Experimental study was carried out on the concrete mixed with machine-made sand and recycled coarse aggregate (MSRAC), three strength grades of concrete were designed by changing the water to cement ratio as 0.36, 0.45 and 0.55, while the sand ratio varied in a range of 32%~38%, 32%~42% and 38%~44% successively. The workability and the mechanical properties such as compressive and splitting tensile strengths and elastic modulus of MSRAC were tested. The results show that although the mechanical properties of MSRAC were influenced by sand ratio, they were still controlled by the water to cement ratio. The ratio of axial compressive strength to cubic compressive strength and the elastic modulus of MSRAC basically satisfy the specifications of the current design code for concrete structures. It should be noticed that the tensile strength of MSRAC is lower than current specification, and tends to reduce with the increase of water to cement ratio.
The undesirable properties of conventional recycled fine aggregate (RFA) often limit its application in the construction industry. To overcome this challenge, a method for preparing completely recycled fine aggregate (CRFA), which crushes all concrete waste only into fine aggregate, was proposed. The obtained CRFA had high apparent density, and its water absorption was lower than that of the conventional RFA. To take advantage of the CRFA, this paper introduced the modified packing density method for the CRFA concrete mix design. The modified packing density method took account of the powder with a particle size of smaller than 75 μm in the CRFA and balanced both the void ratio and the specific surface area of the aggregate system. Concrete (grade C55) was prepared using the CRFA to validate the feasibility of the proposed method. The unit price of the prepared CRFA concrete was around 12.7% lower than that of the natural aggregate concrete. Additionally, the proposed procedure for the concrete mixture design could recycle all concrete waste into the new concrete and replace all the natural fine aggregate in the concrete mixture.
A design method of circularly polarized (CP) micro‐strip antenna is proposed. The coefficients of eigen‐mode and the axial ratio (AR) are derived based on the cavity theory. The radiation feature can be estimated from port impedance. The optimal feeding position is found by means of virtual port method. During the derivation, corner truncated patch antenna is used to verify the method. A cross‐slotted CP micro‐strip antenna is designed, which is working at GPS band. Then the fabrication and measurement of the antenna are conducted. Its measured impedance, AR, radiation pattern agreed well with the simulation results, which verify high efficiency of this method for CP micro‐strip antenna design.
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