Elevated Temperature Exposure Research Articles

Evaluation on static mechanical stability of wrought Inconel 718 superalloy; effect of grain configuration and δ precipitation

Wrought nickel alloys are widely applied in hot static components for aero-engines, acquisition for the underlying mechanism of microstructural evolutions controlling mechanical degradation during elevated-temperature exposure is fundamentally vital to processing optimization as well as serving life prediction. In present work, the differential hot tensile characteristics during 500–2000 h exposure at 650 °C of wrought Inconel 718 alloy having specific microstructures designed via different processing routes were comparatively evaluated. The experimental results showed the static mechanical stability of Inconel 718 alloy was predominantly tailored by the complicated interaction of γ-matrix grain configuration and δ precipitation on grain boundaries (GBs). It mainly involved continuous GB-δ precipitation during the 500–2000 h exposure at 650 °C, which played opposite roles in homogeneous or heterogeneous grain configurations. GB-δ precipitation can improve hot ductility but deteriorate strength for homogeneous grain configuration, adequate GB-δ particles can improve the deformation compatibility between GBs and γ-matrix to achieve good balance between the strength and ductility as well as smaller mechanical fluctuations. The heterogeneous duplexing grain configuration exhibited enhanced mechanical sensitivity to sluggish GB-δ precipitation since the hot ductility was rapidly reduced by tiny δ particles with fracture mode transition. In comparison, appropriate sub-solvus solution prior to aging cycles can introduce GB-δ particles pre-existed in homogeneous grain configuration to benefit in superior long-term static mechanical stability for Inconel 718 alloy.

Interaction of silica fume on flexural properties of 10 mm-thickness geopolymers based on fly ash and ladle furnace slag under the thermal conditions

Studies regarding the properties of geopolymers with silica fume addition at elevated temperature exposure were rarely reported. This paper evaluates the effect of silica fume inclusion on the flexural and thermal performance of geopolymers based on fly ash (FA) and ladle furnace slag (LFS) with thickness of merely 10 mm. Fly ash/slag (FS) geopolymer was prepared by mixing FA and LFS using a weight ratio of 60:40 with an alkali activator (sodium silicate and sodium hydroxide). Silica fume (1, 2, 3, and 4 wt%) was added to prepare FSF geopolymers. The geopolymers were then subjected to the elevated temperature up to 1100 °C after 28-days of curing. Higher flexural strength of 9.1 MPa was achieved in unexposed FSF geopolymers with 3 wt% silica fume addition as compared to unexposed FS geopolymers (7.8 MPa). Flexural strength degraded with higher silica fume content of 4 wt%. Heat treatment significantly improved the flexural strength of geopolymers. Both FS and FSF3 geopolymers had increased strength of 208.9% to 24.1 MPa at 1100 °C and 192.3% to 26.6 MPa at 1000 °C, respectively as compared to the unexposed specimen. The inclusion of silica fume with extreme fineness improved the interconnectivity of the geopolymer matrix, densifying the geopolymer structure and thus enhancing the thermal resistance of geopolymers. However, the dense matrix with low flowability of FSF3 geopolymers could not sustain the high thermal stress and caused strength degradation and crack formation at a high temperature of 1100 °C. Even so, the flexural strength of 1100 °C heat-treated FSF3 geopolymer was 13.2% higher than the unexposed specimen. This demonstrated that silica fume could be incorporated in enhancing the thermal resistance and high strength achievement in geopolymers.

