负温混凝土工程冻害风险评估方法研究

论述了负温混凝土工程冻害风险识别方法 ,并简述了Delphi方法及关联树法的原则 ,从防冻投资、减灾费用、冻害损失三个方面简述了冻害风险估计方法 ,并具体评价了负温混凝土工程冻害风险中常用指标。     

矿渣掺量对高强高性能混凝土强度和耐久性影响的试验研究

研究矿渣掺碍对于高强高性能混凝土性能的影响。水胶比为０．２８,矿渣掺量达４０％,可以配制出早期,后期强度无高于不掺矿渣,而水泥用量高达６００ｋｇ／ｍ＾３的纯水泥混凝土的相应强度,这种配合比的混凝土２８天强度在８７ＭＰａ以上;并且流动性好,可以满足泵送需要。     

Identification and evaluation of modification level for compacted graphite cast iron

The shape of the freezing zone of a thermal analysis cooling curve not only contains the information about the modification level of compacted graphite cast iron (CGI) right after vermicularizing treatment, but also reflects the following fading process during holding. When the freezing zones of two cooling curves are approximately the same, graphite morphologies of the samples cast from the two corresponding melts right after vermicularizing treatment are similar, and those of the two corresponding samples cast after holding for the same period are similar too. Based on the pattern recognition method and database established from a large amount of experimental results, the shape of the freezing zone of a cooling curve can be used to identify the modification level of CGI melt and on-line prediction of a CGI melt quality has been realized.     

再生微粉对超高性能混凝土力学性能和微观结构的影响

研究了两种类型的再生微粉(混凝土粉和砖粉)取代部分硅灰对超高性能混凝土(Ultra-high Performance Concrete,UHPC)力学性能和微观结构的影响。结果表明:混凝土粉的掺入降低了UHPC的力学性能,而砖粉取代15%硅灰时,UHPC的28 d抗压强度和抗折强度分别达到了130 MPa和24 MPa,略高于基准组;相较于混凝土粉,在UHPC中掺入15%的砖粉能够优化混凝土的内部结构;砖粉良好的微集料填充作用和火山灰效应增强了界面过渡区的黏结性能和水化产物的纳观力学性能,从而改善UHPC的微观结构。     

圆钢管微膨胀陶粒混凝土短柱轴压极限承载力计算公式

以陶粒混凝土中的膨胀剂掺量(0、4%、8%、12%)和钢管壁厚(含钢率)为变量,制作了12组(24根)短柱,进行了轴压试验。结果表明:在本试验的膨胀剂掺量范围内,圆钢管微膨胀陶粒混凝土短柱试件的轴压承载力随膨胀剂掺量的增大而逐渐提高;根据试验结果建立了考虑膨胀剂掺量的受圆钢管约束微膨胀陶粒混凝土的强度准则计算公式,进而推导出了考虑膨胀剂掺量的圆钢管微膨胀陶粒混凝土短柱的极限承载力公式。     

An extended (fractal) Overlapping Crack Model to describe crushing size-scale effects in compression

The inherent microstructural disorder strongly influences the mechanical behaviour of heterogeneous materials such as concrete and rocks. Tensile and compression tests, in fact, evidenced a localization of strain and dissipated energy in the post-peak softening branch, with a consequent scale dependence of the stress–strain response. For this reason, the well-known Cohesive Crack Model and the recently proposed Overlapping Crack Model are useful tools for describing the size effects in tension and compression, respectively. In general, strain localization, damage and fracture, which are phenomena affecting the failure of concrete, are not rigorously interpretable in the framework of continuum mechanics. On the other hand, since the flaw and the aggregate distributions in quasibrittle materials are often self-similar (i.e. they look the same at different magnification levels), the microstructure may be correctly modelled by fractal sets. In this paper, the approach based on fractal geometry, that has profitably been applied for the tensile behaviour, is applied to obtain a fractal overlapping law from uniaxial compression tests. According to this approach, it is assumed that energy dissipation, stress and strain are not defined with respect to the canonical physical dimensions, though on fractal sets presenting noninteger physical dimensions. As a consequence, these classical parameters should be substituted by fractal quantities, which become the true material properties.     

浅谈混凝土的施工温度与裂缝

通过多年的现场观察和查阅有关混凝土内部应力方面的专著,对混凝土温度裂缝产生的原因、混凝土温度的控制和预防裂缝的措施等进行阐述。     

辊型优化技术的发展及应用

传统的板形控制策略一般采用“液压弯辊”、“液压弯辊＋可变凸度轧辊”等方法,宝钢与相关科研单位合作,经过十几年的研究,探索出一条采用“液压弯辊＋辊型优化设计”、“液压弯辊＋可变凸度轧辊＋辊型优化设计”等方法来控制板形的新思路。为此,对辊型优化设计的目的、发展进程、机理及应用成果进行了详细介绍,为辊型优化技术的进一步推广应用提供了有益的参考。     

Integrity Problem of Large-Diameter Bored Piles

Bleeding is known to occur in bored piles (drilled pier). The generally accepted view is that bleeding in piles is confined to the upper part of the pile only. Under certain conditions during bleeding, channeling may happen. Practising engineers believed that the associated problems with bleeding and channeling in bored piles can be overcome by overcasting the piles. A case study of extensive integrity tests consisting of cross-hole sonic logging tests and dynamic load tests on bore piles, as well as continuous corings from top to bottom of the piles carried out, revealed that some bored piles have channeling of concrete at various depths. Most of them were larger diameter piles. The finding that bleeding and channeling are not confined to the upper part of the pile is contrary to the generally accepted view. This paper attempts to develop a theory for the bleeding and channeling of concrete to explain the mechanics of the occurrence of channeling in bored piles. The proposed theory is verified by the close correlation of the predictions of the theory with field observations of the case study. Based on the proposed theory, recommendation with regards to the quality of concrete will be made to avoid the occurrence of channeling of concrete in large-diameter bored piles. The implications on the structural performance pertaining to axial capacity, compressibility and durability of bored piles with channels will be investigated.     

Are Available Models Reliable for Predicting the FRP Contribution to the Shear Resistance of RC Beams?

In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.