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Elastic creep theory is used herein to investigate the characteristics of the loading and unloading creep of hydraulic concrete in water. First, tensile and compressive loading and unloading creep tests were designed for hydraulic concrete of different loading ages (14, 28, and 60 days), and the tests were executed in water under unified test conditions. The complete experimental data acquired for creep were then used for comparison and analysis. Next, the whale optimization algorithm was applied to optimize and identify an eight-parameter specific creep model for concrete under tensile and compressive stress. Additionally, the superposition principle was used to predict the specific tensile and compressive creep recovery of concrete in water after unloading. The results reveal that the specific tensile creep of hydraulic concrete in water exceeds the specific compressive creep of hydraulic concrete in water, and that the ratio of specific tensile creep to specific compressive creep is 1.92–3.82 when loading is held for 30 days. Furthermore, the eight-parameter specific creep-prediction model well reflects the temporal evolution of the tensile creep and of the compressive creep of hydraulic concrete in water. When the superposition principle is used to analyze the elastic aftereffect following unloading, the research results reveal that the specific tensile creep is superposed during unloading for the specific tensile creep, whereas the specific compressive creep is superposed during unloading for the specific compressive creep. Under these circumstances, the predicted specific creep recovery is consistent with the measured results and the mean absolute percentage error was 2.99%–17.75%. Thousands of concrete dams have been built around the world to control and divert natural surface water and groundwater. The upstream faces of these dams are long-term affected by water and are subjected to loads such as self-weight and hydrostatic pressure, which produce two important phenomena: wet expansion and creep. When water seeps into the concrete through microscopic pores, the concrete undergoes wet expansion, which modifies the strain state of the concrete. Under a sustained load, the concrete structure deforms and gradually creeps over time. To describe the creep of concrete, numerous creep tests under nonsubmerged conditions have been conducted. However, few reports discussed the wet expansion of concrete under submerged conditions, especially as concerns loaded and unloaded creep tests in water, which provides information on both wet expansion and creep. Therefore, this investigation uses creep tests to determine the physics of concrete under loading and unloading in water. The results reveal that the specific tensile creep of concrete in water exceeds the specific compressive creep of concrete in water. The use of the superposition principle to analyze the elastic aftereffect following unloading reveals some new physical mechanisms. These mechanisms are useful to investigate the real strain state of concrete dams. [ABSTRACT FROM AUTHOR]

Shape is an important physical property of aggregates. However, the large amount of work required to measure with precision the size of coarse aggregate and the lack of relevant tests obscure how the shape of the coarse aggregate affects the strength of concrete. In this work, granite coarse aggregate was first divided into flaky stone and massive stone by manual screening. Next, the coarse aggregate was selected at random for size and volume measurements to obtain and analyze the aggregate shape parameters such as sphericity and flatness. Based on the selected aggregate, three aggregate combinations were designed according to the content of flaky stone. Finally, we measured the compressive strength and splitting tensile strength of hydraulic concrete (7, 28, and 60 days) with water‐binder ratios of 0.33, 0.41, and 0.5. The results show that the three aggregates clearly differ in shape, and the measured compressive strengths and splitting tensile strengths of the concrete with water‐binder ratios of 0.41 and 0.5 are similar. However, the compressive strength of the concrete with water‐binder ratio of 0.33 is significantly correlated with the three selected aggregate combinations. [ABSTRACT FROM AUTHOR]

