Cement and Concrete Research 期刊近期文献总结

Cement and Concrete Research 期刊近期文献总结

Concrete suffers from brittle failure due to its low tensile strength. This drawback can be compensated for by adding reinforcement bars and/or steel fibres, and more recently, macro synthetic fibres. When mixing concrete with these fibres the aggregates could damage the fibres. This paper presents work done on the effect of mixing on the performance of macro synthetic fibre reinforced concrete. Single-fibre pull-out tests were conducted on various fibres in both the original and mixed state. Furthermore, flexural tests were performed to investigate the influence of mixing time and mixer type on the performance. It can be concluded that mixing is beneficial for flat type fibres, but the performance of crimped or embossed fibres remains the same. Furthermore, longer mixing times (> 10 min) in a pan mixer are detrimental to the performance, while the performance in a tilting drum mixer remains unchanged even after a mixing time of 60 min.

混凝土常常由于抗压强度低遭受脆性破坏。这个缺点可以通过加入钢筋和/或钢纤维以及最近的宏观合成纤维来弥补。当混凝土与这些纤维混合时集料可能会损坏纤维。本文介绍了拌合对宏观合成纤维增强混凝土性能的影响。在初始态和拌合态下对各种纤维进行单纤维拔出测试。并且进行弯曲测试以研究拌合时间和搅拌器类型对性能的影响。可以得出结论，拌合对于扁平型纤维是有利的，但是卷曲或压花纤维的性能保持不变。此外，还发现在盘式搅拌机中拌合较长时间（>10分钟）对混凝土性能有害，而在倾翻式鼓式搅拌机中即使拌合超过60分钟，混凝土性能也保持不变。

The most singular characteristic of pervious concrete is its interconnected porosity that allows water to flow through at high rates. The objective of this paper is to develop and validate an advanced DEM-CFD model to assess the permeability of pervious concrete numerically, taking into account the influence of the composition and of the compaction process. An extensive experimental program with 1 aggregate grading size, 4

paste contents and 3 degrees of compaction was conducted to validate the numerical approach. Results show that the DEM-CFD model is capable of predicting the permeability depending on the variables considered here. Moreover, flow parameters derived from the numerical simulations help understand the experimental results. The study confirms that, instead of relying on trial and error experiments, it is possible to use advanced numerical models to accelerate the definition of mixes and the production process, reducing the time, efforts and costs required.

透水混凝土最独特的特征是其具有相互连通的孔隙，使水能够以高速流动。本文的目的是兼顾到成分和压实过程的影响的同时开发和验证一个先进的DEM-CFD模型来评估渗透性混凝土的渗透性。使用一个广泛的实验方案进行验证的数值方法，为1倍集料级配大小，4倍浆体含量和3倍的压实。结果表明，DEM-CFD模型能够根据这里考虑的变量来预测渗透率。此外，从数值模拟得到的流动参数有助于理解实验结果。研究证实，与其依靠试错实验，可以使用先进的数值模型来加速拌合物的定义和生产过程，减少所需的时间，精力和成本。

This paper reports strategies to design the binder phase of ultra-high performance concretes (UHPC) from commonly available cement replacement (fly ash, slag, microsilica, metakaolin) and fine filler (limestone) materials. A packing algorithm is used to extract the number density, mean centroidal distance, and coordination number of the microstructure. Similarly, rheological studies on the pastes provide yield stress, plastic viscosity, and min-slump spread. The selection criteria involves using the three microstructural and three rheological parameters individually or in combination to define packing and flow coefficients. The selection criteria is flexible enough to allow users modify the constraints depending on the application. In this study, only ternary and quaternary blends, with a total cement replacement of 30% by mass are selected for further characterization. The highly efficient microstructural packing in these mixtures and better workability that facilitated dispersion of particles to enhance the reactivity results in beneficial pore structure and mechanical properties.

本文讲述了利用常用水泥替代品（粉煤灰，矿渣，硅微粉，偏高岭土）和细填料（石灰石）材料设计超高性能混凝土（UHPC）粘结相的策略。使用包装算法来计算微观结构的数量密度，平均质心距离和配位数。类似地，根据浆料的流变学研究得出屈服应力，塑性粘度和最小坍落度扩展。选择标准涉及单独或组合使用三个微结构和三个流变参数来定义填充和流动系数。选择标准足够灵活以允许用户根据实际应用修改约束条件。在这项研究中，仅选择三元和四元混合物，总共30％的水泥替代品用于进一步表征。这些混合物中的高效微结构填料和颗粒分散度高带来的良好工作性使得孔结构和机械性能较为优良。

Recently, the structure of the crystalline alkali-silica reaction (ASR) product formed in affected concrete has been identified based on μ-XRD measurements. However, the data were obtained from a single aggregate. In this study, Raman microscopy is applied on crystalline ASR products formed in several aggregates and concrete mixtures, enabling a comparison of their spectra and with it their structure. In a first step, samples from the same concrete used for μ-XRD measurements are analyzed and compared. In a second step, samples from a second structure and from a concrete prism test are measured. In addition to Raman microscopy, SEM with EDX is used to characterize the microstructure. The Raman spectra of the crystalline ASR product are practically identical in all studied aggregates and concrete mixtures, showing it is the same phase. This conclusion is further supported by the microstructural data.

