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Highlights • Phosphorous compounds lower the temperature gradient in hardening shielding concrete. • The lower thermal conductivity of aggregate the higher temperature gradient decrease. • Maximum temperature of hardening shielding concrete stays not affected. Abstract The paper presents the results of the study of the influence of the addition of retarding superplasticising admixture based on triisobutyl phosphate and modified phosphonates on the amount of heat generated by hardening shielding concrete. A four-point measurement of the heat generated during the hardening of concrete with an admixture dose of 0, 0.5, 1.0 and 2.0% by weight of the cement was made and the concurrent measurement of the heat released by the hardening cement paste was measured with an isothermal calorimeter. Based on the results from the calorimeter, the effect of the admixture on the temperature field in the hardening concrete mass elements was simulated for different aggregates. The results indicate that the admixture clearly lowers the temperature gradient in hardening mass concrete. In the simulations, the most clear effect was achieved in the case of concrete with barite aggregate, where the gradient value was reduced from 10°C/m to 8°C/m for an admixture content equal to 2.0%. [ABSTRACT FROM AUTHOR]

Thermal damage control of mass concrete is the key to guarantee the quality of mass projects. Based on several engineering experiences and finite element software ANSYS, the temperature field and stress field of the typical dam section of the Tengzigou hydropower station in Sichuan province were simulated. Considering the actual materials used, cooling measures, etc., maximum tensile stress and compressive stress at different time points derived from the temperature stress field during the time of concrete maintenance were calculated, and the numerical results showed that strength increment under the given conditions was much less than the actual condition. After the concrete of the dam body of the hydro power station were poured, there was no significant temperature stress crack appeared through a long-term observation, and the project condition was in tune with the calculated expectation. The above research results are valuable to further prediction of concrete temperature in different periods, the pre-study of the effect of temperature control measures, and these could offer guidance of the adjustment of temperature control measures in the case of abnormal conditions. [ABSTRACT FROM AUTHOR]

Steel and polypropylene fibers result in a significant enhancement in strength, ductility, and toughness of concrete. This paper investigates experimentally and numerically the effect of these fibers on heat of hydration and early‐age cracking in mass concrete structures. Experimental investigations were conducted on evolution of strength, Young's modulus, and adiabatic heat rise in fly ash concrete mixes with steel and polypropylene fibers. Concrete mixes with ordinary Portland cement, 40% fly ash replacing the cement, 40% fly ash with 0.3 and 0.5% steel fibers, and 40% fly ash with 0.3 and 0.5% propylene fibers were investigated. The evolution of compressive and tensile strength, modulus of elasticity, and adiabatic heat rise using semi‐adiabatic calorimeter for all mixes was measured. The evolution of temperature at several locations in two full‐scale mass concrete blocks with normal concrete and fly ash concrete was measured. A multiphysics‐based finite element simulation of the two field mass concrete blocks was carried out using the software DIANA FEA BV (South Holland, Netherlands), which predicted the heat generation, temperature field, stresses developed in the blocks, and the associated cracking with good accuracy. The effect of steel and polypropylene fibers on heat, temperature, and stress generation in mass concrete blocks was investigated using the experimentally obtained parameters. The polypropylene fibers result in significant performance enhancement for early‐age cracking compared with the steel fibers. [ABSTRACT FROM AUTHOR]

Concrete adiabatic temperature rise is often used to predict temperature development in mass concrete thermal control plans. Several experimental methods are currently being used to obtain the adiabatic temperature rise. This study compared the adiabatic temperature rise from seven concrete mixtures obtained from fully adiabatic, semi-adiabatic, and isothermal calorimetry. The study found a low adiabatic temperature rise difference between semiadiabatic calorimetry and fully adiabatic calorimetry for ordinary portland cement concrete mixtures for 28 days and for mixtures containing Class F fly ash during the first 10 days after mixing. Semi-adiabatic calorimetry did not match well to fully adiabatic calorimetry results when slag cement was used because the rate of heat development could not be well described by a three-parameter heat of hydration model. Adiabatic temperature rises calculated using isothermal calorimetry results did not compare favorably to measured fully adiabatic results, even when temperature effects on hydration rate were accounted for using an Arrhenius apparent activation energy approach. [ABSTRACT FROM AUTHOR]