Determining the long-term mechanical properties of hydraulic concrete currently requires time-consuming and expensive tests, which has hampered investigations into the mechanical properties of long-age hydraulic concrete. In this study, the indoor macroscopic mechanical property tests of long-age hydraulic concrete with different curing ages (90, 180 days and 1, 2, 3 years) and different fly ash contents (0%, 15%, 35%) were designed and carried out on hydraulic concrete with 0.5 water-to-binder ratio by using a high-temperature accelerated-curing method based on equivalent age theory. Further tests were carried out using SEM, XRD, and MIP tests on long-age hydraulic concrete specimens with different fly ash contents to determine and analyze the long-term evolution of the macroscopic and microscopic properties of hydraulic concrete. The results showed that the fly ash content significantly affects the activation energy E a of hydraulic concrete and that the curing time required to reach the designed hydration degree increases with increasing fly ash content. The long-age compressive strength and splitting tensile strength of hydraulic concrete with different fly ash contents increased logarithmically with curing age. After hydration for the curing age of 3 years, the overall microscopic structure of the mortar region of the long-age hydraulic concrete becomes dense, and the main XRD peak is due to quartz. The porosity decreases with increasing curing age, and the main pore types transition from multi-harmful pores (>200 nm) to harmless pores (<20 nm) and less harmful pores (20–50 nm). The multiple correlation coefficient of the long-term strength prediction model established by using the combined exponential prediction model ranges from 0.9152 to 0.9765, which indicates that the combined exponential prediction model based on the strength at the curing age of 28 days better replicates the long-term performance of hydraulic concrete. • Long-age hydraulic concrete tests were conducted based on high-temperature accelerated curing and equivalent age theory. • The evolution of macroscopic and microscopic properties of long-age hydraulic concrete were investigated. • The combined exponential model was established to predict the long-term performance of hydraulic concrete. [ABSTRACT FROM AUTHOR]

• Investigating creep Poisson ratio tests considering loading/unloading under unified test conditions. • The elastic Poisson ratio and creep Poisson ratio differ under different stress states. • The creep (recovery) strain in each direction is not independent under multi-axial stress. Elastic creep theory, which is widely used in concrete dam engineering, assumes that the elastic Poisson ratio and the creep Poisson ratio equal the effective creep Poisson ratio. However, differences in creep test conditions and stress state make this assumption controversial. To accurately clarify the Poisson effect of hydraulic concrete, uniaxial compression creep tests with four loading ages (3d, 14d, 28d, and 60d) and conventional triaxial compression creep tests with three loading ages (14d, 28d, and 60d) are conducted under unified test conditions. And high-precision creep data of transverse and longitudinal for multi-age loading and unloading are obtained. We then denoise the creep data by using a Savitzky-Golay filter. Furthermore, based on the denoised creep data, we calculate the Poisson ratio at each stage for uniaxial compression and conventional triaxial compression. Finally, we compare and analyze the Poisson ratio of each stage in different stress states. The results show that the creep tests have the same noise when conducted under the same test conditions, and the optimal denoising by the Savitzky-Golay filter is obtained with parameters W (window width) = 9 and N (polynomial order) = 6. Under different stress states, the elastic Poisson ratio, creep Poisson ratio and effective creep Poisson ratio are not equal to each other, and the elastic Poisson ratio is greater than the creep Poisson ratio. In addition, under the conventional triaxial stress state, the effective creep (creep recovery) Poisson ratio in each direction is different, which indicates that the creep (creep recovery) in each direction is dependent under multi-axial stress state. [ABSTRACT FROM AUTHOR]

• Investigating creep tests considering loading/unloading under unified test conditions. • The specific creeps in tension are greater than the specific creeps in compression. • Superimposing compressive specific creep are in better agreement with measured values. In order to study the relationship between the magnitude of the tensile and compressive specific creep of concrete, and to compare the measured and predicted creep recovery based on the superposition principle. In this paper, combined with the concrete mix proportion of typical hydraulic engineering, creep tests of hydraulic concrete under loading/unloading with different loading ages (7, 28, and 60 days) are conducted under unified test conditions. Furthermore, the equivalent age theory is introduced to establish eight-parameter specific creep models of tension and compression considering the effect of temperature history, and an optimization algorithm is used to identify the parameters of the models. Finally, the recovery of specific creep under tensile and compressive different creep is discussed in detail based on the principle of superposition. The results show that the specific creep in tension is greater than that in compression in all three creep test groups, and the recovery of specific creep in tension and compression after unloading indicates that the predicted values of the recovery of specific creep obtained by superimposing compressive specific creep are in better agreement with the measured values. [ABSTRACT FROM AUTHOR]