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Early-age cracking in mass concrete structures resulting from thermal stress is a well-documented phenomenon that impacts their functionality, durability, and integrity. The primary cause of these cracks is the uneven temperature rise within the structure due to the exothermic nature of cement hydration. Assessing the likelihood of cracking involves comparing the tensile strength or strain capacity of the concrete with the stresses or strains experienced by the structure. Challenges in evaluating the risk of thermal cracking in mass concrete structures stem from various material and technological factors that influence the magnitude and progression of hydration heat-induced temperature and thermal stress. These complexities can be addressed through numerical analysis, particularly finite element analysis (FEA), which offers comprehensive modeling of early-age effects by considering all pertinent material and technological variables. However, employing FEA poses challenges such as the requirement for numerous input parameters, which may be challenging to define, and the need for specialized software not commonly available to structural engineers. Consequently, the necessity for such advanced modeling, which demands significant time investment, may not always be warranted and should be initially assessed through simpler methods. This is primarily because the definition of massive structures—those susceptible to adverse effects such as cracking due to temperature rise from hydration heat—is not precise. To address these challenges, the authors propose a three-step method for evaluating structures in this regard. The first step involves a simplified method for the classification of massive structures. The second step entails estimating hardening temperatures and levels of thermal stress using straightforward analytical techniques. The third step, reserved for structures identified as having a potential risk of early thermal cracks, involves numerical modeling. The outlined procedure is illustrated with an example application, demonstrating its practicality in analyzing a massive concrete wall constructed on the foundation. [ABSTRACT FROM AUTHOR]

Copyright of Fly Ash Comprehensive Utilization is the property of Hebei Fly Ash Comprehensive Utilization Magazine Co., Ltd. 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.)

This paper describes the author’s method for the direct and continuous measurement of the temperature distribution during the initial period of hardening concrete, together with the results of tests obtained with its use. The first successful test using this method was conducted by the author in May 2001 [7]. In the following years, the author successfully used this method in the study of other structural elements [8] and [9]. He independently developed and made the necessary elements to measure the temperature in hardening concrete. The tested element is a reinforced concrete column with a diameter of 2.0 m and a height of 8.0 m, which is an intermediate support for the flyover under construction along the Wrocław city ring road. The structure consists of two independent continuous 15-span structures made of pre-stressed concrete (Fig. 1). The article additionally presents numerical model of the previously tested reinforced concrete pillar and the calculation results obtained. The numerical calculations were carried out using the Abaqus FEA software [1]. In conclusions, the author summarises the important elements of the on-site test and makes recommendations for further use of this method to predict the temperature distribution in other elements of the structure, provided that they are made of exactly the same concrete mixture.

This study extended the electromechanical impedance (EMI) technique to monitor the 28‐day age of strength gain in mass concrete, although it has been validated in strength monitoring of a lab‐scaled concrete specimen. Embedded piezoelectric (PZT) transducer, namely, aluminum embedded PZT (AEP), that was wrapped by two sandwich aluminum pastes was proposed for EMI monitoring. The workability of the AEP was first verified via finite element analysis, where the effect of hydration heat on the EMI signature of the AEP was evaluated via numerical modeling and prior thermal test. In the experiment, totally four AEP transducers arranged at different loci were applied to monitor strength gain in a mass concrete specimen. As a comparison, the maturity method was also performed to estimate the strength of the specimen. Characteristics of EMI signature and its statistical indices including root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD) were analyzed and correlated to strength development in mass concrete. Monitoring results indicated that the AEP transducers were capable of identifying the strength gain of mass concrete. The logarithmic function between the RMSD/MAPD index values and compressive strength perfectly predicted the strength development, which could be further employed for real‐life and in situ applications. [ABSTRACT FROM AUTHOR]

Mass concrete is widely used in large-scale projects, including metro upper cover structures, water conservancy dams, and heavy equipment foundations, among others, necessitating the process of health monitoring in mass concrete construction. The development of reliable and simple strength-monitoring methods for mass concrete is challenging because the inner temperature of mass concrete is high and changes a lot. This study proposes a strength-monitoring approach for mass concrete using barium titanate–bismuth ferrite/polyvinylidene fluoride (BT–BFO/PVDF) nanocomposite piezoelectric sensors, wherein the new sensors are embedded as actuators and sensors in mass concrete. The stress wave generated by the BT–BFO/PVDF piezoelectric sensors is used to monitor the specimen's strength for 28 days. The piezoelectric voltage received by the sensors in mass concrete is analyzed. The experimental results indicate that the signal received by the BT–BFO/PVDF sensors is not easily affected by the internal temperature of mass concrete compared with that of the traditional PVDF piezoelectric sensors. The signal parameters sensitive to concrete strength variation and the change trend of concrete strength are closely related to the piezoelectric voltage. Therefore, the proposed approach using BT–BFO/PVDF nanocomposite piezoelectric sensors is efficient (error < 10%) in mass concrete monitoring. Moreover, the monitoring results do not need temperature compensation. The physical meaning of the obtained strength prediction formula is proposed. An experimental system based on PVDF dynamic strain-sensing characteristics is established. [ABSTRACT FROM AUTHOR]