Highlights • Impact of climate effects on mockup for mass concrete incorporating pozzolans. • Temperature differential control plan must be less than 25 °C (45 °F). • 1-in. XPS board could enhance insolation effects on mass concrete protection. • Temperature-time gradient has two categories with growth and loss rate. • TDCP included quaternary warning lights executed at jobsite for 2.5 years. Abstract Two mockup blocks were used to construct a temperature differential control plan (TDCP) for temperature differentials less than 25 °C (45 °F) and the climate effect was evaluated. The first block was without insulation and the second with a blanket and 25 mm (1-in) extruded polystyrene (XPS) board. The mixtures were of cement, slag and fly ash, and seven sensors were used. The test results showed that on a rainy day, the maximum temperature differential was greater than 30.9 °C (55.6 °F) without insulation. With a blanket and XPS board, the maximum temperature differential could be dramatically reduced to below 19 °C (34.2 °F), and enhanced the effects on mass concrete protection. TDCP had been used suitably and expediently in the construction duration at jobsite for two and half years long. [ABSTRACT FROM AUTHOR]

Highlights • A DTS system was utilized for temperature control of mass concrete. • Thermal properties of concrete were determined by using the DTS measurements. • A framework of cracking control is developed for mass concrete in construction. Abstract This paper presents a framework of cracking control for a mass concrete structure in a reservoir project, by taking advantage of Distributed Temperature Sensing (DTS) system. The DTS system in this project, mainly consisting of an Optical Backscatter Reflectometer (OBR) interrogation unit and a single fibre-optic cable, was deployed to measure and monitor concrete temperatures of an intake tower in block placement. The temperature measurements in concrete blocks were utilized as the fundamental data to determine the thermal properties of the cast-in-situ concretes, through the inverse analysis method based on temperature simulation. Based on thermal stress simulation using the thermal properties, cracking risks of each concrete block were predicted and evaluated under the modes of temperature control associated with the time-varying construction and ambient conditions, for appropriate modes before and after the concrete placement. The framework of cracking control, developed by integrating the DTS measurement with the temperature forecast and the cracking prediction based on thermal stress simulation and cracking risk evaluation, improves the efficiency of temperature regulation and cracking control in mass concrete construction, and can be further integrated into the intelligent construction management of concrete projects. [ABSTRACT FROM AUTHOR]

Highlights • A precast combined pile-cap and footing was monitored during production. • Setting and hardening kinetics of three high-strength self-compacting concrete mixes were assessed. • New logarithmic and linear–hyperbolic maturity functions were statistically validated. • Maturity functions included crossover effect and predicted better than ASTM C1074-11. • Optimal mix C3 minimized cement and met the strength requirements within [16 °C, 87 °C] Abstract This research applied accelerated bridge construction techniques to the Northern Mexico City Elevated Urban Toll Road. To this end, an 18-m precast combined pile-cap and column element was monitored during production. The recorded high internal temperatures raised concerns, which led to the extraction and testing of concrete cores, yielding satisfactory strengths. The kinetics during the setting and hardening of the three high-strength self-consolidating concrete mixes used in the production of these elements was statistically validated for the temperature range from 4.5 to 88 °C. In a previous study, new maturity functions were developed to predict the strength of equivalent mortars as a function of both the hardening time and isothermal curing temperature, which accounted for the crossover effect and provided better compressive strength predictions than ASTM C1074-11. These functions were applied herein to optimize the production, select the optimal concrete mix, and minimize the total construction time and environmental cost. [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.)

• A multi-component material model was modified for concrete with different GGBFS. • The modified model can estimate heat, temperature rise, and strength of concrete. • Heat generated by different types of GGBFS in hydrated lime water was measured. • Heat generated in concrete mixes with different GGBFS was simulated successfully. • Strength of concrete with various w/cm ratios and air contents was predicted. In this study, a multi-component hydration model of cementitious material was applied to estimate the heat of hydration, adiabatic temperature rise (ATR), and compressive strength of concrete containing ground-granulated blast furnace slag (GGBFS). Different types of GGBFS were hydrated in limewater solution to measure their heat generations. The reference heat of slag in the multi-component hydration model (DuCOM) was revised using the heat measured from each type of GGBFS. Hence, the revised model is sensitive to the chemical compositions of slag. Isothermal and adiabatic heat measurements, as well as compressive strength experiments, were conducted using concrete with four different types of GGBFS. Results show that the proposed model is able to estimate the heat of hydration, adiabatic temperature rise, and compressive strength of concrete mix using different types of GGBFS with various w/cm ratios and air contents. The model predictions versus experimental results show reasonable agreement with the maximum average error percentage of 6.8% and 11% for the heat of hydration and compressive strength, respectively. The proposed method can be a useful technique to obtain the thermal and mechanical properties of GGBFS blended concrete with different cement and GGBFS sources. [ABSTRACT FROM AUTHOR]

