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The hydration heat generated during the concreting of cast-in-place piles causes thermal disturbance to the surrounding permafrost, leading to its thawing. This further affects the stability of the pile foundation and degrades the construction progress. To explore the influence mechanisms of the concrete hydration heat on the permafrost temperature field around the pile, as well as that of different construction seasons on the pile-side boundary conditions and permafrost temperature field, monitoring results of on-site tests and numerical simulation were used to analyze the distribution law of the pile soil temperature field in space and time, and the pile-side boundary conditions and permafrost temperature field during construction seasons. The results show that the temperature trend of the pile foundation can be divided into three stages: a rapid rise phase (0∼2 d), a rapid decline phase (2∼10 d), and a slow decline and stabilization phase (10∼90 d). As the radial distance from the pile center decreases, there occur a corresponding acceleration in temperature increase and an elevated maximum temperature rise (MTR). The influence range of the molding temperature and the hydration heat is about 1∼2 times the pile diameter and less than 1.5 m in the depth direction. Compared to the atmospheric temperature, there is a lag in the change in the permafrost temperature caused by accumulation of ground temperature, and the significant difference between the two leads to an increased rate of heat exchange at the boundary condition. Conducting drilling operation and cast-in-place pile construction in the cold seasons is conducive to reducing the thermal disturbance to the permafrost around the pile in permafrost areas. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hot stuffy self-disintegration has become an advanced and popular steel slag treatment method in recent years, presenting numerous advantages. Hot-stuffy steel slag (HSS) obtained by self-disintegration treatment technology with waste heat has different compositions and properties compared with ordinary steel slag (OSS). Although the properties of OSS as a mineral admixture have been reported by numerous articles, few researches focus on HSS, especially its effect on early cement hydration. In this paper, the early hydration of HSS-cement composite pastes is investigated from the insights of isothermal calorimetry and phase evolution. Effects of HSS on the setting time, hydration heat, reaction product, reaction degree, microstructure, and pore solution were systematically studied and compared with those of OSS. Results show that, unlike OSS, HSS hardly ever retards the early hydration of cement. This is caused by the differences in the composition of HSS and OSS due to the diversity in their production treatment processes. During the hot stuffy self-disintegration, the key retarding component in OSS, such as C12A7, reacts with water and their contents in HSS are reduced. It is found that hot stuffy self-disintegration is an effective method to mitigate the retardation effect of steel slag on the early hydration of cement. This study provides a better understanding of HSS, which is crucial for its utilization in cementitious materials. Highlights: The impact of HSS on the early hydration of cement paste was studied. Hydration kinetics and phase evolution of C-HSS paste were investgated. Unlike OSS, HSS hardly ever retards the early hydration of cement. During the hot stuffy process, the key retarding component in SS is reduced. Hot stuffy self-disintegration effectively mitigates the retarding effect of SS. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study on the hydration heat of ultralight cementitious foams envisaged as insulation materials for building envelopes. The examined porous foam-cement material was additionally enhanced by embedded microencapsulated phase change material (PCM) to improve the desired thermal properties of the material. The heat emission and heat flow were measured at 20 °C and 30 °C for 168 h using the isothermal calorimeter. The experimental study comprised composites with dry densities of 240 kg m−3 and 480 kg m−3, two concentrations of protein-based foaming agent (2% and 4%) and two dosages of the embedded PCM material (10% and 20%). The reference composite without PCM was also tested. The effect of the necessary admixtures used to achieve the stability of ultralight cementitious foams was also examined. The results showed that hydration in ultralight foam-cement composites is retarded, and the values of heat released are lower than those of the paste used to produce the composites. In this regard, the main factors contributing to the lower heat released and its lower rate are the excess water from the foam, the dosage of the foaming agent and the admixtures introduced to achieve the stability of the ultralight composite. The stabiliser was found to be the most retarding admixture. Considering PCM, which was added at 10% and 20% of the paste volume, a rather low influence on the course of the hydration process was observed due to the overall composition of ultralight cementitious foams specially modified for each assumed content of PCM. [ABSTRACT FROM AUTHOR]

