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Alkali-activated slag has been noted as one of potential alternatives to the ordinary Portland cement due to its properties including high early strength performance and capability of ambient curing. However, there is still limited studies available on elucidating the reaction processes towards producing the excellent properties. This study aims to elucidate the mechanism of alkali activation of slag under different molarities of sodium hydroxide, which is one of the most influential factors on the properties of alkali-activated slag. Heat evolution of alkali-activated slag was used as a real-time monitoring technique. For mix designation, the molarity of sodium hydroxide was varied from 6M to 14 M, with solid-to-liquid ratios of 0.6 and alkali activator ratios of 2.0 remaining constant. The calorimetric data obtained was further used for determination of degree of reaction, nucleation and growth rate mechanism using Johnson–Mehl Avrami Kolmogrov model. According to the findings, it was found that regardless of various molarity of sodium hydroxide applied, the nucleation mechanism and growth is governed by instantaneous heterogeneous nucleation with rod-like growth as the n value is approaching 1 in which is observed from the morphology of the alkali-activated slag at lowest molarity applied (6 M). Furthermore, increasing in molarity of sodium hydroxide was found to decrease the total heat evolved and the lowest was obtained when using 14 M.

Abstract: Alkali-activated slag has been noted as one of potential alternatives to the ordinary Portland cement due to its properties including high early strength performance and capability of ambient curing. However, there is still limited studies available on elucidating the reaction processes towards producing the excellent properties. This study aims to elucidate the mechanism of alkali activation of slag under different molarities of sodium hydroxide, which is one of the most influential factors on the properties of alkali-activated slag. Heat evolution of alkali-activated slag was used as a real-time monitoring technique. For mix designation, the molarity of sodium hydroxide was varied from 6 M to 14 M, with solid-to-liquid ratios of 0.6 and alkali activator ratios of 2.0 remaining constant. The calorimetric data obtained was further used for determination of degree of reaction, nucleation and growth rate mechanism using Johnson–Mehl Avrami Kolmogrov model. According to the findings, it was found that regardless of various molarity of sodium hydroxide applied, the nucleation mechanism and growth is governed by instantaneous heterogeneous nucleation with rod-like growth as the n value is approaching 1 in which is observed from the morphology of the alkali-activated slag at lowest molarity applied (6 M). Furthermore, increasing in molarity of sodium hydroxide was found to decrease the total heat evolved and the lowest was obtained when using 14 M. [ABSTRACT FROM AUTHOR]

Desert areas contain abundant desert sand (DS) resources, and high-volume recycling of DS resources as components of cement-based materials can achieve high-value applications. In this paper, DS was processed into desert sand powder (DSP) and replaced with cement in high volumes (20 wt.%–60 wt.%) to produce cement pastes. The mechanical properties, heat evolution, nanomechanical characteristics, microstructure, and economic and environmental impact of cement pastes were studied. The results show that adding 20 wt.% DSP increases the compressive strength of pastes and accelerates cement hydration, compared with the control group (0 wt.% DSP). Meanwhile, incorporating an appropriate amount of DSP (20 wt.%) effectively reduces porosity, increases the proportion of harmless and less harmful pores, and reduces the proportion of more harmful pores. From the perspective of nanoscopic properties, the addition of 20 wt.% DSP increases the C-S-H volume fraction, especially enhancing the transformation of low-density C-S-H to high-density C-S-H. Notably, the sample incorporating 60 wt.% DSP exhibits the lowest values for CI coefficients (13.02 kg/MPa·m3) and Cp coefficients (2.29 USD/MPa·m3), thereby validating the application of high-volume DSP feasibility in cement-based materials. [ABSTRACT FROM AUTHOR]

Desert areas contain abundant desert sand (DS) resources, and high-volume recycling of DS resources as components of cement-based materials can achieve high-value applications. In this paper, DS was processed into desert sand powder (DSP) and replaced with cement in high volumes (20 wt.%–60 wt.%) to produce cement pastes. The mechanical properties, heat evolution, nanomechanical characteristics, microstructure, and economic and environmental impact of cement pastes were studied. The results show that adding 20 wt.% DSP increases the compressive strength of pastes and accelerates cement hydration, compared with the control group (0 wt.% DSP). Meanwhile, incorporating an appropriate amount of DSP (20 wt.%) effectively reduces porosity, increases the proportion of harmless and less harmful pores, and reduces the proportion of more harmful pores. From the perspective of nanoscopic properties, the addition of 20 wt.% DSP increases the C-S-H volume fraction, especially enhancing the transformation of low-density C-S-H to high-density C-S-H. Notably, the sample incorporating 60 wt.% DSP exhibits the lowest values for CI coefficients (13.02 kg/MPa·m3) and Cp coefficients (2.29 USD/MPa·m3), thereby validating the application of high-volume DSP feasibility in cement-based materials.