• Unrestrained ASR volumetric expansion is studied for a mass concrete mixture. • Size effect in anisotropy of expansion is highlighted using literature results. • Interpretation of this effect using mechanical and chemical boundary effects. • Application of 3D laser scan technology in the field of ASR expansion monitoring. • Manuscript submitted for review and possible publication in May 2023. The kinetics related to unrestrained alkali-silica reaction (ASR) expansion is one of the most important parameters for the coupled chemo-mechanical predictive models of concrete structures affected by ASR. It is experimentally assessed using monitored accelerated tests on poured concrete specimens or on cores extracted from the structure. This work presents a critical review on experimental methods to assess the unrestrained ASR volumetric expansion and discusses the influence of size and aspect ratio effects on its anisotropy. It presents the experimental results carried on a mass concrete mixture with maximum aggregate size of 76 mm, representative of an existing hydraulic facility affected by ASR. Specimens of different shapes and sizes were subjected to accelerated expansion test, monitored in expansion for more than 1000 days. Volumetric expansions were assessed using a conventional method (DEMEC strain gauge and an outside micrometer) and a new innovative method using 3D handled laser scanning technology. Conventional expansion measurements indicated that cylindrical cores had an anisotropic expansion like other studies, while large blocks had mostly an isotropic expansion, confirming size effects on unrestrained expansion anisotropy. Explanations based on chemical and mechanical boundary effects were suggested to explain this phenomenon. The non-invasive 3D laser scan measurement technology allowed to quantify ASR swelling of small specimens and to conveniently visualize this swelling through colormaps. The local swelling due to expansion of coarse aggregates was observed, which could not be detected by conventional measurement methods. 3D laser scanning appears a promising method for assessing expansion in view of the prognosis of critical concrete infrastructures affected by internal swelling reactions. [ABSTRACT FROM AUTHOR]

The effect of fly ash type on the sustainability of concrete mixtures has yet to be quantified. This study aims to assess the environmental impacts of low calcium oxide (CaO) and high CaO fly ash in mass concrete mixtures from Thailand. The study analyzed 27 concrete mixtures with varying percentages of fly ash as a cement replacement (0%, 25%, and 50%) for 30 MPa, 35 MPa, and 40 MPa compressive strengths at specified design ages of 28 and 56 days. Sources of fly ash have been located between 190 km and 600 km away from batching plants. The environmental impacts were assessed using SimaPro 9.3 software. The global warming potential of concrete is reduced by 22–30.6% and 44–51.4% when fly ash, regardless of type, is used at 25% and 50%, respectively, in comparison with pure cement concrete. High CaO fly ash has more environmental benefits than low CaO fly ash when utilized as a cement substitute. The reduction in environmental burden was most significant for the midpoint categories of mineral resource scarcity (10.2%), global warming potential (8.8%), and water consumption (8.2%) for the 40 MPa, 56-day design with 50% fly ash replacement. The longer design age (56 days) for fly ash concrete showed better environmental performance. However, long-distance transport significantly affects ionizing radiation and ecotoxicity indicators for terrestrial, marine, and freshwater environments. Furthermore, the results show that a high cement replacement level (50%) may not always have a reduced environmental impact on mass concrete when considering long-distance transportation. The critical distance calculated based on ecotoxicity indicators was shorter than those calculated using global warming potential. The results of this study can provide insights for developing policies to increase concrete sustainability using different types of fly ash. [Display omitted] • High CaO fly ash has more environmental benefits than low CaO in mass concrete. • 44–51.4% in CO 2 reduction when cement is replaced with 50% fly ash. • Longer design age (56 days) enhances sustainability in fly ash concrete production. • More cement replacement in concrete does not always imply less environmental impact. • Fly ash transport impacts ecotoxicity more than global warming potential. [ABSTRACT FROM AUTHOR]