The west artificial island of Shenzhen-Zhongshan Link is located in an offshore environment. The structure size of the cast-in-place tunnel on the island is large, and the section width and the height of the wall body are in gradual changes. During the construction process, in order to ensure the temporary traffic demand of the main line of the tunnel, part of the structural wall of the open tunnel is partially reserved to be poured and closed after traffic conversion. Due to the long time interval between ages, it is easy for cracks to occur in the structure because of asynchronous shrinkage between the old and new concrete. In order to reduce the risk of concrete cracking and ensure the durability of offshore concrete structures, a systematic crack control study was carried out on the post-casting wall of the offshore cast-in-place tunnel. Through comprehensive crack control measures such as finite element simulation analysis, intelligent temperature control system development, and supplemented by investment in temperature control hardware measures, the goal of post -casting wall crack control was achieved, effectively avoiding harmful cracks in the wall. [ABSTRACT FROM AUTHOR]

To improve the existing temperature field control technology for mass concrete and to apply temperature control measures more effectively using inhibitors while reducing construction cost, a regulating model was proposed. This model was based on an adiabatic temperature rise equation for concrete mixed with inhibitors of different delayed heat release times. The distribution of temperature fields for mass concrete subjected to different temperature control measures involving inhibition was investigated using the model. Specifically, under the working conditions of delayed heat release of 0 ~ 3 d, the internal temperature peak and temperature difference between the inner and outer surfaces of the mass concrete decrease continuously as the delayed heat release time increases. However, under the working conditions of delayed heat release of 5 ~ 10 d, heat accumulation in multi-layer poured concrete occurs due to the prolonged delayed heat release time. A three-day inhibition of heat release meets the temperature control objectives, For a oneday inhibition of heat release, the temperature control objectives are achieved by reducing the initial temperature of the concrete in the mold by 1 ~ 2 ℃ . In conclusion, this research introduces a new concept and method for regulating the temperature field of mass concrete. [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.)

Subway stations are important components of subway system planning and urban rail transit where passengers can board, alight, transfer, or wait. With an increase in urban passenger flow, subway stations must meet greater transfer‐space demands commensurate with growing station structure sizes. In this study, the field‐monitoring and analysis method was adopted to investigate the Huaxing Street Station of the Chengdu Metro Line 19 project and explore the temperature‐variation rule in the process of mass‐concrete pouring in the station floor. Based on an ABAQUS large‐finite‐element calculation programme and secondary development of damage and failure research methods, a mechanical model of mass‐concrete pouring in subway‐station floor construction was established. The pouring temperature effect, damage, and failure mechanism of mass‐concrete pouring in subway stations were comprehensively studied. The main results were as follows: (1) the maximum temperature difference between the upper and middle layers of the floor was dominant and reached a peak within 1–3 d after the completion of pouring, and the temperature difference gradually decreased with a decrease in the hydration‐heat reaction. (2) At 0–10 d, the damage ratio of the floor increased by 1.8%, predominantly in the form of longitudinal damage. Within 10–30 d, the damage and failure ratio of the floor increased by 1.86%, primarily in the form of transverse damage and failure. Within 30–40 d, the temperature of the floor stabilized and gradually approached the ambient temperature. The damage and failure ratio of the floor increased by 0.32% at this time. (3) The lower the ambient temperature, the greater was the damage sustained by the floor at different ages, and the ambient temperature had a significant influence on floor damage. [ABSTRACT FROM AUTHOR]

As the water pipe cooling system is widely applied to controlling temperature in mass concrete structures, the precise simulation of the temperature field in mass concrete with cooling pipes embedded is meaningful. This paper presents an isogeometric analysis (IGA) with NURBS for heat transfer in mass concrete with consideration of the cooling pipe. The proposed method not only achieves the same level of accuracy with fewer nodes but also eliminates the time-consuming process of mesh in the traditional FEM. The coarsest parameter space which depicts small pipe and large concrete precisely is constructed to create an efficient model for numerical computation. In addition, the unique k-refinement in IGA is supposed to be the most appropriate encryption mechanism, and the knot insertion vector for effective refinement is calculated by considering the characteristics of temperature gradient distribution around the cooling pipes. In addition, a different calculation parameter has been discussed to show the stability and flexibility of the IGA. The obtained numerical results demonstrate the accuracy and efficiency of the proposed scheme in the simulation of transient temperature fields in concrete structures with cooling systems. [ABSTRACT FROM AUTHOR]