The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry. The specimens were prepared with water-cement ratios of 0.31, 0.38, and 0.45, and the molding temperature was specified at 10 and 20 °C. The experimental results show that, as the water-binder ratio increases, the value of the second temperature peak on the temperature curve of the cement paste decreases, and the age at which the peak appears is delayed. The higher the water-cement ratio, the higher the hydration heat release in the early period of cement hydration, but this trend reverses in the late period. There are intersection points of the total hydration heat curve of the cement pastes under the influence of the water-cement ratio, and this law can be observed at both molding temperatures. With the increase in the molding temperature, the age of the second temperature peak on the temperature curve of the cement paste will advance, but the temperature peak will decrease. The higher the molding temperature, the earlier the acceleration period of the cement hydration began, and the larger the hydration heat of the cement in the early stage, but the smaller the total heat in the late period. A subsection function calculation model of the hydration heat, which was based on the existing models, was proposed in order to predict the heat of the hydration of the concrete. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract As the span of concrete-filled steel tube (CFST) arch bridges increases, the hydration heat temperature effect of concrete inside steel tube becomes more severe, which increases the safety risk during the construction process. Therefore, a numerical simulation of the mechanical response of a long-span CFST arch bridge under the influence of hydration heat was carried out. First, based on the hydration heat conduction theory, a finite element model of the transient temperature field of a CFST arch rib was established. The temperature distribution of the CFST arch rib and its variation with time were revealed, and an approximate formula for the distribution of the hydration heat temperature along the radial direction of the CFST was provided. Subsequently, the variation law of the thermal stress of a CFST during hydration heat release was investigated. Finally, based on the principle of temperature equivalence, a finite element model of the overall CFST arch rib was established to examine the effect of hydration heat on the deformation of the arch rib. The results reveal that the hydration heat temperature field of the CFST arch rib exhibits nonlinear and axisymmetric characteristics. The maximum temperature of the section and the maximum temperature difference can reach 73.5 °C and 33.2 °C, respectively. Because of the influence of the hydration heat, there is a significant stress gradient in the cross section of the arch rib. A maximum radial stress of 2.08 MPa is attained, indicating a risk of concrete cracking. Additionally, the displacement along the transverse and vertical directions of the chord tube exhibits an initial increase, followed by a decrease over time. The maximum transverse displacement of the chord tube reaches 70.6 mm, while the vertical displacement reaches 117.8 mm.

With the rapid development of the construction industry and higher requirements on the properties of materials, extensive studies have been made to improve the property of the concrete and cementitious materials. This paper mainly studies the mechanical property, anti-chlorine ion diffusion, anti-chlorine ion diffusion, anti-freezing performance, hydration process, microstructure and rheological property of the concrete and cementitious materials after adding cellulose nanofibers. Results showed that the compressive strength of C40 concrete with 0.15% cellulose nanofibers added was 75.72 MPa at 56 days of age, 23.11% higher than that of the control group. It was also higher than that of concrete with 0.20% cellulose nanofibers admixture added. When the content of cellulose nanofibers was 0.15%, the flexural strength reached the maximum value of 6.55 MPa, improving by 24% compared with the control group. Under the circumstances of 150 freeze-thaw cycles, the mass loss rate of C50 concrete with 0.15% CNFs admixture registered at 0.41%, reducing by 0.81% compared with the control group. However, when the cellulose nanofibers increased to 0.20%, the mass loss rate of the concrete reached 0.48%, indicating that adding an appropriate amount of cellulose nanofibers could improve the performance of the concrete. The study provides a strong scientific basis for modifying concrete and cementitious materials.

This study focuses on the complex dynamics of heat dissipation within diaphragm walls during concrete hydration, crucial in construction engineering. Experimental measurements from three sites in Poland, featuring diaphragm walls of varying thicknesses, ranging from 1 to 1.5 meters, were compared to a numerical model. The model, using a Finite Difference Method, incorporated stages of execution of adjacent panels and their thermal influence. The results closely mirrored the measured temperatures, validating the accuracy of its predictions. Despite minor discrepancies, mostly within ±3°C, the method effectively approximated real-life scenarios. Suggestions for model enhancements include incorporating the effect of concrete admixtures and refining the modeling of sequential panel execution. The thermal soil parameters, their possible range, and their impact on hydration heat dissipation in deep foundations emerged as crucial insights. This research serves as a foundation for deeper investigations into early-age behavior in deep foundations, aiming to extend the analysis to stress and strain domains to unravel characteristic cracking patterns observed in diaphragm walls.

