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Abstract Longwave radiation is an important open-air environmental factor that can significantly affect the temperature of concrete, but it has often been ignored in the temperature analysis of open-air concrete structures. In this article, an improved analytical model of concrete temperature was proposed by considering solar radiation, thermal convection, thermal conduction and especially longwave radiation. Temperature monitoring of an open-air concrete block was carried out to verify the proposed model and analyze the heat energy characteristics of open-air concrete. As demonstrated by the open-air experiment, under the influence of longwave radiation, the temperature at the top of the concrete block could decrease rapidly at night and even become lower than the minimum temperature at its bottom. Compared with the analytical model that ignores longwave radiation, the improved model that includes it better matches the measured temperature. According to the energy analysis, although solar radiation controls the transient variation in heat energy, the heat exchange caused by longwave radiation were more than that caused by convection on sunlit surfaces, which indicates the importance of considering longwave radiation.

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

The safety condition of concrete gravity dams is influenced by multiple factors, and assessing their safety solely based on a single factor is difficult to comprehensively evaluate. Therefore, this paper proposes a comprehensive modeling and analysis approach to assess dam safety by considering long-term temperature, stress, and strain monitoring data of actual concrete gravity dams. Firstly, the K-means clustering algorithm is utilized to classify the data. Then, the study area of the dam is meshed and three indicator evaluation values for all the elements are calculated. The other elements' evaluation values can be obtained by the Inverse Distance Weighting (IDW) method. Finally, the analytic hierarchy process extended by the D numbers preference relation (D-AHP) method is applied to compute the weights of temperature, stress, and strain and evaluate the dam's safety comprehensively. The effectiveness of this method is validated through application to specific engineering cases. The results demonstrate that compared to assessing methods considering only single factors, the comprehensive evaluation method proposed in this paper can more comprehensively and accurately reflect the actual safety condition of concrete gravity dams, providing important references for engineering decision-making. [ABSTRACT FROM AUTHOR]

The safety condition of concrete gravity dams is influenced by multiple factors, and assessing their safety solely based on a single factor is difficult to comprehensively evaluate. Therefore, this paper proposes a comprehensive modeling and analysis approach to assess dam safety by considering long-term temperature, stress, and strain monitoring data of actual concrete gravity dams. Firstly, the K-means clustering algorithm is utilized to classify the data. Then, the study area of the dam is meshed and three indicator evaluation values for all the elements are calculated. The other elements’ evaluation values can be obtained by the Inverse Distance Weighting (IDW) method. Finally, the analytic hierarchy process extended by the D numbers preference relation (D-AHP) method is applied to compute the weights of temperature, stress, and strain and evaluate the dam’s safety comprehensively. The effectiveness of this method is validated through application to specific engineering cases. The results demonstrate that compared to assessing methods considering only single factors, the comprehensive evaluation method proposed in this paper can more comprehensively and accurately reflect the actual safety condition of concrete gravity dams, providing important references for engineering decision-making.

Cement hydration is an exothermic reaction. It leads to increase in temperature and creates temperature gradients inside concrete structures during early ages. Extremes of such scenarios cause cracking of concrete and, therefore, affect the structural integrity and durability. Hence, prediction of temperature development of the concrete interior is vital in order to identify appropriate temperature control mitigation measures. However, it remains a challenge because, on the one hand, the governing thermal equations do not have closedform solutions, and on the other hand, the thermal behaviour of concrete is influenced by numerous factors, including heat evolution, heat conduction/convection, boundary conditions, etc. One possible solution is to implement numerical modelling via finite element (FE) or finite difference (FD) approaches. Amongst the two approaches, the former has a better simulating capacity to deal with complex problems, whereas the latter is relatively simple and less expensive. In this light, this research expanded an existing 2-dimentional FD temperature prediction tool towards a 3-dimentional (3D) model in view of enhancing the prediction accuracy of the 2D version. The 3D model was validated for three distinct experiments, and the prediction accuracy was found to be notable where the maximum temperature prediction offset was below 2.2%. Then, the significance of using 3D FD temperature modelling for cube shape concrete structures and for pipe-cooled concrete structures was highlighted. [ABSTRACT FROM AUTHOR]

The Phoenix is a new test method that can measure the water-to-cementitious ratio (w/cm) in fresh concrete in 15 min by evaporating the mixing water and scaling the binder content. This work will aim to investigate how the results of the test changes with time after mixing and also the length of time the sample spends in the furnace. The time after mixing is important as the water in the mixture begins reacting with the binder as soon as mixing starts. Also, as materials are stored in the furnace the high temperatures may cause the materials to decompose and this would again change the results of the test. These are important questions that limit the timing in the test method and also provide insight into the early reactions of Portland cement with water. This work uses isothermal calorimetry, w/cm testing over time, thermogravimetric analysis, and degree of hydration tests to establish reasonable limits for the test method. [ABSTRACT FROM AUTHOR]

Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension, coarse-ground cements show lower levels of temperature reduction but also lower thermal gradients.

