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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.)

Massive high-strength concrete is often used for the # 0 segment of continuous box girders in modern large-span bridges. Thus, the release of substantial hydration heat results in thermal cracking during construction, which greatly affects bridge safety and durability. To predict the risk of structural cracking, it is important to clarify the distribution of the temperature gradient associated with the hydration heat in the # 0 segment and develop an accurate and simple method for calculations to assess of cracking. In this study, based on an actual bridge project, the temperature variation of the # 0 segment caused by hydration heat were measured, and the temperature distribution and development were investigated. The finite element method (FEM) was utilized to simulate the temperature field of the # 0 segment. Three thermodynamic methods for the assessment of cracking were compared and analyzed by practical calculations, and the influence of different parameters on the cracking risk was investigated. Measurements showed that the temperature field of the # 0 segment had a skewed unimodal normal distribution in time and a U-shaped distribution of low and high temperatures in outer and inner positions, respectively. The temperature distributions associated with the hydration heat were discontinuous in time for the root section and obeyed different but correlated Gaussian functions along the width of different pouring layers of the intermediate crossbeam at the # 0 segment. Additionally, the results of the FEM simulation were very consistent with the measurements, which verified the accuracy of the FEM simulation. The cracking assessment methods in EC2 and GB 50496 were used to exactly evaluate the cracking of massive concrete structures. On the basis of the results of the study, it was recommended to reduce casting temperature, delay removal of formwork and control curing temperature above 15°C to curb cracking. [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.)

Transient thermal analysis of mass concrete using ANSYS finite element program has become popular. In ANSYS, material properties and heat generation rate of concrete are typically input as constant, time-dependent, or temperature-dependent. However at early-age, the material properties and heat generation rate of mass concrete are significantly time- and temperature-dependent which should not be ignored. In this study, a detailed description of how to correctly predict the early-age thermal behavior of concrete is described and a modified USERMATTH subroutine for ANSYS is presented. In this subroutine, the heat generation rate, thermal conductivity, and specific heat for each element were programmed to be temperature, age, and location dependent. The early-age concrete material properties are described as a function of the degree of hydration. Experimental verification was conducted using three concrete batches containing supplementary cementitious materials delivered by ready-mix trucks. Each concrete batch was used to cast a 1.2-m cube with steel formwork and a 1-m insulated cube. The temperature differentials from the ANSYS simulations and experiments compared well, with a maximum error within 1 °C. Results show that the proposed method can predict the amplitude and time of peak temperatures at different locations. The thermal analysis technique developed in this study can be used to precisely analyze the temperature differentials in a mass concrete structure and help reduce the risk of early-age thermal cracking. [ABSTRACT FROM AUTHOR]

In this study, the non-hypothetical projection pursuit regression (NH-PPR) is proposed. The proposed NH-PPR model can predict the hydration heat based on the four cement phases, FA, SL, cement fineness and hydration time. The NH-PPR model is proposed by using the multiple layer iteration method and the non-hypothetical and non-parametric ridge functions to enhance accuracy and solve the problems caused by the parameter selection and the subjective hypothesis. The modeling data set is applied to train model, the testing data set is regressed and fitted into the model, and then the obtained results are compared with the BP model. To further validate the proposed model, another published data set is used to obtain a higher degree of confidence in the prediction. It is shown that the proposed model obtains the better accuracy, stability and versatility, and avoids the parameter selection and subjective hypothesis.

The optimum curing regime (OCR) empirically obtained from a number of small-sized specimens may be overly conservative or inaccurate due to neglecting the effects of exothermic hydration and geometries of full-sized members related to heat transfer. This study presents a theoretical model considering these effects to determine the OCRs of early strength concrete (ESC) in a Pareto set from an extensive design space. To validate the model, experiments were performed to measure the temperature histories and strength development under steam-curing conditions for a full-sized beam segment and match-cured small cylinders made of ESC. Parametric studies showed that energy savings of 7.5%, 20.4%, 42.7%, and 56.3% in steam curing could be achieved with the increase of the maximum steam temperature, sectional area, cooling period in the curing regime, and compressive strength of ESC, respectively. The most significant energy saving, 66.1%, was realized by including the favorable effects of hydration, compared with the results of OCR without hydration for the section considered in this study. Approximately 28 days or longer are needed in ambient temperatures for flowable fresh normal concrete to reach its hardened strength. The curing period can be shortened significantly by supplying steam for approximately 12 h at elevated temperatures, which accelerates the chemical reactions between cement particles and water (termed hydration) and allows concrete to reach approximately 70% of the target compressive strength in 1 day. Although steam curing may enhance the production efficiency and quality control, it increases the fuel consumption and intensifies the greenhouse effect. In this study, the heat consumption was reduced by the use of early strength concrete and the beneficial effect of increased temperature of ESC through hydration. Using the proposed steam-curing regimes for ESC, significant energy savings of as much as 66.1% were achieved, compared with those attainable through conventional curing regimes that do not include the hydration effect. The proposed curing technology can be applied to any type of concrete to reduce the energy consumption and greenhouse effects in the precast fabrication industry. [ABSTRACT FROM AUTHOR]