In contrast to ordinary portland cement (PC), the manufacturing process of high belite cement (HBC) boasts superior resource utilization, reduced energy consumption, and diminished greenhouse gas emissions. Additionally, HBC exhibits notable strengths in terms of durability and mechanical properties. This study delves into the thermal characteristics of hydration, mechanical behaviour, and failure mechanisms of HBC materials, both with and without fiber admixtures, employing a multifaceted approach encompassing hydration heat experiments, uniaxial compression tests, Brazilian tensile tests, alongside advanced techniques such as acoustic emission (AE) and digital image correlation (DIC). The results indicate that HBC has lower hydration heat release, contributing to a reduction in hydration temperature rise, offering advantages in large-scale structural construction. In terms of strength development, HBC exhibits compressive and tensile strengths similar to PC, while the strength of basalt fiber-reinforced HBC is notably lower than both. In terms of failure modes, both HBC and PC undergo shear failure in uniaxial compression tests, whereas basalt fiber-reinforced HBC experiences splitting failure. In Brazilian tensile tests, HBC and PC exhibit single-direction cracking, while basalt fiber-reinforced HBC shows synchronous cracking at the top, middle, and bottom. Due to the crack-arresting effect of basalt fibers, basalt fiber-reinforced HBC displays a bimodal feature on the stress-strain curve and features a stress plateau on both the stress-strain and strain energy development curves.

Gold tailings is formed as an industrial waste during gold mining and processing. The aim of the current study is to use it to prepare foamed concrete as subgrade filler. The effect of wet density (600, 700 and 800 kg/m3) and tailings content (15, 30, 45 and 60 wt%) on fluidity, compressive strength, elastic modulus, drying shrinkage, freeze–thaw resistance, hydration heat and pore structure were investigated. It was found that incorporating tailings into foamed concrete decreases the compressive strength as tailings adversely affected the pore structure, resulting in increased porosity, enlarged and connected pores, and reduced sphericity. To meet the requirement of subgrade filler, the tailings content was limited to 30 wt% when the designed wet density was 600 kg/m3 and it was 45 wt% when the wet density increased to 700 and 800 kg/m3. Nevertheless, increasing the tailings content effectively reduced the drying shrinkage and early age hydration heat which are favorable for massive foamed concrete construction. Besides, the incorporation of gold tailings is helpful to the freeze–thaw resistance of 600 and 700 kg/m3 foamed concrete for application in seasonal frozen areas. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical studies investigating the impact of three curing conditions on temperature evolution in concrete cubes. The tests were performed on samples of the same volume (3.375 dm3) under different curing conditions: room temperature, insulation boxes, and adiabatic calorimeter. Various cements (Portland cement, Portland composite cement, and blast furnace slag cement) and aggregates (gravel and basalt) were examined. The temperature evolution for all mixtures was analyzed, revealing a correlation between temperature increase and concrete type. Under insulation and adiabatic curing, Portland cement with gravel aggregate exhibited the highest temperature rise, while blast furnace slag cement with basalt aggregate showed the lowest increase. The incorporation of slag, ash, or other mineral additives reduced temperature rise. Additionally, basalt aggregate's higher heat capacity and thermal energy accumulation led to a decreased temperature increase compared to gravel. Using recorded thermal data, a numerical procedure predicting temperature development in nonadiabatic conditions through direct adiabatic tests is proposed. Comparisons between experimental and numerical temperature evolutions confirmed the model's accuracy. [ABSTRACT FROM AUTHOR]

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment. [ABSTRACT FROM AUTHOR]

In the solidification of plasters, promptly identifying layering defects is vital to reduce later inspection and maintenance expenses. Traditional tapping methods for defect detection, while widespread, are inefficient and can damage walls. This study proposes an innovative method utilizing Infrared Thermal Imaging (IRT) for semi real-time detection of layering defects during the solidification phase. The method was applied within the first 48 h following the application of two different plasters (Cement and Gypsum, mixed on-site as needed, not pre-dosed, and applied in a single layer), systematically examining the effects of plaster composition and environmental temperature conditions. The results showed that all preset defects were successfully identified. It was observed that larger defects are more readily detectable at a given thickness, and conversely, thicker defects are more discernible at a fixed size, with the dimension of the defect having a more pronounced impact on absolute contrast than its thickness. Notably, cement plaster exhibited two distinct temporal windows for defect detection, primarily influenced by environmental temperatures. In contrast, gypsum mortar presented two detection phases, with the initial phase being predominantly governed by the heat of hydration and the latter by ambient temperature conditions. The application of IRT technology in this research demonstrates its efficacy in accurately detecting layering defects during the solidification of plasters. This method offers valuable insights and guidance for the application of plaster layers in real-world engineering scenarios, potentially reducing maintenance costs and improving construction quality. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios. [ABSTRACT FROM AUTHOR]