Effect of Er and Si co-microalloying on mechanical properties and microstructures of AlCuMg alloys

The effect of Er and Si on the evolution of precipitates in Al–Cu–Mg alloys during elevated temperature exposure was investigated. The Er segregation in θ′-Al2Cu precipitates and Si/Mg co-segregation at the interfaces of θ'/Al matrix are experimentally observed in Al–Cu–Mg–Si–Er alloy, which finally contributes to the heat resistance of the Al–Cu–Mg–Si–Er alloy. Si enhances formation of the Q″ phases as nucleation sites for the θ′ phases, resulting in a refined distribution of θ′ phases. Al–Cu–Mg alloy with high strength as well as high thermal stability is obtained by co-adding Er and Si. The high-temperature yield strength (YS) of Al–Cu–Mg–Si–Er alloy at 225 °C are increased by 37 MPa compared with that of Al–Cu–Mg alloy. Simultaneously, the addition of Er significantly increases the elongation of Al–Cu–Mg–Si–Er alloy.

Post-fire flexural behaviour and performance of unrestrained cold-formed steel built-up section beams: Experimental and numerical investigation

Cold-formed steel (CFS) sections are light gauge materials widely used to construct industrial structures. CFS construction is gaining more interest among researchers, construction industries, and structural engineers due to its lightweight and cost-effective design. Fire safety in the building is a significant factor to be considered in the design and construction practices. However, limited studies are reported on experimental and finite element modelling (FEM) of back-to-back built-up channel sections under flexure with unrestrained conditions. Nine back-to-back built-up CFS sections were considered for the experiment. CFS test specimens were exposed to elevated temperatures following the ISO 834 standard fire curve for durations of 30 min (821 ℃), 60 min (925 ℃), 90 min (986 ℃), and 120 min (1029 ℃). After the temperature exposure, air- and water-cooling methods were adopted to cool the CFS specimens. The influence of temperature exposure and cooling affects CFS sections' residual load-carrying capacity and failure behaviour. A detailed physical observation was made after cooling conditions to observe the failure behaviour of CFS specimens. Experiments were performed to evaluate the influence of elevated temperature exposure on the ultimate flexural capacity, moment-deformation behaviour, load-strain behaviour and stiffness of CFS. The moment of resistance results obtained from FEM and the Direct Strength Method (DSM) were validated with experimental results. The experimental results showed that, while increasing the temperature exposure and heating duration, the CFS's load-carrying capacity decreases drastically. In the case of cooling conditions, air-cooled specimens exhibited a higher residual strength capacity, about 10–15%, compared to the water-cooled specimens. A good correlation was noted between the experiment and FEM results in failure modes.

Influence of elevated temperature exposure on the interfacial shear strength capacity of binary blended high strength self-compacting geopolymer concrete

The development of sustainable infrastructure is a serious issue faced by modern society. Portland cement is one of the common ingredients in concrete, which influences construction activities. The major issue with the employment of cement in civil-based works is that it is responsible for carbon dioxide emission (CO2-e), the primary greenhouse gas responsible for global warming. Alternative to cement-based concrete, geopolymer concrete (GPC) employs zero cement for concrete production, leading to a reduction in CO2-e. In the case of mass concreting, interface/joints are developed, which are found to be the possible failure spots of brittle fracture. Concrete with different grades (strength) may interface, or other building materials, such as reinforcing materials. The interfacial bond strength has to be examined to ensure the homogeneity of the composite structures. The employment of shear ties at the interface ensures homogeneous behaviour. Moreover, a higher number of shear ties in the shear zone increases the cost of production. The interfacial shear strength (ISS) parameters will be miserably damaged in the concrete structures subjected to fire accidents, which might depend on the intensity of temperature exposure and its duration. The current study investigates the ISS of the High Strength Self-compacting geopolymer concrete (HSGC) in the interface of push-off samples. SCGC was made using binary blended composites, which comprised Fly Ash (FA), Metakaolin (MK), and Ground Granulated Blast Furnace Slag (GGBFS) as precursor materials. The work highlights the need to comprehend the reduction in shear strength of SCGC subjected to high temperatures. The fresh properties of the SCGC composites strictly adhered to the EFNARC guidelines. The SCGC composites, after their curing period, were exposed to 821 ℃, 925 ℃, 986 ℃, and 1029 ℃ following ISO 834 guidelines. Residual mechanical properties were examined after being cooled to room temperature.