A significant portion of calcium silicate slag (CSS) waste is deposited in open landfills, leading to various environmental concerns. CSS powder with high content of active β-C2S is a potential supplementary cementitious material. This study determined the isothermal hydration heat flows of cementitious composites containing 0 – 40% CSS powder using an isothermal calorimeter. The hydration kinetics and parameters were simulated and analyzed using Krstulovic-Dabic model. Results indicated that the first exothermic peak of the cementitious composite containing CSS powder shifted to the left and was significantly higher compared to Portland cement. The second exothermic peak also shifted to the left, but its value decreased significantly. The cumulative hydration heat of the cementitious composite gradually decreased with increasing of CSS powder content. The simulations from the kinetic model showed that the hydration rate of the entire process decreased with the increase of CSS powder incorporation. These findings are expected to provide guidance for the use of CSS powder in low-heat mortars or concrete. [ABSTRACT FROM AUTHOR]

Over the past 20 years, as the depth and diameter of shaft lines increased in China, the cracking and water leakage of the inner walls of frozen shafts have become increasingly severe, resulting in significant safety threats and economic losses. Understanding the stress variation patterns of cast-in-place inner walls under the combined effects of temperature and constraint during construction is a prerequisite for evaluating the crack resistance performance of inner walls and preventing water leakage in frozen shafts. The temperature stress testing machine is an important instrument for studying the early-age crack resistance performance of concrete materials under the combined effects of temperature and constraint. However, existing testing machines have shortcomings in terms of applicable specimen cross-sectional shapes, temperature control methods for concrete structures, and axial loading capacity. In this paper, a novel temperature stress testing machine suitable for the inner wall structure shape, capable of simulating the hydration heat of the inner walls, was developed. Then, a reduced-scale model of the inner wall according to similarity criteria was manufactured indoors. Finally, preliminary investigations of the temperature, strain, and stress variations of the inner wall under 100% end constraint conditions were conducted by simulating the actual hydration heating and cooling process of the inner walls. Results show that the hydration heating and cooling process of the inner wall can be accurately simulated. After approximately 69 h of concrete casting, the accumulated relative displacement and strain of the end-constrained inner wall model were −244.2 mm and 187.8 με, respectively. The end constraint force of the model increased to a maximum value of 1.7 MPa and then rapidly unloaded, causing the model concrete to crack in tension. The temperature stress testing method presented in this paper provides a reference for scientifically formulating technical approaches to prevent cracking in cast-in-place concrete inner walls. [ABSTRACT FROM AUTHOR]

Engineering infrastructure includes a large number of concrete structures. The main binder used in concrete is Portland cement, which reacts with water when mixing. During the chemical reaction (cement hydration) heat is released causing non-uniform temperature distribution and subsequent internal stresses that may crack the concrete. Therefore, accurate prediction of concrete temperature evolution in design and control of concrete temperature in construction are crucial tasks for engineers. This paper presents the development of a finite difference (FD) model for predicting thermal behavior of concrete structures during cement hydration. A formwork or insulation layer that covers the outer of the concrete was accounted for in the model. The temperature profiles calculated by the proposed model show close agreement with those measured from a concrete bridge footing and a concrete cube. The Particle Swarm Optimization (PSO) algorithm was adopted to compute an "equivalent convection coefficient" for the convection boundary condition in the simplified model for several common insulation materials. The results show that using the simplified model along with an equivalent convection coefficient can give a significant reduction in the computation time while the accuracy is still maintained. In addition, an equation for estimating an equivalent convection coefficient for a given insulation material was developed for design and practical purposes. The proposed method can be used in the design of concrete structures and control of concrete temperature to prevent early-age thermal cracking thus ensuring the expected durability and service life. From the obtained results, varying equivalent convection values are also recommended to be used for different insulation materials. [ABSTRACT FROM AUTHOR]

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology 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 Roads & Bridges / Drogi i Mosty is the property of Road & Bridge Research Institute 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 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.)

Copyright of China Sciencepaper is the property of China Sciencepaper 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.)

