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In order to study the influence of the replacement ratio of recycled aggregate and the volume of waste fiber on the fracture performance of concrete, the three-point bending test is carried out on the waste fiber recycled concrete precast beams. Calculate the waste recycled fiber concrete fracture parameters according to the double-K fracture model. The results show that the fracture indexes of recycled fiber are related to the recycled aggregate replacement ratio and the volume content of waste fiber. The larger the replacement rate of recycled aggregate is, the smaller the fracture indexes of the specimens are. The volume content of waste fiber is 0.12%, which has the most significant effect on the fracture performance. The study shows that waste fiber can improve the fracture properties of recycled aggregate concrete.

In order to improve the availability of waste rubber tires and bearing capacity of sand foundation, a new composite foundation transforms the tensile strength of a discarded rubber tire into a hoop-tightening force on granular sand soil, i.e. hoop capacity, is introduced and investigated. Considering the characteristics of the circular enclosed structure of the tire, the tensile strength of the tire strips was obtained by carrying out a tension test of tire strips, and the relationships between earth pressure, settlement and vertical load were discovered by the results of loading tests under the conditions of confined and unconfined. The distribution of circumferential stress at each position of the tire cross section was monitored to evaluate the contribution of each part of the tire to the integral hoop capacity. Based on the theory of annular elasticity, Airy stress-state function is introduced to determine the solutions of stress, strain and displacement in the sand and tire regions based on the stress boundary condition and displacement continuity condition. The results show that the theory prediction curve has a high precision approaching the measured data, which indicates the rationality of the proposed theoretical model in predicting the circumferential stress of this type of waste rubber tire composite foundations. [ABSTRACT FROM AUTHOR]

A liquid chromatographic method for the determination of closantel residues in milk and tissues is developed and validated. An acetonitrile-acetone solution (80:20, v/v) is used for the extraction of closantel residues from milk and animal tissues, and the extract is purified by solid-phase extraction with Oasis MAX cartridges and a mixture of formic acid-acetonitrile (5:95, v/v) as the elution solution. A C(18) bonded silica column is used for chromatographic separation. The mobile phase consists of acetonitrile-water (85:15, v/v) containing 0.05% triethylamine at pH 2.5, adjusted with phosphoric acid with the flow-rate set at 1.0 mL/min. Using the fluorescence emission of closantel at lambda(ex) = 335 nm and lambda(ex) = 510 nm, the calibration curve is linear, with a correlation coefficient of 0.9999 over the concentration range of 10-5000 microg/kg for the tissue sample and 10-5000 microg/L for the milk sample. The detection limit (s/n = 3) is 3 microg/kg for tissue sample and 3 microg/L for milk sample. The intra- and inter-day repeatabilities are between 3.35-7.66% and 4.04-8.67%, respectively. The proposed method enables the quantitative determination of closantel residues at levels as low as 10 microg/kg in animal tissue samples and 10 microg/L in milk samples.