Molybdenum tailings are accumulated in large quantities, occupying the land and polluting the environment. Therefore, the resource utilization of molybdenum tailings is imperative. In this paper, the influence of molybdenum tailings powder (MTs) as admixture on hydration characteristics, including hydration heat, hydration products, phase composition, and mechanical properties evolution of cement paste were investigated. Results showed that the early hydration of cement paste can be promoted when the content of MTs is not more than 15%. The compressive strength of cement paste with 15% MTs at 3, 28, and 120 days was 89.37%, 96.14%, and 91.68% of that of the portland cement (PC) group, respectively. When the content of MTs does not exceed 15%, the second exothermic peak of hydration heat of cement paste appears ahead of time and the peak value increases. With the increase of MTs content, the cumulative heat release of 72 h gradually decreased. The addition of MTs does not produce new hydration products, but introduces the mineral phase of MTs itself, and leads to the early transformation of ettringite (AFt) into monosulfoaluminate (AFm) in paste. There is still a close linear relationship between the compressive strength and cumulative heat release and chemically bound water content after addition of MTs into cement paste. It was also discovered that the pozzolanic activity of MTs in cement paste mainly occurred from 3 to 28 days. After 28 days, the particle-filling effect of MTs was dominant mainly. The research results are expected to provide basic research for the resource utilization of MTs. [ABSTRACT FROM AUTHOR]

This study focuses on the hydration kinetics of supersulfated cement (SSC). The hydration heat release characteristics are analyzed, and a kinetic model for hydration is established. Then, the hydration kinetic parameters, such as hydration mechanism constant N, reaction rate constant K, and reaction rate constant Ea, are discussed. The results show that increasing the temperature promotes the nucleation of hydration products, thereby leading to the early attenuation of SSC hydration. Meanwhile, the water-to-cement ratio has little effect on the hydration process. A new hydration kinetic model considering the time-varying nature of hydration is proposed. In this model, SSC hydration after the induction period is primarily controlled by diffusion rather than by the nucleation of hydration products. The hydration process of SSC consists of a finite number of hydration cycles, and the ettringite (AFt) crystallization pressure is responsible for overcoming the "coating effect" to allow a new hydration cycle to begin. Hence, weakening the "coating effect" and increasing the AFt crystallization pressure are promising strategies to improve the degree of slag hydration. Finally, the activation energy of SSC is higher than that of cement. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio. [ABSTRACT FROM AUTHOR]

This paper introduces a 1-D finite difference model for analyzing the temperature distribution throughout the hardening phase in concrete structures. The model accounts for the degree of hydration-dependent internal heat rate and the solar irradiance on the receiving surface of a concrete structure, allowing for more accurate predictions of early-age behavior of concrete. The research involves the development and validation of the 1-D model using temperature measurements from an on-site concrete footing. Mesh sensitivity studies were conducted to optimize grid size for thermal analysis. The paper also explores the determination of suitable 2-D width-to-height ratios for employing the 1-D model, providing practical guidelines for its application. Major findings indicate that the 1-D model can accurately predict temperature evolution in early-age concrete and offers a cost-effective alternative to more complex 2-D, 3-D finite difference, and finite element models. For preliminary analysis and quick assessments, the 1-D model is advantageous due to its computational speed, and it holds significant potential for concrete temperature control and construction optimization.

This article concentrates on the numerical analysis of hydration heat resulting in formation of cracks on the experimental block of the spillway at Orlik Reservoir and its verification with the experimental measurement. In order to eliminate the maximum of critical factors which could lead to appearance of early age cracking and faulty execution of the spillway, an experimental block was concreted. It served as a trial block for all steps of the execution process as well as a validating temperature measurement during cement hydration to confirm with the preliminary numerical analysis. [ABSTRACT FROM AUTHOR]

Cement is one of the main sources of negative environmental impact of concrete. One way to reduce this impact of concrete could be through the reduction of the cement content. This could be achieved by replacing a part of cement with mineral additives such as fly ash, blast-furnace slag, silica fume, metakaolin (MK), etc. in concrete. In this paper, the effect of curing temperature on MK blended cements is investigated. Isothermal calorimetry and compressive strength tests are performed on mortars prepared with various replacement levels of cement by MK (5%, 15% and 25%) and cured at different temperatures (10°C, 20°C and 40°C). Further, water porosity test and microscopic observations were carried out to confirm the findings. Results showed that the pozzolanic activity of MK is conditioned by the curing temperature and its levels of replacement. [ABSTRACT FROM AUTHOR]