Autoclaved aerated concrete is an excellent thermal insulation wall material, but with a large amount of waste. This paper describes the high-temperature activation and rehydration activity of waste cement–lime–sand autoclaved aerated concrete (SAAC) and discusses the high-temperature phase transition of SAAC. SAAC calcined at 750 °C was confirmed to be a metastable and amorphous state, which could hydrolyze Ca2+ ions with reactivity in water. The conductivity curve demonstrates that the concentration of ions in the suspension decreases rapidly at 150–250 min, and the hydration reaction turns dominant at this time. The hydration heat curve also displays a hydration exothermic peak at 2.5 h. In addition, the conductivity measurement of suspension and the exothermic measurement of hydration reaction proves that SAAC calcined at 750 °C has a hydration activity and can rehydrate with SiO2 in the system. The rehydration activity was verified by replacing 30% cement in the standard test block with calcined SAAC because the calcined SAAC at 750 °C has high hydration activity, and its activity index reached 89.58%. Fly ash is a commonly used cement admixture at present. Hence, the SAAC calcined at 750 °C and the fly ash were used to replace 30% of the cement in the cement test block, respectively. The results of this comparative experiment vividly showed that the reaction activity of SAAC calcined at 750 °C was higher than that of fly ash. Therefore, according to this research, SAAC has activity after calcination at 750 °C and can be hydrated again. [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.)

The concrete hydration heat and different construction methods directly affects the early crack resistance of massive concrete structures and may lead to concrete cracks. In this work, the hydration heat test and finite element simulation were conducted to investigate the early cracking resistance and the main influencing factors of the massive concrete bridge pier. The size of the bridge pier was 8 m (length) × 4 m (width) × 22.5 m (height), and the pier was poured in two layers (8.5 m/14 m) with an interval of 37 h. The internal temperature of the pier was tested 16 days after the concrete pouring using pre-buried temperature sensors, and the crack expansion on the surface of the pier was continuously observed during the test period. The test obtained a maximum concrete temperature of 64.25 °C after 100 h after the concrete pouring, and 3 cracks were found on the surface of the pier. The pier simulation model is established according to the actual situation in the test, The maximum temperature inside the bridge pier obtained from the simulation is 61.73 ℃, and the temperature field development pattern and the crack expansion on the pier surface were basically consistent with the test, which confirmed the reliability of the simulation method. Besides, the simulation process found that the maximum main tensile stress on the surface of the bridge pier was 2.77 MPa, which was mainly distributed near the interface of the 2 layers, indicating that the layered pouring scheme adopted in the test was improper. The effect of layered casting schemes on the early cracking resistance of massive concrete has rarely been discussed, and further simulations revealed that: the maximum main tensile stress can be reduced by gradually improving the number of layers, layer height and interval between each layer. By changing the original layered pouring scheme to 3 layers with an interval of 3 days between each layer, the maximum principal tensile stress is reduced to 1.50 MPa, and early cracking of the bridge pier can be avoided. This work provides a general numerical analysis method with high accuracy, parameterization and quantification for early crack control of massive concrete structures in a multi-factor complex environment.

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.

In this study, a rational theoretical expression and effective numerical realization of the hydration temperature evolution of concrete are presented. The proposed novel numerical method is based on the Fourier's law for heat flux, the heat source function which is obtained from the dissolution of cement clinker by the modified Parrot and Killoh model, and also takes into account the Arrhenius equation. Experimental temperature measurements performed on three different specimens under semi-adiabatic and adiabatic conditions are used to validate the proposed model. The results show that the measured semi-adiabatic and adiabatic temperatures of the SCM-blended concrete mixtures are in general agreement with the simulation results. The method proposed in this study can also predict the temperature field of mass concrete, providing guidance for practical engineering.

Spodumene tailing is the associated solid waste of extracting lithium from spodumene. With the increase in the global demand for lithium resources, its emissions increase yearly, which will become a key factor restricting the economic development of the mining area. Mechanical and hydration reactions, as well as the microstructure of early CSTB, are studied under different tailings–cement ratios (TCR) and solid mass concentration (SC) conditions. The results show that the uniaxial compressive strength of early CSTB has a negative exponential correlation with the decrease in TCR and a positive correlation with the increase in SC: when the age of CSTB increases to 7 days, the strength increases with the rise in SC in an exponential function, and the sensitivity of strength to TCR is higher than that of SC. Compared to other tailings cemented backfill materials, the addition of spodumene tailings reduces the sulfate ion concentration and leads to a new exothermic peak (i.e., the third exothermic peak) for the hydration exotherm of CSTB. Additionally, with the increase in TCR or decrease in SC, the height of the third exothermic peak decreases and the occurrence time is advanced. At the same time, the duration of induction phase was prolonged, the period of acceleration phase was shortened, and the total amount of heat released was significantly increased. The decrease in TCR or the increase in SC led to the rise in the number of hydration products which can effectively fill the internal pores of CSTB, enhance its structural compactness, and increase its compressive strength. The above study reveals the influence of TCR and SC on the early strength, hydration characteristics, and microstructure of CSTB and provides an essential reference for the mix design of underground backfill spodumene tailings. [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.)

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.)

