In the construction industry, natural aggregates (NA) can be replaced by recycled concrete aggregates (RCA), which can address the issue of construction-waste disposal and resolve the dilemma between demand and supply. This paper aims to systematically review the modification of RCA techniques and their application in producing recycled aggregate concrete (RAC). First, the pretreatment approaches for enhancing the properties of RCA are introduced. Next, the improved efficiency of these approaches and their influences on the workability, mechanical strengths, and permeability of RAC are analyzed and discussed. Subsequently, the effectiveness of different techniques and their cost/environmental impact are compared. Finally, some case studies of the application of RCA in infrastructure are presented, and the remaining challenges and perspectives are discussed. The results of this review work can extend the knowledge of RCA and RAC, as well as serving as a source of inspiration for further studies.
In this paper, the hydrophobic nano-calcium carbonate (CaCO3) was prepared by organic matter (the bolaform surfactant Disodium Sulfodehydroabietate as template) modifying surface structure of calcium carbonate (made by anhydrous sodium carbonate and anhydrous calcium chloride) at 40°C for 2h. The prepared hydrophobic nano-CaCO3 was characterized by means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM) and. The nano-CaCO3 with mean particle size of 64.4 nm was obtained in the range of 0.5~1.5µm by calculation. The contact angle of nano-CaCO3 with liquid solid was 117.49°. The hydrophobic property become stronger.
Wood nondestructive testing technology is a new and comprehensive subject. X-ray computed tomography (CT) scanning technology has been applied to the detection of internal defects in the logs for the purpose of obtaining prior information that can be used to arrive at better log sawing decision. Thus, the recognition of internal defects becomes more and more important work A method in log CT image edge detection of defects based on multifractal theory was applied in the paper. The Holder exponent of image pixels was computed first, then its multifractal spectrum was estimated and different image pixels were classified, Based on multifractal theory, the set of both singular edge points and smoothing edge points is the set of image edge points. Experimental result showed that the method of log CT image in the edge detection based on multifractal theory was a more effective and more local method.
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