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This paper presents a new numerical method to optimize the mix proportion of self-compacting concrete (SCC) at paste level based on a paste rheological threshold theory that the SCC formulated paste must satisfy the criteria to ensure SCC with good flowability and segregation resistance. A total of 12 mini-slump flow tests were initially conducted, and relevant rheological characteristics were derived. The correlation between mixture variables and rheological characteristics was determined using a bilinear interpolation method. A self-compacting area at paste level was defined by choosing the mixture whose rheological characteristics satisfied the criteria. The economical mixture was obtained from the area, and an iteration process was introduced to ensure that the rheological characteristics of this mixture satisfied the criteria. Finally, an optimized SCC mixture from an economical aspect was achieved, and the robustness of the mixture was also analyzed. [ABSTRACT FROM AUTHOR]

An angular composite model (ACM) is applied to analyse the bistatic scattering from two-dimensional sea surfaces. When the local scattered angle lies in the specular region, Kirchhoff approximation (KA) is used to evaluate the specular reflection, which predominates the total scattering in this region; the small perturbation method (SPM) is employed to deal with the diffuse reflection dominated by small roughness, as the local scattered angle is situated out of the specular region. This avoids dwelling on the tough question about how to choose the proper cut-off wave number like in the well-known two-scale model (TSM). Numerical illustrations are carried out for bistatic scattering coefficients versus wind speed, incident angle, incident frequency and polarization state, respectively. The comparison of numerical results of the ACM and other experimental and theoretical models in several configurations shows that the ACM is robust to give accurate numerical evaluations for bistatic scattering of rough sea surfaces. [ABSTRACT FROM AUTHOR]

A versatile composite surface model (VCSM) is presented for estimation of the electromagnetic backscattering coefficient of the sea. Taking into account the statistical characteristics of the sea surface and the validity conditions of component models for the small-scale and large-scale surfaces in the composite surface model (CSM), a method for the two-scale decomposition of sea surfaces is introduced. On this basis, the cutoff wavenumber with wind speed dependence and incident wave frequency dependence is applied to separate the sea spectrum into large- and small-scale components at different sea states with increased accuracy. Then, numerical results of the backscattering coefficient are evaluated and discussed in the case of different wind speeds, polarizations as well as incident frequencies. Finally, the VCSM is verified through the comparisons with the available experimental data, and the comparisons of the VCSM results and the classical CSM results also show that the VCSM behaves better. [ABSTRACT FROM AUTHOR]

Hydropower dams are subjected to soft water penetration during their service lives. Concrete deterioration due to calcium leaching will decrease the durability of concrete and affect dam safety. The long-term performance of concrete dams due to calcium leaching should be evaluated and predicted accurately to complete reinforcement work in a timely manner. In this paper, a methodology that combined microscopic tests and numerical analysis to evaluate the long-term performance of dam concrete due to calcium leaching is proposed. The current state of concrete is evaluated by analyzing the components of sediments and seepage water through microscopic and spectroscopic tests, such as X-ray photoelectron spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The long-term degradation of concrete was predicted by utilizing a multi-scale model of calcium leaching, which considered the micro-pore structure of cement hydrates flux with time. The simulated results using this calcium leaching model showed a good agreement with other experiments. Finally, a real case study including field inspection was performed and the long-term durability of dam concrete was predicted through microscopic tests and finite element analysis method. It implies that the proposed method could provide calculation and theoretical basis for the durability analysis of concrete dams due to calcium leaching. [ABSTRACT FROM AUTHOR]