Elevation in Rearing Temperature within Optimum Range Mitigate Immunosuppressive and Metabolic Stress Effect of High or Low Dietary Protein Level in Labeo Rohita Fingerlings

In the present study, Labeo rohita fingerlings were maintained either at ambient water temperature (26ºC) for five weeks or exposed to 32ºC for one week then later maintained at 26ºC for four weeks. Fingerlings reared under different temperature regimes were fed with any of the four experimental diets containing 20, 30, 40 or 45% protein. Serum cortisol level was higher at 26ºC compared to 32ºC, and decrease with the increase in dietary protein level up to 40%. Fingerlings fed 30% and 40% protein recorded similar WBCS count and respiratory burst activity which was lower and higher respectively compared to 20% and 45% protein fed fingerlings. Correspondingly, lower WBCS count and higher NBT were recorded following exposure to higher temperature (32ºC) for one week compared to 26ºC exposure group. Significantly lower survival was recorded in groups fed with lowest (20%) and highest (45%) dietary protein level whereas fingerlings exposed to 32ºC for one week exhibited higher survival (%) compare to 26ºC. Present results indicate that both lower and higher level of dietary protein may cause metabolic stress to fingerlings, as might consequently lead to the depressed immunity and exposure of elevated temperature (32ºC) for one week mitigates this immunosuppressive effect.

Disturbances in growth, oxidative stress, energy reserves and the expressions of related genes in Daphnia magna after exposure to ZnO under thermal stress

The toxicological effects of metal contamination are influenced by the ambient temperature. Therefore, global warming affects the toxicity of metal contamination in aquatic ecosystems. ZnO is widely used as a catalyst in many industries, and causes contamination in aquatic ecosystems. Here, we investigated the effects of ZnO concentration under elevated temperature by observing growth, oxidative stress, energy reserves and related gene expression in exposed Daphnia magna. Body length and growth rate increased in neonates exposed to ZnO for 2 days but decreased at 9 and 21 days under elevated temperature. ZnO concentration and elevated temperature induced oxidative stress in mature D. magna by reducing superoxide dismutase (SOD) activity and increasing malondialdehyde (MDA) levels. In contrast, juveniles were unaffected. Carbohydrate, protein and caloric contents were reduced throughout development in D. magna treated with ZnO and elevated temperature in all exposure periods (2, 9 and 21 days). However, lipid content also decreased in mature D. magna treated with ZnO cultured under elevated temperature, while that of juveniles showed an increase in lipid content. Therefore, energy was perhaps allocated to physiological processes for detoxification and homeostasis. Moreover, expression patterns of genes related to physiological processes changed under elevated temperature and ZnO exposure. Taken together, our results highlight that the combination of temperature and ZnO concentration induced toxicity in D. magna. This conclusion was confirmed by the Integrated Biological Response (IBR) index. This study shows that changes in biological levels of organization could be used to monitor environmental change using D. magna as a bioindicator.

Enhancing the thermal stability of alkali-activated Fe-rich fayalite slag-based mortars by incorporating ladle and blast furnace slags: Physical, mechanical and structural changes

A proper and detailed understanding of the thermal stability of Fe-rich fayalite slag-based alkali-activated materials (AAMs) is important due to their potential use in refractory and fire-resistant applications. Here, fayalite slag (FS) was used as the main precursor for AAMs. The effects of incorporating ladle slag (LS) or blast furnace slag (BFS) and different temperature exposures up to 1000 °C were investigated through visual observation, compressive strength, ultrasonic pulse velocity (UPV), thermal conductivity, x-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope coupled with electron probe microanalyzer (SEM-EPMA). The experimental results indicated that the incorporation of LS or BFS as additional calcium and aluminum sources positively affected the high-temperature behavior of blended mortars, which exhibited a reduction in voids, cracks, and thermal shrinkage while having higher residual strength and thermal stability than solely FS-based AAMs. This was mainly due to the differences in mineralogical transformation and the phases formed. Interestingly, the joint effect of elevated temperature exposure and the addition of LS or BFS enhanced the formation of more stable crystalline phases and densified the structure of blended mortars at 1000 °C.