The manuscript is concerned with the phase-field modeling of thermal cracking in massive hardening concrete structures. Owing to the exothermic reactions, known as hydration, a considerable amount of heat is generated during the setting and hardening of concrete. Since concrete has relatively low thermal conductivity and fairly high heat capacity, sharp temperature gradients may occur between the interior and exterior parts of massive concrete structures. This uneven temperature distribution results in a non-uniform thermal expansion that, in turn, may lead to thermal cracking in conjunction with restraining external boundary conditions. Hence, it is of key importance to conduct the crack risk assessment of massive concrete structures at various stages of their construction and thereafter where real-size experiments are often unrealizable. To this end, we develop a multi-field computational approach to simulate thermal cracking in hardening concrete. In particular, we propose a novel chemo-thermo-mechanical model developed within the framework of the theory of reactive porous media coupled with a quasi-brittle phase-field regularized cohesive zone model to explicitly account for the initiation and propagation of thermal cracks. In the model, chemical, thermal, mechanical, and phase-field fracture problems are coupled through the constitutive equations. To our best knowledge, this is the first study where a quasi-brittle phase-field fracture model is used to model thermal cracking in hardening massive concrete through a novel incremental formulation. The potential of the proposed approach is demonstrated through the benchmark thermomechanical problems of a normal concrete member and a roller-compacted concrete dam. In the latter, original multi-field interface elements are devised between the lifts. [Display omitted] • A novel cohesive phase-field fracture model for thermal cracking in hardening mass concrete. • A new thermodynamically consistent incremental formulation. • Incorporation of heat loss and reduced heat conduction at new crack surfaces. • Original multi-field interface elements between lifts of RCC dams. • Representative examples illustrating the predictive capacity. [ABSTRACT FROM AUTHOR]

In this research, the major problem of mass concrete (Differences in Temperature) was studied. Expanded polystyrene and perlite were added in different percentages to investigate the effects on some mechanical properties and thermal conductivity of concrete. Two stages of work were performed. In first stage, reference mix was designed at proportion (1cement: 1.41sand: 2.72gravel) with (0.4) water cement ratio. Four tests were conducted, these tests including density, compressive strength, flexural strength and thermal conductivity through exponential equation depending on dry density. In the second stage, polystyrene beads and perlite were added as volumetric ratio with (10, 15, 20, 25, and 30) percentages to the original size of reference mix and conducted the tests and study their effects .The results showed a significant improvement in thermal insulation and reduced thermal conductivity (40 , 22) % by using (30) % of polystyrene and perlite respectively. The decreasing in some mechanical properties can be seen and this decreasing did not have serious effects on the design efficiency of the structure which conformed with the specifications.

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.)

Prediction of hydration temperature and induced stresses in mass foundation slabs, due to the hydration effects is a difficult task. The complexity of this issue is compounded by transient and non-linear thermo-mechanical phenomena as well by a significant number of contributing technological and material factors that affect the early-age volume changes. This is a probable reason for the limited number of simple analytical methods allowing for the estimation of these effects. This work presents a new proposal in the discussed field. The submitted analytical method for determining the hydration temperature rise, its differentials at a cross-section and induced thermal stresses in mass concrete foundation slabs considers the majority of important technological and material factors, such as the initial temperature of the concrete, the ambient temperature, the thermal properties of the concrete and the heat exchange conditions on the slab surfaces. In stress analysis, both self-balanced and restraint stresses are calculated. Finally, the method is validated in FE analysis conducted for the slabs with various heights and made of different types of cements, as well as by the thermal measurements from the construction site. Due to the limited number of methods allowing for the analytical estimation of the early age thermo-mechanical effects in slabs, this new proposal can be useful in the assessment of these effects.

This paper is mainly to study the effects of insulation thickness (0 - 3) cm on temperature field and evaluating cracking in the mass concrete by using Finite Element Midas Civil 2011. The finite element method is developed for simulation analysis of the temperature field in the concrete in early age mass concrete. From the results temperature field and evaluating cracking for the mass concrete it is concluded that insulation with adequate thickness at the face of massive concrete should be used to reduce the temperature differentials and control cracking of early-age concrete. Finally, the results are applied to provide some references for the constructions in the mass concrete such as dams, bridges beams, bridge piers, foundations of bridges and buildings.