The importance of nanomaterials has been known for many years, but their usage in cement and concrete production is not accelerated and emphasized extensively. Cement and concrete are the base input material for the construction industry, and the industry is facing tremendous pressure to reduce its greenhouse gas emission (GHG); in 2021, the cement industry emitted about 7% GHG, equal to 2.5 Giga Ton gases of global GHG emission. It is estimated that by enhancing various supplementary cementitious materials (SCM), approximately 9% of the GHG emission of the cement industry can be reduced globally. It is also known that the cement hydration process is very sensitive and altered by many factors such as temperatures, amount of water, surface area, chemical properties, mineral phases, and type of SCM used. The alteration of hydration has adverse influences on cement and concrete performance. Nanomaterials can play an essential role by offsetting the adverse effects of high usage of SCMs in the cement, helping in increasing sustainability by reducing the intensity of CO2, and offering value-added features like self-sensing self-cleaning, antibacterial, anti-fungal, anti-algae, and antistain in the cement other than cement strength, which may promote the use of blended cement and replace ordinary Portland cement in the construction industry. This comparative review aims to understand nanomaterials' advantages and challenges and compare their role and their influence on the cement hydration process based on the types of nanomaterials and their nature as Pozzolanic Nanomaterial (nano SiO2, nano MgO, Nano CaCO3, Nano Metakaolin), Metal oxide Nanomaterial (nano TiO2, nano CuO, nano ZnO, nano Al2O3, nano Fe2O3) and Carbon Based Nanomaterial (Carbon Nanotubes CNTs, Carbon Nano Fibers CNFs, Graphene Oxides). [ABSTRACT FROM AUTHOR]

A number of materials are studied in the field of magnetic hyperthermia. In general, the most promising ones appear to be iron oxide particle nanosystems. This is also indicated in some clinical trial studies where iron-based oxides were used. On the other hand, the type of material itself provides a number of variations on how to tune hyperthermia indicators. In this paper, magnetite nanoparticles in various forms were analyzed. The nanoparticles differed in the core size as well as in the form of their arrangement. The arrangement was determined by the nature of the surfactant. The individual particles were covered chemically by dextran; in the case of chain-like particles, they were encapsulated naturally in a lipid bilayer. It was shown that in the case of chain-like nanoparticles, except for relaxation, a contribution from magnetic hysteresis to the heating process also appears. The influence of the chosen methodology of magnetic field generation was also analyzed. In addition, the influence of the chosen methodology of magnetic field generation was analyzed. The application of a rotating magnetic field was shown to be more efficient in generating heat than the application of an alternating magnetic field. However, the degree of efficiency depended on the arrangement of the magnetite nanoparticles. The difference in the efficiency of the rotating magnetic field versus the alternating magnetic field was much more pronounced for individual nanoparticles (in the form of a magnetic fluid) than for systems containing chain nanoparticles (magnetosomes and a mix of magnetic fluid with magnetosomes in a ratio 1:1). [ABSTRACT FROM AUTHOR]

The paper presents the research results of the supercritical water oxidation (SCWO) of poultry manure continuously fed into a tubular reactor both in the absence and presence of methane as an auxiliary fuel. The tests were conducted at a temperature gradient along the vertical axis of the reactor (top to bottom: 390–600 °C), a pressure of 25 MPa, and varying reagent flow rates. It is shown that due to heat generation during methane oxidation the energy consumption from external sources is reduced by 1.3–1.5 times depending on the ratio of reagent flow rates. The gas products contain CO 2 , N 2 , and trace amounts of N 2 O. The ash residues are predominantly composed of calcite and hydroxyapatite. The addition of methane results in a reduction in the content of phenols and polycyclic aromatic hydrocarbons present in the aqueous effluent, while content of N-bearing aromatics increases. The formation of nitrophenols was observed at elevated oxygen concentrations in the reaction mixture. It was revealed that excess oxygen plays a pivotal role in the efficacy of organic nitrogen removal. The formation of mineral acids and a high level of ammonia in the reaction mixture during the SCWO of poultry manure result in corrosion of stainless steel and copper seals, which in turn leads to an increased concentration of chromium and copper in the aqueous effluent. The results obtained indicate the potential for utilizing natural gas in an environmentally friendly and resource-saving manner for poultry manure processing by SCWO in autothermal mode. [Display omitted] • Continuous SCWO of poultry manure with and without methane were investigated. • Methane reduces both energy input and phenols and PAHs in aqueous effluent. • Oxidation ratio increases organic nitrogen removal efficiency. • Further study should focus on avoidance of chromium and nitrophenols in effluent. [ABSTRACT FROM AUTHOR]