Liquid accelerating agents have the advantages of simple operation and fast construction, and have become indispensable admixtures in shotcrete. However, most liquid accelerating agents in the market at present contain alkali or fluorine, which adversely affect concrete and seriously threaten the physical and mental health of workers. Therefore, in view of the above deficiencies, it is necessary to develop a new type of alkali-free fluorine-free liquid accelerating agent. In this paper, the polyaluminum sulfate early strength alkali-free liquid accelerator is prepared using polymeric aluminum sulfate, diethanolamine, magnesium sulfate heptahydrate and nano-silica. The influence of this agent on the setting time of fresh cement paste and compressive strength of the corresponding cement mortar is determined. Thermogravimetric analysis curves, X-ray diffraction and scanning electron microscopy images are obtained to investigate the mechanism. Findings show that the initial setting time and the final setting time of cement paste are 2 min 30 s and 7 min 25 s. The compressive strengths of cement mortar cured for 1 d, 28 d and 90 d are 2.4 MPa, 52.2 MPa and 54.3 MPa respectively. Additionally, the corresponding flexural strengths are 3.4 MPa, 9.8 MPa, 11.8 MPa. When the mass rate of accelerator is 7%, the mechanical strengths of cement mortar are the highest. The additions of fly ash and blast furnace slag can affect the mechanical of cement mortar mixed with accelerator. When the mass ratio of the fly ash and blast furnace slag is 15%, the mechanical strengths of cement mortar reach the highest. Moreover, the hydration heat release rate of cement is increased by the accelerator and the corresponding time of hydration heat peak is decreased by the accelerator. The accelerator can decrease the amount of needle-like hydration products and improve the compactness. The mechanical strengths are improved by consuming a large amount of Ca(OH)2 and forming more compact hydration products. It is recommended that the optimum dosage range of the polyaluminum sulfate early strength alkali-free liquid accelerator is 7%. [ABSTRACT FROM AUTHOR]

Accurately simulating the temperature field of frozen shaft lining in its early age (28 days) is difficult due to the influence of low temperature freezing and the heat of hydration in concrete. The temperature-dependent variation of the thermal properties of concrete and surrounding rock makes the simulation even more challenging. This study proposed a simulation method by considering the concrete maturity to characterize the spatiotemporal variation of temperature field in early age. In accordance with Arrhenius and heat conduction theories, a 3D temperature field control equation containing a model of hydration exothermic with equivalent age was established. The thermal parameters of rock and concrete at different temperatures were obtained through laboratory tests, and the temperature field of the lining was analyzed numerically by using ANSYS Parametric Design Language. The reliability of this method was verified by comparing with the measured data. Comparison results show that the proposed model successfully reflects the facts that the maximum temperature rise at different locations of the lining and the time taken to reach the maximum temperature rise are different. The temperature field in the early age shows five stages: induction period, linear growth period, nonlinear growth period, cooling period, and stabilization period. In the first 3 days, the temperature gradient between the inside and outside of the lining is large, which is prone to early temperature damage. This study provides a significant reference for early temperature damage and lining structure design optimization. [ABSTRACT FROM AUTHOR]

As a new type of cementitious material, magnesium oxysulfate cement (MOS) shows advantages of fire resistance, low alkalinity, light weight, insulation, and good thermal conductivity. Effects of n (MgO)/n (MgSO4) and n (H2O)/n(MgSO4) on the thermal conductivity and microstructure mechanism of magnesium oxysulfate cement are studied. The phase composition and microstructure of MOS cement hydration products are analyzed by X-ray diffraction and scanning electron microscopy. The hydration process of MOS cement is measured by hydration heat release rate. The results show that the mixture with higher molar ratio of MgO/MgSO4 and lower molar ratio of H2O/MgSO4 can produce more hydration products, which benefits the thermal conductivity and densification of MOS cement. The thermal conductivity is optimal when n (MgO)/n (MgSO4) is 12:1 and n(H2O)/n(MgSO4)is 19:1. The maximum thermal conductivity can reach 2.07 W/(m⋅K). [ABSTRACT FROM AUTHOR]

Thermal cracks are the major problem as temperature increases in massive concrete structures. It is imperative to investigate the temperature rise and to find effective techniques to control the heat of hydration of massive concrete. In this research, based on a segmental model test of high rise building raft, the temperature field for the bottom, middle and top surface concrete of the raft caused by the heat of hydration were measured. Blast furnace slag cement (CEM III/A 42.5N) was used due to its lower percentage of C3A and C3S and lower surface area. The tested temperature rise curves indicated that the temperature increases quickly but diminishes gradually. The maximum temperature rise at the middle surface of the concrete reached 56oC, and the maximum temperature difference between the middle and the top surface was 15.80oC. The most extreme temperature difference between the top surface and the surrounding environmental temperature was 26.5oC. So, using slag cement controlled the heat of hydration of concrete leading to environmentally friendly concrete mixes.