This study focused on investigating the early-age thermal behavior of drilled shafts under different surrounding soil’s thermal properties. Four 1.8 m (6 ft) diameter drilled shafts were constructed using two different concrete mixes and two different soil conditions. A finite element (FE) model was developed to estimate the temperature development of drilled shafts at early-age and validated using temperatures measured from full-scale drilled shafts constructed in the field. The validated analytical model was then used to perform a parametric analysis to evaluate the effects of the surrounding soils at different moisture conditions on change in thermal behavior of drilled shafts at early-age. Results indicated that the FE model developed was capable of accurately predicting temperature development of drilled shafts at early-age. A drier surrounding soil (i.e., gravimetric moisture content of 0% through 6%) was able to serve as a better insulating material that leads to reduced temperature difference in the drilled shafts. Also, it was identified the use of high-volumefly ash concrete mix in conjunction with relatively low heat of hydration can reduce the temperature difference in the drilled shaft.

The low rates of biodegradation of organic pollutants in wastewater have been attributed to the daily fluctuation of temperatures, which affects microbial metabolism and activities in reactors.  This work aimed to develop a method to degrade sewage pollutants using a synergistic effect of bacterial consortium and thermal energy, while a grey concrete pond served as the control. The results demonstrated that the temperature profile of ICCP showed that all through the experiment, the temperature was above 25 °C, which is a suitable temperature for mesophilic bacterial growth. A properly-stabilised effluent was achieved by the ICCP with a low biodegradation index between 0.11 and 0.14.  The values of BOD (95%) and COD (74%) removal efficiencies were obtained at a 10-day retention time in ICCP, which is in accordance with standard of the United State Environmental protection Agency. Moreover, a comparison between a control and ICCP revealed that the latter emits heat energy 30% higher than the first. The temperature of 30 °C (dark) and 30.8 °C (light) produced a BOD removal > 90%. Therefore, this method could be considered to bridge the gap in daily fluctuation of temperature for enhanced biodegradation.•Designing of a thermal coated concrete pond to investigate their thermal performance during the dark and light condition•Bioremediation test for selection of  mixed bacteria strain of high degradation potential used as   inoculum•A detention time of 10 days under natural sunlight used for investigation for concentration balance of organic  pollutant., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

Mass concrete defines elements where heat formation due to exothermic hydration reactions can induce tension cracking as a result of excessive temperature differentials upon cooling. These conditions are anticipated in dams, large footings, and, in some cases, pier columns and caps where internal cooling systems can be used to moderate the effects. Until 2006, drilled shafts were not recognized by the Florida Department of Transportation as mass concrete due to the relatively small diameters (4 ft [1.2 m] diameter being the most common) and/or the perception that the surrounding environment was not conducive to producing mass concrete conditions. This paper presents the results of a full-scale shaft demonstration project where a 9 ft (2.74 m) diameter shaft was constructed with a 3.8 ft (1.17 m) diameter central void to control temperature and reduce costs. Peak and differential temperatures were shown to stay well within specified limits without the need for internal cooling systems. [ABSTRACT FROM AUTHOR]

Thermal cracking has significant impact on the safety and durability of mass concrete. This paper aims to find the reason for cracking of a prototype bridge structure and consider which influencing factors are the most important. For this model experiments on mass concrete in bridge structures were designed and conducted and thermally cracking was induced. Fiber bragg grating sensors were used to monitor the temperature and strain within concrete in real time, as well as the strain around the embedded cooling pipes. Thermal properties of concrete were deduced from these monitoring data and then used in the numerical analyses to verity the calculation accuracy. In the context of engineering practice, the primary influencing factors on the cracking of mass concrete were investigated by numerical analyses. The optimized temperature control methods were proposed to prevent the occurrence of thermal cracking of mass concrete. [ABSTRACT FROM AUTHOR]

The material properties of concrete are greatly influenced by age, temperature, humidity and loading history, particularly at early ages. However, concrete properties are often predicted using prediction models or a few experiments at a construction site, which can not consider these influential factors, causing a great difference between actual and predicted properties. This paper presents an approach to predict various concrete properties with simple laboratory experiments to minimize the differences in the concrete properties due to the curing conditions. In this approach, the concrete properties were determined by comparing the experimental data with the analytical results. The thermal expansion coefficient, elastic modulus, autogenous shrinkage, and creep coefficient were predicted by optimizing the equations of each material property. In addition, the predicted concrete properties were verified with those obtained from various experiments for elastic modulus, autogenous shrinkage and stress-independent strain. The elastic modulus, autogenous shrinkage, and stress-independent strain were mostly predicted within a 10% error range. Therefore, this study confirms that the proposed approach can be used to predict concrete properties at early ages, that are greatly influenced by various factors. [ABSTRACT FROM AUTHOR]