This study monitors the early-age reaction kinetics and measures the heat of reaction of alkali-activated ground granulated blast-furnace slag (GGBFS) using an isothermal calorimeter, and the initial setting and possible product formations by measuring ultrasonic pulse velocity (UPV). The GGBFS was activated with alkaline activator solutions of different concentrations in terms of modulus ratio (Ms) and Na2O% content. Results reveal that GGBFS is highly sensitive to the compositions of the alkaline solutions. Increasing the alkalinity of the activator results in better dissolution of species and consequently an increased heat evolution with a relatively shorter setting time. The activator concentration also affects the rate of product formations as well as the morphological features. Activators with higher Ms lead to homogeneous slag morphology. The abundance of silicate species in the alkaline solution also plays an important role in its structural formation. scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS) microstructural characterizations supports the advanced dissolution of particles in a more alkaline environment. The presence of C-(A)-S-H gels in alkali-activated slag pastes was detected. [ABSTRACT FROM AUTHOR]

Graph storage technology is confronted with an enormous challenge as far as the compact and complex graph-structure data. This phenomenon is derived from social networks with spatially intensive data. Since a hot event can cause the generation of a network cluster, which consists of a massive duplicate associated entities in the social networks, the space utilization and processing speed of graph data is obstructed. Therefore, it is necessary to design a graph storage mechanism specifically for the above data. In this paper, we propose a Graph compression Storage engine based on spatial Cluster entity Optimization (GSCO), which improves the native graph storage model through the proposed the many-to-one mapping structure and a Heat Evolution Elimination algorithm (H2E). Firstly, we define the spatial cluster entity formally and confirm the compressed storage objects. Then, we introduce the many-to-one relationship to transfer the mapping structure between the node and property. It compresses the data to raise the space utilization of the graph database. Finally, we propose the H2E algorithm that allows the representative nodes to be anchored an extended period in memory according to the heat evolution acceleration. It increases the hit rate and throughput and reduces the I/O operation by deleting the redundancy of data. Extensive experiments results show that the proposed GSCO storage model is better than Neo4j for reading and writing data in spatial clustering entity. It significantly promotes the effectiveness of graph operation, including the data loading, the common queries, and the clustering test.

A number of materials are studied in the field of magnetic hyperthermia. In general, the most promising ones appear to be iron oxide particle nanosystems. This is also indicated in some clinical trial studies where iron-based oxides were used. On the other hand, the type of material itself provides a number of variations on how to tune hyperthermia indicators. In this paper, magnetite nanoparticles in various forms were analyzed. The nanoparticles differed in the core size as well as in the form of their arrangement. The arrangement was determined by the nature of the surfactant. The individual particles were covered chemically by dextran; in the case of chain-like particles, they were encapsulated naturally in a lipid bilayer. It was shown that in the case of chain-like nanoparticles, except for relaxation, a contribution from magnetic hysteresis to the heating process also appears. The influence of the chosen methodology of magnetic field generation was also analyzed. In addition, the influence of the chosen methodology of magnetic field generation was analyzed. The application of a rotating magnetic field was shown to be more efficient in generating heat than the application of an alternating magnetic field. However, the degree of efficiency depended on the arrangement of the magnetite nanoparticles. The difference in the efficiency of the rotating magnetic field versus the alternating magnetic field was much more pronounced for individual nanoparticles (in the form of a magnetic fluid) than for systems containing chain nanoparticles (magnetosomes and a mix of magnetic fluid with magnetosomes in a ratio 1:1).

