC test, Zeta potential, particle size, and other analytical methods. Experimental results indicate that the pyrrole ring groups, quaternary amine groups, long-chain sulfonate groups, and benzenesulfonic acid groups can effectively improve the high-temperature stability of polymers in an aqueous solution. Quaternary ammonium groups and pyrrole rings can enhance the polymer adsorption with clay under high temperatures and high salinity conditions due to charge attraction. However, these functional groups hinder the clay dispersion and reduce the stability of drilling fluids. Hydration groups, such as sulfonic and carboxylic acid groups, can better maintain the colloidal stability of drilling fluids under high temperatures and high salinity, and benzene sulfonic acid groups are the optimal hydration groups. After the polymer is adsorbed on the clay surface, the benzene sulfonic acid group assists in forming a thicker hydration film on the clay surface, effectively hindering the damage of high temperature and high salinity on the clay. The findings and observations of this study provide theoretical support for the development of high-temperature and salt resistance polymers for water-based drilling fluids of ultra-deep wells.

Study on the Oil Well Cement-Based Composites to Prevent Corrosion by Carbon Dioxide and Hydrogen Sulfide at High Temperature

Complex wells with high temperature and the presence of carbon dioxide and hydrogen sulfide acid gas require the use of high-temperature and high-density anti-corrosion cement slurry for cementing operations, and conventional cement slurry does not have the advantages of high density, high-temperature resistance, or corrosion resistance. In order to avoid the severe corrosion of cement slurry by carbon dioxide and hydrogen sulfide at high temperatures, solid phase particles with different particle sizes are combined with polymer materials to form a dense, high-density, high-temperature- and corrosion-resistant cement slurry. In this paper, we consider the use of manganese ore powder weighting agent, composite high-temperature stabilizer, inorganic preservative slag and organic preservative resin to improve the corrosion resistance of cement slurry, design a high-density cement slurry that is resistant to high temperature and carbon dioxide and hydrogen sulfide corrosion, and evaluate the performances of the cement slurry at 180 °C. The results show that the manganese ore powder weighting agent effectively improves the density of the cement slurry. Using composite silica fume with different particle sizes as a high-temperature stabilizer can ensure the rheology of the cement slurry and improve the ability of the cement sample to resist high-temperature damage. The use of slag and resin as preservatives can effectively reduce the corrosion degree in cement slurry. The high-temperature corrosion-resistant cement slurry systems with different densities designed using these materials exhibit good rheological properties, with water loss of less than 50 mL and a thickening time of more than four hours. The compressive strength decreased by less than 5.8% after 28 days at high temperatures. After being corroded by hydrogen sulfide and carbon dioxide (total pressure 30 MPa, 16.7% hydrogen sulfide and 6.7% carbon dioxide) under high temperature (180 °C) for 30 days, the corrosion depth of the cement sample was less than 2 mm, the reduction of compressive strength was low, and the corrosion resistance was strong. These research results can be used for cementing operations of high-temperature oil and gas wells containing hydrogen sulfide and dioxide.

Intermediate- and high-temperature damage of bitumen modified by HDPE from various sources

This research investigated the effect of high-density polyethylene (HDPE) from various sources on the damage-related behaviour of bitumen in the intermediate- and high-temperature domains. For this purpose, base bitumen was modified by the mass fraction of 1.5% of HDPE from post-industrial recycled pellets and from post-consumer recycled flakes. The experimental programme consisted of the multiple stress creep and recovery from 40 to 70°C and of the linear shear strain amplitude sweep at 10, 20, and 30°C. The HDPE significantly reduced the non-recoverable creep compliance but increased the elastic recovery. The post-industrial HDPE-modified bitumen exhibited superior resistance to permanent deformation, with its crystallinity recognised as the most important factor. This reduced the susceptibility of its behaviour to shear stress and temperature. The HDPE-modified bitumen had a considerably longer fatigue life, but its sensitivity to premature failure at low temperatures and the conspicuously high brittleness represented the main issue for further improvements.