In this article, the potential of employing self-compacting geopolymer concrete in massive elements has been investigated. The main binder consisted of 85% ground granulated blast furnace slag and 15% fly ash. An alkaline solution of sodium hydroxide and sodium silicate was utilised. The effects of four parameters (binder content, water-to-binder [W/B] ratio, Na2O% and coarse-to-fine aggregate [C/F] ratio) on the fresh, mechanical and thermal properties of Massive Self-Compacting Geopolymer Concrete (MSCGC) mixes were evaluated. Taguchi's design of experiments was used to minimise the number of trial mixes. The heat of geopolymerisation of MSCGCs was monitored using a semi-adiabatic chamber and then applied to concrete samples using a temperature match curing system. The maximum compressive and splitting tensile strengths and modulus of elasticity were 62.7 MPa, 5.04 MPa and 33.26 GPa, respectively. Binder content was identified as the most significant parameter affecting the thermal and mechanical properties of the mixtures. The impact of the C/F ratio was greater than the W/B ratio on the thermal characteristics. The results of a numerical analysis reveal that although a higher binder content enhances the mechanical properties of the MSCGCs, it leads to an increased risk of cracking owing to greater heat production. [ABSTRACT FROM AUTHOR]

In engineering practice, similar surface insulation measures are typically applied to different parts of mass concrete surfaces. However, this can lead to cracking at the edges of the concrete surface or the wastage of insulation materials. In comparison to flat surfaces, the edges of mass concrete structures dissipate heat more rapidly, leading to more pronounced stress concentration phenomena. Therefore, reinforced insulation measures are necessary. To reduce energy consumption and enhance overall insulation effectiveness, it is essential to study the specific insulation requirements of both the flat surfaces and edges of concrete separately and implement targeted surface insulation measures. Taking the bridge abutment planned for pouring in Nanjing City as the research object, this study established a finite element model to explore the effects of different ambient temperatures and different surface heat dissipation coefficients on the early-age temperature and stress fields of different parts of the abutment's surface. Based on simulation results, reasonable heat dissipation coefficients that meet the requirements for crack prevention on both the structure's plane and edges under different ambient temperatures were obtained. The results indicate that under the same conditions, the reasonable heat dissipation coefficient at the edges was smaller than that on the flat surfaces, indicating the need for stronger insulation measures at the edges. Finally, mathematical models correlating ambient temperature with reasonable heat dissipation coefficients for the structure's plane and edges at these temperatures were established, with high data correlation and determination coefficients (R2) of 0.95 and 0.92. The mathematical models were validated, and the results from finite element calculations were found to be consistent with those from the mathematical models, validating the accuracy of the mathematical models. The conclusions drawn can provide references for the insulation of similar engineering concrete planes and edges. [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.)

In many emerging economies, the impact of fly ash utilization for mass concrete applications considering industry practices is yet to be quantified. This study quantifies the environmental and economic impacts of fly ash utilization in mass concrete, considering different mix design strategies in actual practice. Thirty-one (31) concrete mixtures from batching plants in the Philippines with 28-day strength design of 13.8–69.0 MPa have been analyzed using life cycle assessment (LCA) in SimaPro 9.3. Results show that when cement is replaced by 10, 15, and 20% of fly ash by weight, the global warming potential values are reduced by 8.5–9.4%, 8.5–20.7%, and 2.4–19.2%, respectively. Increased fly ash replacement shows a more beneficial impact on normal to high-strength than low-strength concrete mixtures in all 18 midpoint categories. Contribution analysis shows that aggregates significantly affect land use, while admixture affects marine eutrophication. A comparative LCA with mixtures from Thailand suggests that designing the compressive strength of fly ash concrete at 56 days will significantly improve its sustainability compared to a 28-day design. The economic benefit of using fly ash is greater for high-strength than for low-strength mixtures. This study will contribute to improving the sustainability of mass concrete production and benefit countries with similar practices. [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]

Hydration heat of early-age sidewalls can cause cracks owing to thermal stress, reducing the durability of underground space structures. The heat can be removed by the flowing water in the cooling pipe system. However, the cooling pipe may cause thermal stress due to the temperature gradient in the region adjacent to the cooling pipe, resulting in concrete cracking. To minimize the temperature peak of sidewalls and cracking risks in the region adjacent to the cooling pipe, the crack-distribution characteristics, temperature, and strain evolution of an early-age sidewall with a cooling pipe system are analyzed by concrete temperature and strain tests. Furthermore, a model that accounts for the early-age behavior of concrete and cooling-pipe effects is developed and solved. Finally, the effects of cooling-pipe parameters and ambient temperature on the sidewall's temperature field and cracking risk are analyzed. The results indicate that the cracks emerge in the first two weeks after concrete pouring; most are vertical, and a few oblique cracks emerge in the wall corner. The tensile stress in the region adjacent to the cooling pipe gradually decreases along the flow direction. Reducing the water temperature and increasing the flow rate reduces the sidewall's temperature peak and cooling rate. However, they increase the cracking risk in the region adjacent to the cooling pipe. When the flow rate exceeds 0.6 m3/h, further increasing the flow rate does not significantly affect the temperature field. Reducing the distance between cooling pipes reduces the temperature peak, cooling rate, and cracking risk in the region adjacent to the cooling pipe. In high-temperature environments, the cracking risk in the region adjacent to the cooling pipe increases significantly. [ABSTRACT FROM AUTHOR]