The pulsed current waveform is essential for the precise control of nugget size in resistance spot welding (RSW). Understanding this link may enable high-quality RSW for the emerging materials. To shed light on this issue, a 3D electrical-thermal-mechanical coupled model is developed to simulate transient multi-physical fields and nugget shapes in RSW. The effects of pulsed current waveforms on the heat evolution and nugget formation are elaborated. The model is validated by calculating nugget size and weld indentation well consistent with the experimental measurements. The results show that with the same energy input, although the continuous and pulsed currents can provide acceptable nugget sizes, the "ramp-up" pulsed current with a high initial current can well match the variations of temperature-dependent electric resistance and lead to an enlarged nugget size. The electrode temperature maintains at a low level with an extended electrode life. This work will provide a better understanding of the heat evolution and nugget formation during RSW process under different multi-pulsed current waveforms, and thus can help to select a proper current waveform. [ABSTRACT FROM AUTHOR]

Summary: Cementing is the key factor in releasing ocean oil and gas resources, but more than 70% of marine cementing faces the challenge of hydrates decomposition. Thus, during this study, the micro‐encapsulated phase change material Micro‐P1 was prepared by paraffin wax, urea formaldehyde resin and graphene oxide through in situ polymerization. Firstly, the application performances of Micro‐P1 were studied, and the results show that the performances were significantly improved by graphene oxide. Secondly, a novel cement slurry containing Micro‐P1 was prepared, and the heat evolution was successfully controlled by Micro‐P1. Thirdly, the thermal control mechanism of Micro‐P1 on heat evolution of cement slurry was also investigated, which indicated the heat evolution was controlled through endothermic effect firstly. Simultaneously, the hydration reaction of cement slurry was delayed by Micro‐P1, in this way, the heat evolution was further controlled. The highlights of this study is that the heat evolution was successfully controlled by using Micro‐P1, and provides technical support for exploration and development of ocean oil and gas resources, especially hydrates formation. Furthermore, the thermal control mechanism of Micro‐P1 on the heat evolution was firstly investigated in this study. [ABSTRACT FROM AUTHOR]

Design of progressive building materials with increased utility value is the key issue for the development of reliable modern building structures. Compared to the conventional materials, progressive building materials are supposed to exhibit not just adequate mechanical, and thermal properties, but they are also supposed to be applicable in sophisticated solutions, such as in self-sensing, self-heating or magnetic-shielding systems. In terms of electric properties, the most of building materials are electric insulators which is the main limiting factor for their applicability in such sophisticated solutions. However, this deficiency can be solved by the addition of a proper amount of electrically conductive admixtures. Within the paper, electrically conductive alkali-activated aluminosilicate with 8.89 mass.% of carbon black admixture was designed and its materials properties necessary for calculations of heat evolution by the action of an electric source were experimentally determined. The electrical conductivity of such material equal to 5.57x10-2 S m-1 was sufficiently high to ensure self-heating ability. It was observed good agreement of experimentally determined data with those modeled by means of heat equation on sample with dimensions 40 x 40 x 10 mm. Finally, one- and two-layered large-scaled heating elements based on materials with experimentally determined properties were designed and calculations were conducted to determine the voltage level necessary for one-hour heating from 268.15 K and 273.15 K to 278.15 K in the middle-top point of the construction. [ABSTRACT FROM AUTHOR]

• The early-age heat evolution of CPB was studied by the isothermal calorimeter. • The coupled effect of cement content and temperature was investigated. • The results were analysed from a chemical point of view. • The Krstulovic-Dabic model was utilised for hydration kinetics analysis. Understanding the early-age hydration kinetics of cemented paste backfill (CPB) is necessary for its successful application. In this paper, the early-age hydration heat evolution of CPB was experimentally studied using an isothermal calorimeter considering the coupled effects of cement content and temperature. We employed the Krstulovic-Dabic kinetic model to investigate the hydration mechanism and kinetic parameters of CPB. The results showed that increasing the tailings-cement ratio (TCR) decreased the hydration heat flow (N) and cumulative heat (Q) of CPB due to the decreased amount of cement. Additionally, increasing the TCR elongated the induction stage while shortening the acceleration stage. Increasing the temperature, increased the peak value of N, shortened its appearance time, and shortened/diminished the induction stage due to the increased chemical kinetics of hydration. The exponent and rate constant values in the Krstulovic-Dabic model decreased with the increase of TCR and the decrease of temperature. The hydration mechanism was nucleation and crystal growth (NG) → phase boundary reaction (I) → diffusion (D) for most CPB slurries, except for CPB slurries at TCR = 10/12 and temperature = 40 °C, where the hydration mechanism was changed to NG → D. This study indicates that the isothermal calorimeter, together with kinetic models, is a reliable tool for investigating the hydration kinetics of CPB, which can be incorporated into CPB design in the future. [ABSTRACT FROM AUTHOR]