The effect of elevated temperature on self-compacting concrete: Physical and mechanical properties

Concrete’s thermal properties are more complex than for most materials because not only is the concrete a composite material whose constituents have different properties, but its properties also depend on moisture and porosity. Exposure of concrete to elevated temperature affects its mechanical and physical properties. In the current study, M40 and M80 grades of plain self-compacting concrete (SCC) mixes are developed using Nan Su mix design principles to investigate the effect of elevated temperatures on 1) weight and compressive strength 2) compressive strength of SCC when tested cool and hot 3) effect of 2, 4 and 6 hrs. exposure duration of elevated temperatures on compressive strength 4) modulus of elasticity 5) size of testing specimen and 5) effect of thermal cycles on SCC mixes. Results derived the following conclusions 1) the M80 specimens lose more strength than M40 SCC specimens when subjected to elevated temperatures ;2) specimens heated and then permitted to cool before testing lose more strength than those tested while hot; 3) the longer the duration of heating before testing, the larger the loss in strength; 4) The decrease in modulus of elasticity caused by elevated-temperature exposure is more pronounced than the decrease in compressive strength. 5) Small test specimens generally incur greater strength losses than larger ones and 6) Specimens subjected to several cycles of heating and cooling lose more strength than those not subjected to thermal cycling.

Parameter optimization: Effect of Humidity and Fabrication Process on Flexural Strength of Kenaf/Polylactic Acid Biocomposite

Biocomposite from kenaf reinforced polylactic acid (Kenaf/PLA) has the potential to replace a synthetic reinforcement and matrix in polymer composite applications. Kenaf is well known as a natural fiber that can be replaced with synthetic fiber and reinforced with synthetic resin, whether thermoset or thermoplastic. An increase in environmental impact drives increased usage of a biodegradable polymer such as PLA in the application of biocomposite. However, moisture uptake from the humidity and elevated temperature exposure during fabrication of composite is mostly a factor that affects the properties of biocomposite. Therefore, this study aims to optimize the factors consisting of humidity exposure, temperature and time holding during hot press using the design of experiment (DOE) by Box-Behnken Design (BBD) approach. The kenaf/PLA was exposed to the humidity range from 40% up to 80% before undergoing composite fabrication. Then produce the composite using a hot press molding where the parameter consists of elevated temperature (range from 160 <sup>o</sup>C up to 200 <sup>o</sup>C) and time holding (range from 3 minutes up to 10 minutes) that possibly affects the mechanical properties of kenaf/PLA. These three factors were evaluated based on optimizing maximum results on flexural properties, where all the combination factors were assessed using DOE. Using analysis of variance (ANOVA) revealed that humidity exposure and hot press temperature are essential factors affecting kenaf/PLA flexural strength. The results indicated that the selected humidity and hot press parameters were 40 %RH, 160 <sup>o</sup>C press molding temperature, and a 3-minute heating duration for optimal flexural strength. The parameter will obtain 111.61 MPa of flexural strength. Implementing the chosen factor can produce the kenaf/PLA biocomposite with an optimum flexural strength of 111.61 MPa.

Fire residual stress–strain curves of corroded thermo-mechanically treated (TMT) reinforcing steel bars

Thermo-mechanically treated (TMT) reinforcing steel bars are extensively employed in RC buildings these days because of their superior thermal- and seismic-resisting characteristics, which enable them to sustain most of their strengths during earthquakes. The distinctive cross-sectional phase distribution (CSPD) of martensite, bainite, and pearlite in TMT rebars makes them outstanding. The current study examines the extent to which TMT reinforcing steel bars' mechanical properties deteriorate as a result of exposure to a combination of corrosion-induced CSPD damage and high temperatures. The research attempted to model an accidental fire in an aging structure with corroded members as a result of exposure to extreme environmental conditions. Heated residual tensile tests on rebar specimens subjected to various combinations of corrosion-induced damage and high temperatures were used in the experiment. The results show a significant loss in the key mechanical characteristics of reinforcing steel due to the superimposition of elevated temperature exposure on corrosion-induced damage to CSPD.

