Numerical Simulation on Moisture Transport in Cracked Cement-based Materials in view of Self-healing of Crack

The moisture transport in cracked cement-based materials was investigated with priority by numerical simulation.The cracked cement-basis material was treated as two components system,including the cracks and cementitious mortar.The mass balance between the water in the cracks and in the cement mortar was considered.From the modeling results,it was seen that the water or vapor filled the crack immediately when the cracked cementitious mortar was put into contact with the water or vapor.The water/vapor penetrates into the mortar from the crack surfaces,as well as the external surface exposed in the outside condition.The existence of cracks increases the penetration of water/vapor into the cementitious mortar.As the basis for studying the self-healing in cracked concrete,the simulation on moisture transport provided important information about the water distribution and movement inside the cracked concrete.

Modelling of Time Dependency of Chloride Diffusion Coefficient in Cement Paste

A computer-based model and method was presented to predict the time dependency of chloride diffusion coefficients in cement paste. The HYMOSTRUC3D model was applied to generate a 3D representative elementary volume （REV） of cement paste. In the simulation of microstructure, both of cement hydration and chloride binding were considered. With the simulated microstructure of cement paste, the finite element method was applied to simulate the diffusion process of chloride through the saturated cement paste. Based on the Fick’s first law, the chloride diffusion coefficient can be calculated. In this method, the influences of age and w/c ratio on the chloride diffusion coefficient were evaluated. The simulated chloride diffusivities with various w/c at different time were compared to experimental data obtained from the literature. The experimental results indicate that the chloride diffusion coefficient decreases with the increase of time and the decrease of w/c ratio. The trend of simulated relationship （diffusion coefficient vs time, diffusion coefficient vs w/c ratio） fits very well with the experiments.

多媒体音箱市场攻略

让一个音箱发声很简单，但是能让它发出好声却并不容易。建一家音箱工厂不困难，但创立一个音箱品牌却并不轻松。

Nanomechanical Characteristics of Interfacial Transition Zone in Nano-Engineered Concrete

This study investigates the effects of nanofillers on the interfacial transition zone(ITZ)between aggregate and cement paste by using nanoindentation and statistical nanoindentation techniques.Moreover,the underlying mechanisms are revealed through micromechanical modeling.The nanoindentation results indicate that incorporating nanofillers increases the degree of hydration in the ITZ,reduces the content of micropores and low-density calcium silicate hydrate(LD C-S-H),and increases the content of highdensity C-S-H(HD C-S-H)and ultra high-density C-S-H(UHD C-S-H).In particular,a new phase,namely nano-core-induced low-density C-S-H(NCILD C-S-H),with a superior hardness of 2.50 GPa and an indentation modulus similar to those of HD C-S-H or UHD C-S-H was identified in this study.The modeling results revealed that the presence of nanofillers increased the packing density of LD CS-H and significantly enhanced the interaction(adhesion and friction)among the basic building blocks of C-S-H gels owing to the formation of nano-core-shell elements,thereby facilitating the formation of NCILD C-S-H and further improving the performance of the ITZ.This study provides insight into the effects of nano fillers on the ITZ in concrete at the nanoscale.

预测水化水泥浆体离子扩散性能的一种新方法

为了预测水泥基复合材料的离子扩散性能并进而将其用于耐久性研究与寿命预测模型中,基于Einstein-Smoluchowski公式,提出了一个将宏观离子扩散行为和微观粒子Brown运动相关联的方法。为了验证这个方法的可靠性,首先用计算机模拟的方法生成一个水化水泥浆体的微观结构(HYMOSTRUC3D),然后用自回避随机行走算法预测这个微观结构的离子有效扩散系数。在这个过程中,应用统计分析的方法确定了水泥浆体微观结构的代表性体积单元的大小,此后在这个代表性体积单元的基础上,通过与文献数据比较,验证了用该方法预测水泥浆体宏观氯离子扩散行为的合理性,最后应用该方法预测了水泥浆体氯离子有效扩散系数随水胶比和养护龄期变化的关系。