In order to analyze the characteristics of temperature and thermal stresses of surge tank in construction period, based on the fundamental theory of temperature field and thermal stress field, as well as the application of ANSYS software, a program was created to analyze the thermal field and stress field of No. 6 throttled tailrace surge tank in Baihetan Hydropower Station. Lots were taken into consideration in the simulation analysis of construction process, for instance, structural features, diverse temperature control measures, etc. According to the simulation results, the maximum temperature of shunt pier was controlled from 42 ℃ to 43 ℃ by controlling the pouring temperature and water cooling. Standards and measures were proposed as a technological basis to the surge tank construction in Baihetan Hydropower Station. [ABSTRACT FROM AUTHOR]

The compensation of thermal shrinkage with the delayed expansion of MgO expansive agent has been used not only in mass concrete, but also in some underground sidewall in subway stations in China. This study investigated the expansion behaviors and crack resistance of three kinds of MgO with different reactivity values (90 s, 150 s and 250 s) in concrete based on a comprehensive test system including the length test using the differential strain gauge, a dual-ring test and the environment simulation test chamber. The results showed that the expansion behavior of MgO expansive agent was closely related to its reactivity value and the temperature history of concrete. MgO with lower reactivity value (90 s, 150 s) showed larger expansion in concrete than MgO with higher reactivity value (250 s) under the temperature history of low temperature rise and high cooling rate, while MgO with higher reactivity value showed larger expansion at temperature fall stage and better crack resistance under the temperature history of high temperature rise, low cooling rate and long cooling period. The results indicate that the reactivity value of MgO expansive agent should be properly selected according to the characteristics of temperature histories of different concrete structures to give full play of its shrinkage compensating efficiency. [ABSTRACT FROM AUTHOR]

Using cooling pipes is a main temperature control measure for mass concrete dams during construction, the influence of the layout of cooling pipesto the internal temperature and stress of concrete is significant. In this paper, Xiajiang gravity dam was taken as an example, the ANSYS finite element model was used to analyze the influence of different layout of cooling pipes to the internal temperature and stress of concrete during the construction period of mass concrete. The results show that the way of encrypted water pipes layout can effectively improve the cooling effect of concrete, hut if the pipe spacing is too small, it will lead to greater tensile stress on the surface of concrete, resulting in cracks on the surface of concrete. [ABSTRACT FROM AUTHOR]

A research project was performed to characterize both the setting and hardening of three high-strength self-consolidating concrete mixes used in the production of precast combined pile-cap and column elements (column footings) of the Elevated Highways in Mexico City. By monitoring an eighteen-meter-high column footing during its production, the wide range of internal concrete temperatures experienced by this massive structure at an early age was registered, from 5 to 90 °C. Concrete maturity method was applied to the equivalent mortars after ASTM C1074-11 . The analysis of the experimental results allowed the statistical validation of new maturity functions for the equivalent mortar mixtures, which provided better predictions for the relative strength than the deterministic procedure of ASTM C1074-11 for the concrete ages and the wide range of curing temperatures tested. The maturity functions make up the cross-over effect, namely the influence of the internal temperature experienced by concrete on its long-term compressive strength. [ABSTRACT FROM AUTHOR]

The mass concrete side wall, which is poured on the concrete floor in open section of the west artificial island of Hongkong-Zhuhai-Macao Bridge island and tunnel project, is easy to crack due to the strong constraint of the shrinkage by the floor. In order to solve the problem of side wall cracking, we used the finite element software to simulate the temperature stress of the side wall, theoretically analyzed the characteristics of the temperature stress distribution of the side wall, and on the basis of this, we studied the key technology of controlling the crack of concrete side wall. Then we embedded the strain sensor in the inner side wall concrete, tested the change of the internal concrete strain in the side wall after taking crack control technology, and verified the correctness of theoretical analysis.The practice results show that there is no crack in the side wall, and the intended purpose is achieved. [ABSTRACT FROM AUTHOR]

