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One of the massive by-products of concrete
to concrete recycling is the crushed concrete fines, that is often 0 - 4mm.
Although the construction sector is to some extent familiar with the
utilization of the recycled coarse fraction (>4 mm), at present there is no
high-quality application for fines due to its moisturized and contaminated
nature. Here we present an effective recycling process on lab scale to separate
the cementitious powder from the sandy part in the crushed concrete fines and
deliver attractive products with the minimum amount of contaminants. For this
study, a lab scale Heating-Air classification system was designed and
constructed. A combination of heat and air classification, resulted in a proper
separation of finer fraction (0 - 0.250 mm), from coarser fractions. Heating of
the materials was followed by ball milling to enhance the liberation of the
cementitious fraction. Experiments were carried out at different heating
temperatures and milling durations. Experimental results show that by heating
the materials to 500℃ for 30 seconds, the required time of ball milling is diminished by
a factor of three and the quality of the recycling products satisfies well the
market demand. In addition, the removal of contaminants is complete at 500℃. The amount
of CaO in the recovered finer fraction from the recycling process is comparable
with the amount of CaO in low-quality limestone. By using this fraction in the
cement kiln as the replacement of limestone, the release of the chemically
bound CO2 could be reduced by a factor of three.
CdSe quantum dots (QDs) (2 - 3 nm) were synthesized by chemical precipitation method. Optical and structure properties of the products were investigated by scanning tunneling microscope (STM), X-ray diffraction (XRD), and ultra violet-visible (UV-Vis) spectrophotometer. The results show that high-quality cubic CdSe QDs were obtained. It is also obtained that temperature is one of the most important factors the affect on the particle size and optical properties of the prepared QDs samples.