Using limestone powder (LP), the by-product of manufactured sand, to replace part of fly ash (FA) or manufactured sand could not only turn waste into treasure and decrease the price of concrete, but could also enhance the performance of concrete and reduce environmental pollution. However, the impact of various LP incorporation methods on the performance of mass concrete was inconsistent. In this paper, the effects of LP on the workability, compressive strength, constrained expansion rate, hydration temperature and impermeability of mass concrete were studied by replacing FA or manufactured sand alone and replacing FA and manufactured sand simultaneously. The results showed that the impact of LP on the performance of mass concrete was equal when it replaced FA alone and FA and manufactured sand at the same time. When the replacement amount was 20%, the workability, expansibility and early strength of concrete were improved, but the later strength and impermeability were slightly reduced. The workability, compressive strength, expansibility and impermeability of mass concrete were improved when manufactured sand was replaced alone, and the optimal dosage was 10%. The LP, moreover, reduced the hydration temperature peak of concrete in three kinds of mixing methods, but the temperature peak appeared earlier. At lower dosages, LP optimized pore structure and promoted the early hydration of cement through filler effects and nucleation effects. When LP replaced manufactured sand, the microstructure of concrete was more dense, so the replacement of manufactured sand had a better effect on the improvement of concrete properties. A reference value for the use of LP in mass concrete is provided in this study. [ABSTRACT FROM AUTHOR]

Copyright of Water Conservancy Science & Techonlogy & Economy is the property of Water Conservancy Science & Technology & Economy 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 Subway stations are important components of subway system planning and urban rail transit where passengers can board, alight, transfer, or wait. With an increase in urban passenger flow, subway stations must meet greater transfer‐space demands commensurate with growing station structure sizes. In this study, the field‐monitoring and analysis method was adopted to investigate the Huaxing Street Station of the Chengdu Metro Line 19 project and explore the temperature‐variation rule in the process of mass‐concrete pouring in the station floor. Based on an ABAQUS large‐finite‐element calculation programme and secondary development of damage and failure research methods, a mechanical model of mass‐concrete pouring in subway‐station floor construction was established. The pouring temperature effect, damage, and failure mechanism of mass‐concrete pouring in subway stations were comprehensively studied. The main results were as follows: (1) the maximum temperature difference between the upper and middle layers of the floor was dominant and reached a peak within 1–3 d after the completion of pouring, and the temperature difference gradually decreased with a decrease in the hydration‐heat reaction. (2) At 0–10 d, the damage ratio of the floor increased by 1.8%, predominantly in the form of longitudinal damage. Within 10–30 d, the damage and failure ratio of the floor increased by 1.86%, primarily in the form of transverse damage and failure. Within 30–40 d, the temperature of the floor stabilized and gradually approached the ambient temperature. The damage and failure ratio of the floor increased by 0.32% at this time. (3) The lower the ambient temperature, the greater was the damage sustained by the floor at different ages, and the ambient temperature had a significant influence on floor damage.

The durability of mass concrete structures may be compromised due to stresses and cracking induced by temperature rise due to cement hydration and concrete’s insulating capacity. Delayed ettringite formation and thermal cracking may occur when maximum temperatures and maximum temperature differences are greater than the allowable limits. Through a real-world case study in Douglasville, Georgia, this work investigates how modeling, construction decisions, and thermal limits influence the construction decisions of a mass concrete footing and abutment wall. Thermal control measures deemed necessary to satisfy thermal limit criteria for the abutment wall construction included precooling the concrete using liquid nitrogen and post-cooling the abutment wall using internal cooling pipes. Both measures, however, increased the cost and complexity of construction. The footing also required pre-cooling of the concrete even though it was not classified as mass concrete. In this work, the temperature development of the footing and the wall is modeled through a progressive approach based on laboratory-scale isothermal calorimetry. Based on the modeling, alternative design and construction options to satisfy thermal limits imposed by several Department of Transportation (DOT) guidelines, but at lower cost and complexity, are considered. A performance-based temperature difference limit (PBTDL) that considers a certain project’s mechanical performance and material properties is introduced as an alternative to the current difference limit prescribed by DOTs, which in certain cases can be inflexible, overly conservative, and overly simplified. The analysis also investigates the geometric hard limit specified by certain DOTs to classify mass concrete. The investigation shows that the cost and complexity of mass concrete construction can be significantly reduced with progressive modeling, performance-based decision-making, and a holistic outlook on the mass concrete problem.

