Programmers: concrete women and abstract men?

Abstract Sherry Turkle and Seymour Papert have identified a hands-on and experimental 'concrete' approach to computer programming as feminine, and as a fully formed way of knowing how to program, rather than as either a learning style or as a stage in development. This paper differentiates between concrete styles of learning how to program, and the concrete style of programming. Learning strategy is decoupled from programming style, and the hypothesis that women are more likely than men to prefer a concrete style of programming is tested by means of examining responses to practical examples of concrete and abstract styles. The responses suggest that there is no significant difference between women and men in their attitude toward a concrete style of programming.     

Fracture of concrete structure using simplified meshless method

Numerical analysis of fracture in concrete is studied with a simplified meshless method. In this meshless method, the crack is represented by a set of disconnected cohesive crack segments that are required to pass through meshless nodes. The crack method therefore falls in the category of discrete crack methods. However, in contrast to most other methods where the crack is represented as continuous line/surface, no representation of the crack surface is needed. Hence, there is no need to track the crack path. Branching cracks and coalescing cracks are a natural outcome of the analysis and no specific algorithms need to be incorporated to model such complicated events. Besides the simplicity of the method, the accuracy is maintained. This is demonstrated through several examples.     

YF混凝土高效减水剂研制

YF高效减水剂在结构上不同于萘系和蜜胺系减水剂 ,其显著特点是在用量很少的情况下即可达到强烈的分散效果 ,可用在高强混凝土、流态混凝土、免振混凝土、泵送混凝土、商品混凝土等     

现拌和预拌混凝土的回弹-强度曲线比较

混凝土的无损检测是混凝土质量控制的一个重要方面，本文根据现拌混凝土的配制特点，分别拌制C10、C20、C30C40等级的混凝土，在14天和28天龄期进行回弹和抗压强度试验，对试验数据进行回归分析和统计分析，结果表明，现拌和预拦混凝土回弹-强度曲线存在显著差异。差异的大小与混凝土的强度等级有关，在检测预拌混凝土的强度时，应考虑到这种差异。     

混凝土非匀质强度损伤统计分析

论述了混凝土材料强度的概率统计特性，把损伤力学用于混凝土的强度分析，计算了混凝土的名义强度。在此基础上定义了一种新的损伤变量，运用损伤变量的概念，定性地探讨了混凝土强度的尺寸效应。     

Plastic shrinkage cracking in cementitious repairs and overlays

A study was undertaken to investigate the influence of mixture proportions on plastic shrinkage cracking in cementitious repairs and overlays. The following variables were studied: water-cement ratio (w/c), sand-cement ratio (s/c) aggregate-cement ratio (a/c), fly-ash content, and the presence of a shrinkage reducing admixture (SRA). A recently developed bonded overlay method was used. In this method, the cementitious material to be investigated is cast on a substrate base with protuberances and the entire assembly is subjected to drying in an environmental chamber. With a high degree of restraint, cracking develops in the overlay over time which is then characterized with the help of magnification device and image analysis software. Results indicate that a lower water-cement ratio significantly reduces crack widths and crack areas and also reduces the ‘time to first crack’. The exact influence of s/c on cracking could not be established. The study further demonstrated that increasing the a/c provided internal restraint and significantly reduced early-age cracking. The addition of Class C fly-ash increased the amount of cracking but also increased the ‘time to first crack.’ This was however true only to a certain threshold value of fly-ash content beyond which fly-ash can be effective in reducing early age shrinkage cracking. Finally, the addition of a shrinkage reducing admixture was effective in reducing cracking but the cracks occurred sooner.     