The water state plays a crucial role in influencing the rheological characteristics of cementitious materials. This research aims to elucidate the effect of supplementary cementitious materials (SCMs) with various features on the rheological parameters of blended cement paste from the standpoint of particle interactions and water state and migration. Quantitative analysis of gel/absorbed water, capillary/flocculation water, and free water in blended cement paste were conducted to offer a comprehensive explanation of their structural build-up process. Both fly ash (FA) and ground granulated blast furnace slag (GGBFS) exhibit the ability to reduce water freedom degree and increase rheological parameters, albeit through distinct mechanisms. FA primarily restricts water freedom by reducing the content of capillary water with high freedom degree and increasing the content of adsorbed water with low freedom degree. GGBFS reduces water freedom degree by forming smaller flocculation structures and increasing the content of flocculation water. Although tungsten tailings powder (TTP) also increases the content of adsorbed water, the primary factor impacting its rheological properties is the weakening of interparticle interactions due to the increased mean distance between particles. This research offers guidance on regulating rheological performance of cementitious materials. • Rheological behavior of cement pastes containing various SCMs were investigated. • Different states of water in blended cement pastes were quantitatively analyzed. • The mechanism underlying the impact of water state on rheological behavior was revealed. [ABSTRACT FROM AUTHOR]

The physical properties of C 4 A 3 $-C 2 S (ye´elimite-belite) clinker system will change with the proportion of C 4 A 3 $ or C 2 S, but the effect of mineral proportion change on hydration mechanism is not systematic and unclear. The C 4 A 3 $-C 2 S binary system was established by experiments, and its hydration process was characterized. The kinetic response of C 4 A 3 $-C 2 S binary hydration system was studied by Kondo model. The results showed that the change of design mineral ratio directly affects the hydration process and the hydration mechanism. The experiment and analysis show that when the design mineral ratio of C 2 S was lower than 65 wt%, the dominant factor of hydration was mainly controlled by nucleation mechanism (The hydration acceleration period is particularly significant), and when the ratio of C 2 S was higher, it would be controlled by diffusion mechanism. The precise value of the boundary reaction control is between 65 wt% (design mineral ratio of C 2 S) to 75 wt%. Only when the hydration kinetics of the binary system is controlled by the diffusion mechanism, the CH product can be stably crystallized. The classical Kondo model is suitable for the C 4 A 3 $-C 2 S hydration system. • The classical Kondo model is suitable for the C4A3$-C2S hydration system. • When C2S lower than 65 wt%, the hydration was controlled by nucleation mechanism. • When C2S was higher(AP: C2S≥75 wt%), it would be controlled by diffusion mechanism. • Mechanism presents similar evolution in acceleration, deceleration and steady periods. [ABSTRACT FROM AUTHOR]

With the growing rate of urbanisation, deep foundations are playing an ever-larger role in the development of cities, reaching deeper than before to fulfil the requirements of new constructions. While current European standards include design procedures for structural and geotechnical design, they lack provisions for massive deep foundations with regard to early-age thermal effects. This paper presents aspects of the phenomenon especially important for deep foundations and discusses normative requirements that influence their thermal behaviour. Further, the paper describes the methods and results of the research carried out in the United Kingdom on 1.50-m-thick diaphragm walls of a deep circular shaft. Shaft features are described, as well as the materials used. The measurements were carried out using vibrating wire strain gauges coupled with temperature readings. The results presented refer to one of the test panels concreted in January 2020. The temperature results are analysed together with the influence of work scheduling on the readings. Strain results that indicate contractive behaviour of the test panel are investigated together with the possible causes leading to such readings. Plans and directions for future research are discussed.

We evaluated the effects of hydration heat inhibitors on the early hydration heat release process of cement and its main mineral components. We used a microcalorimetric method to determine the effects of various proportions and properties of hydration heat inhibitors on the hydration of portland cement, tricalcium silicate, and tricalcium aluminate: concentration (C) = 40% m/m hydroxydiphosphonic acid (HEDP) (1-hydroxyethylidene-1,1-diphosphonic acid) and C = 40% m/m diethylene triamine pentonyphosphonic acid (DTPMPA) (diethylenetriaminepentamethylene phosphonic acid). We also analyzed and tested the heat release rate and cumulative heat release during the hydration of cement and its main mineral components. The hydration heat inhibitors decreased the heat release rate of cementitious materials by means of adsorption, chelation, precipitation, complex formation, and control of calcium hydroxide crystals. Among these materials, the hydration heat inhibitor had the most substantial effect on the composition of tricalcium silicate clinker, reducing the peak temperature at the initial stage of hydration and delaying its occurrence time. These results are pertinent to controlling and selecting the early hydrothermal release process of cement systems.