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.

Abstract Large structural elements have been commonly observed in increasingly tall buildings, employing mass concrete elements in their foundations. In these elements, the internal heat generated by the cement hydration can be decisive for the occurrence of pathological manifestations arising from the balance of stresses and also by delayed ettringite formation. This article presents a practical and expedited method, through diagrams, for a preliminary assessment of the thermo-tensional risk involved in the concreting of large-scale elements. For the development of thermal risk diagrams, the commercial software TSA-2D was used, where 64 numerical computational simulations were conducted, varying the parameters with the greatest influence on the concrete thermal phenomenon (minimum dimension of the structural element, cement content per cubic meter, cement hydration heat, concrete placement temperature, and ambient temperature). The result of this methodology, when compared to computational simulations and field monitoring in a specific case study, showed a good correlation, with the potential for application and reproducibility, considering the natural limitations of an expeditious practice that needs to be evaluated on a case-by-case basis, but which provide an important guideline in the early decision-making on-site. Furthermore, the maximum absolute error between the results of computational simulation and field monitoring was only 1.6%.

As the water pipe cooling system is widely applied to controlling temperature in mass concrete structures, the precise simulation of the temperature field in mass concrete with cooling pipes embedded is meaningful. This paper presents an isogeometric analysis (IGA) with NURBS for heat transfer in mass concrete with consideration of the cooling pipe. The proposed method not only achieves the same level of accuracy with fewer nodes but also eliminates the time-consuming process of mesh in the traditional FEM. The coarsest parameter space which depicts small pipe and large concrete precisely is constructed to create an efficient model for numerical computation. In addition, the unique k-refinement in IGA is supposed to be the most appropriate encryption mechanism, and the knot insertion vector for effective refinement is calculated by considering the characteristics of temperature gradient distribution around the cooling pipes. In addition, a different calculation parameter has been discussed to show the stability and flexibility of the IGA. The obtained numerical results demonstrate the accuracy and efficiency of the proposed scheme in the simulation of transient temperature fields in concrete structures with cooling systems.

Mathematical physics equations are often utilized to describe physical phenomena in various fields of science and engineering. One such equation is the Fourier equation, which is a commonly used and effective method for evaluating the effectiveness of temperature control measures for mass concrete. One important measure for temperature control in mass concrete is the use of cooling water pipes. However, the mismatch of grids between large-scale concrete models and small-scale cooling pipe models can result in a significant waste of calculation time when using the finite element method. Moreover, the temperature of the water in the cooling pipe needs to be iteratively calculated during the thermal transfer process. The substructure method can effectively solve this problem, and it has been validated by scholars. The Abaqus/Python secondary development technology provides engineers with enough flexibility to combine the substructure method with an iteration algorithm, which enables the creation of a parametric modeling calculation for cooling water pipes. This paper proposes such a method, which involves iterating the water pipe boundary and establishing the water pipe unit substructure to numerically simulate the concrete temperature field that contains a cooling water pipe. To verify the feasibility and accuracy of the proposed method, two classic numerical examples were analyzed. The results showed that this method has good applicability in cooling pipe calculations. When the value of the iteration parameter a is 0.4, the boundary temperature of the cooling water pipes can meet the accuracy requirements after 4~5 iterations, effectively improving the computational efficiency. Overall, this approach provides a useful tool for engineers to analyze the temperature control measures accurately and efficiently for mass concrete, such as cooling water pipes, using Abaqus/Python secondary development. [ABSTRACT FROM AUTHOR]

In order to prevent temperature cracks in mass concrete walls in the basement of a project's cultural relics restoration building, a simulation analysis of the heat of hydration and anti-cracking properties was carried out by taking the sample basement wall as a simulation example and combining the underground conditions of the restoration building with the material properties. The results show that the wall panel concrete reaches the temperature peak of 63.2 °C at the age of 1.2 d, the maximum temperature rise is 33.2 °C, the maximum temperature difference between the inner and outer surface is 14.4 °C, the maximum difference between the outer and outer surface is 18.8 °C. the maximum cooling rate is 7.2 °C/d, and the cooling rate doesn't satisfy the requirement of temperature control index of 2.0 °C/d of GB 50496-2018 "Standard for construction of mass concrete". Wall panels in the external fixed constraints on the length of the edge of the edge is very easy to crack, the age of cracking is 3.2~6.3 d, in this stage heat preservation, moisturizing and other anti-cracking measures should be taken. [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.)