This study focuses on the complex dynamics of heat dissipation within diaphragm walls during concrete hydration, crucial in construction engineering. Experimental measurements from three sites in Poland, featuring diaphragm walls of varying thicknesses, ranging from 1 to 1.5 meters, were compared to a numerical model. The model, using a Finite Difference Method, incorporated stages of execution of adjacent panels and their thermal influence. The results closely mirrored the measured temperatures, validating the accuracy of its predictions. Despite minor discrepancies, mostly within ±3 ◦C, the method effectively approximated real-life scenarios. Suggestions for model enhancements include incorporating the effect of concrete admixtures and refining the modeling of sequential panel execution. The thermal soil parameters, their possible range, and their impact on hydration heat dissipation in deep foundations emerged as crucial insights. This research serves as a foundation for deeper investigations into early-age behavior in deep foundations, aiming to extend the analysis to stress and strain domains to unravel characteristic cracking patterns observed in diaphragm walls. [ABSTRACT FROM AUTHOR]

The effects of different contents of a MgO expansive agent and phosphorus slag on the mechanical properties, shrinkage behavior, and the heat of hydration of concrete were studied. The slump flow, setting time, dry shrinkage, and hydration heat were used as sensitive parameters to assess the response of the considered specimens. As shown by the results, in general, with an increase in the phosphorus slag content, the hydration heat of concrete decreases for all ages, but the early strength displays a downward trend and the dry shrinkage rate increases. The 90-d strength and dry shrinkage of concrete could be improved with a phosphorus residue content between 0%-20%, with the best performances in terms of mechanical properties and shrinkage characteristics being achieved for a content of 20 kg/m³. On the basis of these results, it can be concluded that appropriate amounts of phosphorus slag and MgO expansive agent can be used to improve the compressive strength of concrete in the later stage by reducing the hydration heat and dry shrinkage rate, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a series of polyethylene glycol (PEG)/hydrochloric acid-modified sepiolite (HSEP) composite phase change materials (PCMs) are fabricated via vacuum impregnation. HSEP exhibits high adsorption capacity, rendering it superior to natural sepiolite as carriers for PEG. The resulting composite PCMs possess a melting enthalpy of up to 88.9 J/g and maintain stable thermal performances and chemical structures over 100 heating–cooling cycles between room temperature and 65 °C, thus, indicating long-term reliability. Calorimetry studies on cement paste containing 30% composite PCMs reveal a 24.14% reduction in 3-day cumulative hydration heat. However, the mechanical strength and thermal conductivity of the cement paste are adversely affected. Hence, carbon fibers (CFs) are introduced as reinforcement, resulting in a 28-day compressive strength of 45.6 MPa for cement paste containing 20% composite PCMs and 0.6% CFs. The fabricated composite PCMs are promising functional materials for hydration heat control and energy storage in concrete structures. [ABSTRACT FROM AUTHOR]

Massive high-strength concrete generates significant hydration heat during casting, which indirectly influences the risk of structural cracking by affecting the internal temperature gradient distribution. This paper investigated the effect of layered pouring methods on internal temperature gradients in massive concrete using the precast bent caps of a Shanghai bridge project as a case study. The temperature-time development patterns of each poured layer were studied through three sets of physical experiments. Temperature gradient distribution functions were established to specify the spatial temperature distribution trends of each layer. The interconnectedness between the spatial temperature distributions of adjacent poured layers was explored based on the established distribution functions. Targeted anticracking suggestions for layered poured concrete were provided based on these correlations. Additionally, a novel temperature control measure for managing hydration heat was proposed. The feasibility of this measure was verified through practical experiments. Moreover, corresponding finite element models were established to investigate the influence of parameters such as structural lead, outer wall pipe radius, and cooling water flow rate on the internal temperature field of concrete. The hydration heat-time patterns of the poured layers all showed a skewed single-peak distribution. The hydration heat of odd- and even-numbered layers exhibited different Gaussian distribution patterns in the lateral direction; the correlation between the spatial temperature distributions of adjacent layers could be quantified by the ratio of the standardized variance of the Gaussian distribution function of temperature for each corresponding layer. Implementing temperature control measures at specific reasonable positions and using a natural logarithmic function to calculate the design limits of structural dimensions could effectively prevent structural cracking. The newly proposed hydration heat control measure improved the temperature gradient distribution within the concrete. Reducing the structural lead, increasing the outer wall pipe radius, and increasing the cooling water flow rate all resulted in a decrease in the peak temperature inside the concrete. Finally, a structural lead of 0.4 was recommended for actual construction projects, for which the outer wall pipe radius should not exceed 30 mm.