Continuum Microviscoelasticity Model for Aging Basic Creep of Early-Age Concrete

We propose a micromechanics model for aging basic creep of early-age concrete. Therefore, we formulate viscoelastic boundary value problems on two representative volume elements, one related to cement paste (composed of cement, water, hydrates, and air), and one related to concrete (composed of cement paste and aggregates). Homogenization of the “nonaging” elastic and viscoelastic properties of the material’s contituents involves the transformation of the aforementioned viscoelastic boundary value problems to the Laplace-Carson (LC) domain. There, formally elastic, classical self-consistent and Mori-Tanaka solutions are employed, leading to pointwisely defined LC-transformed tensorial creep and relaxation functions. Subsequently, the latter are back-transformed, by means of the Gaver-Wynn-Rho algorithm, into the time domain. Temporal derivatives of corresponding homogenized creep and relaxation tensors, evaluated for the current maturation state of the material (in terms of current volume fractions of cement, water, air, hydrates, and aggregates; being dependent on the hydration degree, as well as on the water-cement and aggregate-cement ratios) and for the current time period since loading of the hydrating composite material, allow for micromechanical prediction of the aging basic creep properties of early-age concrete.     

Investigation on the cracking behavior of concrete cover induced by corner located rebar corrosion

Non-uniform corrosion of reinforcement causes concrete cracking in chloride contaminated RC structures. Due to the special boundary conditions, the concrete cover with corner located rebar is often subjected to the attack of chloride ions in a marine environment from two directions, and thus the corresponding non-uniform corrosion distribution should be different from the one for side-located rebar. The aim of the work is to explore the effect of corner located rebar corrosion on the cracking of cover concrete. For corner located rebar, an improved non-uniform corrosion distribution model was established based on the analysis results of two-dimensional chloride diffusion in concrete. Considering the heterogeneities of concrete, a meso-scale mechanical model and method for the study on the failure behavior of concrete cover was built. In the analysis model and method, the non-uniform radial displacement distribution was adopted to simulate the corrosion expansion behavior of the rebar. The cracking of concrete cover with corner located rebar was simulated and studied. The present approach was verified by the available experimental observations. The influences of concrete heterogeneity, corrosion distribution types, rebar diameter and concrete cover thickness on the failure patterns of concrete cover and the expansive pressure were investigated. The simulation results indicate that the developed approach can well describe the cracking behavior of cover concrete and the corrosion-expansion behavior of steel rebar.     

Modeling the cracking of cover concrete due to non-uniform corrosion of reinforcement

In situations when external chloride penetration is the cause of depassivation, the corrosion process may start from the outer region of a rebar, which might expand non-uniformly. Therefore, the main objective of the present work is to explore the effect of non-uniform corrosion on cracking behavior of cover concrete. The influences of concrete heterogeneities and the porous layer generated at the rebar/concrete interface on the failure patterns and the corrosion level of cover concrete are considered. The random aggregate structures of concrete are built, and the concrete is regarded as a composite composed of three phases, i.e. the aggregate, mortar matrix, and the interfacial transition zones (ITZs). The plasticity damaged model is employed to describe the mechanical properties of the mortar matrix and the ITZs, and it is assumed that the aggregate is elastic. Non-uniform radial displacement with a half ellipse shape is adopted to describe the expansion distribution of the corrosion products. The failure pattern and the corrosion pressure of cover concrete, and the critical corrosion level when the cover concrete cracks due to non-uniform corrosion expansion are studied based on the meso-scale numerical method. The comparison of the simulation results with the available test results on the failure pattern of cover concrete shows fairly good agreement. Moreover, the influence of meso-structural heterogeneities is explored, and the cracking behavior obtained under non-uniform and uniform expansion conditions are compared. Finally, the influences of cover thickness, rebar diameter and the location of rebar (namely side-located rebar and corner-located rebar), on the failure pattern and the corrosion level are examined.     

DXS水库面板坝趾板设计

根据DXS水库面板坝基础工程地质条件,对平趾板与斜趾板两种布置形式进行比较,为减少开挖量,降低上游的高边坡,采用斜趾板与延长防渗板的布置型式。并结合工程实际简要介绍了该面板坝趾板设计要点。工程投运3年多,面板坝趾板混凝土质量良好,趾板无裂缝,水库无渗漏,大坝运行正常。