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An investigation was undertaken to assess the potential for heavy metal leaching from gold tailings (GTs) when used GTs as fine aggregate for concrete. The leaching behavior in different pH leaching solutions and long-term leaching features of gold tailings concrete were studied. A kinetic model was used to predict the total amount of heavy metal leaching that will occur in next thirty years. The results reveal that the levels of Ba, Cd, Cr, Pb, Mn and Cu in GTs exceed the natural levels of these elements found in Chinese soil. Significantly, the leaching of Ba, Cd, Pb, Mn and Cu is more evident. GTs content shows a positive correlation with the leaching amount of heavy metals, and the cumulative leaching amount of heavy metals drops dramatically after 16 d. Based on 30 years leaching amount prediction, the leaching amount of Pb, Cu and Ba is 2 - 3 mg / L, while the leaching amount of Cd, Cr and Mn is less than 1 mg / L. These findings indicate that the GTs is sufficiently cured in concrete, thereby reducing the risk of long-term leaching of heavy metals. [ABSTRACT FROM AUTHOR]

The powders interlayer was applied for transient liquid phase (TLP) bonding of SiCp/Al composites using pulse current heating. Pulse current got though the joint with powder interlayer and generated the effect of Joule heat and spark plasma sintering to achieve the TLP bonding of SiCp/Al composites sheet. The results show that there is the good TLP bonded joint without defects under the conditions of vacuum:1.39×103 Pa; Pulse current density: 115 A/mm2; holding time: 15-60 min; original pressure: 0.5 MPa. The results reveal the dense joint without pores composed of the Al-based solid solution, pure Ti zone, Al2Cu, and Al3Ti intermetallic phase. Furthermore, the thermal and isothermal effects of pulse current on in situ synthesis of TLP bonded joints of SiCp/Al composites using mixed Al-Cu-Ti powder interlayer are analyzed and discussed. According to microstructure of joint, pulse current promote to in situ form the intermetallic compound, which can provide higher mechanical properties of joint.

The soil and groundwater in Northwest China contain a large number of aggressive sulfate ions, magnesium ions and chloride ions, which leads to the durability degradation of in-service recycled aggregate concrete (RAC), and seriously restricts the use of RAC in new structures in Northwest China. In order to study the durability degradation law of RAC with multiple cementitious materials system subjected to compound salt erosion, the durability failures of different parts of RAC structural components were simulated by three modes: full immersion, partial immersion, alternating dry and wet immersion, and the durability tests of compound salt erosion of RAC were carried out. Taking the relative dynamic elastic modulus, weight loss rate and relative compressive strength as the indicators, the durability degradation law of RAC subjected to compound salt erosion under different erosion modes was studied, and the influences of the matching mode and replacement rate of supplementary cementitious materials in multiple cementitious materials system on the durability degradation law of RAC were analyzed. Under the full immersion mode, the relative dynamic elastic modulus of fly ash-slag double-mixed RAC decreases slowly. Under the partial immersion mode, the introduction of supplementary cementitious materials reduces the resistance of RAC to compound salt erosion. Under the alternating wet and dry immersion mode, the physical and mechanical properties of RAC increase first and then decrease, and the multiple cementitious materials system RAC shows better resistance to salt erosion than that of pure cement RAC. [ABSTRACT FROM AUTHOR]

High temperature is one of the worst conditions to engineered cementitious composite (ECC). In this paper, the tensile behaviors of PVA fiber reinforced ECC(PVA-ECC) and steel fiber+PVA fiber reinforced ECC (HyECC) at room temperature and after 200 °C, 400 °C, 600 °C elevated temperature exposure were studied. The results indicate that equally replacing PVA fibers by steel fibers degraded the tensile hardening ability of PVA-ECC at room temperature. The elevated temperature posed a significant effect on the tensile strength and toughness of PVA-ECC and HyECC. Tensile strain hardening behavior of the two types of ECCs was eliminated after high temperature exposure. Tensile strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature. The addition of steel fiber slowed down the decay rate of tensile strength and toughness of HyECC. Elevated temperature changed the microstructures of PVA-ECC and HyECC. The softening at 200 °C and decomposing at 400 °C of PVA fiber was the main reasons for the tensile behavior degradation of the two kinds of ECCs. [ABSTRACT FROM AUTHOR]

This artical investigated the effects of sulphur-fixing ash and ground slag on the performance of cement slurry and concrete performance in a circulating fluidized bed, and its feasibility as a concrete admixture was explored. The results show that with the increase of solid sulfur ash, the cement slurry fluidity and the concrete fluidity are significantly reduced, and the impact of the ground slag is not large, the solid sulfur ash and the ground slag are conducive to the improvement of the compressive strength of the concrete, and the impravement effect of solid sulfur ash is more significant. In order to improve the working performance of ground slag and solid sulfur ash concrete, special additives have been developed, which can effectively improve the problem of poor working performance of concrete. Solid sulfur ash and ground ash with qualified stability can be used to prepara C20~C50 concrete that meet the requirements. [ABSTRACT FROM AUTHOR]

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