Study on mechanical properties of locked coil wire rope under and post fire

• Carry out the static tensile test of the locked coil wire rope under and after high temperature. • Obtain the mechanical properties and failure mode of locked coil wire rope under and post fire. • The reduction law of locked coil wire ropes under and post fire is obtained. • Compared with the existing research, the failure mechanism of cable is studied. • The prediction method of temperature dependent mechanical properties is proposed. As a new type of strand with excellent performance, a locked coil wire rope has been commonly used in all types of prestressed spatial structures. Owing to its unique section, it has a different temperature distribution, bearing mechanism, and failure mode from a traditional cable. In this study, static tensile tests of locked coil wire rope specimens were conducted under and after elevated-temperature treatments, and reduction laws of the mechanical properties of the strand were obtained. Based on the test results, a method for prediction of the mechanical properties of locked coil wire ropes under and after elevated-temperature exposure was developed. The research showed that the failure of a locked coil wire rope is ductile failure. Its ultimate strength begins to decrease when the heating temperature exceeds 200 °C. When the temperature reaches 400 °C, the strength of the strand is lower than 50 % of that at room temperature. The heat treatment process reduces the strength and ductility of the strand. When the heating temperature of a strand reaches 400 °C, it should be replaced in time after a fire. The research results provide a theoretical basis for fire resistance and post fire assessment of prestressed structures.

Axial behavior of square and circular concrete columns confined with CFRP sheets under elevated temperatures: Comparison with welded-wire mesh steel confinement

The main goal of this study was to carry out an experimental investigation of the effectiveness and the efficiency of using carbon fiber-reinforced polymer (CFRP) strips and welded wire mesh jackets for retrofitting square and circular columns exposed to highly elevated temperatures. The investigated variables included the geometry of the column, strengthening scheme, and heating temperature. The samples were divided into three groups. The first group contains column samples not exposed to elevated temperatures and had no strengthening applied. The second category contains un-strengthened column samples subjected to elevated temperatures; the third category comprises strengthened column samples exposed to elevated temperatures. The elevated temperature exposure consisted of heating the specimens to 600 °C for 3 h. The column samples were subjected to axial compression testing till failure. The test results showed that both the circular and square columns exhibited reductions in axial capacity and initial stiffness when exposed to elevated temperatures. The use of welded wire mesh confinement around the circular and square columns exposed to elevated temperatures provided a more significant increase in strength as well as stiffness compared to strengthening the columns with unidirectional CFRP strips. In contrast, the CFRP repaired heated columns exhibited a significant increase in ductility and deformation capability without any reduction in strength than the WWM jacketed heated columns. Furthermore, the confinement effectiveness of CFRP jacketing provides considerable confinement to micro-cracked concrete compared to the WWM jacketed RC circular columns. However, in square columns the confining effectiveness for WWM was better compared to CFRP strips. Moreover, the use of CFRP strips were ineffective for recovering the stiffness of columns exposed to elevated temperatures. In addition, the results demonstrated that the use of welded wire mesh confinement and CFRP strips are cost-effective retrofitting techniques that could be used for circular and square RC columns.