最近，基于μ-XRD测量，在受影响的混凝土中形成的结晶碱-硅反应（ASR）产物的结构已被确定。但是，这些数据是从一种单一的集料中获得的。在这项研究中，拉曼显微镜适用于在几种集料和混凝土混合物中形成的结晶ASR产物，从而能够比较它们的光谱和它们的结构。在第一步中，分析和比较来自用于μ-XRD测量的相同混凝土的样品。在第二步中，测量来自第二结构和混凝土棱镜测试的样本。除了拉曼显微镜之外，使用具有EDX的SEM来表征微观结构。结晶ASR产品的拉曼光谱在所有研究的聚集体和混凝土混合物中实际上是相同的，表明它是相同的相。这一结论得到了微观结构数据的进一步验证。

The growth rate of calcium-silicate-hydrate (C-S-H) was analyzed by following the evolution of calcium and silicon concentrations in supersaturated solutions. In these experiments, the supersaturated solution was produced by mixing a saturated calcium hydroxide solution and a solution obtained from the hydration of tricalcium silicate. A continuous decrease of the silicon concentration over time was observed during the experiments and the C-S-H formation rate was calculated from the amount of silicon that was precipitated between two consecutive analyses. The data obtained in this study demonstrate that the interfacial growth rate of C-S-H depends mainly on the supersaturation with respect to this phase, the availability of calcite as a substrate for heterogeneous nucleation and the calcium concentration in solution. A mean value of approximately 10 nmol of C-S-H per m2 per second was obtained for the interfacial growth rate of C-S-H in conditions that are relevant for the hydration of tricalcium silicate.

通过检测过饱和溶液中钙和硅浓度的演变来分析硅酸钙水合物（C-S-H）的生长速率。在这些实验中，通过混合饱和氢氧化钙溶液和由硅酸三钙水化得到的溶液来制备过饱和溶液。在实验期间观察到硅浓度随时间的连续降低，并且由两次连续分析之间沉淀的硅的量计算C-S-H形成速率。在本研究中获得的数据表明，C-S-H的界面生长速率主要取决于该相的过饱和度，方解石作为非均相成核的底物的可用性和溶液中的钙浓度。对于在与硅酸三钙水合有关的条件下的C-S-H的界面生长速率，获得每平方米每秒约10nmol C-S-H的平均值。

Much is unknown about the reaction processes responsible for the formation and polycondensation of geopolymers and other alkali activated materials. In this work, isothermal calorimeter and in-situ XRD were adopted to study the heat and mineral evolution of NaOH activated fly ash, metakaolin and ground granulated blast furnace slag. Both activator concentration and temperature have profound influences on duration of exothermal geopoly-

merization peaks. NaOH activated fly ash is more temperature dependable, with much higher activation energy than metakaolin and slag. The dissolution of source precursor is rapid and the formation of new phases can be detected by the end of the initial dissolution period. The in-situ XRD measurement together with the PONKCS analysis method promotes quantitative estimation of amorphous evolution during alkali activation.

关于地质聚合物和其它碱活化物质的形成和缩聚反应过程存在许多未知。本文采用等温量热仪和原位XRD研究了NaOH活化粉煤灰，偏高岭土和磨细粒高炉矿渣的热和矿物演化。活化剂浓度和温度都对地质聚合峰的放热持续时间有深远的影响。NaOH活化的粉煤灰温度更可靠，活化能比偏高岭土和炉渣高得多。前驱体的溶解迅速，并且在初始溶解期结束时可以检测到新相的形成。原位XRD测量与PONKCS分析方法一起促进了碱活化期间无定形进程的定量评估。

Numerous researches have reported that there is a tendency chloride content first climbs to the maximum then declines with depth increasing in the surface layer of concrete under cyclic drying-wetting environments, which is temporally called ‘maximum phenomenon’ in this paper. This research focuses on the impact of different carbonation conditions on this phenomenon for both pastes and mortars. The distribution of chloride suggests that coupled effect of carbonation and capillary suction/moisture evaporation is more likely to lead to the formation of maximum phenomenon than the merely effect of capillary suction/moisture evaporation. Furthermore, analysis of pore structure and phase composition reveals that this particular phenomenon is directly related to the release of bound chloride fixed in Friedel's salt triggered by carbonation. In addition, the forming process of maximum phenomenon is proposed in the end based on Friedel's salt decomposition under cyclic drying and wetting condition.

大量的研究表明，在循环干湿环境下，混凝土表层随氯化物含量先上升后下降，随着混凝土表层深度的增加而下降，暂时称之为“最大现象”。本研究的重点是不同的碳化条件对浆体和试块的这种现象的影响。氯化物的分布表明，碳酸化和毛细管吸/水分蒸发的耦合效应更可能导致形成最大现象，而不仅仅是毛细管吸/水蒸发的影响。此外，孔结构和相组成的分析表明，这种特殊的现象直接关系到碳酸化引发的Friedel's盐中固定的结合氯化物的释放。此外，在循环干燥和润湿条件下，基于Friedel's盐分解，提出了最大化现象的形成过程。