Electrochemical tests on corrosion rate of reinforcement were performed on six concrete specimens reinforced with a single bar equipped with temperature and concrete moisture sensors. The specimens were kept in a climatic and corrosion chamber where ambient temperature was changing discretely in a temperature range of 7 °C ÷ 35 °C, and similarly humid conditions were changing in a range of 30% ÷ 90%. The tests were also conducted on specimens immersed in water at 7 °C and 35 °C. Temperature and moisture content in concrete at the bar surface were monitored throughout the tests. The objective of this work was to analyse the influence of rapid changes in climatic conditions maintained for a few-day cycles, on corrosion rate of reinforcement in concrete. The tests demonstrated that the current corrosion process models for concrete reinforcement which assumed an immediate response of corrosion rate to a change in climatic conditions, was correct only for temperature. [ABSTRACT FROM AUTHOR]

Hot weather concreting is unavoidable in the construction industry. Producing desirable workability in different temperatures needs careful recognition of temperature effects on workability. Several studies have shown that slump flow model of concrete is not only specified by the content of its ingredients, but that is also determined by fresh concrete placement temperature, ambient temperature, humidity, wind speed, etc. In this study slump flow prediction of conventional concretes using artificial neural network (ANN) models are presented. This paper discusses that to what extent inclusion of fresh concrete temperature can influence slump flow prediction of ANN models. It is also detailed that how variations in the "as placed" concrete temperature change the workability and influence of ingredients on workability. The results show that: (i) the ANN models of slump flow that incorporate the concrete temperature are a little more accurate and slightly has higher prediction precision than those they do not; and (ii) the ANN models are more precise in predicting slump flow rather than non-linear and linear regression models. [ABSTRACT FROM AUTHOR]

Abstract: Concrete bridge decks are cast in segments using multiple mix batches in a process that can extend up to an entire working day. Construction codes state that the initial concrete must stay plastic over the entire casting operation, however this requirement is practically impossible to achieve with regular casting and curing procedures. This paper reports the experimental evaluation of the performance of a suggested pouring sequence of class K concrete designed for bridge decks, where retarding and accelerating admixtures were used to achieve homogeneous thermo-mechanical concrete properties based on uniform setting and curing at early age. The proposed pouring sequence was investigated in both laboratory conditions as well as in outdoors environment. In order to optimize the resulting properties, the effects of different curing methods were investigated. Taking into consideration variation in environmental conditions at a regular construction season of late spring and summer in West Virginia, the suggested sequence was able to achieve uniform setting times as well as thermal properties while being placed along an entire working day. [ABSTRACT FROM AUTHOR]

Predicting “regular” dam deformations for prevailing conditions and comparing them with observed deformations is an essential part of dam surveillance. In many cases prediction and comparison are carried out automatically and an alarm is triggered in the case of larger deviations. The main contributors to the deformations of arch dams are water loading and the fluctuation of concrete temperature. In general, the deformations exhibit an instantaneous elastic part, a time dependent reversible part and an irreversible part. Prediction of dam deformations can be based on deterministic models, purely statistical models or so-called hybrid models, which are a combination of the first two. Deterministic models rely on static analyses, statistical models on the statistical analysis of previous deformation data. For annual reservoirs, both water loading and temperature vary in cycles over a period of one year and it is extremely difficult to identify the various factors contributing to an observed deformation. This is particularly true for time-dependent reversible displacements due to the water loading and the portion caused by temperature variation. The present article deals with the analysis of arch dam deformations based on hybrid models. Particular attention is given to the analysis of the deformations due to temperature fluctuation and to the long-term deformations. The proposed procedure is employed for the analysis of the deformations of the 186 m high Zillergruendl arch dam. [ABSTRACT FROM AUTHOR]

• Round robin test (RRT) performed with active participation of 34 laboratories. • All constituting materials shipped to national contact points. • Detailed protocols prepared with preconditioning, mixing and testing procedure. • Consistency, temperature, density, air content and compressive strength analysed. • With the adopted approach possible to prepare a common reference concrete for RRT. Round Robin Testing (RRT) is a well-known method for assessing the reproducibility of a test or verification of a new test procedure of almost any kind. In the EU funded network COST Action TU1404 "Towards the next generation of standards for service life of cement-based materials and structures", an Extended Round Robin Testing program (RRT+) was planned as a fundamental tool to obtain input data for a range of concrete properties and validate non-standardised testing techniques. In this paper, detailed information on the planning, conduction and analysis of Phase 1 of the RRT+ is presented. The aim of Phase 1 was to define and confirm the best practice for creating a comparable reference concrete mix for RRT programmes. With a total of 45 laboratories from Europe, Japan and Canada, RRT+ was one of the most extensive round robin testing programmes targeting cement-based materials. [ABSTRACT FROM AUTHOR]