Mine water is rich in various chlorides, which will inevitably affect the performance of the cemented paste backfill (CPB). In this study, the TAM Air isothermal calorimeter was used, the effects of typical chlorides (NaCl, CaCl2 and MgCl2) in mine water on the hydration heat and hydration heat flow in the solidification stage of fresh CPB were studied, and the effects of chlorides on the setting time of fresh CPB were analyzed. The hydration products of CPB samples containing different chlorides were tested by the X-ray diffractometer and thermal gravimetric analyzer. The results show that NaCl and CaCl2 can promote the early hydration reaction of CPB; and the promoting effect of CaCl2 is more significant; while MgCl2 consumes OH- in the solution and reduce the pH of the solution, thus inhibiting the early hydration reaction of CPB. With the increase of chloride concentration, the promoting effect of NaCl on the early hydration of the CPB first increases and then decreases, the promoting effect of CaCl2 increases constantly, and the inhibitory effect of MgCl2 also increases continuously. Besides, CaCl2 can significantly shorten the hydration time of CPB in the induction stage and acceleration stage, and the higher the CaCl2 concentration, the higher the cumulative hydration heat and the hydration heat release rate of CPB in the same hydration stage. This study comprehensively evaluates the influence of typical chlorides in mine water on the early hydration process and setting time of the fresh CPB, providing a reference for the clean utilization of mine water, fly ash, gangue and other solid wastes.

Recycled clay brick powder (RCBP) was used to replace partially cement to prepare composite cementitious materials, and the hydration kinetics and microstructure evolution of the composite cementitious materials were investigated by measuring the types of hydration products, hydration heat and microstructure. The results show that RCBP has little effect on the types of hydration products. However, at the later stage of cement hydration, the pozzolanic reaction occurs between RCBP and Ca(OH)2. Meanwhile, RCBP promotes the dispersion and dissolution of cement and provides many nucleation sites for C–S–H gel, increases the effective water-binder ratio and accelerates the heat release of cement hydration, however, the cumulative heat release decreases with the dosage of RCBP. In addition, RCBP can increase porosity at early stage of hydration, but the pozzolanic reaction between RCBP and Ca(OH)2 at the later stage of hydration would produce more hydration products, filling the pores, refining the pore diameter and improving the pore structure. Furthermore, RCBP affects the formation and microstructure of C–(A)–S–H gel, and promotes the formation of spherical C–(A)–S–H gel. [ABSTRACT FROM AUTHOR]

To further explore the effects of limestone powder (LP) on the hydration of Portland cement as well as the formation and transformation mechanism of calcium carboaluminate phases, the hydration reaction between LP and tricalcium aluminate (C3A) is thoroughly studied in this paper. Due to the crucial influence of gypsum on the hydration of C3A, two systems are well studied, viz. the C3A–LP–H2O and the C3A–LP–CaSO4·2H2O–H2O system. The replacement levels of LP are 0, 5 mass%, 15 mass% and 25 mass% by mass of total binder. The hydration behavior of these two systems are studied using isothermal calorimetry, XRD and quantitative XRD, and chemical shrinkage. The obtained results show that more LP delays the formation of hemicarboaluminate. In the C3A–LP–CaSO4·2H2O–H2O system, the formation of calcium carboaluminate phases only begins after gypsum is consumed. Moreover, LP can reduce the chemical shrinkage resulting from the volume increase of the formation of calcium carboaluminate phases. [ABSTRACT FROM AUTHOR]

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To study the effect of different curing temperatures on the hydration reaction of slag cement, four different curing temperatures of 20,40,60 and 90 t were set in this study. The initial hardening of cement was detected by ultrasonic detector, the hydration heat of samples was analyzed and tested by isothermal calorimeter, and the hydration reaction mechanism of slag cement at different temperatures has been systematically analyzed combined with micro test analysis. The results show that the hardening time of slag cement will decrease with the increase of temperature. With the increase of curing temperature, the hydration heat release of slag cement is also greater, and the hydration degree is also greater. However, compared with high temperature, the slow rate of hydration heat release of slag cement at low temperature is more obvious, and the peak value of heat release is also delayed. The change of curing temperature does not change the type of hydration products, but only affects the total amount of Ca(OH)2 and calcium vanadium stone. The higher the temperature, the less the total amount of Ca(OH)2 and the more the total amount of vanadate. When the curing temperature is 40 t, the slag has been completely covered by hydration products, and the gel on the slag surface becomes needle like. [ABSTRACT FROM AUTHOR]