This research investigates the impact of reduced graphene oxide (rGO) on the temperature gradient and associated stresses of mass mortar blocks. When the thermal stresses induced by the temperature gradient between the core of mass mortar or concrete blocks and their surfaces exceed the tensile strength of the concrete, cracking can occur. The measurements of temperature evolution at several locations in two mortar blocks with dimensions of 0.48 m x 0.41 m x 0.68 m are obtained from the literature. The first block was cast with a reference mix (REF) which contains only ordinary Portland cement, whereas the cement was replaced by 1.2% rGO for the other block. A finite element simulation of the two blocks was carried out and the measured temperature evolution was captured with a reasonable precision. Subsequently, numerical simulation was used to investigate the influence of rGO on the temperature rise and the associated potential of cracking in the mass mortar blocks with dimensions of 1 m x 1 m x 1 m and 2 m x 2 m x 2 m. It is noted that the rGO has a significant effect on reducing the the cracking indices of mass mortar blocks. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering 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.)

Thermal management of mass concrete can adversely impact a project's cost and schedule, both during planning and in execution. Nomograms are presented as aids to quickly identifying and making tradeoffs among promising thermal management options. First, the temperature of fresh concrete and a worst-case adiabatic temperature estimate is provided by a nomogram based on simple physical models. A subsequent nomogram accounts for the impact of size, shape, and environment and is based on a surrogate model generated from many three-dimensional (3-D) finite element simulations without postcooling. Finally, nomograms for postcooling are given, similarly founded on finite element-derived surrogate models, for two classes of cooling pipe layouts. The use of these nomograms, with an awareness of their estimated error, is discussed for the initial development of mass concrete thermal management plans. [ABSTRACT FROM AUTHOR]

Temperature is the most important factor to consider while constructing mass concrete. The resultant temperature is the result of cement hydration and other factors, resulting in the production of thermal cracks at an early age. As a result, the prediction of temperature fields in massive concrete structures has been a significant challenge. A temperature nomogram is created in this study by using numerical methods to quickly determine the maximum temperature in concrete structures with various characteristics, such as cement content and the initial temperature of concrete mixtures. The obtained monogram can be used to predict the maximum temperature in mass concrete structures in order to prevent thermal cracks during construction and thereafter.

Early-age cracking in mass concrete structures resulting from thermal stress is a well-documented phenomenon that impacts their functionality, durability, and integrity. The primary cause of these cracks is the uneven temperature rise within the structure due to the exothermic nature of cement hydration. Assessing the likelihood of cracking involves comparing the tensile strength or strain capacity of the concrete with the stresses or strains experienced by the structure. Challenges in evaluating the risk of thermal cracking in mass concrete structures stem from various material and technological factors that influence the magnitude and progression of hydration heat-induced temperature and thermal stress. These complexities can be addressed through numerical analysis, particularly finite element analysis (FEA), which offers comprehensive modeling of early-age effects by considering all pertinent material and technological variables. However, employing FEA poses challenges such as the requirement for numerous input parameters, which may be challenging to define, and the need for specialized software not commonly available to structural engineers. Consequently, the necessity for such advanced modeling, which demands significant time investment, may not always be warranted and should be initially assessed through simpler methods. This is primarily because the definition of massive structures—those susceptible to adverse effects such as cracking due to temperature rise from hydration heat—is not precise. To address these challenges, the authors propose a three-step method for evaluating structures in this regard. The first step involves a simplified method for the classification of massive structures. The second step entails estimating hardening temperatures and levels of thermal stress using straightforward analytical techniques. The third step, reserved for structures identified as having a potential risk of early thermal cracks, involves numerical modeling. The outlined procedure is illustrated with an example application, demonstrating its practicality in analyzing a massive concrete wall constructed on the foundation.

Mass concrete is widely used in large-scale projects, including metro upper cover structures, water conservancy dams, and heavy equipment foundations, among others, necessitating the process of health monitoring in mass concrete construction. The development of reliable and simple strength-monitoring methods for mass concrete is challenging because the inner temperature of mass concrete is high and changes a lot. This study proposes a strength-monitoring approach for mass concrete using barium titanate–bismuth ferrite/polyvinylidene fluoride (BT–BFO/PVDF) nanocomposite piezoelectric sensors, wherein the new sensors are embedded as actuators and sensors in mass concrete. The stress wave generated by the BT–BFO/PVDF piezoelectric sensors is used to monitor the specimen’s strength for 28 days. The piezoelectric voltage received by the sensors in mass concrete is analyzed. The experimental results indicate that the signal received by the BT–BFO/PVDF sensors is not easily affected by the internal temperature of mass concrete compared with that of the traditional PVDF piezoelectric sensors. The signal parameters sensitive to concrete strength variation and the change trend of concrete strength are closely related to the piezoelectric voltage. Therefore, the proposed approach using BT–BFO/PVDF nanocomposite piezoelectric sensors is efficient (error < 10%) in mass concrete monitoring. Moreover, the monitoring results do not need temperature compensation. The physical meaning of the obtained strength prediction formula is proposed. An experimental system based on PVDF dynamic strain-sensing characteristics is established.