Summary: Based on the low hydration heat and temperature rise requirements of cement slurry used in natural gas hydrate layer, two novel microencapsulated phase change materials (MPCM‐1 and MPCM‐2) with different melting point were designed and synthesized; then, the heat evolution of cement slurry was controlled by MPCM‐1 and MPCM‐2 through physical means; the decomposition of hydrates was avoided. Before synthesizing MPCM‐1 and MPCM‐2, the micromorphology, particle size, and distribution of paraffin wax emulsion were studied. Then, the MPCM‐1 and MPCM‐2 containing paraffin wax with urea formaldehyde resin shell was synthesized by in situ polymerization, and the chemical structure and performances were investigated. The melting point of MPCM‐1 and MPCM‐1 is 23.09°C and 35.85°C; the phase change enthalpy is 97.49 and 85.69 J/g. The MPCM‐1 and MPCM‐2 were added into cement slurry, and the controlling effects on heat evolution were studied. As a result, it was found that the hydration heat and temperature rise of cement slurry were successfully reduced by using MCPM‐1 and MPCM‐2. Simultaneously, the investigations of fly ash and slag cement slurry were accomplished. Moreover, the fly ash and slag cement slurry containing microencapsulated phase change materials was prepared. It was shown that the 24 and 48‐hour hydration heat were reduced by 1.10 × 105 and 10.5 × 105 J, respectively. Highlights: A novel microencapsulated phase change material (MPCM) was synthesized.Heat evolution was controlled at different temperature intervals by MPCM.Limiting the temperature rise was achieved by physical and chemical means.Reducing the hydration heat was realized by physical and chemical means.The application of MPCM was significantly increased. [ABSTRACT FROM AUTHOR]

Highlights • Effect of cementitious additives on alkali-activated fly ash (AAFA) properties was studied. • Flowability reduced with addition of cementitious additives. • Only one peak was observed in the heat evolution curve from all AAFA mixtures tested. • Addition of slag largely changed the porosity and pore size distribution. • Early strength development improved with addition of metakaolin. Abstract Alkali-activated fly ash (AAFA) is usually cured at elevated temperature, which limits its wide field applications. However, several studies have shown that properties of AAFA cured at ambient temperature can be significantly improved by incorporating different cementitious additives. This research investigated the impact of substituting a small portion of fly ash with different potential cementitious additives such as slag, metakaolin, and silica fume on various properties of AAFA mixtures at ambient curing conditions. Toward that end, several experimental observations including workability, geopolymerization heat released, compressive strength, Young's modulus, electrical resistivity, chloride permeability, and pore structure distribution were made. The effects of alkaline solution concentration combined with the different chemical compositions on mechanical properties and permeability characteristics were also investigated. An ordinary Portland cement was also included in the testing program as a comparative reference. Test results showed that the AAFA mixtures exhibited lower heat as compared to ordinary Portland cement mixture, and the results of heat evolution were in line with early-age strength development. The inclusion of metakaolin resulted in a significant improvement in the early strength and stiffness. The inclusion of slag led to the improvement of the mechanical and permeability properties of AAFA cured at ambient temperature, and the effect of sodium silicate (SS) to sodium hydroxide (SH) solution ratio was found to be more profound when the slag was used as an additive. Incorporating silica fume in the AAFA mixtures decreased the mechanical properties and increased the volumetric percentage of large capillary pores. [ABSTRACT FROM AUTHOR]

• Cement blended with slag and nano-silica is prepared and hydration properties studied. • Nano-silica can improve the hydration of slag and cement. • Hydration promoting effect of nano-silica decreases as Nano silica increases because of agglomeration. • Combined use of slag and nano-silica can be a good substitute for Portland cement. The cement industry accounts for nearly 7% of carbon dioxide (CO 2) emissions globally and is facing tremendous pressure to reduce the emission intensity. Supplementary cementitious materials (SCM) are a quick and effective lever to lower CO 2 emissions. The cement hydration process is a sensitive mechanism and is greatly influenced by many factors such as hydration environment, type of SCM, and the amount used in the cement, which affect the cement's physical and mechanical performance. The SCM adversely impacts cement performance, especially prolonged setting and slow initial compressive strength development, compared to ordinary Portland cement (OPC). The importance of nanomaterials has been known for decades; their usage in cementitious materials is now accelerated as they can play an essential role by offsetting the adverse effects of the high usage of SCMs in cement. They help in reducing the intensity of CO 2 and offer value-added features. A lab experiment is carried out to understand the role of nano SiO 2 at different dosages on the Portland slag cement (PSC) hydration by studying heat evolution profiles, compressive strengths, TG-DTA, XRD, and SEM images. Results have revealed that 1% nano SiO 2 accelerates early settings time and compressive strength compared to OPC. It will promote slag-based blended cement (PSC) and replace ordinary Portland cement in the construction industry to reduce the CO 2 footprint of the cement and construction industry. A model of NS's role during PSC hydration is also given. [ABSTRACT FROM AUTHOR]