Ultrahigh performance concrete–properties, applications and perspectives

Over the last twenty years,remarkable advances have taken place in the research and application of ultra-high performance concrete(UHPC),which exhibits outstanding mechanical properties and excellent durability.It has shown great potential for the next generation infrastructure construction from the sustainability point of view.This paper will give an overview on UHPC,with particular focus on the properties,applications and perspectives.After several decades of development,several types of commercial UHPC materials are available in the market,and the properties of UHPC have been characterized by numerous experimental and field tests.Generally speaking,the performance(e.g.mechanical properties and durability)of UHPC is much better than normal concrete(NC)and high performance concrete(HPC).Therefore,the uses of UHPC are growing all over the world,in both fields of new construction and retrofitting.Nevertheless,it is still a special material and technology,which is not worldwide accepted.So some application prospects of UHPC are briefly introduced in the paper,and the efforts,which have to be made to turn UHPC into a widespread‘regular’technology,are discussed.This paper aims to help designers,engineers,architects and infrastructure owners to know the capacities of UHPC and thus to increase the applications of this material.

混凝土修复中水分交换对水泥水化、微观结构和界面黏结强度的影响(英文)

修复材料浇注到旧混凝土上后,在毛细作用驱动下修复材料和旧混凝土之间存在水分交换。此过程会引起修复材料中水含量的变化,从而影响修复材料的水化过程和微观结构以及界面的黏结强度。研究了修复材料和旧混凝土之间水分交换对修复材料的水化程度、孔隙率和黏结强度的影响。结果表明:饱和的旧混凝土可以为修复材料提供更多的水,促进了修复材料的水化。当旧混凝土不饱和时,不饱和的旧混凝土从修复材料里吸取大量的水分,导致修复材料水灰比降低。因此,修复材料的水化程度和孔隙率也降低了。同时,降低的水灰比提高了界面的黏结强度。

How to Make Capsules Containing Rejuvenators for Their Use in Asphalt Concrete

Rejuvenators are products designed to restore original properties to oxidized asphalt binders by restoring the original ratio of asphaltenes to maltenes. But,for a rejuvenator to be successful,it must penetrate the pavement surface. Besides,application of a rejuvenator will also reduce the skid resistance of the pavement. To solve this,these rejuvenators can be encapsulated and mixed in asphalt concrete. Once the stress in the capsules reaches a certain threshold,the particles break and the rejuvenator is released,giving back the original properties of the pavement. The objective of this paper is to show how these capsules behave and define the most appropriate testing methods to find their effect on asphalt concrete. For this,two different types of rejuvenators will be encapsulated and their effect on the properties of the capsules investigated. Besides,the release mechanisms of the capsules will be unravelled.

水泥净浆微观结构断裂破坏过程的三维模拟(英文)

在微观层次上研究了水泥净浆的断裂破坏过程,提出了两种模拟水泥净浆微观结构断裂破坏过程的方案,即:格构模型HymLat方案和通用格构模型ImgLat方案。在HymLat方案中,被分析的水泥净浆微观结构只能是由球形颗粒组成,但在ImgLat方案中,研究对象不局限于由球形颗粒组成的微观结构,所有能由像素表达的微观结构都能采用ImgLat方案进行分析。这两种方案的共同之处是水泥净浆的微观结构均由HYMOSTRUC3D模型模拟得到,而断裂破坏过程都使用GLAK(Generalized Lattice Analysis Kernel)通用格构模型分析核心代码模拟仿真。对这两种方案在通用性和计算效率方面的差异进行了比较。

开裂混凝土氯离子传输性能研究综述:实验研究和计算机模拟(英文)

目的:综述开裂混凝土中氯离子传输性能的研究方法、研究进展、最新研究成果和研究方向。结论:实验研究和计算机模拟均表明开裂混凝土中氯离子传输性能与裂缝形貌、混凝土组成和混凝土受力状态等因素有关。现有研究虽已取得一定成果,但是仍需深入研究其他因素对开裂混凝土氯离子传输性能的影响,如冻融循环、疲劳和饱和度等。在此基础上才能准确预测开裂混凝土结构在氯盐环境中的服役寿命。