In engineering practice, similar surface insulation measures are typically applied to different parts of mass concrete surfaces. However, this can lead to cracking at the edges of the concrete surface or the wastage of insulation materials. In comparison to flat surfaces, the edges of mass concrete structures dissipate heat more rapidly, leading to more pronounced stress concentration phenomena. Therefore, reinforced insulation measures are necessary. To reduce energy consumption and enhance overall insulation effectiveness, it is essential to study the specific insulation requirements of both the flat surfaces and edges of concrete separately and implement targeted surface insulation measures. Taking the bridge abutment planned for pouring in Nanjing City as the research object, this study established a finite element model to explore the effects of different ambient temperatures and different surface heat dissipation coefficients on the early-age temperature and stress fields of different parts of the abutment’s surface. Based on simulation results, reasonable heat dissipation coefficients that meet the requirements for crack prevention on both the structure’s plane and edges under different ambient temperatures were obtained. The results indicate that under the same conditions, the reasonable heat dissipation coefficient at the edges was smaller than that on the flat surfaces, indicating the need for stronger insulation measures at the edges. Finally, mathematical models correlating ambient temperature with reasonable heat dissipation coefficients for the structure’s plane and edges at these temperatures were established, with high data correlation and determination coefficients (R2) of 0.95 and 0.92. The mathematical models were validated, and the results from finite element calculations were found to be consistent with those from the mathematical models, validating the accuracy of the mathematical models. The conclusions drawn can provide references for the insulation of similar engineering concrete planes and edges.

Abstract The temperature stress in mass concrete structure is relatively high during construction, which usually leads to temperature cracks. To solve this problem, concrete blocks are usually placed by setting wide slots. Connecting the truncated steel bars at the position of the wide slots by welding or extruding sleeves has many disadvantages. To solve the problem of temperature-induced stress loss, a new type of slightly curved arc HRB400 (SCAHRB400) steel bars was proposed without cutting off the steel bars in this article. Tensile tests and numerical simulations were performed for five types of SCAHRB400 steel bars considering geometric and material nonlinearity. Based on the test results and numerical simulation results, the equivalent stress–strain relationships of SCAHRB400 steel bars were established, and the emergence of the plastic zone of SCAHRB400 steel bars in the tensile process were observed, the tensile properties of SCAHRB400 steel bars were analyzed and discussed. The test results indicate that SCAHRB400 steel bars are prone to local yielding near the crown of large arches and at the connection of horizontal and arc sections. The numerical simulation equivalent stress–strain curves have good regularity. The equivalent stress–strain curves of slightly curved arc HRB400 and HRB335 steel bars have the similar changing law. When the stress is small, the tensile stiffness and compressive axial stiffness of slightly curved arc HRB400 and HRB335 steel bars are similar; when the stress is large, the axial stiffness of SCAHRB400 steel bars is greater than that of slight curved arc HRB335 steel bars. Through test and numerical simulation studies, the theoretical basis can be established for the engineering application of new slightly curved arc steel bars in mass concrete.

Value-added utilization of steel slag as a hydration heat controlling material to prepare sustainable and green mass concrete was systematically investigated in this study. Effects of high-volume steel slag on reducing the heat release and temperature rise as well as on the workability, strength and durability of mass concrete were studied and compared with those of high-volume fly ash. Results show that the addition of high-volume steel slag efficiently reduces the heat release of the blended system. Steel slag demonstrates superior heat reduction compared to fly ash, especially at 25 °C (reduced by 35%), and is comparable/closer at 50 °C. High-volume steel slag concrete shows reducing temperature rise (especially before 7 d), and presents smaller porosity, prolonged setting time, slower fluidity loss, good compressive strength, and permeability resistance compared with high-volume fly ash concrete. The utilization of steel slag as a hydration heat controlling material to prepare sustainable and green mass concrete with blast furnace slag is a potential and value-added utilization method of steel slag, which is in favor of sustainability.