• Addition of GGBFS improves the carbonation resistance of calcined clay-GGBFS geopolymer. • The increase in activator modulus reduces the initial and final setting time. • GGBFS enhances the formation of amorphous phases (C-(A)-S-H/C-(N)-A-S-H) leading to better densification. • pH of hardened geopolymer pastes increases with increasing GGBFS content. • Increasing GGBFS content in binder results in lower porosity and higher compressive strength. Alkali-activated materials are obtained from the alkaline activation of a precursor rich in SiO 2 and Al 2 O 3 , which can be derived from by-products or industrial residues. Calcined clay is a potential candidate as a precursor for this type of material. Large amounts of suitable clays for alkali-activated materials are available around the world. This paper evaluated the performance of different alkaline-activated mortars using calcined clays (low grade) and ground-granulated blast-furnace slag (GGBFS), including physical and mechanical performance, reaction products phases, microstructure, and resistance to accelerated carbonation. The results indicate that the increase in GGBFS content up to 60% has a significant effect on the properties of the mortars, due to the effect of Ca-rich phases such as C-(A)-S-H/C-(N)-A-S-H, promoting the densification of the microstructure, and an increase in pH from 11.91 to 12.78 for specimens with 100% calcined clay and 60% GGBFS respectively, leading to a better carbonation resistance. On the other hand, adding GGBFS leads to a reduction in concrete initial and final setting time and lowers thermal stability compared to the reference calcined clay material. The increase in the modulus ratio of the activator from 1 to 1.5 also improves the mechanical properties and resistance to carbonation of geopolymer mortars with various binder compositions. [ABSTRACT FROM AUTHOR]

This paper investigated the heat evolution of pastes containing inert and active materials with different particle sizes. Ground river sand was used as an inert material while ground granulated blast furnace (GGBF) slag was used as an active material. Ground river sand (GRS) and GGBF slag were ground to have the same particle size and were used separately as a replacement of Portland cement type I at rates of 50 - 70 % by weight of the binder. Heat evolution of pastes containing GRS and GGBF slag was measured using an isothermal conduction calorimeter up to 72 h. The results showed that GRS with different particle sizes had a slight effect on the heat evolution of pastes. GGBF slag with median particle size d50 of 4.4 µm and d50 of 17.8 µm had a small effect on the heat evolution of pastes during the first 24 h, and the pastes also had very low heat evolution for up to 72 h. At the same replacement rate of Portland cement, however, the heat evolution due to the slag reaction was slightly increased when the particle size of the GGBF slag was decreased. Finally, the higher is the cement replacement by GGBF slag, the higher is the slag reaction. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have found their use in concrete technology for increasing energy efficiency of building envelopes. In recent years, however, new potential applications for PCMs in concrete have been suggested, for example for reducing freeze-thaw damage and melting of ice forming on top of concrete pavements. A recent application of PCMs in concrete technology is their use for mitigating early-age cracking in hydrating concrete. The focus on this paper is therefore on theoretical considerations related to this particular application of phase change materials. In particular, the focus is on simulating microencapsulated PCMs, which show very promising experimental results. Numerical models are developed for 2 scales: the meso-scale, in which the PCM microcapsules are simulated as discrete inclusions in the cementitious matrix; and the macro-scale, where the effect of PCM microcapsule addition is considered in a smeared way. On the meso-scale, the effect of PCM volume percentage, their phase change temperature, and latent heat of fusion on simulated adiabatic heat evolution are assessed. On the macro-scale, influence of these parameters on the temperature evolution in semi-adiabatic (field) conditions and tensile stress development are simulated. The outcomes of this study provide valuable insights related to the influence of PCM microcapsule parameters on the behaviour of cementitious materials, enabling tailoring composites for different environmental conditions. [ABSTRACT FROM AUTHOR]