Genetic variation for terminal heat stress tolerance in winter wheat.

In many regions worldwide wheat (Triticum aestivum L.) plants experience terminal high temperature stress during the grain filling stage, which is a leading cause for single seed weight decrease and consequently for grain yield reduction. An approach to mitigate high temperature damage is to develop tolerant cultivars using the conventional breeding approach which involves identifying tolerant lines and then incorporating the tolerant traits in commercial varieties. In this study, we evaluated the terminal heat stress tolerance of 304 diverse elite winter wheat lines from wheat breeding programs in the US, Australia, and Serbia in controlled environmental conditions. Chlorophyll content and yield traits were measured and calculated as the percentage of non-stress control. The results showed that there was significant genetic variation for chlorophyll retention and seed weight under heat stress conditions. The positive correlation between the percent of chlorophyll content and the percent of single seed weight was significant. Two possible mechanisms of heat tolerance during grain filling were proposed. One represented by wheat line OK05723W might be mainly through the current photosynthesis since the high percentage of single seed weight was accompanied with high percentages of chlorophyll content and high shoot dry weight, and the other represented by wheat Line TX04M410164 might be mainly through the relocation of reserves since the high percentage of single seed weight was accompanied with low percentages of chlorophyll content and low shoot dry weight under heat stress. The tolerant genotypes identified in this study should be useful for breeding programs after further validation.

Natural plant inducer 2-Amino-3-Methylhexanoic acid protects physiological activity against high-temperature damage to tea (Camellia sinensis)

Increasing frequency of extreme summer high-temperature (HT) has become one of the most important limiting factors affecting tea production in China. 2-Amino-3-methylhexanoic acid (AMHA) is a unique natural plant inducer against HT stresses. In this study, the field efficacy and physiological mechanism of AMHA for improving tea plant resistance against HT in the summer was studied using the temperature-sensitive tea cultivar “Longjing 43″. It was observed that field-grown tea plants treated with 100 or 1000 nM AMHA maintained erect and normal stems and foliage under HT stress. The optimal concentration of AMHA for counteracting HT in field-grown tea plants was 100 nM. At three days after treatment (DAT), AMHA at 100 nM increased net photosynthetic rate Pn by 199% and stomatal conductance Gs of tea plants by 215% of tea plants. The fast chlorophyll a rise kinetics and JIP-test analysis further confirmed that AMHA improved the overall photosynthetic activity of photosystem II (PSII) mainly through enhancing the fraction of active oxygen evolving complex (OEC) centers, PSII energetic connectivity and electron transport efficiency. PIABS reflecting PSII overall activity in 100 nM AMHA-treated tea plants was increased by 95%, 51%, 39%, and 48% at 3, 5, 7, and 14 DAT, respectively, compared to mock. At the same dose, AMHA also increased osmotic adjustments for the rapid accumulation of amino acids and soluble sugars, which increased by 21% and 145% at 7 DAT, respectively. In addition, AMHA significantly enhanced the activities of peroxidase (POD), catalse (CAT) and superoxide dismutase (SOD), reducing oxidative damage on membrane lipids. Even at 14 DAT, 100 nM AMHA led to 50%, 75% and 19% increase in POD, CAT and SOD activity in tea plants relative to mock, respectively. Clearly, exogenous application of AMHA facilitated HT resistance by alleviating physiological damage in field-grown tea plants due to improved photosynthetic performance, osmotic adjustments and antioxidant enzyme activities.

Thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) after exposure to elevated temperatures

An experimental investigation on the influence of elevated temperatures on the thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) is presented. In total, 315 concrete specimens from 7 different mixtures with different replacement ratios (0, 30 %, 50 % and 100 % by weight) of two kinds of LWAs, namely cloud concrete stone (CCS) and fly ash ceramsite (FAC), were prepared. The workability of fresh concrete mixtures including slump, J-Ring and T500 tests was first conducted aiming at meeting the requirements of self-compacting performance. Hardened concrete specimens were then exposed to different elevated temperatures (i.e. 200 °C, 400 °C, 600 °C and 800 °C) increased with a heating rate of 10 °C/min. A series of tests including the apparent morphology, ultrasound pulse velocity (UPV), residual compressive strength and capillary water absorption were carried out on unheated control concrete and after air-cooling period of heated concrete. Finally, the thermal analysis and microstructural observation were further conducted through the thermogravimetry (TG), differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP), laser scanning microscopy (LSM) and scanning electron microscope (SEM) to characterize the evolution of high temperature damage. Generally, the high temperature resistance of HSSC-LWAC shows an increasing trend as the LWAs content increases, while the residual mechanical strength increases and then decreases with an increase of the temperature gradient. The microstructural observation indicates that the evolution behavior of thermal damage promotes the continuous development of micropores in the interfacial transition zones (ITZ) to form wider microcracks, resulting in the degradation of residual mechanical properties.

Reduction of High-Temperature Damage on Paeonia ostii through Intercropping with Carya illinoinensis

Paeonia ostii is an emerging woody oil crop, but the high temperature in summer is extremely unfavorable for its growth and development. Understory intercropping cultivation would provide shaded environments which could effectively reduce the ambient temperature. In order to explore whether understory intercropping cultivation would reduce the effects of high-temperature stress on P. ostii, the changes of leaf physiological indicators and leaf microstructures of sole-cropping and intercropping P. ostii were investigated. P. ostii that intercropping cultivated under Illinois pecans (Carya illinoinensis (Wangenh.) K. Koch) with 4 m × 4 m and 4 m × 8 m rowing spaces were used as samples in this study. The results showed that with continuous high temperature, the high-temperature damage index of P. ostii kept increasing, whereas the leaf relative water content continued to decline. Compared to sole-cropping, the high-temperature damage index, relative electrical conductivity, proline content, antioxidant enzymes superoxide dismutase (SOD), and ascorbate peroxidase (APX) activities of intercropping P. ostii under C. illinoinensis were significantly decreased, whereas the leaf relative water content was higher. Moreover, compared to sole-cropping, intercropping P. ostii under C. illinoinensis increased SPAD and chlorophyll contents, made mesophyll cell ultrastructures more intact, and made the chloroplasts rounder and more filled with starch granules and lipid globules, leading to enhanced photosynthesis (Pn) and transpiration rates (Tr). Notably, the reduction of high-temperature damage on intercropping P. ostii under C. illinoinensis with 4 m × 4 m rowing spaces was more significant than that under C. illinoinensis with 4 m × 8 m rowing spaces. This research provides some reference values for efficient plantation of P. ostii in the middle and lower reaches of the Yangtze River in China.

Properties and improvement of ultra-high performance concrete with coarse aggregates and polypropylene fibers after high-temperature damage

Ultra-high performance concrete containing coarse aggregates (UHPC-CA) is more cost-effective, with its low cost and easy access to materials, but its high-temperature performance and self-healing capability after post-fire curing remain to be further explored. In this paper, after high temperature, the compressive strength increases by approximately 20 MPa within 400 °C, and the micro-characteristics reveal that this is mainly because the temperature promotes the cement hydration reaction and pozzolanic reaction, which plays the role of secondary accelerated curing. Due to the continuous decomposition of substances, the flexural strength and ultrasonic pulse velocity gradually decrease; the mass loss, total porosity, and the amount of absorbed water increase, especially the sorptivity coefficient, which increases by more than 100 times after 800 °C. The residual values of all properties of UHPC-CA are best maintained by adding all of the finer PP fibers. Relying on many unhydrated gelling materials, UHPC has a more significant self-healing potential, improving its mechanical properties and permeability in all three post-fire curing environments. The most significant effect is seen in the water environment, where its recovery rate of strength exceeds 50 % in all cases. The self-healing enhancement of UHPC does not come from a single source, but from multiple combinations of physical and chemical reaction processes.