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Analyzing and modeling the thermal behavior of mass concrete elements has been widely investigated by several researchers. Lately, many contemporary finite element packages have embedded modules for analyzing thermal behavior. Unfortunately, these packages are quite complex and require experts to be properly implemented. This paper proposes a simple and practical approach using the 3D-Finite Difference Model (3D-FDM) developed by MS-Excel to overcome the complexity of the other FE models. The model is utilized to predict the thermal behavior of actual bridge pile caps (3D model) rather than the previously developed 2D models in earlier research. The results of the analysis are compared with the concrete temperatures that were experimentally obtained from the site. Site data was collected using 18 thermocouple probes (K type) that were installed in two pile caps. These thermocouples were installed before concrete pouring to monitor the temperatures generated due to the exothermic reaction of the cement, which occurs during casting and the maturity period of concrete. The readings were registered every 3 hours for 7 days after concrete placement. This research provides a comparison between the recorded site data and the thermal analysis based on the proposed 3D-FDM. Results proved that concrete temperature time histories at different locations of the bridge pile caps could be properly predicted using the developed 3D-FDM. [ABSTRACT FROM AUTHOR]

This study provides the results of an experiment on the possibility of using high-volume ground granulated blast furnace slag (HVGGBFS)-based concrete as mass concrete. In addition to the control concrete, the total weight of the binder was 75% ground granulated blast furnace slag (GGBFS) and 25% ordinary Portland cement (OPC). For the aggregates, both natural and recycled aggregates were used. Three specimens with dimensions of 800 mm × 800 mm × 800 mm were prepared to simulate mass concrete. The workability, temperature aging and strength of the mass concrete were tested. The test results showed that utilizing HVGGBFS concrete as mass concrete can significantly reduce the heat of hydration due to the low heat of hydration of GGBFS, while the heat of hydration of GGBFS and recycled aggregate combination is 11.2% higher than normal concrete, with a slump that is 31.3% lower than that of plain concrete. The results also showed that the use of recycled aggregates in HVGGBFS concrete can significantly reduce workability. However, the compressive strength is higher than when natural aggregates are used due to the alkali activation effect caused by the recycled aggregates. The compressive strength at 7 and 28 days increased by 33.7% and 16.3%, respectively. [ABSTRACT FROM AUTHOR]

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]

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Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering 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 Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering 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.)

Hydration heat of early-age sidewalls can cause cracks owing to thermal stress, reducing the durability of underground space structures. The heat can be removed by the flowing water in the cooling pipe system. However, the cooling pipe may cause thermal stress due to the temperature gradient in the region adjacent to the cooling pipe, resulting in concrete cracking. To minimize the temperature peak of sidewalls and cracking risks in the region adjacent to the cooling pipe, the crack-distribution characteristics, temperature, and strain evolution of an early-age sidewall with a cooling pipe system are analyzed by concrete temperature and strain tests. Furthermore, a model that accounts for the early-age behavior of concrete and cooling-pipe effects is developed and solved. Finally, the effects of cooling-pipe parameters and ambient temperature on the sidewall’s temperature field and cracking risk are analyzed. The results indicate that the cracks emerge in the first two weeks after concrete pouring; most are vertical, and a few oblique cracks emerge in the wall corner. The tensile stress in the region adjacent to the cooling pipe gradually decreases along the flow direction. Reducing the water temperature and increasing the flow rate reduces the sidewall’s temperature peak and cooling rate. However, they increase the cracking risk in the region adjacent to the cooling pipe. When the flow rate exceeds 0.6 m3/h, further increasing the flow rate does not significantly affect the temperature field. Reducing the distance between cooling pipes reduces the temperature peak, cooling rate, and cracking risk in the region adjacent to the cooling pipe. In high-temperature environments, the cracking risk in the region adjacent to the cooling pipe increases significantly.

The temperature stress in mass concrete structure is relatively high during construction, which usually leads to temperature cracks. To solve this problem, concrete blocks are usually placed by setting wide slots. Connecting the truncated steel bars at the position of the wide slots by welding or extruding sleeves has many disadvantages. To solve the problem of temperature-induced stress loss, a new type of slightly curved arc HRB400 (SCAHRB400) steel bars was proposed without cutting off the steel bars in this article. Tensile tests and numerical simulations were performed for five types of SCAHRB400 steel bars considering geometric and material nonlinearity. Based on the test results and numerical simulation results, the equivalent stress–strain relationships of SCAHRB400 steel bars were established, and the emergence of the plastic zone of SCAHRB400 steel bars in the tensile process were observed, the tensile properties of SCAHRB400 steel bars were analyzed and discussed. The test results indicate that SCAHRB400 steel bars are prone to local yielding near the crown of large arches and at the connection of horizontal and arc sections. The numerical simulation equivalent stress–strain curves have good regularity. The equivalent stress–strain curves of slightly curved arc HRB400 and HRB335 steel bars have the similar changing law. When the stress is small, the tensile stiffness and compressive axial stiffness of slightly curved arc HRB400 and HRB335 steel bars are similar; when the stress is large, the axial stiffness of SCAHRB400 steel bars is greater than that of slight curved arc HRB335 steel bars. Through test and numerical simulation studies, the theoretical basis can be established for the engineering application of new slightly curved arc steel bars in mass concrete. [ABSTRACT FROM AUTHOR]