Fracture characteristics of dredged sand concrete beams in composite salt environment

Abstract

[Objective] In order to realize that dredged sand from the Yangtze River can be used in construction of hydraulic structures near estuary, [Methods]proportion of dredged sand to the mass of fine aggregate was defined as the Content. 5 kinds of concrete trabecular specimens with different Content were designed, and the specimens were placed in 4 different salt environments(composed of NaCl and Na_2SO₄ solution) for full immersion erosion. Non-standard three-point bending tests were carried out on the specimens with erosion time of 30 d, 60 d and 90 d and those without erosion. The mechanical properties were studied and the crack development was monitored by acoustic emission(AE) technology. [Results] The results show:(1) Crack resistance of concrete gradually decreases with increase of the dosage. For every 12.5% increase, the peak breaking load decreases by about 5%. When the dosage is greater than or equal to 37.5%, the peak breaking load drops by more than 30%.(2) The higher ion concentration is, the more obvious erosion effect is, and addition of Cl~- can alleviate the erosion process of SO₄^2-.(3) The analysis of AF-RA values shows that tensile cracks are the main cracks in early stage, and the proportion of shear cracks increases gradually with the process of crack expansion. The proportion of shear cracks is the smallest when the content is 12.5%, and the fracture development is the best. The higher the ion concentration, the larger the proportion of shear fractures, the more incomplete the fracture development. The research result provide experimental basis for the application of dredged sand concrete in water conservancy and water transportation engineering under salt environment. [Conclusion] The addition of dredged sand and the erosion of salt environment have obvious deterioration effect on the mechanical properties of concrete. The accumulate counts of AE showed three stages, reflecting fracture characteristics and verifying boundary effect.

Keywords

dredged sand / fracture / composite salt corrosion / acoustic emission(AE) / concrete / mechanical properties / AF-RA