Experimental Study of Loading and Unloading Tensile and Compressive Creep of Hydraulic Concrete in Water

Abstract

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.