Respiration and heat production in the shoots of bilberry ( Vaccinium myrtillus L.) were studied at the beginning of growth after breaking bud dormancy by means of transfer of the shoots to indoor conditions (November-April) and upon natural sprouting in spring (May). The buds released from dormancy at the beginning of winter sprouted slower and showed lower respiratory activity than the buds that started growing in May. In May, cytochrome respiratory pathway in sprouting buds was 1.3 times more active than energetically ineffective alternative pathway, whereas activity of cytochrome pathway in December was 1.4 times lower as compared with the alternative. In November-December, the rate of heat evolution by the buds was 3-5 times lower than in April-May. In case of early breaking of bud dormancy, the share of respiration energy dissipated as heat was 30% on average. In the buds whose growth was induced later, the value of this parameter was twice as much. The ratio between heat evolution and respiration depended on temperature. High temperature more intensely activated heat evolution than respiration, which caused a decrease in the level of metabolic energy available for growth. In the temperature range of 5-15°C characteristic of the beginning of vegetation, the share of respiration energy dissipated as heat was 2-3 times lower than at 20-30°C, which reflects a great adaptability of V. myrtillus to climatic conditions of the region. Our data suggest that progression through a full cycle of winter dormancy is physiologically important for shoot growth. Early dormancy release brought about changes in respiration and energy balance of the shoots in the initial stage of extra-bud growth. [ABSTRACT FROM AUTHOR]

We investigated the effect of the heat generated in organic light-emitting diodes (OLEDs) on their performance with a focus on the thermo-physical properties of the substrates. OLEDs were fabricated on polyethylene terephthalate (PET), polyimide (PI), and glass substrates, and the instantaneous and time-resolved performances of the OLEDs were compared. The device operation temperature ( T ) was predicted via heat transfer analysis using the finite element method (FEM). The value of T during operation was experimentally measured using an infrared (IR) camera, and the results were compared with the numerically calculated values. The effects of T on the time-resolved electroluminescence (EL) spectra of the OLEDs on the different substrates were also investigated. The experimental results of this study agreed well with the numerical predictions that the T of the OLEDs on the polymers are higher than the T of the OLEDs on glass during operation due to the relatively low thermal diffusivity ( α ) of the polymer substrates used in this study. The results also showed that the performance and reliability of the flexible OLEDs (f-OLED) are highly dependent on the heat extraction capabilities of the substrates; thus, the current density ( J ), luminescence ( L ), voltage ( V ) characteristics, and efficiencies ( η ) over time of the OLEDs on PET and PI are inferior to the OLEDs on the glass substrate. [ABSTRACT FROM AUTHOR]

The physicochemical characteristics of calcined clay influence yield stress of limestone calcined clay cements (LC3), but the independent influences the clay's physical and chemical characteristics as well as the effect of other variables on LC3 rheology are less well-understood. Further, a relationship between LC3 hydration kinetics and yield stress – important for informing mixture design – has not yet been established. Here, rheological properties were determined in pastes with varying water-to-solid ratio (w/s), constituent mass ratios (PC:metakaolin:limestone), limestone particle size and gypsum content. From these data, an ML model developed allowed the independent examination of the different mechanisms by which metakaolin fraction influences yield stress of LC3, identifying four predictors – packing index, Al 2 O 3 /SO 3, total particle density and metakaolin fraction relative to limestone (MK/LS) – most significant for predicting LC3 yield stress. A methodology based on kernel smoothing also identified hydration kinetics parameters best correlated with yield stress. • Variations in LC3 yield stress can be captured by hydration kinetics parameters. • LC3 yield stress can be well-predicted from four compositional variables. • Composition-yield stress linkages can be elucidated with Machine Learning. [ABSTRACT FROM AUTHOR]

Self-sustaining exothermal reaction of synthesis in multilayer foil consisting of intermetallic forming elements may proceed by means of self-propagation of high-temperature synthesis reaction front through foil (self-propagating high-temperature synthesis (SHS) or as a result of synthesis reaction running through the entire volume (autoinflammation (AI)). The latter is realized under the condition of foil heating up to a certain critical temperature, at which the synthesis reaction runs in the entire volume without external heat supply. In the work influence of foil heating rate on AI temperature was studied in the case of Ti/Al multilayer foil. It is shown that there exists a certain critical heating rate, below which foil AI is not observed, and at heating rates above the critical rate AI temperature decreases with increase of heating rate. Dependence of AI temperature on heating rate is nonmonotonic: at low heating rates AI temperature abruptly decreases, and at further increase of heating rate AI temperature remains practically unchanged. Such nonmonotonic dependence of foil AI temperature on heating rate is associated with running of the process of thermally activated solid phase reactions in it, which are accompanied by formation of intermetallic interlayers on the boundary between titanium and aluminium layers, preventing diffusion mixing of elements. With increase of heating rate, interlayer thickness decreases, promoting AI temperature lowering. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of sodium aluminate (SA) on cement and concrete properties were studied. [•] SA can promote setting behavior and hydration heat release rate at first peak. [•] SA will change AFt to AFm, AFm contributes to chloride penetration resistance. [•] SA promotes AFm forming rate, but depresses calcium silicate hydration process. [•] SA enhances early age strength, but impairs later age strength of concrete. [Copyright &y& Elsevier]