Cement solidification was a widely used method to broaden the resource utilization of dredged sludge. However, the organic matter in sludge limit the application of cement solidification. The fulic acid (FA) was used to simulate the natural organic matter in sludge. With the increase in FA content, the sludge gradually changed from low-liquid-limit clay to high-liquid-limit clay. The unconfined compression test showed that the strength of cement-solidified dredged sludge (CDS) decreased with FA content. The influence mechanism of the FA on cement solidification was revealed by a water content test, a hydration heat test, scanning electron microscopy, and thermogravimetric analysis. FA hindered the conversion of pore water to combined water and reduced the hydration heat inside CDS. The FA in sludge weakened the internal bond within CDS by hindering the development of C-S-H gel from spheroidal to flake. At the same time, the final amount of hydrates such as C-S-H, C-A-H and AFt also decreased in the CDS containing FA. The weakening mechanism of FA on the strength of CDS can be attributed to three aspects: (1) FA adsorbed on the surface of cement minerals and hindered the contact between cement minerals and pore water; (2) acidic FA reduced the pH of the pore liquid in CDS; (3) the carboxyl and hydroxyl functional groups of FA adsorbed calcium ions in pore liquid through ion coordination. [ABSTRACT FROM AUTHOR]

Copper and zinc tailing powder (CZTP) is finely ground waste after copper minerals and zinc minerals have been extracted from ores during beneficiation. CZTP has certain potential cementitious properties and can be used in composite cementitious materials. The pore size distribution and hydrate phase assemblage of the hardened samples are investigated using MIP and XRD. SEM is employed to examine the microstructure of the specimens. The chemically bonded water is used to measure the degree of hydration. CZTP lowers the hydration heat evolution rate and the total hydration heat. The hydration heat evolution rate reduces as the w/b ratio rises, whereas the total hydration heat of blended cement paste rises. CZTP diminishes the strength development of the Portland-CZTP system, and the strength decreases as the CZTP level increases. CZTP reduces the critical pore diameters of the Portland-CZTP system with w/b = 0.3 after curing for 3 d and 28 d, while increasing the critical pore diameters of samples with w/b = 0.45 at the same age. CZTP increases the gel micropores of Portland-CZTP. Although CZTP increases the pore volume content of blended cement pastes with w/b = 0.3, the volume of harmful pores decreases. The pore volume content of the Portland-CZTP system decreases as the w/b ratio increases. However, the volume of harmful pores increases with a higher w/b ratio. The main hydration products in the Portland-CZTP system are portlandite, ettringite, and C-S-H. CZTP mainly played the role of filling or acting as a microaggregate in the Portland-CZTP system. [ABSTRACT FROM AUTHOR]

In order to reduce the thickness of the frozen shaft and avoid shaft cracking caused by hydration heat of mass concrete, C100 high-performance concrete is adopted as the deep shaft material in the west air shaft of Zhaogu No.2 mine. After multiple and multi-site comparison of raw materials, P.II52.5 portland cement, basalt gravel with compressive strength of 148 MPa, mechanism sand without fineness modulus of 2.8 and low-temperature early-strength collapse-protected polycarbarate high-performance water reducer were determined as the raw materials for C100 high-performance concrete. By mixture ratio test, the C100 concrete cement∶ sand∶ gravel∶ admixture∶ mineral powder∶ water∶ water reducing agent is 395∶600∶1 100∶120∶100∶105∶29. Ultimately, no cracks appeared in the borehole wall of C100 freezing section, which ensured good performance of pressure bearing and water sealing. After 28 days of shaft lining casting, field sampling was conducted to measure the strength. The test results showed that the C100 high-performance concrete reached 117% of the designed strength level, which exceeded the standard of 1.15 times of the designed strength as the minimum requirement for the concrete strength of shaft engineering.

Over the past 20 years, as the depth and diameter of shaft lines increased in China, the cracking and water leakage of the inner walls of frozen shafts have become increasingly severe, resulting in significant safety threats and economic losses. Understanding the stress variation patterns of cast-in-place inner walls under the combined effects of temperature and constraint during construction is a prerequisite for evaluating the crack resistance performance of inner walls and preventing water leakage in frozen shafts. The temperature stress testing machine is an important instrument for studying the early-age crack resistance performance of concrete materials under the combined effects of temperature and constraint. However, existing testing machines have shortcomings in terms of applicable specimen cross-sectional shapes, temperature control methods for concrete structures, and axial loading capacity. In this paper, a novel temperature stress testing machine suitable for the inner wall structure shape, capable of simulating the hydration heat of the inner walls, was developed. Then, a reduced-scale model of the inner wall according to similarity criteria was manufactured indoors. Finally, preliminary investigations of the temperature, strain, and stress variations of the inner wall under 100% end constraint conditions were conducted by simulating the actual hydration heating and cooling process of the inner walls. Results show that the hydration heating and cooling process of the inner wall can be accurately simulated. After approximately 69 h of concrete casting, the accumulated relative displacement and strain of the end-constrained inner wall model were −244.2 mm and 187.8 με, respectively. The end constraint force of the model increased to a maximum value of 1.7 MPa and then rapidly unloaded, causing the model concrete to crack in tension. The temperature stress testing method presented in this paper provides a reference for scientifically formulating technical approaches to prevent cracking in cast-in-place concrete inner walls.

