Abstract
The acoustic emission (AE) characteristics, change law of the ultrasonic velocity, and internal failure mode of cemented waste concrete-coal gangue backfilling (CWCGB) with 600 days of curing time were studied under uniaxial loading conditions. Waste concrete particles of 5 mm acting as fine aggregates substituted for 30% and 50% fine coal gangue in the cemented coal gangue backfilling (CGB). AE was used to test the ring count and changing rule of the accumulated energy, locate the event for positioning, and calculate the number of events. The average ultrasonic wave velocity was measured via an ultrasonic detector. The characteristics of the microfractures were observed via a scanning electron microscope. The results showed that the specimens with 30% and 50% waste concrete replacement rates underwent ultrasonic wave velocity stabilization and a rapid decline stage under uniaxial compression; for the former case, the decline started earlier. The AE ring count attained peaks at the pore compression stage, yield stress point, stress peak value, and residual stress stage with no added waste concrete and 30% and 50% waste concrete substitution rates. The value and consequent frequency of the ringing count peak and cumulative energy slope increased with increasing waste concrete substitution rate. A microcrack was observed at the interfacial transition zone between the cement paste and gangue owing to the alkali-aggregate reaction effect. However, a better bonding performance was exhibited by the waste concrete particles and paste.
Highlights
As a major construction material, concrete is widely used owing to the rapid growth in the urbanization in China. e demolition of old constructions generates a large amount of waste concrete, which is disposed at will and leads to various environmental problems
It is reported that more than 200 Mt of waste concrete is currently being produced each year in China [1]. erefore, concrete recycling producing recycled aggregate concrete (RAC) to partially substitute the natural aggregates has been recognized as an effective approach to offset their shortage and for waste concrete disposal. e other effective method of using waste concrete is to use it in cemented coal gangue backfilling (CGB)
When an ultrasonic wave is transmitted through a material, the ultrasonic rate changes owing to the closure, initiation, and expansion of the cracks in the material under uniaxial compression. erefore, acoustic emission (AE) and ultrasonic monitoring are used to monitor the occurrence of backfilling
Summary
As a major construction material, concrete is widely used owing to the rapid growth in the urbanization in China. e demolition of old constructions generates a large amount of waste concrete, which is disposed at will and leads to various environmental problems. Waste concrete of −5 mm partly replaced the ne coal gangue within CGB, the failure mode and structural change in the CWCGB were re ected by using AE and performing ultrasonic testing under uniaxial loading, and the internal mechanism of the destruction was revealed by the micromorphology. It provided the experimental foundation for the obtaining the optimum ratio of CWCGB and establishing an acoustic system for evaluating the back ll body stability
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