Highlights: [•] Properties of HSC made from GCR–GFA mixture were tested and compared to OPC concrete. [•] GCR–GFA mixture could be used as new cementing material to produce HSC without OPC. [•] GCR–GFA concretes had characteristic of elasticity modulus similar to OPC concrete. [•] Water permeability of HSC made from GCR–GFA mixture was the same OPC concrete. [•] Concrete made from GCR–GFA mixture had much lower heat evolution than OPC concrete. [ABSTRACT FROM AUTHOR]

Abstract: Two different sources of bagasse ash with low and high loss on ignition (LOI) were used in this experiment. Ordinary Portland cement was replaced by bagasse ash at the levels of 20%, 30%, and 40% by weight of binder. The effects of LOI, fineness, and cement replacement of bagasse ash on the compressive strength of concrete were investigated. Additionally, the heat evolution of concrete mixed with ground bagasse ash with low LOI was also measured. The results revealed that the compressive strength of concrete containing unground bagasse ash was much lower than that of control concrete (CON). Concrete mixed with low LOI ground bagasse ash had a slightly higher compressive strength than the mixture with high LOI ground bagasse ash. The replacement of cement by ground bagasse ash with low and high LOI at 30% and 20% by weight of binder, respectively, result in a compressive strength at 28days as high as that of CON concrete. Finally, the temperature of bagasse ash concretes could be reduced by 13–37% relative to CON concrete, depending on the level of cement replacement by ground bagasse ash with low LOI. [Copyright &y& Elsevier]

To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rate, which leads to high water requirement, while fine SCMs fractions present relatively high hydration (or pozzolanic reaction) rate. Cement clinker fractions in the range of 8-24 μm show proper hydration rate in early ages and continue to hydrate rapidly afterward. Coarse cement clinker fractions largely play 'filling effect' and make little contribution to the properties of blended cement regardless of their hydration activity (or pozzolanic activity). The hydration process of blended cement can be optimized by arranging high activity SCMs, cement clinker, and low activity SCMs in fine, middle, and coarse fractions, respectively, which not only results in reduced water requirement, high packing density, and homogeneous, dense microstructure, but also in high early and late mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: To improve the properties of blended cement and utilize cement clinker and supplementary cementitious materials (SCM) more efficiently, a new gap-graded particle size distribution (PSD) based on close packing theory was proposed, then blended cements with the gap-graded PSD were prepared by mixing cement clinker and SCM fractions homogeneously. The experimental results show gap-graded blended cement pastes present a lower water requirement, a higher packing density, and a more homogeneous, denser microstructure than reference cement (prepared by co-grinding). As a result, both early and late properties of the gap-graded blended cements with only 25% clinker content can be comparable with those of Portland cement. This investigation supports that a high performance blended cement with low clinker content can be prepared using the gap-graded PSD and arranging a high activity SCM, clinker, and a low activity SCM (or inert filler) in the fine, middle and coarse fractions, respectively. [Copyright &y& Elsevier]

Gas motion in the gravity field through porous heat-evolutional bodies, which can result from natural or man-made disasters (such as the explosion of the reactor at the Chernobyl Nuclear Power Plant), is investigated. A mathematical model and an original numerical method based on a combination of explicit and implicit finite-difference schemes are proposed for studying time-dependent gas flows through axisymmetric porous heat-evolutional bodies. The cooling of axisymmetric porous elements of smoothly converging and stepwise converging shapes, as well as the effect of the geometry of a heat-evolutional element on its cooling process have been investigated. The axisymmetric and plane gas flows through porous heat-evolutional elements were compared and it has been found that the cooling mode of an axisymmetric body may differ from the cooling mode of a plane body not only in quantity but also in quality. [ABSTRACT FROM AUTHOR]

Isothermal conduction calorimetry, differential thermal analysis (DTA)–thermogravimetric analysis (TG) analysis, and SEM observations have proved the activation effect of Ca(OH) released from the CS hydration upon blast furnace slag (BFS). Five sample mixtures of BFS and CS and two samples of pure BFS and CS were submitted to reaction with water inside the calorimeter at room temperature. The values of hydration heat were recorded up to 7 days. Samples were stored in humidity during 28 days and then were submitted to DTA–TG and SEM analysis. The effect of Ca(OH) upon heat evolution of sample mixtures has been quantified and its influence upon the formation of new hydrates and microstructure of pastes was evidenced. [ABSTRACT FROM AUTHOR]