This study aims to develop a novel low-heat cement slurry using phase change microcapsule additives to reduce the decomposition of hydrate-bearing sediments during cementing. Microcapsules were prepared by coating mixed alkanes with polymethyl methacrylate, and lipophilic-modified graphite was incorporated to enhance the thermal conductivity of microcapsules. The effects of microcapsules upon the hydration heat, pore distribution, and compressive strength of the cement slurry/stone were studied through a variety of tests. The results showed that the phase-change temperature, thermal enthalpy, and encapsulation efficiency of the microcapsules were 8.99–16.74 °C, 153.58 Jg−1, and 47.2%, respectively. The introduction of lipophilic-modified graphite reduced the initial phase-change temperature of microcapsules by 0.49 °C, indicating an improvement in their temperature sensitivity. The maximum hydration heat of cement slurry decreased by 41.3% with 7% dosage of microcapsules; the proposed microcapsules outperformed comparable low-heat additives. Moreover, the presence of microcapsules could reduce the number of large pores in (and thereby improve the compressive strength of) cement stone. The innovation of this study is that it comprehensively and intuitively confirms the feasibility of the application of low-heat cement slurry with MPCM as the key in hydrate sediments rather than just focusing on the reduction of hydration heat; furthermore, a self-made cementing device was developed to simulate the cementing process of hydrate deposition. The results show that the thermal regulation of microcapsules inhibited the temperature increase rate of the cement slurry, significantly reducing the damage caused to the hydrate. These findings should improve the safety and quality of cement in offshore oil and gas well applications. [ABSTRACT FROM AUTHOR]

Coral wastes are produced during the construction of island. The use of coral wastes in concrete is beneficial to economy and environment. Coral waste as aggregate in concrete has been studied well. Now, coral powder (CP) as mineral admixture to replace cement partially in concrete is a different approach to reuse coral waste. However, the use of more CP in concrete will definitely affect the property of cement-based material. In order to improve the mechanical property and use more CP in construction, ground-granulated blast-furnace slag (GGBFS), a kind of latent hydraulic material, is considered in this study. Furthermore, the synergetic effect of CP and GGBFS on the hydration of Portland cement (PC) is seldom researched systematically. In this study, CP and GGBFS are mixed into cement in five proportions to research the hydration process of cement paste comprehensively by isothermal calorimetry test, X-ray diffraction, and thermogravimetric analysis. The properties of the GGBFS-CP-PC ternary system, such as the chemical shrinkage and compressive strength, are also determined. The results show that the existence of GGBFS will influence the secondary hydration of C3A when the mass ratio of GGBFS to cement is above 0.25 in binder. The reaction of CP is accelerated by the active alumina phase in GGBFS. The presence of GGBFS can promote the formation of carboaluminate. During the infrastructure construction in island, it is reasonable to use CP in concrete, and the use of CP together with GGBFS can ensure the mechanical properties of concrete structures. [ABSTRACT FROM AUTHOR]

In order to investigate the effect and mechanism of coupled mechanical–chemical activation on the hydration activity of copper slag powder, copper slag powder with different grinding time and content was applied to prepare composite cement. The hydration heat and rate of the composite cement paste were tested for 120 h. The mechanical properties and microstructure of the samples were characterized by compressive strength activity index, XRD, and SEM. The findings revealed that the specific surface area of the copper slag powder increased by 27.84%, 20.14%, and 10.92%, respectively, when the grinding time increased from 30 min to 120 min. The particle size distribution of the copper slag powder after grinding for 90 min and 120 min was superior to that of cement. The compressive strength activity index of the paste specimen increased with the extension of the copper slag grinding time when the copper slag powder content remained constant. Chemical activator CaO further stimulated the hydration activity of copper slag powder, increased the hydration heat of copper slag powder-based composite cement paste, and promoted the compressive strength of composite cement-hardened paste at different ages. With the increase in copper slag powder content, the porosity of the hardened paste increased, resulting in a decrease in compressive strength at different ages. [ABSTRACT FROM AUTHOR]

There is limited measure available to quantify the effect of polycarboxylate-ether based superplasticizer (PCE) on the microstructure of cement-based systems during the first 24 h. To fill this gap, the backscattered electron image analysis (BSE-IA) alongside the ternary technique is used in this study to separate composed phases quantitively and then calculate the average spacing between cement particles. Besides, together with an examination of hydration heat, the skeleton development of reaction products is investigated. The results show that cement hydration is not a constant process, and the developing mode for hydration products region varies with the particle size of cement. In this regard, numerous hydration products may gather around small cement particles and then adsorb other unhydrated particles, forming the continuous region. By contrast, the particles possessing relatively large size are surrounded by noticeable pores, which interrupt the continuity of the hydration products region. When introducing PCE, the agglomeration of cement particles and the average spacing between cement particles reduced, manifesting as an enlarged hydration products region alongside a decreased porosity at the area surrounding large particles. However, this leads to a decreased hydration degree for cement and extends the setting time of cement paste.