The objective of this study is to investigate the influence of fly ash (FA), granulated blast furnace slag (GBFS), and a high-efficiency crack-resistant agent (HECRA) on the workability, mechanical properties, hydration heat (HH), adiabatic temperature rise (ATR), and volume stability of mass concrete (MC). Preliminary experiments determined that the total replacement of FA and GBFS in dual blending should be within 35% to 40%, with the GBFS content not exceeding 15%. A total of 16 concrete mix designs (MD) were formulated, including a control mix (comprising only cement (C)) and ternary blends (comprising C, FA, and GBFS), with the HECRA added at 0%, 4%, and 8% of the mass of cementitious materials. The workability of the MC was assessed through tests for air content (AC), bulk density (BD), slump, flow, and setting time. The mechanical strength, HH, ATR, and shrinkage rate of the MC were individually evaluated through compressive strength (CS) tests, HH experiments, ATR tests, and shrinkage measurements. A grey relational evaluation model was employed to establish correlations between C, FA, GBFS, and the HECRA concerning overall performance. Supported by the entropy value method, a comprehensive performance evaluation model was created. The results indicate that, compared to the control mix, the other groups exhibited reductions in mechanical performance, rates of HH, cumulative ATR, and increased self-volume deformation (SVD). These findings suggest that including FA, GBFS, and a HECRA can mitigate the HH and SVD of MC, albeit at the expense of its strength. According to the comprehensive performance evaluation model, when the C-to-FA-to-GBFS ratio is 6:3:1, and the HECRA constitutes 8% of the mass of cementitious materials, the specimens demonstrate the best overall performance. At 28d, the CS is 48.46 MPa, satisfying the design strength requirements for C35 concrete. The comprehensive performance of the large volume crack-resistant concrete with low temperature rise (LCCT) produced in this study meets engineering needs. It provides theoretical references for the mixed design of MC.

This article concentrates on the numerical analysis of hydration heat resulting in formation of cracks on the experimental block of the spillway at Orlik Reservoir and its verification with the experimental measurement. In order to eliminate the maximum of critical factors which could lead to appearance of early age cracking and faulty execution of the spillway, an experimental block was concreted. It served as a trial block for all steps of the execution process as well as a validating temperature measurement during cement hydration to confirm with the preliminary numerical analysis.

The hydration heat generated during the concreting of cast-in-place piles causes thermal disturbance to the surrounding permafrost, leading to its thawing. This further affects the stability of the pile foundation and degrades the construction progress. To explore the influence mechanisms of the concrete hydration heat on the permafrost temperature field around the pile, as well as that of different construction seasons on the pile-side boundary conditions and permafrost temperature field, monitoring results of on-site tests and numerical simulation were used to analyze the distribution law of the pile soil temperature field in space and time, and the pile-side boundary conditions and permafrost temperature field during construction seasons. The results show that the temperature trend of the pile foundation can be divided into three stages: a rapid rise phase (0∼2 d), a rapid decline phase (2∼10 d), and a slow decline and stabilization phase (10∼90 d). As the radial distance from the pile center decreases, there occur a corresponding acceleration in temperature increase and an elevated maximum temperature rise (MTR). The influence range of the molding temperature and the hydration heat is about 1∼2 times the pile diameter and less than 1.5 m in the depth direction. Compared to the atmospheric temperature, there is a lag in the change in the permafrost temperature caused by accumulation of ground temperature, and the significant difference between the two leads to an increased rate of heat exchange at the boundary condition. Conducting drilling operation and cast-in-place pile construction in the cold seasons is conducive to reducing the thermal disturbance to the permafrost around the pile in permafrost areas.