The heat evolved during the hydration process may not dissipate properly due to the large size and poor thermal conductivity of mass concrete. Embedded cooling pipes of circulating water are generally used for heat removal from the interior of the concrete mass. This study experimentally shows that forced cooling helps reduce the interior temperature significantly; however, it leads to a reverse thermal gradient around the cooling pipe. This paper conducts a three-dimensional finite-element simulation of the hydration heat in concrete with a forced cooling system, modeling the circulating water with three-dimensional elements with diffusion and dispersion properties which accurately predict the experimentally observed temperature profile. Finite-element analysis also indicates the presence of high thermal stresses in concrete near the cooling pipe, mainly due to the extreme temperature gradient and temperature fluctuations. The results suggest a careful monitoring of heat removal using forced cooling to avoid a large thermal gradient and the likelihood of cracking. [ABSTRACT FROM AUTHOR]

This paper presents a solution strategy, based on a parallel Genetic Algorithm (GA), to optimize the construction of massive concrete structures. The optimization process aims at minimizing the construction cost, considering the following design variables: the concrete mixes, the placing temperature, the height of the lifts, and the time intervals between placing the lifts. The cracking tendency is taken into account by a penalty scheme imposed to the fitness function of the GA. A thermo-chemo-mechanical model is used to calculate the transient fields of hydration, temperature, stress, strain, and cracking tendency. This model is implemented in a finite element code that is, in turn, parallelized. To demonstrate the efficiency of the proposed methodology, the simulation of the construction of a structure similar to the real thick foundation of an industrial building is presented. It shows that the optimization procedure here presented is feasible and is ready to be used in real engineering applications. [ABSTRACT FROM AUTHOR]

In long-lasting mass concrete structures the desired material properties of the concrete mix to realize a durable concrete and a concrete surface without cracks conflict with each other. The requirement of concrete with high durability leads to high thermal energy release and therefore, as another consequence, to high crack risk. Crack reduction is achieved by use of concrete with low hydration energy, which on the other hand leads to a decrease in concrete durability. Besides from optimized base materials and concrete technology, a gradient material distribution in the cross-section could reduce the problem since durable concrete is needed near the surface and the requirement of low-hydration energy is located in the center of the member. A simplified model is used to investigate the possible effect of a gradient concrete material distribution in mass concrete structures on crack reduction. The results of the analysis show that gradient concrete might contribute to lowering the constraint stresses and therefore the crack risk during concrete hardening. [ABSTRACT FROM AUTHOR]

To prevent the cracking of mass concrete in marine environment, lead to the phenomenon of corrosion intensifies, without arrangement of the cooling water pipe, according to the principle of the mix proportion design of mass concrete with low cement dosage and large dosage of admixture and adding the right amount of MgO anti-cracking agent, through the optimization of mixture ratio design and impact analysis of MgO on the properties of concrete, we determined that using 52% cement, 20% fly ash, 20% mineral powder, and 8% MgO anti-cracking agent has good effect of gelled material system. The prepared concrete has excellent work performance, mechanical properties, and durability, through the construction of the test section, this mass concrete structure does not appear obvious cracks, which can meet the construction requirements of mass marine engineering concrete. [ABSTRACT FROM AUTHOR]

Delayed ettringite formation and thermal cracks are two main concerns of temperature rise in mass concrete structures. The mass concrete containing limestone blended cement and fly ash has different hydration heat that was not well predicted by commercially available software. The purpose of this study is to provide such data for designers or software developers. In this study, results of thermocouple measurement at the construction site are compared with a widely used commercial finite element model (FEM) and a widely used concrete design software package. Verification of the FEM with experimental data has been completed with cement ASTM C595 Type I limestone blended cement (IL) with a 25% replacement by mass of ASTM C618 Type C fly ash (FC). In this study, the same mixture design of construction site was used in modeling of hydration heat of full scale building. The heat of hydration for cement Type I-II and 25% of FC and cement Type IL are predicted to compare the results of hydration heat generated by different mix proportions. The FEM result has a much better compatibility with the construction site data with respect to the commercial concrete software results. The prediction accuracy of finite element results is about 15% more for the maximum temperature rise and 30% more for the peak time. Cement Type IL has greater hydration heat than cement Type I-II. Applying measured ambient temperature and calorimetry results are two main factors in precise prediction of hydration heat. [ABSTRACT FROM AUTHOR]

This paper is an experimental investigation and analytical simulation of thermal effects on mass concrete structures in the tropics. A study of the temperature rise of a 1.1 m × 1.1 m × 1.1 m experimental mass concrete block, well instrumented with thermocouples to monitor the temperatures distribution was performed. A validated finite element model was used to predict the temperature development of the hydrating experimental mass concrete block. Thermal stress analysis was performed to give an estimate of stresses induced by the thermal gradient of the concrete block section and the crack index was used to quantify the probability of thermal cracking. A parametric study on the effect of the surface area to volume ratio (SVR) of mass concrete was performed to quantify the maximum allowable thermal gradient as well as the induced thermal stresses that may cause thermal cracks. For SVR less than 0.36, thermal cracks may occur at early ages of concrete strength development in the tropics.

