Mineral Additives to Enhance Early-Age Crack Resistance of Concrete under a Large-Temperature-Difference Environment

The large temperature difference condition in Northwest China threatens a myriad of concrete structures during construction, with the daily temperature varying by around 40 °C. To investigate the macro-mechanical properties and microstructural characteristics of concrete containing different amounts of mineral admixtures under such harsh conditions, this investigation used an environmental chamber to simulate a saline soil erosion environment with a large temperature difference. Four types of concrete containing different proportions of fly ash and slag were prepared and exposed in the environmental chamber with a daily temperature change of −5~40 °C to investigate their compressive strength, flexural strength, and fracture properties. Moreover, the X-ray diffraction (XRD) characteristics, microscopic morphological characteristics, pore structure characteristics, and post-erosion chloride ion distribution characteristics were also observed and recorded. Results showed that the mineral admixture could improve the early strength development of the concrete and effectively improve the fracture performance of the concrete. The average compressive strength growth rate of concrete from day 3 to day 14 was 83.25% higher than that of ordinary concrete (OC) when 15% fly ash and 15% slag were added. In addition, the fracture energy of the concrete was maximized when 15% fly ash and 20% slag were added, which was 50.67% higher than that of OC; furthermore, the internal compactness and pore structure were optimized, and the resistance to saline soil erosion was strong. This provides a basis for the practical application of compounded mineral admixture-modified concrete in an arid environment with a large temperature difference and saline soil erosion.

Fluid-Thermal-Structural Characteristics of Spiral Square Channel

The extremely hot environment attributed to the combustion and aerodynamic heating exposes the scramjets to intense thermal-structural loads. The scramjet life is limited due to the wall cracks caused by the large temperature difference. The focus of this study was performing coupled 3D fluid-thermal-structural analysis of the cooling jacket for scramjet engines. Firstly, the mathematical models and the simulation method were established. The three-dimensional computational fluid dynamics numerical simulations were based on the conservation equations of mass, momentum, and energy. Strain compatibility, equilibrium equations, and constitutive law of elastic solids were applied for the 3D static thermal-structural analysis. Secondly, the fluid-thermal-structural analysis was performed. Results show that both large temperature difference and structure geometry have an obvious impact on the deformation of the cooling channel. Highest deformation (2.1%) of the straight square channel occurs at the middle of the hot side ligament. Compared with the straight square channel, the maximum temperature of the triangular channel and the spiral square channel is reduced by 7.3% and 26.1%, and the total deformation is increased by 5.0% and reduced by 28.3%, respectively.

Synthesis and characterization of a quaternary copolymer retarder for cementing in a long sealing section with large temperature difference

We synthesized a retarder, which has excellent thickening performance in the temperature range of 90–150 °C.