Massive concrete caps usually adopt cooling pipe water cooling to reduce the negative impact of the hydration heat of cement in construction. However, unreasonable cooling pipe layout, water temperature, and water speed often lead to low cooling efficiency of caps and concrete cracks caused by the excessive temperature difference between the surface and the inside, which can affect the safety and durability of structures. An improved calculation model for massive concrete caps was proposed to reveal the relationship between the transient temperature field of massive concrete caps and the cooling pipe layout and the value of relevant parameters. The proposed model considered the heat of cement hydration, solar radiation, air convection, and the heat exchange of cooling pipes through water. The boundary value conditions were identified through the least-squares method and physical test data, and a prediction model for the transient temperature field of massive concrete based on water cooling through cooling pipes was established. On this basis, the cooling pipe layout and cooling pipe parameters such as spacing, water temperature, and water flow rate were analyzed in accordance with the basic principles of heat conduction. Results demonstrate that, the influence of solar radiation cannot be ignored in the prediction of the transient temperature field of massive concrete caps. The single-circulation side-byside arrangement of cooling pipes is better than other layout methods. The internal temperature of caps is negatively correlated with the spacing of cooling pipes, but a considerably small spacing of cooling pipes can increase the amount of cooling pipes and the cost of temperature control. Lowering the water temperature can effectively control the temperature difference between the inside and the outside and reduce the risk of concrete cracking. Changing the water flow rate of the cooling pipes can reduce the maximum temperature inside the caps. However, when the water flow rate of the cooling pipes exceeds 2.4 cubic meters per hour, continuing to increase the cooling pipe water flow rate is not effective in reducing the maximum value of the transient temperature field of the caps. This study provides a good reference for temperature control in the construction of massive concrete caps for bridges. [ABSTRACT FROM AUTHOR]

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Molybdenum tailings powder (MTs) has potential pozzolanic activity and can be used as a mineral admixture. In order to comprehend the influence of MTs powder on the cement hydration process, the hydration heat and kinetics of composite cementitious materials (CCMs) were investigated using an isothermal calorimeter and the Krstulovic–Dabic model. Furthermore, the influences of fly ash (FA), slag (SL), and MTs powder on hydration heat were compared and analyzed, considering the same content. The results show that the proper amount of MTs can promote the hydration of CCMs. When the content of MTs is 5% and 15%, the second exothermic peak of the CCMs appears 2.30% and 4.27% earlier, and the exothermic peak increases by 2.72% and 1.34%, respectively. The cumulative heat release of CCMs gradually decreases with an increasing content of MTs powder. When the replacement of MTs, FA, and SL is 15%, respectively, the second exothermic peak of CCMs increases by 1.34%, −16.13%, and −12.04% for MTs, FA, and SL, respectively. The final heat release of MTs is higher than that of FA, but lower than that of SL. The hydration process of CCMs undergoes three stages: nucleation and crystal growth (NG), interactions at phase boundaries (I), and diffusion (D). [ABSTRACT FROM AUTHOR]

A large amount of phosphogypsum, ground granulated blast-furnace slag and slaked lime were employed to prepare the gypsum slag cement. The effect of phosphogypsum content on the hydration process and long-term strength of gypsum slag cement was investigated through hydration heat, chemical shrinkage, pH value of pore solution and compressive strength tests, combined with XRD and SEM-EDS. The results show that the third peak of heat release curves of cement pastes gradually decreases when the phosphogypsum content increases from 40% to 70% (mass fraction, the same below). The chemical shrinkage at 14 d increases from 0. 066 mL·g-1 to 0.193 mL·g-1, and chemical shrinkage rate significantly increases during the early hydration stage (0 ~ 1 d). The pH value of pore solution tends to stabilize within 28 d. Compared with 28 d compressive strength, the 90 d compressive strength is enhanced by 12. 3% ~ 27. 8%. XRD and SEM-EDS reveales that the cement pastes mainly consists of gypsum, quartz, ettringite and C-S-H gel. At the age of 28 d, the ettringite content decreases from 7.48% to 2.84%, and the Ca/Si ratio (molar ratio) of C-S-H gel increases from 1.08 to 2.24 with the increase of phosphogypsum. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the heat generated during the hydration process in cementitious composites containing multi-walled carbon nanotubes (MWCNTs). The cumulative heat release and heat flow of these cementitious composites were measured over a period of 168 h using isothermal calorimetry. Three different MWCNT dosages, 0.05 wt%, 0.1 wt%, and 0.2 wt%, along with two different sonication times for the solution, which were 20 min and 60 min, were applied in the experimental program. The results reveal that the incorporation of MWCNTs and the use of a naphthalene-based superplasticizer to disperse the nanotubes generally led to a reduction in heat emission during the early stages of hydration, a lower first peak value in the initial stage of hydration, and a significant delay in the acceleration period compared with the reference sample lacking this superplasticizer. Furthermore, the results demonstrate that both the dosage of multi-walled carbon nanotubes (MWCNTs) and the sonication time have an impact on the heat emission and hydration process since the same amount of superplasticizer was applied to all pastes. An increase in the MWCNT dosage led to a decrease in the rate of hydration heat at the main peak for all pastes. Additionally, longer sonication times resulted in lower values of heat generated, reduced main peak values in the heat rate evolution, and generally extended delays in the occurrence of the main peak. [ABSTRACT FROM AUTHOR]