Mechanical Properties of Ultra-Lightweight Geopolymer Composite after Elevated Temperature Exposure

This paper investigates the mechanical properties of a new type of ultra-lightweight geopolymer composite (ULGC) exposed to elevated temperatures up to 700 °C. This ULGC materials, using ground granulated blast furnace slag, fly ash, and silica fume as the precursor as well as fly ash cenosphere as lightweight aggregates, has a density of less than 1400 kg/m3 and compressive strength up to 40 MPa and thus it has high structural efficiency compared to other types of concrete materials. The effect of polyvinyl alcohol (PVA) fiber dosage and PVA fiber length on the compressive strength, bending strength as well as mass loss of ULGCs after elevated temperature exposure were evaluated, combining a two-factor analysis of variance. The results indicated that when the temperature was below 300 °C, the PVA fiber could improve the mechanical properties of ULGC. However, when the temperature was higher than 300 °C, due to the melting of fibers, the positive effect of fiber dosage on bending strength significantly reduced, and fiber dosage exhibited a negative effect on compressive strength. The ULGCs containing 6mm and 18mm fibers showed better bending strength, while the effect of fiber length on compressive strength of ULGC was negligible.

Crumb rubber geopolymer mortar at elevated temperature exposure

Crumb rubber geopolymer mortar at elevated temperature exposure

Response mechanisms to ocean warming exposure in Effrenium voratum (Symbiodiniaceae).

Ocean warming is an extreme environment event that has profound and lasting impacts on Symbiodiniaceae. However, their response mechanisms to elevated temperature exposure are poorly understood. In this study, the physiological and transcriptional responses of Effrenium voratum (Symbiodiniaceae) to ocean warming were examined. After exposure to 30°C, no significant variations in growth, chlorophyll a, or photosynthetic and respiration rates were observed, while a higher temperature (34°C) significantly reduced these physiological measurements. Meanwhile, lipid content and fatty acid composition were altered at high temperature (i.e., elevated degree of fatty acid saturation). Such biochemical constituents likely contributed to the mitigation of the negative effects of elevated temperatures. Furthermore, higher expression levels of genes related to the synthesis and elongation of fatty acids were detected at high temperature. The adjustment of lipids and fatty acid composition may be a potential mechanism by which E. voratum may survive under future global warming. ONE SENTENCE SUMMARY: The adjustment of lipids and fatty acid composition may be a potential mechanism by which E. voratum acclimate to future global warming.

Thermal insulating and fire resistance performances of geopolymer mortar containing auto glass waste as fine aggregate

This research investigates the use of auto glass waste (AGW) as fine aggregates to improve the thermal insulation and fire resistance properties of the high-calcium fly ash geopolymer mortar. The AGW was used to replace natural sand (NS) at 0%, 20%, 40%, 60%, 80%, and 100% by volume. The physical and mechanical properties of geopolymer mortars containing AGW before and after elevated temperature exposure at 300, 600, and 900 °C were evaluated. The results indicated that the incorporation of AGW had a slight effect on the workability and strength of geopolymer mortars, but a significant improvement in the thermal insulating and fire-resistant characteristics. Although the increase in AGW volume led to a decrease in the compressive strength, the use of 100% AGW provided an acceptable 28-day compressive strength of 84% compared with the geopolymer mortars containing only NS. The incorporation of 100% AGW resulted in the thermal insulating mortar which was a very low thermal conductivity of 64% of NS mortar. The fire-resistant mortar at 900 °C exposure with the highest relative compressive strength of 218% and compressive strength of 113 MPa was obtained with 100% AGW. This research provides the reference for the application of AGW as a fine aggregate replacement to produce fly ash geopolymer mortar as green building materials with excellent thermal insulating and fire-resistant applications.

Formulation, Physico-chemical Evaluation and Comparative Stability Studies of Dillenia indica (pulp) based Antidandruff and Anti Hair Fall Cream with Marketed Brand

