Abstract
The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15–30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible.
Highlights
In Japan, the power supply includes renewable [1], thermal [2], and nuclear energy [3]; global environmental issues and the recent power supply situation mean that renewable energy is expected to expand substantially
I and II, it was not possible to compare samples from the same discharge source, but the decrease in loss on ignition (LOI) was due to the difference in equipment rather than the fly ash characteristics
One reason for the larger LOI in experiment I was that the mode of the bubble diameter generated from the air diffuser was about 200 μm, which was about 10 times larger than that of the fly ash particles, and it was difficult to collect or raise the unburned carbon to the surface
Summary
In Japan, the power supply includes renewable [1], thermal [2], and nuclear energy [3]; global environmental issues and the recent power supply situation mean that renewable energy is expected to expand substantially. Increasing the proportion of renewable energy in the energy mix will take time, and thermal power generation will still be required. Global fly ash production is estimated to be 400–500 million tons per year and the utilization rate in cement and concrete components is about 30% [4,5]. The total amount of coal ash generated by Japan’s electric power industry and general industry exceeded 10 million tons and 97.4% of the coal ash was used, and 96.3% of the total was used in the cement industry as a raw material
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