The temperature change caused by hydration leads to early-age cracking in concrete box girder. The early-age cracking risk is further improved with low air temperature and large daily temperature difference, especially in Northwest China. To fill this gap, a temperature experiment and numerical simulation were performed on an actual concrete box girder segment in Northwest China. The temperature field, thermal stress and cracking risk were analyzed using evolution curves, distribution curves and contours. The key parameters that influence the hydration heat temperature, including the cement hydration heat release, cement content, height-width ratio of web, initial temperature, convective coefficient of top plate surface, were analyzed. An anti-cracking case based on parameters analysis was put forward. The results indicated that the temperature evolution can be divided into three stages: warming, cooling and environment significantly impacting. Along the thickness of each plate, temperature distributed is single peak in the center. Along the width or height, temperature distributed is double peaks at axillary position for the top and bottom plates, and single peak in center for the web. The axillary position and web have high thermal stress and significant cracking risks. The temperature difference of each plate, and the early-age cracking risk can be reduced by effectively adjusting the key parameters. Among these, the former two parameters are the most significant factors. The maximum cracking risk can be decreased by 15.7% for every 50 kJ/kg hydration heat reduction. The maximum cracking risk can be decreased by 13.1% for every 50 kg/m3 cement content reduction.

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment.

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios.

The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio.

Phosphogypsum is an industrial waste generated in the production of fertilizers causing environmental problems. Calcined phosphogypsum (CPG) is obtained by low-temperature calcination and dehydration of phosphogypsum. CPG is mainly used to produce building materials. However, mechanical strength properties and water resistance of CPG materials is extremely poor, which leads to its relatively low utilization rate in construction industry. To address this issue, various amount of Ordinary Portland cement (OPC), fly ash (FA), rice husk (RH) and modified admixtures (AD) were mixed with the CPG to obtain CPG-based composite cementitious materials, which enhanced the water resistance and mechanical strength of the corresponding hardened materials. The influence of different contents of cement on the setting time, hydration heat, hydration products, mechanical properties, water absorption, heavy metal leaching and deterioration coefficient of the composite cementitious material is investigated. The results showed that the optimal mixing ratio of CPG: OPC: FA: RH was 57: 20: 10: 13 considering the water resistance and mechanical strength properties of CPG-based composite cementitious materials. On these conditions, the compressive strength, the flexural strength, water absorption and deterioration coefficient of the specimens at 28 days are 6.1 MPa, 4.6 MPa, 29.4% and 0.66 respectively, which were in line with the national standard of phosphorus building gypsum wallboard. It was demonstrated that two skeleton types are present in the samples prepared using CPG-based composite cementitious materials, which had a synergistic support effect on the structure. The first skeleton was formed by gypsum dihydrate crystals (CaSO4·2H2O) and provided strength to the specimens at an early stage, while the second skeleton was formed by ettringite (AFt) and C–S–H gels, which provided strength at a later stage. The skeletons make the hardened materials denser and more waterproof. Moreover, the composite materials exhibited a positive solidification effect on heavy metals present in CPG.

The addition of a temperature-rising inhibitor (TRI) to aeolian sand paste materials (ASPM) to produce paste-like filling mining materials can solve multiple problems. First, it may alleviate the environmental problems caused by solid waste treatment in mines to achieve sustainable use of solid waste. Second, It may solve the problem of rapid temperature rise in mines caused by the rapid heat release during filling body hydration. Therefore, this study explored the hydration of an ASPM with different TRI contents and its mechanical properties, setting time, and microstructure. The results show that at TRI contents of 0–1.0%, the peak heat-release rate of the ASPM is reduced by 16.0%, the early hydration heat release is reduced by 14.2%, and the delay of the heat-release peak is more prominent. TRI inhibits the hydration of ASPM primarily within 7 d, which reduces the early strength of the ASPM by a maximum of 43.4%. However, with the increase in age, the strength difference gradually decreases, and TRI even becomes beneficial for the development of strength in later stages. In addition, the high content of TRI has a significant retarding effect on ASPM hydration. The temperature rise test shows that TRI can reduce the temperature increase rate and delay the peak temperature increase rate, which can effectively solve the problem of concentrated heat release by backfill. This paper provides a theoretical basis for the application of TRIs in cemented paste backfill.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)