Acoustic emission (AE) is capable of monitoring the cracking activities inside materials. In this study, embedded sensors were employed to monitor the AE behavior of early age concrete. Type 1–3 cement-based piezoelectric composites, which had lower mechanical quality factor and acoustic impedance, were fabricated and used to make sensors. Sensors made of the composites illustrated broadband frequency response. In a laboratory, the cracking of early age concrete was monitored to recognize different hydration stages. The sensors were also embedded in a mass concrete foundation to localize the temperature gradient cracks.

Due to complex structure, large scale, and cold climate, the temperature field and stress field during construction of BoYi Station is different with ordinary mass concrete. Therefore the corresponding crack prevention method must be explored. In order to simulate the complicated construction course, cold climate, multiple materials and unusual structure, a finite element program is adopted. In 5 numerical simulation cases, different temperature control methods are tried to decrease the tensile stress of mass concrete. Based on the simulation analysis and combined with the engineering experience, the scheme and indexes of temperature control and crack prevention are recommended. The mainly measures are controlling pouring temperature, insulation of concrete surface, pipe cooling, block partition and extra steel bar reinforcement. The values of temperature indexes are sharply lower than that of ordinary hydropower station mass concrete. The suggested measures and indexes in this paper, which are various with season, structure position and material, may provide some reference to similar large hydropower station workshop in cold area.

Mass concrete has been commonly known for its thermal stresses which arise due to the entrapment of hydration temperature susceptible to thermal cracking. The utilization of mineral additives is a promising and widely adopted technique to mitigate such effects. This paper presents the thermal, physico-chemical, mechanical, and morphological behaviour of mass concrete with blends of bentonite (BT) and fly ash (FA). Apart from the rise in temperature due to hydration, the compressive strength, ultrasonic pulse velocity (UPV), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) analysis, and microstructure were studied. The results of this study revealed that the substitution of BT and FA significantly improved the compressive strength and development rate of UPV in the mass concrete samples. The FA concrete (FC) specimen presented the lowest temperature during the peak hours compared to all other concrete mixes studied in this research. Bentonite concrete (BC) was also found to be more effective in controlling the escalation of temperature in mass concrete. Scan electron microscopy (SEM) micrographs presented partially reacted FA particles in a mix. XRD and DTA analysis indicated that the concentration of calcium hydroxide (CH) declined by substituting FA and BT, specifically in ternary blends, which was due to the dilution effect and consumption of CH through the pozzolanic reaction.

The current work presents the complex investigation of the influence of cement and aggregate type on the thermo-mechanical behavior of mass concrete. Six types of cement with different amounts of non-clinker constituents and four types of aggregates are used in experimental tests. Particular attention was given to the low clinker cements with high amounts of siliceous fly ash and ground blast furnace slag. The experimental research covered the determination of thermal, mechanical, and rheological properties of early age concrete with different constituents. Experimental results have been used both to validate the numerical model and analysis of exemplary foundation slab. The results confirm the importance of the concrete mix composition and it has been shown that the early-age volume deformation and possible cracking is the result of the concerted action of thermal and mechanical properties of concrete. The obtained results indicate granite as the best aggregate for mass concrete. Considering the type of cement, much better behaviour of mass concrete has been noted for cements with fly ash and composite cements containing both fly ash and slags than cements only with slag.

Relevant data indicate that the length of the bridge accounts for 6.3% of the total length of the Mombasa-Nairobi Standard Gauge Railway. In order to solve the temperature cracks of bridge pier mass concrete, we carried out the temperature control test of a test pier in section 2, studied and discussed a set of construction control technology for mass concrete in this section from the aspects of raw materials selection, mix proportion optimization, concrete production, transportation, placing, maintenance and temperature monitoring measures, and put forward specific temperature control indexes. The construction technique presented in this paper is a useful supplement to the mass concrete in the bridge pier of Mombasa-Nairobi Standard Gauge Railway. It could provide a reference for other similar engineering with high temperature and dry environment in Africa. [ABSTRACT FROM AUTHOR]