Study on recycle of concrete sludge produced at concrete mills in Toyama Prefecture

抄録

The questionnaire survey was conducted to investigate the actual condition of disposal & recycle of concrete sludge and those cost in Toyama Prefecture to explore the possibility of recycling. The results showed that the most popular method was disposal of dewatered and dried sludge as dewatered cake at final landfill site which accounted for around 55%. The other 7% was recycled as sludge water, and 38% was recycled as reused concrete after solidification. These recycle methods will be regarded as promising recycle methods. The production rate of sludge varied depending on disposal method, and this rate for solidification method was 0.5 % which is half of that of dewatered sludge. The unit cost of disposal was lower for solidification than that for dewatered sludge. However, some sludge showed higher concentration of Cr ⁶⁺ leaching than the environmental quality standard. The strength property of concrete was studied when the sludge was mixed as cement or fine aggregate. It is clear that the standard strength was not fulfilled with the increase of mixed ratio of sludge as a substitute for cement. The result showed that almost half of sludge produced at concrete mills in Toyama Prefecture was recycled. The recycle of sludge water will be further promoted with the care of Cr⁶⁺ concentration due to the high leaching potential of some sludge. However, the mixing ratio of sludge will not be increased too much to meet the strength criterion for paving slag, requiring for other efficient recycle methods.