Background: Dillenia Indica as a medicinal plant is one of the widely used herbs by the various tribes of entire North East (mostly in Assam) and traditionally the jelly like content inside the fruit was used to treat dandruff and falling hairs.
 Objectives: The current work was performed with an objective to assess the antidandruff and anti hair fall property of Dillenia indica (pulp), the jelly like content inside the fruit with a marketed brand.
 Methods: With utilization of different concentrations of Dillenia indica (pulp) as main drug and with other chemicals different cream formulations are made and optimized. All the formulations along with marketed brand are investigated for their physico-chemical properties. Stability studies of freeze-thaw, elevated temperature exposure and thermal stability study was performed. All the results of the formulations were compared with marketed brand.
 Results: All the result of freeze-thaw, elevated temperature exposure and thermal stability study of all formulations (F1,F2,F3) shows similar characteristic behavior with marketed brand except in elevated temperature exposure where all the formulations fails to withstand the temperature excluding the marketed brand (BRYLCREEM). Physico-chemical parameters like pH, FFA, TFM has been studied for formulations F1, F2, F3 and with brand product. All the formulations along with brand product are showing similar kind of result along with similar Spreadability and homogeneity.

Ocean Warming and Heat Stress Impact Molecules of Keystone Significance in a Predatory Marine Gastropod

Water temperature is a major abiotic driver, controlling the rates and nature of biochemical reactions and subsequently affecting the physiology of marine organisms. However, relatively little is known about the implications of heat stress or predicted ocean climate change on marine secondary metabolites. The predatory gastropod Dicathais orbita is a useful model organism for climate change and natural product studies. Here we determine the upper thermal limit (CTMax) of D. orbita and investigate the effects of thermal stress on the bioactive compounds stored in their biosynthetic organ, the hypobranchial gland. Two CTMax experiments were undertaken, along with a static heat stress experiment where whelks were exposed to an elevated temperature of 30°C for one week, compared to a 20°C seawater control. An additional 35-day ocean climate change experiment used combinations of temperature (ambient: 23°C and future: 25°C) and pCO2 (ambient: ~380 ppm and future: ~765 ppm). The impacts on secondary metabolites in all experiments were assessed using liquid chromatography-mass spectrometry. The mean CTMax of the whelks, from the northern limit of their distribution, was found to be 35.2°C using a rapid temperature increase rate of 1°C/1 h, but was only 30.6°C when a gradual heating rate of 1°C/12 h was used. The overall composition of the secondary metabolites was significantly affected by heat stress in all four experiments, but not by elevated pCO2 in the ocean climate change experiment. The proportion of the choline ester murexine was significantly reduced in heat-stressed snails compared to the controls. Tyrindoxyl sulphate was significantly reduced under prolonged exposure to future temperature, whereas the relative abundance of the oxidation product, 6-bromoisatin significantly increased with elevated temperature exposure. Despite the fact that intertidal gastropods like D. orbita might be able to buffer the impact of external temperatures within the predicted future range, this study provides evidence that ocean warming could have significant implications for secondary metabolite production and/or storage in marine invertebrates. Impacts on bioactive molecules with multifunctional ecological roles could have implications for predator populations with possible flow on effects in some marine communities.

Effects of perlite/fly ash ratio and the curing conditions on the mechanical and microstructural properties of geopolymers subjected to elevated temperatures

This paper investigated the mechanical and microstructural properties of geopolymer mortars before and after elevated temperature exposure. The mortars were based on blends of finely ground raw perlite (RP) and Class F fly ash (FA). RP–FA blends were alkali-activated with 10 M NaOH solution. The synthesis of geopolymer mortars was conducted at 90 °C during 4, 8, and 24 h, with different RP/FA mass ratios (100/0; 75/25; 50/50; 25/75; 0/100). Several experiments regarding the hardened properties were performed after curing for 7, 28 and 90 days. After curing, the geopolymer mortars were heated up to elevated temperatures of 400 °C, 600 °C, and 800 °C, separately. Influence of elevated temperature on the geopolymer properties were determined in terms of the mass loss, strength loss, and alterations in the microstructures after exposure to elevated temperatures. The best results were observed on the geopolymer mortars made with the RP/FA mass ratio of 25/75. The flexural and compressive strength values of the mortars after exposure to 800 °C were higher than the values after exposure to 600 °C. New crystalline phases were detected in the mortars after being subjected to 800 °C.