Abstract
In order to study the mechanical properties of recycled aggregate concrete (RAC) at different ages, 264 standard cubes were designed to test its direct shear strength and cube compressive strength while considering the parameters of age and recycled aggregate replacement ratio. The failure pattern and load–displacement curve of specimens at direct shearing were obtained; the direct shear strength and residual shear strength were extracted from the load–displacement curves. Experimental results indicate that the influence of the replacement ratio for the front and side cracks of RAC is insignificant, with the former being straight and the latter relatively convoluted. At the age of three days, the damaged interface between aggregate and mortar is almost completely responsible for concrete failure; in addition to the damage of coarse aggregates, aggregate failure is also an important factor in concrete failure at other ages. The load–displacement curve of RAC at direct shearing can be divided into elasticity, elastoplasticity, plasticity, and stabilization stages. The brittleness of concrete decreases with its age, which is reflected in the gradual shortening of the elastoplastic stage. At 28 days of age, the peak direct shear force increases with the replacement ratio, while the trend is opposite at ages of 3 days, 7 days, and 14 days, respectively. The residual strength of RAC decreases inversely to the replacement ratio, with the rate of decline growing over time. A two-parameter RAC direct shear strength calculation formula was established based on the analysis of age and replacement rate to peak shear force of RAC. The relationship between cube compressive strength and direct shear strength of recycled concrete at various ages was investigated.
Highlights
Humans have produced a lot of pollution in the process of developing nature, such as contaminated material, construction rubbish
In order to provide a basis for the establishment of early age recycled concrete finite element model and engineering design, the present paper explores the fundamental shear properties of recycled aggregate concrete (RAC) at early ages
The overall residual strength of RAC decreases with rising replacement ratio at all ages, but the rate of reduction and the underlying reason is different among samples
Summary
Humans have produced a lot of pollution in the process of developing nature, such as contaminated material, construction rubbish. Yu [18] carried out experiments on plain concrete to explore its shear mechanical properties and proposed a corresponding compression–shear failure criterion based on shear tests on normal and high strength RAC. By analyzing the mechanical properties, including compressive strength, tensile splitting strength, modulus of elasticity, and shrinkage of RAC at early ages, Hu [33] indicated that the equations for these properties at early ages are not inconsistent between NAC and RAC. In order to provide a basis for the establishment of early age recycled concrete finite element model and engineering design, the present paper explores the fundamental shear properties of RAC at early ages. Relationships between shear strength and residual strength while considering the effects of replacement ratio and curing aging are analyzed based on experimental results
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